JP6973503B2 - Delta-sigma modulators, transmitters, semiconductor integrated circuits, and computer programs - Google Patents

Description

The present invention relates to delta-sigma modulators, transmitters, semiconductor integrated circuits, and computer programs.
This application claims priority based on Japanese Application No. 2017-236348 filed on December 8, 2017, 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

Translated by Takao Waho and Akira Yasuda (Original author Richard Schreier, Gabor C. Temes), "Introduction to ΔΣ Analog / Digital Converter", Maruzen Co., Ltd., p. 81, 2007

LAWRENCE R. RABINER, NANCY Y. GRAHAM, AND HOWARD D. HELMS, "Linear Programming Design of IIR Digital Filters with Arbitrary Magnitude Function", IEEE TRANSACTIONS ON ACOUSTICS, SPEECH, SPIES. ASSP-22, NO. 2, APRIL 1974 PP. 117-123

The ΔΣ modulator according to one embodiment includes a first adder that adds a first input signal and a second input signal having adjacent frequencies, a loop filter, an output of the first adder, and an output of the loop filter. A second adder that adds the above, a quantizer that generates quantization data based on the output of the second adder, a feedback signal that feeds back the output of the quantizer, and an output of the first adder. The loop filter is provided with a differential device for obtaining the difference between the two and the difference, and the loop filter corresponds to the frequency of the first pass band corresponding to the frequency of the first input signal and the frequency of the second input signal. In addition to having a second pass band, in the frequency characteristics of the ΔΣ modulator, a pole and a pole and a pole and the like are placed between the first noise blocking band corresponding to the first passing band and the second noise blocking band corresponding to the second passing band. It has a filter characteristic in which at least one of the zero points is provided at one or more.

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 the embodiment is a semiconductor integrated circuit used in a delta-sigma modulator that performs delta-sigma modulation on a first input signal and a second input signal having adjacent frequencies, and is the first input signal. The first adder that adds the second input signal and the second input signal, the loop filter, the second adder that adds the output of the first adder and the output of the loop filter, and the output of the second adder. A delta-sigma that generates quantized data based on The loop filter has a first pass band corresponding to the frequency of the first input signal and a second pass band corresponding to the frequency of the second input signal, and in the frequency characteristics of the ΔΣ modulator. It has a filter characteristic in which at least one of a pole point and a zero point is provided between the first noise blocking band corresponding to the first passing band and the second noise blocking band corresponding to the second passing band.

Further, the computer program according to the embodiment is a computer program for causing a computer to perform distortion compensation processing of ΔΣ modulation performed on data representing the first input signal and the second input signal having adjacent frequencies. Quantification based on the first addition step of adding the plurality of input signals to the computer, the second addition step of adding the output of the first addition step and the output of the loop filter, and the output of the second addition step. A quantization data generation step for generating data, a difference step for obtaining a difference between a feedback signal fed back from the output of the quantization data generation step and an output of the first addition step, and outputting the difference to the loop filter. A computer program for executing a process including, the loop filter has a first pass band corresponding to the frequency of the first input signal and a second pass band corresponding to the frequency of the second input signal. In the frequency characteristics of the ΔΣ modulator, at least one of a pole point and a zero point is provided between the first noise blocking band corresponding to the first passing band and the second noise blocking band corresponding to the second passing band. It is a computer program having the above-mentioned filter characteristics.

FIG. 1 is a block diagram showing an example of a transmitter. FIG. 2 is a block diagram showing a configuration of the ΔΣ modulator according to the first embodiment. FIG. 3 is a graph showing the frequency-amplitude characteristics of the ΔΣ modulator, and shows an example of the setting mode of the _upper limit value Fupper (ω) and the lower limit value F _{lower (ω).} FIG. 4 is a graph showing an example of frequency-amplitude characteristics by the noise transfer function NTF (z) of the ΔΣ modulator of the present embodiment. FIG. 5A is a diagram showing an example of arrangement of poles and zeros in the noise transfer function NTF (z) of the ΔΣ modulator of the present embodiment. FIG. 5B is a diagram showing the arrangement of poles and zeros when the noise transfer function NTF (z) is obtained when the first noise blocking band and the second noise blocking band are set independently of each other as a comparative example. .. FIG. 6 shows the frequency-amplitude characteristics of the noise transfer function NTF (z) of the ΔΣ modulator of the present embodiment shown in FIG. 5A and the frequency-amplitude characteristics of the noise transfer function NTF (z) shown in FIG. 5B. It is a comparison figure. FIG. 7 is a diagram showing an example of frequency-amplitude characteristics of a conventional ΔΣ modulator capable of outputting an output signal including a plurality of signals having different frequencies.

