JP6996517B2 - Delta-sigma modulators, transmitters, semiconductor integrated circuits, processing methods, and computer programs - Google Patents

Description

The present invention relates to a delta-sigma modulator, a transmitter, a semiconductor integrated circuit, a processing method, and a computer program.
This application claims priority based on Japanese Application No. 2016-255766 filed on December 28, 2016, and incorporates all the contents described in the Japanese application.

Patent Document 1 describes a delta-sigma modulator capable of outputting an output signal including a plurality of signals having different frequencies.
This delta-sigma modulator adds a plurality of input ports to which a plurality of input signals having different frequencies are given, a plurality of loop filters provided corresponding to the plurality of input ports, and the outputs of the plurality of loop filters. It is equipped with an adder.

Japanese Unexamined Patent Publication No. 2014-165846

The ΔΣ modulator according to one embodiment includes a first adder that adds a plurality of input signals having different frequencies, a loop filter to which the output of the first adder is given, and a quantum that quantizes the output of the loop filter. The loop filter includes a quantizer, and receives the output of the quantizer as a feedback signal, and blocks noise near the frequency of each of the plurality of input signals.

Further, the transmitter according to the embodiment includes the above-mentioned delta-sigma modulator and a transmitter unit to which the output of the quantizer is given.

Further, the semiconductor integrated circuit according to one embodiment is a semiconductor integrated circuit used in a delta-sigma modulator that performs delta-sigma modulation on a plurality of input signals having different frequencies, and adds a plurality of input signals having different frequencies. It comprises a 1 adder, a loop filter to which the output of the first adder is given, and a quantifier that quantizes the output of the loop filter, and the loop filter feeds back the output of the quantifier. To prevent noise near the frequency of each of the plurality of input signals.

Further, the processing method according to the embodiment is a processing method for performing ΔΣ modulation on a plurality of input signals having different frequencies, and includes a first addition step of adding the plurality of input signals having different frequencies. The filter step includes a filter step that performs loop filtering processing on the output by the first addition step and a quantization step that quantizes the output by the filter step, and the filter step feeds back the output by the quantization step. The loop filter processing is performed by a loop filter that blocks noise in the vicinity of the frequency of each of the plurality of input signals.

Further, the computer program according to the embodiment is a computer program for causing a computer to execute a process for performing ΔΣ modulation on data representing a plurality of input signals having different frequencies, and the computer has a plurality of different frequencies. A first addition step that outputs data obtained by adding the input signals of the above, a filter step that performs loop filter processing on the output by the first addition step, and a quantization step that quantizes the output by the filter step. The filter step is a computer program that executes processing including conduct.

FIG. 1 is a block diagram showing a configuration of a ΔΣ modulator according to the first embodiment. FIG. 2 is a diagram showing an example of the power spectrum of the output signal obtained by the ΔΣ modulator of the first embodiment obtained by simulation. FIG. 3 is a diagram showing another example of the power spectrum of the output signal obtained by the ΔΣ modulator of the first embodiment obtained by simulation. FIG. 4 is a block diagram showing a configuration of the ΔΣ modulator according to the second embodiment. FIG. 5 is a diagram showing an example of the power spectrum of the output signal obtained by the ΔΣ modulator of the second embodiment obtained by simulation. FIG. 6 is a block diagram showing a configuration of the ΔΣ modulator according to the third embodiment. FIG. 7 is a block diagram showing an example of a wireless communication device using a ΔΣ modulator.

[Problems to be solved by this disclosure]
The delta-sigma modulator described in Patent Document 1 includes a plurality of loop filters corresponding to each of the plurality of input ports. For this reason, for example, if an input signal is not given to either of the input ports, the function of the loop filter corresponding to the input port to which the input signal is not given may not be exhibited, resulting in a useless configuration. Yes, I could not respond appropriately.

The present disclosure has been made in view of such circumstances, and an object of the present invention is to provide a delta-sigma modulator capable of appropriately responding even if one of a plurality of input signals is not given. And.

[Effect of this disclosure]
According to the present disclosure, even if any one of a plurality of input signals is not given, it can be appropriately dealt with.
First, the embodiments will be listed and described.

[Outline of Embodiment]
(1) In the ΔΣ modulator according to the embodiment, the first adder that adds a plurality of input signals having different frequencies, the loop filter to which the output of the first adder is given, and the output of the loop filter are quantized. The loop filter includes a quantizer to be quantized, and the loop filter accepts the output of the quantizer as a feedback signal and blocks noise near the frequency of each of the plurality of input signals.

According to the ΔΣ modulator having the above configuration, the loop filter has a characteristic of blocking noise near the frequency of each of the plurality of input signals, and the output of the first adder to which the plurality of input signals are added is loop-filtered. Therefore, even if one of a plurality of input signals is not given, the other given input signals can be given to the loop filter. As a result, even if any one of the plurality of input signals is not given, it can be appropriately dealt with by changing the setting of the loop filter or the like.

(2) In the delta-sigma modulator, the loop filter includes an internal filter circuit to which a difference between the output of the adder and the feedback signal is given, and the internal filter circuit includes a plurality of filters connected in series. It is preferably composed of.
In this case, the order of the transfer functions of a plurality of filters can be lowered with respect to the order of the transfer functions of the internal filter circuit as a whole.

(3) Further, in the delta-sigma modulator, the loop filter includes an internal filter circuit to which a difference between the output of the adder and the feedback signal is given, and the plurality of internal filter circuits connected in parallel. It is preferable that it is composed of a filter of.
In this case as well, the order of the transfer functions of the plurality of filters can be lowered with respect to the order of the transfer functions of the internal filter circuit as a whole.
Further, since the plurality of filters are connected in parallel, it is possible to prevent the influence of the error generated by each of the plurality of filters from being applied to each other among the plurality of filters.

(4) Further, in the delta-sigma modulator, it is preferable that the internal filter circuit has a pass band in the vicinity of the frequency of each of the plurality of input signals.
In this case, the characteristic of the internal filter circuit that the pass band is provided in the vicinity of the frequency of each of the plurality of input signals can be realized by the plurality of filters.