[Problems to be solved by this disclosure]
By providing a plurality of loop filters corresponding to each of the plurality of input ports, it is possible to configure a delta-sigma modulator capable of outputting an output signal including a plurality of signals having different frequencies.
Further, it is also conceivable to configure a ΔΣ modulator capable of outputting an output signal including a plurality of signals having different frequencies by giving an addition signal obtained by adding the plurality of input signals to one loop filter.

In both the case of using a plurality of loop filters and the case of using a single loop filter, the delta-sigma modulator has a frequency characteristic having a band in which noise is blocked corresponding to the frequency of each of the plurality of input signals. It is necessary to set such a noise transfer function.

FIG. 7 is a diagram showing an example of frequency-amplitude characteristics of a conventional ΔΣ modulator capable of outputting an output signal including a plurality of signals having different frequencies.
In FIG. 7, it is shown that a band in which quantization noise is blocked (noise blocking band) exists in the frequency band corresponding to two input signals having different frequencies.

Here, in the delta-sigma modulator, the quantization noise that has passed through the loop filter is negatively fed back, but if the power of the quantization noise in the band other than the noise suppression band becomes larger than necessary, it is in the band other than the noise suppression band. Even the quantization noise is negatively fed back, and oscillation may occur. The occurrence of such oscillation may affect the operation of the delta-sigma modulator.
Therefore, in a band other than the noise suppression band, it is preferable to set the frequency-amplitude characteristic so that the power of the quantized noise does not become larger than necessary.

For example, in the frequency characteristic of a ΔΣ modulator that outputs an output signal including only one signal, there is only one noise blocking band corresponding to one input signal. For this reason, in a delta-sigma modulator that outputs an output signal containing only one signal, by adjusting the parameters for setting the noise suppression band, the amplitude of the band other than the noise suppression band does not become larger than necessary. It can be adjusted indirectly.

However, the frequency characteristics of the ΔΣ modulator that can output an output signal including multiple signals with different frequencies include a noise blocking band corresponding to multiple input signals and a band other than the noise blocking band in which quantization noise is not suppressed. Is included.
Therefore, as shown in FIG. 7, the band other than the noise blocking band includes the band B located between the two noise blocking bands arranged adjacent to each other.

The amplitude in the band B between the two noise blocking bands tends to be relatively larger than the other bands due to the influence from both noise blocking bands because the two noise blocking bands are adjacent to each other. Furthermore, the closer the two noise suppression bands are, the greater the tendency. Moreover, even if an attempt is made to indirectly adjust the amplitude of the band between the two noise suppression bands by setting both noise suppression bands, it is difficult to adjust the amplitude appropriately due to the influence from both noise suppression bands.
Therefore, in a ΔΣ modulator capable of outputting an output signal including a plurality of signals having different frequencies, the amplitude in the band B between the two noise blocking bands becomes larger than necessary, and good frequency characteristics can be obtained. It was sometimes difficult.

The present disclosure has been made in view of such circumstances, and is a good frequency even when the signal frequencies are close to each other in a delta-sigma modulator capable of outputting an output signal including a plurality of signals having different frequencies. The purpose is to provide a technique capable of obtaining amplitude characteristics.

[Effect of this disclosure]
According to the present disclosure, in a delta-sigma modulator capable of outputting an output signal including a plurality of signals having different frequencies, good frequency-amplitude characteristics can be obtained even when the frequencies of the signals are close to each other.

[Outline of Embodiment]
First, the contents of the embodiments will be listed and described.
(1) The ΔΣ modulator according to the embodiment includes a first adder that adds a first input signal and a second input signal having adjacent frequencies, a loop filter, an output of the first adder, and the loop. A second adder that adds the output of the filter, a quantizer that generates quantization data based on the output of the second adder, a feedback signal that feeds back the output of the quantizer, and the first addition. The loop filter includes a differential device that obtains a difference from the output of the device and gives the difference to the loop filter, and the loop filter has a frequency of a first pass band and a frequency of a second input signal corresponding to the frequency of the first input signal. In addition to having a second pass band corresponding to the above, in the frequency characteristics of the ΔΣ modulator, between the first noise stop band corresponding to the first pass band and the second noise stop band corresponding to the second pass band. , Has a filter characteristic in which at least one of a pole point and a zero point is provided at least one.

According to the ΔΣ modulator having the above configuration, at least one of a pole point and a zero point is provided between two noise blocking bands adjacent to each other in the frequency characteristic by the noise transfer function of the ΔΣ modulator. By adjusting the pole or zero point, it is possible to suppress the amplitude in the band between the two noise blocking bands so as not to be unnecessarily large. As a result, the frequency-amplitude characteristic can be set appropriately.

(2) In the delta-sigma modulator, the frequency characteristic is preferably a filter characteristic as an elliptic function filter or a quasi-elliptic function filter.
In this case, in the noise transfer function of the delta-sigma modulator, a pole or a zero point can be appropriately provided in the band between two passing bands adjacent to each other.

(3) Further, in the delta-sigma modulator, in order to suppress the occurrence of oscillation, it is preferable that the absolute value of the noise transfer function that determines the frequency characteristic is 2 or less.
(4) More preferably, the absolute value of the noise transfer function is 1.5 or less.

(5) Further, in the delta-sigma modulator, the frequency characteristic is a filter characteristic as an elliptic function filter or a quasi-elliptic function filter, and the absolute value of the noise transfer function is preferably 1.5 or less.

(6) 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.

(7) 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 first input signal and a second input signal having adjacent frequencies. A first adder that adds one input signal and the second input signal, a loop filter, a second adder that adds the output of the first adder and the output of the loop filter, and the second addition. The difference between the quantifier that generates quantized data based on the output of the device, the feedback signal that feeds back the output of the quantifier, and the output of the first adder is obtained, and the difference is given to the loop filter. The loop filter comprises a delta-sigma modulator, the loop filter having a first pass band corresponding to the frequency of the first input signal and a second pass band corresponding to the frequency of the second input signal, and the ΔΣ modulator. In terms of frequency characteristics, a filter characteristic in which at least one of a pole point and a zero point is provided between the first noise blocking band corresponding to the first passing band and the second noise blocking band corresponding to the second passing band. Have.

(8) Further, the computer program according to the embodiment is a computer program for causing a computer to perform distortion compensation processing of ΔΣ modulation performed on data representing the first input signal and the second input signal having adjacent frequencies. Based on the first addition step of adding the plurality of input signals to the computer, the second addition step of adding the output of the first addition step and the output of the loop filter, and the output of the second addition step. The difference between the quantization data generation step that generates the quantization data, the feedback signal that feeds back the output of the quantization data generation step, and the output of the first addition step is obtained, and the difference is output to the loop filter. It is a computer program that executes a process including a difference step, and the loop filter sets a first pass band corresponding to the frequency of the first input signal and a second pass band corresponding to the frequency of the second input signal. In addition, in the frequency characteristics of the ΔΣ modulator, at least one of a pole point and a zero point is provided between the first noise blocking band corresponding to the first passing band and the second noise blocking band corresponding to the second passing band. Is a computer program having one or more filter characteristics.

[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.
[Transmitter configuration]
FIG. 1 is a block diagram showing an example of a transmitter.
In FIG. 1, the transmitter 100 includes a plurality of quadrature modulators (primary modulators) 102 and 103, and a ΔΣ modulator (secondary modulator) 1.

Each of the plurality of orthogonal modulation units 102 and 103 is configured as a digital orthogonal modulator that performs orthogonal modulation by digital signal processing on a baseband signal that has been converted into digital data. The quadrature modulation units 102 and 103 perform quadrature modulation as primary modulation for the _{baseband signals I 1} , Q ₁ , I ₂ and Q _2.
The quadrature modulation units 102 and 103 perform quadrature modulation, up-conversion, and the like on the baseband signal, and output the RF (Radio Frequency) signal as digital data.
The RF signal is a signal radiated into space as a radio wave, and is, for example, a signal used for mobile communication and broadcasting services.

The quadrature modulation units 102 and 103 are configured to output _{RF signals U 1} and U _{2 having radio frequencies different from each other.} The plurality of RF 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 RF signals (input signals) U ₁ and U ₂ , and a pulse signal (quantized data) including _{a plurality of RF signals U 1} and U _2. Can be output.
Pulse signal ΔΣ modulator 1 outputs the frequency RF signals U _1, U ₂ as an analog signal into a plurality of RF signals U _1, U ₂ corresponding frequency band to each of the frequencies of the frequency band of the pulse signal It is included as an ingredient.

The output signal of the ΔΣ modulator 1 is given to the first band bus filter 105 and the second band pass filter 106, which are analog filters, via the transmission line 104.
The transmitter 100 of the present embodiment transmits a pulse signal, which is an output signal of the ΔΣ modulator 1, as a transmission signal.