(5) Further, in the delta-sigma modulator, the loop filter includes a second adder that outputs the addition result of the output of the first adder and the output of the internal filter circuit as the output of the loop filter. It is preferable that it is.

(6) In the ΔΣ modulator, the loop filter sets the noise level of the band between the noise blocking bands adjacent to each other among the noise blocking bands that block the noise in the vicinity of the frequency of each of the plurality of input signals. It is preferable to suppress the noise level so that it is lower than the noise level of a band other than the band between the noise blocking bands adjacent to each other.
In this case, it becomes easy or unnecessary to remove the noise in the band between the noise blocking bands adjacent to each other.

(7) Further, the transmitter according to the embodiment includes the ΔΣ modulator according to (1) above and a transmitter unit to which the output of the quantizer is given.

(8) Further, the semiconductor integrated circuit according to the embodiment is a semiconductor integrated circuit used in a delta-sigma modulator that performs delta-sigma modulation on a plurality of input signals having different frequencies, and can receive a plurality of input signals having different frequencies. A first adder for adding, a loop filter to which the output of the first adder is given, and a quantizer for quantizing the output of the loop filter are provided, and the loop filter is the output of the quantizer. Is accepted as a feedback signal, and noise near the frequency of each of the plurality of input signals is blocked.

(9) Further, the processing method according to the embodiment is a processing method for performing ΔΣ modulation on a plurality of input signals having different frequencies, and is a first addition for adding the plurality of input signals having different frequencies. The filter step includes a step, a filter step that performs loop filtering processing on the output by the first addition step, and a quantization step that quantizes the output by the filter step, and the filter step is an output by the quantization step. Is received as a feedback signal, and the loop filter processing is performed by a loop filter that blocks noise in the vicinity of the frequency of each of the plurality of input signals.

(10) Further, the computer program according to the embodiment is a computer program for causing a computer to execute a process for performing ΔΣ modulation on data representing a plurality of input signals having different frequencies, and causes the computer to perform a frequency. A first addition step that outputs data obtained by adding a plurality of different input signals, a filter step that performs loop filter processing on the output by the first addition step, and quantization that quantizes the output by the filter step. A computer program that executes a process including steps, wherein the filter step receives the output from the quantization step as feedback data, and the loop filter blocks noise near the frequency of each of the plurality of input signals. Perform filtering.

[Details of the embodiment]
Hereinafter, preferred embodiments will be described with reference to the drawings.
In addition, at least a part of each embodiment described below may be arbitrarily combined.
[About the first embodiment]
FIG. 1 is a block diagram showing a configuration of a ΔΣ modulator according to the first embodiment. As shown in FIG. 1, the delta-sigma modulator ₁ includes input ports 2a and 2b to which _two input signals U1 and U2 having different frequencies are input. The ΔΣ modulator 1 outputs a single output signal V (quantized signal: ΔΣ modulated signal) including two received input signals U ₁ and U ₂ from the output port 4.

The delta-sigma modulator 1 includes a first adder 5 that adds input signals U ₁ and U ₂ , a loop filter 6, and a quantizer 7 that outputs an output signal V.
The first adder 5 adds the input signals U ₁ and U ₂ received by the input ports 2a and 2b, and gives the added output to the loop filter 6.

The output of the first adder 5 is given to the loop filter 6, and the output signal V output from the quantizer 7 is given as a feedback signal. The output signal V fed back to the loop filter 6 is fed back through the path 8 connecting the output end of the quantizer 7 and the loop filter 6. Hereinafter, the output signal V fed back to the loop filter 6 via the path 8 is also referred to as a feedback signal.

The loop filter 6 includes a differencer 9 and a filter circuit 10.
The differencer 9 is given the output of the first adder 5 and a feedback signal. The differencer 9 obtains the difference between the output of the first adder 5 and the feedback signal.
The difference, which is the output of the difference device 9, is given to the filter circuit 10.
The output of the filter circuit 10 is given to the second adder 11 provided after the filter circuit 10.

The filter circuit 10 includes a first filter 15, a second filter 16, and a third adder 18.
The first filter 15 and the second filter 16 are connected in parallel to the difference device 9. Therefore, the output of the difference device 9 is given to the first filter 15 and the second filter 16, respectively.
The third adder 18 adds the output of the first filter 15 and the output of the second filter 16. The output of the third adder 18 is given to the second adder 11 as the output of the filter circuit 10.

The second adder 11 adds the output of the first adder 5 and the output of the filter circuit 10, and outputs the addition result as the output of the loop filter 6.
The output of the second adder 11 is given to the quantizer 7. The quantizer 7 is a two-level quantizer and outputs a 1-bit pulse train as an output signal V. As described above, the output signal V of the quantizer 7 is given to the loop filter 6 as a feedback signal via the path 8.
The output signal V from the quantizer 7 is output from the output port 4.

Here, the output signal V is represented by a function in the z region as shown in the following equation (1).
V (z) =
U ₁ (z) + U ₂ (z) + NTF (z) E (z) ... (1)

In the above equation (1), V (z) is an output signal, U ₁ (z) and U ₂ (z) are input signals, NTF (z) is a noise transfer function of the filter circuit 10, and E (z) is delta-sigma modulation. It is the quantization noise of the vessel 1.
From the above equation (1), the output of the difference device 9 is expressed as the following equation (2).
U ₁ (z) + U ₂ (z) -V (z) =
U ₁ (z) + U ₂ (z)
-(U ₁ (z) + U ₂ (z) + NTF (z) E (z))
= -NTF (z) E (z) ... (2)

From the equation (2), the output of the differencer 9 has the inverse characteristic of the noise component included in the output signal V (z).
The filter circuit 10 of the present embodiment has a first pass band including the frequency band of the input signal U ₁ and a second pass band including the frequency band of the input signal U ₂ , and has a first pass band and a second pass band. In a band other than the band, it is set to have a filter characteristic (noise transmission function NTF (z)) that blocks the passage of a signal.
Therefore, the filter circuit 10 outputs a signal having the opposite characteristic of the noise component in the first pass band including the frequency band of the input signal U ₁ and the second pass band including the frequency band of the input signal U ₂ , and the second. It is given to the adder 11. The signal having the opposite characteristic is added to the output of the first adder 5 by the second adder 11. The output of the first adder 5 to which the signal having the opposite characteristic is added is quantized by the quantizer 7, and the output signal V is fed back to the filter circuit 10.

As described above, the loop filter 6 of the present embodiment repeatedly adds a signal having an inverse characteristic of the noise component in the first pass band and the second pass band to the output of the first adder 5, thereby increasing the output signal. The noise in the first pass band and the second pass band in V is suppressed.
Therefore, the loop filter 6 of the present embodiment has a filter characteristic having two bands of blocking noise in the first pass band and the second pass band.
That is, the loop filter 6 of the present embodiment has a characteristic of blocking noise in the vicinity of the frequencies of the input signals U ₁ and U ₂ .

Further, the ΔΣ modulator 1 includes a control unit 19 for controlling the first filter 15 and the second filter 16. The control unit 19 can store a plurality of setting parameters that determine the filter characteristics of each of the first filter 15 and the second filter 16. The control unit 19 has a function of controlling the filter characteristics of the first filter 15 and the second filter 16 by selectively giving a plurality of stored setting parameters to the first filter 15 and the second filter 16. ing.

The ΔΣ modulator 1 of the present embodiment can also be configured by a computer including a CPU, a storage unit, and the like. In this case, the computer can realize each functional unit of the ΔΣ modulator 1 by reading and executing a computer program or the like stored in the storage unit. When the ΔΣ modulator 1 is configured by a computer, the ΔΣ modulator 1 processes data representing each signal (input signal, output signal, etc.).

Further, the ΔΣ modulator 1 of the present embodiment can be configured by, for example, a semiconductor integrated circuit such as FPGA (Field Programmable Gate Array). When the ΔΣ modulator 1 is configured by a semiconductor integrated circuit, each functional unit such as the filter circuit 10 and the quantizer 7 included in the ΔΣ modulator 1 is configured by using various semiconductor elements included in the semiconductor integrated circuit. Will be done.

Further, the ΔΣ modulator 1 includes an FPGA which is a programmable integrated circuit, and a computer having a function of giving circuit configuration information regarding the circuit configuration of the FPGA to the FPGA and causing the FPGA to configure the circuit according to the circuit configuration information. It can also be configured by a system.
In this case, the storage unit of the computer stores a program for causing the computer to execute a process for giving the circuit configuration information to the FPGA, and one or a plurality of circuit configuration information.
The computer gives the circuit configuration information stored in the storage unit to the FPGA. The FPGA to which the circuit configuration information is given constitutes a circuit according to the given circuit configuration information.
The storage unit of the computer stores circuit configuration information indicating a circuit configuration for configuring the ΔΣ modulator 1 in the FPGA.
The computer can make the FPGA configure the digital signal processing unit 2 by giving the FPGA the circuit configuration information for configuring the ΔΣ modulator 1.

As described above, the filter circuit 10 included in the ΔΣ modulator 1 of the present embodiment has a first pass band including the frequency band of the input signal U ₁ and a second pass band including the frequency band of the input signal U ₂ . It is set to have the filter characteristics (noise transmission function NTF (z)).
Further, the noise transfer function NTF (z) of the filter circuit 10 is set for at least the first pass band and the second pass band, and the band between the two pass bands in the output signal V.

Assuming that the transfer function of the first filter 15 constituting the filter circuit 10 is L ₁ (z) and the transfer function of the second filter 16 is L ₂ (z), the noise transfer function NTF (z) of the filter circuit 10
Is expressed as the following equation (3).
NTF (z) = L ₁ (z) + L ₂ (z) ... (3)

The filter circuit 10 of the present embodiment is a fourth-order IIR (Infinite Impulse Response) filter.
The transfer function L ₁ of the first filter 15 and the transfer function L ₂ of the second filter 16 are set based on the noise transfer function NTF (z) of the filter circuit 10 as a fourth-order filter.
Here, the first filter 15 and the second filter 16 are set as a second-order IIR filter.

As shown in the above equation (3), the transfer function L ₁ of the first filter 15 and the transfer function L ₂ of the second filter 16 are added to each other, so that the noise transfer function NTF (z) of the filter circuit 10 is used. It is set to be.

The following equation (4) is an example of a general equation of the noise transfer function NTF (z) of the filter circuit 10.

The above equation (4) shows a noise transfer function when the filter circuit 10 is configured as an n-th order IIR filter. In equation (4), A ₀ , A ₁ , ... _Ann , B ₁ , ... B _n are parameters of each term constituting the denominator and the numerator, and are setting parameters that determine the filter characteristics.

Since the denominator and numerator in the above equation (4) are polynomials of z, they can be expressed as a product of lower-order polynomials, for example. Therefore, the above equation (4) can be decomposed into a partial fraction having a lower order polynomial as a denominator and a numerator. That is, the equation (4) can be expressed as the sum of a plurality of polynomials having a lower order.

The following equation (5) shows an example when the noise transfer function NTF (z) shown in the above equation (4) is decomposed into a plurality of polynomials.

Equation (5) shows a case where the noise transfer function NTF (z) of the nth-order filter circuit 10 is decomposed into partial fractions representing the transfer function of the second-order filter and expressed as the sum of these. In equation (5), i is an integer from 1 to I, for example, assuming that the number of decomposed partial fractions is I. Ki is the coefficient of each decomposed partial fraction, and A _{1, i} , ... _{An, i} , B _{1, i} , ... B _{n, i} are the terms that make up the denominator and molecule in the partial fraction. This is a setting parameter that determines the filter characteristics when the noise transfer function NTF (z) is decomposed into partial fractions.

As described above, the noise transfer function NTF (z) of the filter circuit 10 can be decomposed into the transfer functions of a plurality of second-order filters after being designed as a high-order filter.

In the present embodiment, a fourth-order IIR filter is used to realize a filter characteristic having a first pass band including the frequency band of the input signal U ₁ and a second pass band including the frequency band of the input signal U ₂ . The setting parameters are obtained according to the above equation (4).