Bandpass filters 105 and 106 are provided corresponding to both RF signals _U 1, _{U 2.} First band-pass filter 105 has a bandpass which passes RF signals _{U 1.} Further, the second bandpass filter 106 has a pass band through which the _{RF signal U 2 is passed.}

When the pulse signal output by the ΔΣ modulator 1 is given to the first bandpass filter 105, the first bandpass filter 105 removes frequency components (noise components, etc.) outside the band of the _{RF signal U 1 from the pulse signal.} Output the signal. Thus, the first band-pass filter 105 outputs a RF signal _{U 1.}
When the pulse signal output by the ΔΣ modulator 1 is given to the second bandpass filter 106, the second bandpass filter 106 outputs a signal from which the frequency component outside the band of the _{RF signal U 2 is removed from the pulse signal.} .. Therefore, the second bandpass filter 106 outputs the _{RF signal U 2.}
These RF signals U ₁ and RF signals U ₂ are given to an amplifier or the like and are radiated into space as radio waves or transmitted via a transmission path.

Since the pulse signal that is the output of the transmitter 100 is a digital signal, _{it is possible to transmit the RF signals U 1} and U ₂ as digital signals to a long distance through a high-speed transmission line such as an optical fiber.
Further, since a plurality of RF signals can be included in one data stream, a plurality of RF signals can be transmitted by one transmission line.

[Structure of delta-sigma modulator]
FIG. 2 is a block diagram showing a configuration of the ΔΣ modulator 1 according to the first embodiment. As shown in FIG. 2, .DELTA..SIGMA modulator 1 comprises input ports 2a to two different RF signal (input _signal) U 1 frequency, _{U 2} is input, the 2b. The ΔΣ modulator 1 outputs a single output signal V (ΔΣ modulated signal: quantized data) including two received RF signals U ₁ and U _{2 from the output port 4.}

The delta-sigma modulator 1 includes a _{first adder 5 for adding RF signals U 1} and U ₂ (first input signal and second input signal), a loop filter 6, an output of the first adder 5, and a loop filter 6. A second adder 7 that adds the outputs of It is provided with a difference device 9 for obtaining a difference from the output of the device 5 and giving it to the loop filter 6.

The first adder 5 adds the RF signals U ₁ and U ₂ received by the input ports 2a and 2b. The output of the first adder 5 is given to each of the second adder 7 and the differencer 9.
The output of the first adder 5 is given to the differencer 9, and the output signal V output from the quantizer 8 is given as a feedback signal. The output signal V given to the differencer 9 as a feedback signal is fed back through the path 10 connecting the output end of the quantizer 8 and the differencer 9. Hereinafter, the output signal V fed back to the differential device 9 via the path 10 is also referred to as a feedback signal.

The differencer 9 obtains the difference between the feedback signal and the output of the first adder 5, and outputs the difference to the loop filter 6.
The loop filter 6 includes a first filter circuit 15, a second filter circuit 16, and a third adder 18.
The first filter circuit 15 and the second filter circuit 16 are connected to the difference device 9 and the third adder 18 in parallel with each other. The output of the differencer 9 is branched by the branch portion 20 and given to the first filter circuit 15 and the second filter circuit 16.
The third adder 18 adds the output of the first filter circuit 15 and the output of the second filter circuit 16. The output of the third adder 18 is given to the second adder 7 as the output of the loop filter 6.

The second adder 7 adds the output of the first adder 5 and the output of the loop filter 6.
The output of the second adder 7 is given to the quantizer 8. The quantizer 8 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 8 is given to the loop filter 6 as a feedback signal via the path 10.
The output signal V from the quantizer 8 is given to the output port 4 and output.

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

The transfer function L (z) of the loop filter 6 is represented by the sum of the transfer function of the first filter circuit 15 and the transfer function of the second filter circuit 16.
The transfer function L (z) of the loop filter 6 can be expressed as the sum of polynomials of lower order than the transfer function L (z), as will be described later.
In the present embodiment, the transfer function L (z) of the loop filter 6 is represented as the sum of the two terms, and the characteristics corresponding to these two terms are set as the characteristics of the first filter circuit 15 and the second filter circuit 16.

As a result, the transfer function L (z) of the loop filter 6 (the noise transfer function NTF (z) of the ΔΣ modulator 1) can be configured by a filter circuit having a transfer function of lower order than the transfer function L (z). can.

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 loop filter 6 and the quantizer 8 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 delta-sigma modulator 1 by giving the FPGA circuit configuration information for configuring the delta-sigma modulator 1.