Regarding the noise transfer function NTF (z), by optimizing a plurality of zeros and poles, each setting parameter in the above equation (4) is obtained, and the above-mentioned filter characteristics having a plurality of pass bands are realized. be able to. For the optimization of zeros and poles, for example, "Translated by Takao Waho and Akira Yasuda (Original author Richard Schreier, Gabor C. Temes) Introduction to ΔΣ type analog / digital converter, Maruzen Co., Ltd., 2007, pages 88 to 99. The method described in "Page" can be used.

After obtaining the setting parameter based on the above equation (4), the noise transfer function NTF (z) based on the obtained setting parameter is decomposed into two partial fractions. The two decomposed partial fractions show a transfer function that represents a second-order IIR filter. As a result, the setting parameters for each of the partial fractions obtained by decomposing the noise transfer function NTF (z) are obtained.
The setting parameters when the noise transfer function NTF (z) is decomposed into partial fractions are given to the first filter 15 and the second filter 16 for each partial fraction.
The first filter 15 and the second filter 16 to which the setting parameters are given are set to the transfer function represented by the partial fractions obtained by decomposing the noise transfer function NTF (z) into partial fractions.

The setting parameters when the noise transfer function NTF (z) is decomposed into partial fractions are stored in the control unit 19. The first filter 15 and the second filter 16 are set to the transfer function by being given a setting parameter from the control unit 19.

As described above, in the present embodiment, the noise transfer function NTF (z) of the filter circuit 10 which is the fourth-order IIR filter is decomposed into two transfer functions representing the second-order IIR filter, and the two decomposed transmissions. The functions are set as the transfer function L ₁ of the first filter 15 and the transfer function L ₂ of the second filter 16.

Therefore, the third adder 18 that adds the output of the first filter 15 and the output of the second filter 16 includes the first pass band including the frequency band of the input signal U ₁ and the frequency band of the input signal U ₂ . The output of the filter circuit 10 as a fourth-order IIR filter having a noise transfer function NTF (z) having a second pass band is given to the second adder 11.

In the delta-sigma modulator of the above conventional example, two loop filters are provided corresponding to each of the two input ports, and the transfer function of the internal filter of each loop filter is the transfer function of the input signal given to the corresponding input port. It is individually set to have a passband only near the frequency.

On the other hand, in the present embodiment, the transfer function L ₁ of the first filter 15 constituting the filter circuit 10 and the transfer function L ₂ of the second filter 16 use the noise transfer function NTF (z) of the filter circuit 10 as a partial fraction. It is said to be the transfer function obtained by decomposing. Therefore, the transfer functions of the first filter 15 and the second filter 16 are not set individually as in the case of the above-mentioned conventional example, and even if they are set to have the same pass band as the above-mentioned conventional example, both are set. The individual transfer functions of the filters 15 and 16 are not always the same as in the above conventional example.
That is, the first filter 15 and the second filter 16 of the present embodiment are connected to each other in parallel to form a filter (filter circuit 10) having desired characteristics.

Since the filter circuit 10 of the present embodiment is configured by using a plurality of filters (first filter 15 and second filter 16), the first filter 15 has the characteristic of having a plurality of pass bands. And can be realized by the second filter 16.
Therefore, the order of the transfer functions of the first filter 15 and the second filter 16 can be lowered with respect to the order of the noise transfer function NTF (z) of the filter circuit 10 as a whole. As a result, even if a high-order filter is configured, the processing load of the filter circuit 10 can be suppressed.

Further, in the filter circuit 10 of the present embodiment, since the first filter 15 and the second filter 16 are connected in parallel, both of them are compared with the case where the first filter 15 and the second filter 16 are connected in series, for example. It is possible to prevent the influence of the error generated in each of the filters 15 and 16 from reaching each other between the two filters 15 and 16.

FIG. 2 is a diagram showing an example of the power spectrum of the output signal obtained by the ΔΣ modulator of the first embodiment obtained by simulation. FIG. 2A is a diagram showing an example of the power spectrum of the output signal V by the ΔΣ modulator 1 of the first embodiment, and FIG. 2B in FIG. 2 is a diagram of FIG. 2A. It is an enlarged view of a main part.
In (a) in FIG. 2 and (b) in FIG. 2, the frequency of the input signal U ₁ is 940 MHz, the frequency of the input signal U ₂ is 1025 MHz, and the first pass band in the filter circuit 10 is set to around 940 MHz. The case where the two pass bands are set to around 1025 MHz is shown.
In this case, the order of the filter as the filter circuit 10 is the fourth order, and the order of the filter for forming both pass bands as the filter characteristics is set to the second order.

As shown in (a) in FIG. 2 and (b) in FIG. 2, the power spectrum of the output signal V includes an input signal U ₁ having a frequency of 940 MHz and an input signal U ₂ having a frequency of 1025 MHz. It is appearing. Further, a noise-blocked band (quantized noise blocking band) is formed at two locations, around 940 MHz and around 1025 MHz. Within these quantized noise blocking bands, the quantized noise is sufficiently suppressed as compared with other bands.

As described above, the ΔΣ modulator 1 of the present embodiment receives a plurality of input signals U ₁ and U ₂ having different frequencies, and includes the input signals U ₁ and U ₂ in a single output signal V without interfering with each other. Can be output.

Further, as shown in (a) in FIG. 2 and (b) in FIG. 2, the noise level of the band between two quantization noise blocking bands adjacent to _each other is the noise corresponding to the input signal U1. The noise level on the frequency side lower than the blocking band and the noise level on the frequency side higher than the noise blocking band corresponding to the input signal U ₂ appear lower.

This is because the loop filter 6 has two quantization noise blocking bands, and the noise level of the band between these two quantization noise blocking bands is other than the band between the two quantization noise blocking bands. This is because it has a characteristic of suppressing the noise level so as to be lower than the noise level in the band.

Further, the filter circuit 10 is set to the noise transfer function NTF (z) that can realize the above-mentioned filter characteristics in the loop filter 6.
In the ΔΣ modulator 1 of the present embodiment, the noise transfer function NTF (z) of the filter circuit 10 that determines the quantization noise blocking band is configured to set the first pass band and the second pass band. It is possible to set the characteristics of at least the band between the first pass band and the second pass band.
That is, when setting the noise transfer function NTF (z) of the filter circuit 10, it is possible to adjust not only the two quantized noise blocking bands but also the characteristics of the band between the two quantized noise blocking bands. There is.
The characteristics of the band between the two quantization noise blocking bands are also determined by the above-mentioned setting parameters.

For example, when two loop filters are provided corresponding to each of the two input ports as in the conventional ΔΣ modulator, the filter characteristics of the internal filter of each loop filter are set to the corresponding input ports. It is individually set to have a passband only near the frequency of the given input signal. Therefore, it is difficult to adjust the noise level in the band between the quantized noise blocking bands corresponding to the two input signals.

On the other hand, in the present embodiment, as described above, the noise transfer function NTF (z) of the filter circuit 10 is set for at least the first pass band, the second pass band, and the band between the two pass bands. Is possible. Therefore, the loop filter 6 has a filter characteristic of suppressing the noise level in the band between the two quantization noise blocking bands so as to be lower than the noise level in the other bands.

As described above, the loop filter 6 of the present embodiment has a filter characteristic of suppressing the noise level in the band between the two quantization noise blocking bands so as to be lower than the noise level in the other bands. , It becomes easy or unnecessary to remove the noise in the band between the quantization noise blocking bands adjacent to each other.

Here, the noise level of the band between the two quantization noise blocking bands is the other band (the band on the frequency side lower than the noise blocking band corresponding to the input signal U ₁ and the noise corresponding to the input signal U ₂ ). It is preferably 10 dB lower than the band on the frequency side higher than the blocking band). Since the noise level is 10 dB lower, it can be easily removed when removing the noise contained in the band between the two quantized noise blocking bands in the subsequent processing.

Further, the noise level of the band between the _two quantization noise blocking bands is preferably 48 dB lower _than the signal levels of the input signals U1 and U2.
In this case, the noise level of the band between the two quantization noise blocking bands can be set to a level that does not need to be removed with respect to the signal levels of the input signals U ₁ and U ₂ .

In the ΔΣ modulator 1 of the present embodiment, the loop filter 6 has a characteristic of blocking noise in the vicinity of the frequencies of the plurality of input signals U ₁ and U ₂ , and the plurality of input signals U ₁ and U ₂ are input. Since the output of the added first adder 5 is given to the loop filter 6, even if one of the input signals U ₁ and U ₂ is not given, the loop filter is used for the other given input signals. Can be given to 6. As a result, even if any of the input signals is not given, for example, the setting parameters of the filters 15 and 16 constituting the loop filter 6 are changed to the setting parameters corresponding to the given input signals. Can be done and can be dealt with appropriately.

FIG. 3 is a diagram showing another example of the power spectrum of the output signal obtained by the ΔΣ modulator of the first embodiment obtained by simulation. FIG. 3A is a diagram showing another example of the power spectrum of the output signal V by the ΔΣ modulator 1 of the first embodiment obtained by simulation, and FIG. 3B in FIG. 3 is a diagram. It is an enlarged view of the main part of (a) in 3.
(A) in FIG. 3 and (b) in FIG. 3 show a case where only the input signal U1 having a frequency of 975 MHz is applied to the ΔΣ modulator ₁ .
Further, in this case, the case where the pass band in the filter circuit ₁₀ is set to around 975 MHz corresponding to the input signal U1 and the order of the filter for forming this pass band as a filter characteristic is set to the fourth order is shown. ing.

The setting parameters given to both the filters 15 and 16 for setting the pass band in the filter circuit 10 to around 975 MHz are stored in the control unit 19.
The first filter 15 and the second filter 16 are set so that the pass band in the filter circuit 10 has _a characteristic corresponding to the input signal U1 by being given a setting parameter from the control unit 19.

As shown in (a) in FIG. 3 and (b) in FIG. 3, an input signal U1 having _a frequency of 975 MHz appears in the power spectrum of the output signal V. Further, the quantization noise blocking band is formed only in the vicinity of 975 MHz.
As described above, the ΔΣ modulator 1 can include the input signal U ₁ in the output signal V and output it even if only the input signal U ₁ is given.

Further, since the order of the filter when forming the pass band of the filter circuit 10 as the filter characteristic is set to the fourth order, the quantization noise in the loop filter 6 is compared with the case where the order of the filter is set to the second order, for example. The bandwidth of the blocking band can be made wider, and the blocking characteristics of the quantization noise can be made steeper.

That is, if the filter characteristics of the filter circuit 10 are appropriately adjusted as in this example, even if the input signal U ₂ is not given, both filters 15 targeting the plurality of input signals U ₁ and U ₂ . , 16 capabilities can be used _only for the input signal U1, and the capabilities of both filters 15 and 16 can be utilized without waste.

In the present embodiment, even if the input signal U ₂ is not given among the input signals U ₁ and U ₂ , the output of the first adder 5 is given to the loop filter 6, so that the setting parameters of the filters 15 and 16 are given. Can be appropriately dealt with, such as changing to _a setting parameter corresponding to the input signal U1.

In the above, when only the input signal U ₁ having a frequency of 975 MHz is given to the ΔΣ modulator 1, the filter characteristic of the loop filter 6 (filter circuit 10) is set to the characteristic corresponding to the input signal U ₁ . However, for example, when the filter characteristics of the loop filter 6 are set to the characteristics corresponding to the input signals U ₁ and U ₂ , and only one of the input signals U ₁ and U ₂ is given to the ΔΣ modulator 1, the loop filter 6 is used. The filter characteristics may be maintained and used as they are.
This is because even in this case, the ΔΣ modulator 1 can include the input signal U ₁ in the output signal V and output it when only the input signal U ₁ is given.