[About the noise transfer function of the delta-sigma modulator]
The output signal V of the ΔΣ modulator 1 is represented by a function in the z region as shown in the following equation (1).
V (z) = E (z) + U ₁ (z) + U ₂ (z) +
L (z) (U ₁ (z) + U ₂ (z) -V (z)) ... (1)
V (z) = U ₁ (z) + U ₂ (z) + (1 / (1 + L (z))) E (z)
= U ₁ (z) + U ₂ (z) + NTF (z) E (z) ... (2)

In the above equations (1) and (2), V (z) is an output signal, U ₁ (z) and U ₂ (z) are RF signals, and L (z) is a transfer function L (z) of the loop filter 6. , NTF (z) is the noise transfer function of the ΔΣ modulator 1, and E (z) is the quantization noise of the ΔΣ modulator 1.

From the above equation (2), the output of the difference device 9 is expressed as the following equation (3).
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) ... (3)

From the equation (3), the output of the differencer 9 has the inverse characteristic of the noise component included in the output signal V (z).
The loop filter 6 of the present embodiment has a first pass band including the frequency band _{of the RF signal U 1 and a second pass band including the frequency band of the RF signal U 2} , and has a first pass band and a second pass band. In bands other than the band, it is set to have a filter characteristic that blocks the passage of signals.

Therefore, the loop filter 6 outputs a signal having an inverse characteristic of the noise component in the first pass band including the frequency band _{of the RF signal U 1 and the second pass band including the frequency band of the RF signal U 2, and the second.} Give to the adder 7. Signal having the inverse characteristic is added to the second adder 7 outputs of the first adder 5 (signal obtained by adding the RF signals U _1, U _2). The output of the first adder 5 to which the signal having the inverse characteristic is added is quantized by the quantizer 8, and the output signal V is fed back to the loop filter 6.

When an output is given from the differential device 9, the loop filter 6 of the present embodiment outputs a signal having the opposite characteristics of the noise component in the first pass band and the second pass band. The output of the loop filter 6 is repeatedly added to the output of the first adder 5. As a result, the noise in the first pass band and the second pass band in the output signal V is suppressed.
Therefore, the noise transfer function NTF (z) of the ΔΣ modulator 1 of the present embodiment has two noise suppression bands (first noise suppression band and second passage band) in the first pass band and the second pass band by the loop filter 6. It is set to have a frequency-amplitude characteristic (frequency-quantized noise characteristic) having a noise blocking band).
That is, the noise transfer function NTF (z) that determines the frequency-amplitude characteristic of the ΔΣ modulator 1 is set by the filter characteristic of the loop filter 6.

The filter characteristic (transfer function L (z)) of the loop filter 6 is set based on the noise transfer function NTF (z) obtained after the noise transfer function NTF (z) is obtained.
Hereinafter, a method of setting the noise transfer function NTF (z) will be described.
The noise transfer function NTF (z) of the delta-sigma modulator 1 is configured as an IIR (Infinite Impulse Response) filter. Therefore, the noise transfer function NTF (z) is expressed by the following equation (4).

In equation (4), z _i and _pi are parameters corresponding to the values of each i.
From the equation (4), the noise transfer function NTF (z) can be expressed as a fraction by the denominator polynomial D (z) and the numerator polynomial N (z) as in the following equation (5).

Here, Lee's criteria (Lee transfer: "Translated by Takao Waho and Akira Yasuda (Original author Richard Schreier, Gabor C. Temes)," Introduction to ΔΣ type analog / digital converter ", Maruzen Co., Ltd., p. 81" ), If the absolute value of the noise transfer function NTF (z) is smaller than 1.5, it is highly likely that the noise transfer function is stable.
That is, as shown in the following equation (6), the absolute value of the noise transfer function NTF (z) may be an allowable value G (for example, 1.5) or less.

When the permissible value G is larger than 1.5, for example, even if the permissible value G is set to 2, a substantially stable operation may be obtained. Therefore, the permissible value G may be set to 2. In this case, the degree of freedom in obtaining the noise transfer function NTF (z) can be increased.
However, when emphasizing stable operation, it is more preferable to set the allowable value G to 1.5 or less.

By squared both sides of the equation (6), it can be transformed as shown in the following equation (7).

It should be noted that m = 0, 1, 2, ... N.
_{Here, if the parameters a m} and b _m in the equation (5) are obtained, the noise transfer function NTF (z) is determined.
Therefore, in _{order to obtain the parameters a m} and b _m in the equation (5), the parameters c _m and d _m in the equation (7) are obtained.

Since cos (ωt) = (e ^jωt + e ^−jωt ) × (1/2), the above equation (7) can be expressed as the following equation (8). In addition, ω is a frequency and t is a time.

In equation (8), the square of the denominator polynomial D (z) (hereinafter, also referred to as D (z) ^) and the square of the numerator polynomial N (z) (hereinafter, also referred to as N (z) ^). ) Naturally satisfies the following equations (9) and (10).

Further, as shown in the equation (11), the upper limit value _Fupper (ω) (the square of the allowable value G) and the lower limit value F _lower (ω) are obtained for the square of the noise transfer function NTF (z). ) Is set.

_{After setting the upper} limit value Fupper (ω) and the lower limit value F _lower (ω) in the equation (11) to appropriate values according to the frequency ω, the upper limit value _{Fupper is based on the equation (11).} The constraints of D (z) ^ and N (z) ^ regarding (ω) and the constraints _{of D (z) ^ and N (z) ^ regarding the lower limit value Frequency (ω) are obtained.}
Further, the equations (9) and (10) are also constraints of D (z) ^ and N (z) ^.
These formula (9), equation (10), and on the basis of the equation (11) than those obtained D (z) ^ and N (z) ^ constraints, obtains a function containing a parameter _c m, the _{d m,} the by focusing the value of the function, determined in equation (7) parameter _c m, the _{d m.}
The parameter c _m, in order to obtain the d _m, it is possible to use the simplex method.

Determined parameters _c m, the _{d m} by substituting the above equation (7), the parameters _a m in the formula (5), can be obtained _{b m.}
Thereby, the noise transfer function NTF (z) satisfying the conditions limited by the set _upper limit value Fupper (ω) and the lower limit value F _{lower (ω) can be obtained.}

In the present embodiment, it is necessary to obtain the noise transfer function NTF (z) of the ΔΣ modulator 1 having a frequency characteristic having a plurality of (two) noise blocking bands.
Therefore, in the present embodiment, the upper limit value _Function (ω) and the lower limit value _Flower (ω) are appropriately set according to the two noise blocking bands and the band outside the noise blocking band, and then noise is generated. Find the transfer function NTF (z).

From the above equation (11), the constraint conditions of D (z) ^ and N (z) ^ regarding the _{upper limit value Fupper (ω) are expressed by the following equation (12).}

Here, in the present embodiment, as shown in the equation (12), the frequency ω is a value in the first noise blocking band and the second noise blocking band (in the first pass band and in the second pass band). In this case, the upper limit value _Frequency (ω) is set to the square of the coefficient α (α ^2). The frequency omega be a value outside both noise stop band, the upper limit value _{F upper} (ω) is set to 1.5 ^2.

Further, the constraint conditions of D (z) ^ and N (z) ^ regarding the _{lower limit value Flower (ω) are expressed by the following equation (13).}
Further, the lower limit value _Flower (ω) is obtained by multiplying the _upper limit value Fupper (ω) by the square of the coefficient β (ω) (β (ω) ² ) as shown in the equation (14). Be done. That is, the lower limit value F _lower (ω) is set with reference to the _{upper limit value F upper (ω).}

FIG. 3 is a graph showing the frequency-amplitude characteristics of the ΔΣ modulator 1, and shows an example of the setting mode of the _upper limit value Fupper (ω) and the lower limit value F _{lower (ω).} In the figure, the vertical axis shows the logarithm of the square of the amplitude.

The upper limit value _Fupper (ω) and the lower limit value F _lower (ω) are set for each of the discretely set frequencies.
In FIG. 3, circles indicate _{points where the upper} limit value Fupper (ω) is set, and cross marks _{indicate points where the lower} limit value F lower (ω) is set.
In FIG. 3, the broken line is a diagram showing the logarithm of the squared noise transfer function NTF (z) of the ΔΣ modulator 1.
Further, in FIG. 3, the frequency f1 is the center frequency of the RF signal U _1, there is shown a first noise rejection band including the frequency f1. Further, the frequency f2 is _{the center frequency of the RF signal U 2} , and the second noise blocking band including the frequency f2 is shown.

_{As shown in FIG. 3, the upper} limit value Upper (ω) in the frequency in the first noise blocking band and the second noise blocking band is set to ^{α 2.} Therefore, the value of the upper limit value _{F upper (ω)} in FIG. 3 has a 10 log ₁₀ alpha ^2. In addition, α is set to a value between 0.01 and 0.05.

_{The upper limit Fupper} (ω) at frequencies outside both noise suppression bands is set to ^{1.5 2.} Therefore, the value of the upper limit value _{F upper (ω)} in FIG. 3 has a _{10 log} 10 1.5 ^2.