If the control unit 19 stores both the setting parameters corresponding to both the input signals U ₁ and U ₂ and the setting parameters corresponding to only the input signal U ₁ , the control unit 19 is preset. The setting parameters to be given to both filters 15 and 16 may be selected based on the instruction, or the setting parameters to be given to both filters 15 and 16 based on the acquired information such as the number of input signals and the frequency may be acquired. May be selected.
When the control unit 19 selects the setting parameters to be given to both the filters 15 and 16 based on the information of the input signal, the control unit 19 can change the setting parameters according to the input signal, and the filter circuit 10 has. The capabilities of both filters 15 and 16 can be appropriately allocated to the input signal.

As described above, according to the present embodiment, when both the input signals U ₁ and U ₂ are given and used, the output including the input signals U ₁ and U ₂ is used by using both filters 15 and 16. It can output a signal.
Even when the input signal U ₂ of the input signals U ₁ and U ₂ is not given, the filter order of the filter circuit 10 can be adjusted appropriately to increase the filter order and widen the bandwidth. The capabilities of both filters 15 and 16 targeting a plurality of input signals U ₁ and U ₂ can be used only for the input signal U ₁ .
That is, when both the input signals U ₁ and U ₂ are given and used, it can be used to output an output signal including the input signals U ₁ and U ₂ , and the input signals U ₁ and U ₂ can be output. If one of the input signals is not given, it can be used to widen the bandwidth for outputting the other input signal.

As described above, according to the present embodiment, when both the input signals U ₁ and U ₂ are given and used, and when one of the input signals U ₁ and U ₂ is not given. In any case, the capabilities of both filters 15 and 16 can be utilized without waste.

[About the second embodiment]
FIG. 4 is a block diagram showing a configuration of the ΔΣ modulator according to the second embodiment.
The ΔΣ modulator 1 of the present embodiment receives three input signals U ₁ , U ₂ , and U ₃ having different frequencies, and a single output signal V including the three received input signals U ₁ , U ₂ , and U ₃ . Is different from the first embodiment in that the above-mentioned first embodiment is output.

The ΔΣ modulator 1 of the present embodiment includes three input ports 2a, 2b, 2c to which input signals U ₁ , U ₂ , and U ₃ are input. The first adder 5 adds the input signals U ₁ , U ₂ , and U ₃ received by the input ports 2a, 2b, and 2c, and gives the added output to the loop filter 6.

The filter circuit 10 of the present embodiment includes a first filter 15, a second filter 16, and a third filter 17, and is composed of three filters. The filters 15, 16 and 17 are connected in parallel to the differencer 9.
The third adder 18 adds the output of the first filter 15, the output of the second filter 16, and the output of the third filter 17. The output of the third adder 18 is given to the second adder 11 as the output of the filter circuit 10.

The filter circuit 10 of the present embodiment has a first pass band including the frequency band of the input signal U ₁ , a second pass band including the frequency band of the input signal U ₂ , and a third pass band including the frequency band of the input signal U ₃ . It is set to be a noise transfer function NTF (z) having a band.
Further, the noise transfer function NTF (z) of the filter circuit 10 is set for at least the first pass band, the second pass band, the third pass band, and the band between the pass bands in the output signal V. ing.

The filter circuit 10 of the present embodiment is a sixth-order IIR filter.
In the present embodiment, the noise transfer function NTF (z) of the filter circuit 10 which is the sixth-order IIR filter is decomposed into three transfer functions representing the second-order IIR filter, and the decomposed three transfer functions are the first. It is set as the transfer function L ₁ of the 1 filter 15, the transfer function L ₂ of the second filter 16, and the transfer function L ₃ of the third filter 17.

As a result, the third adder 18 that adds the output of the first filter 15, the output of the second filter 16, and the output of the third filter 17 has a first pass band including the frequency band of the input signal U ₁ and an input signal. The output as a sixth-order IIR filter having a noise transfer function NTF (z) having a second pass band including the frequency band of U ₂ and a third pass band including the frequency band of the input signal U ₃ is added to the second. Give to vessel 11.

The setting parameters given to both the filters 15 and 16 for setting the three pass bands of the first pass band, the second pass band, and the third pass band with respect to the characteristics of the filter circuit 10 are the control unit 19. Is remembered in.
The first filter 15 and the second filter 16 are set so that the filter characteristics of the filter circuit 10 include three pass bands by being given setting parameters from the control unit 19.

FIG. 5 is a diagram showing an example of the power spectrum of the output signal obtained by the ΔΣ modulator of the second embodiment obtained by simulation. FIG. 5A is a diagram showing an example of the power spectrum of the output signal V by the ΔΣ modulator 1 of the second embodiment obtained by simulation, and FIG. 5B in FIG. 5 is a diagram in FIG. It is an enlarged view of the main part of (a).
In (a) in FIG. 5 and (b) in FIG. 5, the frequency of the input signal U ₁ is 940 MHz, the frequency of the input signal U ₂ is 980 MHz, and the frequency of the input signal U ₃ is 1025 MHz. The case where the first pass band is set to the vicinity of 940 MHz, the second pass band is set to the vicinity of 980 MHz, and the third pass band is set to the vicinity of 1025 MHz is shown.
In this case, the order of the filter as the filter circuit 10 is 6th, and the order of the filter for forming each pass band as a filter characteristic is set to 2nd.

As shown in (a) in FIG. 5 and (b) in FIG. 5, the power spectrum of the output signal V includes an input signal U ₁ having a frequency of 940 MHz and an input signal U ₂ having a frequency of 980 MHz. _, The input signal U3 having a frequency of 1025 MHz has appeared.
Further, in the present embodiment, the band in which the quantization noise is suppressed appears as a relatively wide band including the input signals U ₁ , U ₂ , and U ₃ .

As described above, the delta-sigma modulator 1 of the present embodiment receives a plurality of input signals U ₁ , U ₂ , U ₃ having different frequencies, and unitizes the input signals U ₁ , U ₂ , U ₃ without interfering with each other. It can be included in the output signal V of.
Further, even if one or two input signals among the input signals U ₁ , U ₂ , and U ₃ are not given, the output of the first adder 5 is given to the loop filter 6. Therefore, for example, the setting parameters of the filters 15 and 16 constituting the loop filter 6 can be appropriately changed to the setting parameters corresponding to the given input signal.