_{Further, the lower} limit value Flower (ω) at the frequency within both noise suppression bands and the frequency outside both noise suppression bands is set to a value obtained by multiplying the _upper limit value Fupper (ω) by β (ω) ^2. .. Therefore, the value of the lower limit value Flower (ω) _{in FIG. 3 is a value that is 10} log 10 β (ω) ² _{lower than} the value of the upper limit value F _upper (ω). Note that β (ω) is set to a value between 1 and 10.

Further, β (ω) is set to a different value depending on whether the frequency ω is a frequency within both noise suppression bands and a frequency outside both noise suppression bands. When the frequency ω is a frequency within both noise suppression bands, β (ω) is set to a smaller value than when the frequency is outside both noise suppression bands. _{As a result, the difference between the upper} limit value Fupper (ω) and the lower limit value F _lower (ω) when the frequency ω is a frequency within both noise suppression bands is larger than that when the frequency is outside both noise suppression bands. Set small.

In the present embodiment, the case of obtaining the lower limit value _{F lower} (omega) the upper limit value _{F upper} the (omega) as a reference, the lower limit value _{F lower} (omega) is the upper limit value _{F upper} (ω) On the other hand, it may be set to an independent value.

_{By setting the upper} limit value Frequency (ω) and the lower limit value _Frequency (ω) as described above, as shown in FIG. 3, the noise transfer function NTF (z) (of the ΔΣ modulator 1 is squared. Has a first noise blocking band and a second noise blocking band, and has a frequency-amplitude characteristic suppressed so that the amplitude of the band outside both noise blocking bands does not become larger than necessary.

As shown in FIG. 3, both noise suppression is performed in the frequency characteristics obtained by the noise transfer function NTF (z) obtained by setting the upper limit value and the lower limit value in both noise suppression bands and the band outside both noise suppression bands. A zero point and a pole point are provided in the band and the band outside both noise blocking bands.

In particular, in the present embodiment, a zero point and a pole point are provided in a band outside both noise suppression bands, and therefore, between two noise suppression bands (first noise suppression band and second noise suppression band) adjacent to each other. At least one of a pole point and a zero point is provided in the band of.

Constraints of D (z) ^ and N (z) ^ for the _upper limit value Function (ω) and the lower limit value F _lower (ω) set as described above, and D according to equations (9) and (10). (z) ^ and N (z) ^ based on the constraints to obtain the parameters _c m, _{d m} in the formula (7), further, by obtaining the parameters _a m, _{b m} in the formula (5) , The noise transfer function NTF (z) satisfying the conditions limited by the _upper limit value Fupper (ω) and the lower limit value F _{lower (ω) is obtained.}
The frequency characteristic of the noise transfer function NTF (z) of the ΔΣ modulator 1 obtained in the present embodiment has the filter characteristic as an elliptic function filter.

The method of obtaining the noise transfer function NTF (z) based on the constraints of D (z) ^ and N (z) ^ is, for example, "LAWRENCE R.RABINER, NANCY Y.GRAHAM, ANDHOWARD D.HELMS". , "Linear Programming Design of IIR Digital Filters with Arbitrary Magnitude Function", EEEE TRANSACTIONS ON ACOUSTICS, SPEECH, AND SIG. ASSP-22, NO. 2, APRIL 1974 PP. 117-123 ”is according to the method described.
The above document describes a design method for designing a general low-pass filter having one pass band as an elliptic function filter.
In this embodiment, the filter design method described in the above document is applied to the noise transfer function NTF (z) of the ΔΣ modulator 1.

When the noise transfer function NTF (z) is obtained by the above method, the transfer function L (z) of the loop filter 6 is obtained from the noise transfer function NTF (z) based on the above equation (2).
The loop filter 6 having the transfer function L (z) has a first pass band corresponding to the frequency f1 of the _{RF signal U 1} and a second pass band corresponding to the frequency f2 of the _{RF signal U 2, and is ΔΣ modulated.} It has a filter characteristic in which at least one of a pole point and a zero point is provided in the band between the two noise blocking bands corresponding to both pass bands, which is the band in the frequency characteristic by the noise transmission function NTF (z) of the device 1. ..

Further, each term obtained by decomposing the transfer function L (z) into the sum of the two terms becomes the transfer function of the first filter circuit 15 and the second filter circuit 16. The obtained transfer functions of the first filter circuit 15 and the second filter circuit 16 are reflected in the first filter circuit 15 and the second filter circuit 16 by the control unit 19 (FIG. 2).
As a result, the ΔΣ modulator 1 has a frequency-amplitude characteristic according to the noise transfer function NTF (z) obtained by the above method.