Further, the loop filter 6 of the present embodiment forms a quantization noise blocking band at three locations corresponding to the input signals U ₁ , U ₂ , and U ₃ , and is located between the two quantization noise blocking bands. It is a filter characteristic that suppresses the noise level in the band so that it is lower than the noise level in other bands.
Therefore, each quantization noise blocking band appears as if they are connected to each other, and as shown in (a) in FIG. 5 and (b) in FIG. 5, the band in which the quantization noise is suppressed is the input signal. It appears as a relatively wide band including U ₁ , U ₂ , and U ₃ .

[About the third embodiment]
FIG. 6 is a block diagram showing a configuration of the ΔΣ modulator according to the third embodiment.
The ΔΣ modulator 1 of the present embodiment is different from the first embodiment in that the first filter 15 and the second filter 16 constituting the filter circuit 10 are connected in series.

Similar to the first embodiment, the filter circuit 10 of the present embodiment has a noise transfer function NTF having a first pass band including the frequency band of the input signal U ₁ and a second pass band including the frequency band of the input signal U ₂ . It is set to be (z).

As described above, the noise transfer function NTF (z) of the filter circuit 10 has a polynomial with a denominator and a numerator of z, and can be expressed as a product of lower-order polynomials. That is, the above equation (4) can be expressed as a product of a plurality of polynomials having a lower order.

The following equation (6) shows an example when the noise transfer function NTF (z) shown in the above equation (4) is expressed as a product of a plurality of polynomials.

Equation (6) shows a case where the noise transfer function NTF (z) of the nth-order filter circuit 10 is decomposed into partial fractions representing the transfer function of the second-order filter and expressed as a product thereof. In equation (6), C ₁ , C ₂ , ... D ₁ , D ₂ , ... Are the coefficients of each term constituting the denominator and numerator in each polynomial.
As described above, the noise transfer function NTF (z) of the filter circuit 10 can be expressed as the product of the transfer functions of a plurality of second-order filters after being designed as a high-order filter.

The filter circuit 10 of this embodiment is a fourth-order IIR filter.
In the present embodiment, the noise transfer function NTF (z) of the filter circuit 10 which is a fourth-order IIR filter is the product of two transfer functions representing a second-order IIR filter, and these two transfer functions are the first. It is set as the transfer function L ₁ of the filter 15 and the transfer function L ₂ of the second filter 16.

As a result, the second filter 16 to which the output of the first filter 15 is given has a first pass band including the frequency band of the input signal U ₁ and a second pass band including the frequency band of the input signal U ₂ . The output as a fourth-order IIR filter having the transfer function NTF (z) is given to the second adder 11.

Similar to the first embodiment, the ΔΣ modulator 1 of the present embodiment also accepts a plurality of input signals U ₁ and U ₂ having different frequencies, and outputs the input signals U ₁ and U ₂ as a single output without interfering with each other. It can be included in the signal V and output.
Further, even if one of the input signals is not given, the output of the first adder 5 is given to the loop filter 6. Therefore, for example, the setting parameters of the filters 15 and 16 constituting the loop filter 6 can be appropriately changed to the setting parameters corresponding to the given input signal.

Further, since the filter circuit 10 of the present embodiment is also configured by using a plurality of filters (first filter 15 and second filter 16), the characteristic of the filter circuit 10 that it has a plurality of pass bands is the first filter. It can be realized by 15 and the second filter 16. Therefore, the order of the transfer functions of the first filter 15 and the second filter 16 can be lowered with respect to the order of the noise transfer function NTF (z) of the filter circuit 10 as a whole. As a result, even if a high-order filter is configured, the processing load of the filter circuit 10 can be suppressed.

[About wireless communication equipment]
FIG. 7 is a block diagram showing an example of a wireless communication device using a ΔΣ modulator. (A) in FIG. 7 is a block diagram showing an example of a wireless communication device using the above-mentioned ΔΣ modulator 1. In (a) in FIG. 7, the wireless communication device 20 includes a plurality of quadrature modulators (primary modulators) 21 and 22, a ΔΣ modulator (secondary modulator) 1, a first band bus filter 25, and the like. It includes a second bandpass filter 26.
The plurality of quadrature modulation units 21 and 22 perform quadrature modulation as primary modulation for the baseband signals I ₁ , Q ₁ , I ₂ and Q ₂ , respectively. Since the frequencies w ₁ and w ₂ of the local transmitters 21a and 22a are different from each other, the plurality of quadrature modulators 21 and 22 output radio signals (RF signals) U ₁ and U ₂ having different frequencies, respectively.
The plurality of radio signals U ₁ and U ₂ are input signals to the ΔΣ modulator 1.

The ΔΣ modulator 1 performs ΔΣ modulation as a secondary modulation on a plurality of radio signals (input signals) U ₁ and U ₂ , and outputs a pulse signal including the plurality of radio signals U ₁ and U ₂ . The output signal of the ΔΣ modulator 1 is given to both bandpass filters 25 and 26 via the transmission line 24, respectively.
_The bandpass filters 25 and 26 are provided corresponding to _both radio signals U1 and U2. The _first bandpass filter 25 has a pass band through which the radio signal U1 is passed. Further, the second bandpass filter 26 has a pass band through which the radio signal U ₂ is passed.
The _first bandpass filter 25 removes noise outside the band of the radio signal U1. Further, the noise outside the band of the radio signal U ₂ is removed by the second bandpass filter 26.

The radio signal U ₁ output from the first bandpass filter 25 is amplified by the power amplifier 31 and output from the antenna 32.
The radio signal U ₂ output from the second bandpass filter 26 is amplified by the power amplifier 33 and output from the antenna 34.

The wireless communication device 20 can operate in a dual band mode (multi-band mode) in which a plurality of wireless signals having different frequencies are simultaneously output.
Further, since the output of the ΔΣ modulator 1 is a digital signal, it is possible to transmit the radio signal as a digital signal to a long distance through a high-speed transmission line 24 such as an optical fiber.
Further, since a plurality of radio signals can be included in one digital data stream, the plurality of radio signals can be transmitted by one transmission line 24.

(B) in FIG. 7 is a block diagram showing another example of a wireless communication device using the ΔΣ modulator 1.
In this example, the first bandpass filter 25 is provided after the ΔΣ modulator 1, but the second bandpass filter 26 is not provided, which is the same as the example of (a) in FIG. It's different.
The first bandpass filter 25 in the wireless communication device 20 in FIG. 7 (b) has a pass band through which _a plurality of wireless signals _U1 and U2 pass together. _{The first} bandpass filter 25 removes noise outside the band of the plurality of radio signals U1 and U2.

For example, as shown in FIGS. 2 and 6, when the noise level in the band between the plurality of radio signals U ₁ and U ₂ is sufficiently lower than the signal levels of the radio signals U ₁ and U ₂ , 1 The _first bandpass filter 25 can be configured to remove out-of _- band noise of the plurality of radio signals U1 and U2. This is because the noise level existing between the plurality of radio signals U ₁ and U ₂ is sufficiently low and does not need to be removed.

As described above, the loop filter 6 included in the ΔΣ modulator 1 of the present embodiment is a filter that suppresses the noise level in the band between the two quantization noise blocking bands so as to be lower than the noise level in the other bands. Since it is a characteristic, when it is necessary to remove the noise in the band between the delta-sigma noise blocking bands containing the radio signals U ₁ and U ₂ adjacent to each other, the process of removing the noise is performed. It can be simplified.

The ΔΣ modulator 1 used in the wireless communication device 20 shown in (a) in FIG. 7 and (b) in FIG. 7 is any of the ΔΣ modulators 1 of the first to third embodiments described above. May be used.
The ΔΣ modulator 1 of the second embodiment can receive three input signals, but can receive two radio signals U ₁ and U ₂ . In this case, if the setting parameters of the filters 15, 16 and 17 constituting the loop filter 6 are changed to the setting parameters corresponding to the radio signals U ₁ and U ₂ , even if the radio signal U ₃ is not given. The capabilities of the filters 15, 16 and 17 can be used for the radio signals U ₁ and U ₂ , and the capabilities of the filters 15, 16 and 17 can be utilized without waste.

〔others〕
It should be noted that the embodiments disclosed this time are exemplary in all respects and are not restrictive.
Further, in each of the above embodiments, the case where the filter circuit 10 is configured by using two or three filters is illustrated, but it may be configured by using a larger number of filters.
The scope of the present invention is shown by the scope of claims, not the above-mentioned meaning, and is intended to include the meaning equivalent to the scope of claims and all modifications within the scope.

1 Modulator 2a, 2b, 2c Input port 4 Output port 5 1st adder 6 Loop filter 7 Quantifier 8 Path 9 Difference device 10 Filter circuit 11 2nd adder 15 1st filter 16 2nd filter 17 3rd filter 18 3rd adder 19 Control unit 20 Wireless communication device 21, 22 Quadrature modulator 21a, 22a Local transmitter 24 Transmission line 25 1st band bus filter 26 2nd band pass filter 31 Power amplifier 32 Antenna 33 Power amplifier 34 Antenna

Claims (10)

A first adder that adds multiple input signals with different frequencies,
A loop filter to which the output of the first adder is given, and
A quantizer that quantizes the output of the loop filter,
Equipped with
The loop filter is a delta-sigma modulator that receives the output of the quantizer as a feedback signal and blocks noise in the vicinity of the frequency of each of the plurality of input signals. The loop filter includes an internal filter circuit to which a difference between the output of the first adder and the feedback signal is given.
The ΔΣ modulator according to claim 1, wherein the internal filter circuit is composed of a plurality of filters connected in series. The loop filter includes an internal filter circuit to which a difference between the output of the first adder and the feedback signal is given.
The ΔΣ modulator according to claim 1, wherein the internal filter circuit is composed of a plurality of filters connected in parallel. The ΔΣ modulator according to claim 2, wherein the internal filter circuit has a pass band in the vicinity of the frequency of each of the plurality of input signals. The ΔΣ modulator according to claim 4, wherein the loop filter includes a second adder that outputs the addition result of the output of the first adder and the output of the internal filter circuit as the output of the loop filter. .. The loop filter sets the noise level of the band between the noise blocking bands adjacent to each other among the noise blocking bands that block the noise near the frequency of each of the plurality of input signals, among the noise blocking bands adjacent to each other. The ΔΣ modulator according to any one of claims 1 to 5, which suppresses the noise level to be lower than the noise level in a band other than the intervening band. The ΔΣ modulator according to any one of claims 1 to 6.
A transmitter comprising a transmitter to which the output of the quantizer is given. A semiconductor integrated circuit used in a delta-sigma modulator that performs delta-sigma modulation on multiple input signals with different frequencies.
A first adder that adds multiple input signals with different frequencies,
A loop filter to which the output of the first adder is given, and
A quantizer that quantizes the output of the loop filter,
Equipped with
The loop filter is a semiconductor integrated circuit that receives the output of the quantizer as a feedback signal and blocks noise near the frequency of each of the plurality of input signals. It is a processing method for performing delta-sigma modulation on multiple input signals with different frequencies.
The first addition step of adding a plurality of input signals having different frequencies, and
A filter step that performs loop filtering processing on the output from the first addition step, and
A quantization step that quantizes the output of the filter step,
Including
The filter step is a processing method in which the output from the quantization step is received as a feedback signal, and the loop filter processing is performed by a loop filter that blocks noise in the vicinity of the frequency of each of the plurality of input signals. It is a computer program for causing a computer to execute a process for performing delta-sigma modulation on data representing a plurality of input signals having different frequencies.
The first addition step of outputting the data obtained by adding the plurality of input signals having different frequencies to the computer, and
A filter step that performs loop filtering processing on the output from the first addition step, and
A quantization step that quantizes the output of the filter step,
Is a computer program that executes processing including
The filter step is a computer program that receives the output from the quantization step as feedback data and performs the loop filter processing by a loop filter that blocks noise near the frequency of each of the plurality of input signals.

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