According to the ΔΣ modulator 1 of the present embodiment, in the frequency characteristic of the ΔΣ modulator 1 by the noise transfer function NTF (z), at least one of the pole point and the zero point is in the band between the two noise blocking bands adjacent to each other. Since one or more are provided, by adjusting this pole or zero point, it is possible to suppress the amplitude in the band between the two noise blocking bands so as not to become larger than necessary. As a result, the frequency-amplitude characteristic can be appropriately set, and it is possible to suppress negative feedback of quantized noise outside both noise suppression bands. As a result, the ΔΣ modulator 1 can be operated stably.

That is, the frequency characteristics of the ΔΣ modulator 1 capable of outputting an output signal including two RF signals having different frequencies include two noise blocking bands and a band other than the noise blocking band in which the quantization noise is not suppressed. .. Further, the band other than the noise blocking band includes a band located between the two noise blocking bands.
The amplitude in the band between the two noise blocking bands tends to be relatively larger than the other bands due to the influence from both noise blocking bands because the two noise blocking bands are adjacent to each other. Furthermore, the closer the two noise suppression bands are, the higher the tendency.
Therefore, in a ΔΣ modulator capable of outputting an output signal including a plurality of signals having different frequencies, the amplitude in the band between the two noise blocking bands may be larger than necessary, and good frequency-amplitude characteristics. Was sometimes difficult to obtain.

In particular, in the 5th generation mobile communication system, the use of frequency bands such as 3.5 GHz and 4.5 GHz is considered, and when speeding up by carrier aggregation using these, the frequency band used is about 1 GHz. May be adjacent at intervals.
In such a 5th generation mobile communication system, when carrier aggregation is performed using a ΔΣ modulator configured to output an output signal including a plurality of signals having different frequencies, the two frequency bands used are 1 GHz. By adjoining each other at a certain interval, the amplitude in the band between the two used frequency bands (both noise blocking bands) may be relatively larger than that in the other bands.

Therefore, in order to perform carrier aggregation in the 5th generation mobile communication system, good frequency-amplitude characteristics are used when a ΔΣ modulator configured to output an output signal including a plurality of signals having different frequencies is used. Will be particularly difficult to obtain.

On the other hand, according to the ΔΣ modulator 1 of the present embodiment, at least one of a pole point and a zero point is provided in the band between the two noise blocking bands, and the pole point or the zero point can be adjusted by adjusting the pole point or the zero point. , Frequency-amplitude characteristics can be set appropriately.
As a result, even if the ΔΣ modulator 1 of the present embodiment is used for carrier aggregation in the 5th generation mobile communication system, the frequency-amplitude characteristics can be appropriately set and stable operation can be performed. ..

FIG. 4 is a graph showing an example of the frequency-amplitude characteristic of the ΔΣ modulator 1 of the present embodiment by the noise transfer function NTF (z). Further, FIG. 5A is a diagram showing an example of arrangement of poles and zeros in the noise transfer function NTF (z) of the ΔΣ modulator 1 of the present embodiment. Further, FIG. 5B shows, as a comparative example, the arrangement of the poles and zeros when the noise transfer function NTF (z) is obtained when the first noise blocking band and the second noise blocking band are set independently of each other. , Is a diagram showing the arrangement of poles and zeros in the noise transfer function NTF (z) shown in FIG. 7.

In FIG. 4, the mark shown on the upper side of the paper surface of the diagram showing the noise transfer function NTF (z) is a mark indicating the frequency in which the pole and the zero point are arranged, and the circle mark is the mark in which the zero point is arranged. Indicates the frequency. The cross marks indicate the frequencies at which the poles are arranged.

As shown in FIG. 4, in the frequency characteristics of the ΔΣ modulator 1 due to the noise transfer function NTF (z), zeros are provided in the first noise blocking band and the second noise blocking band, and outside both noise blocking bands. Also has poles and zeros.
In particular, the band A between the first noise blocking band and the second noise blocking band is provided with two poles.

Further, as shown in FIG. 5B, when the first noise blocking band and the second noise blocking band are set independently of each other, the poles are provided only in both noise blocking bands, so that each pole point is on the circumference. It is concentrated in a specific part.
On the other hand, in the present embodiment, as shown in FIG. 5A, the poles and zeros are arranged scattered on and within the circumference, and the frequency by the noise transfer function NTF (z) of the ΔΣ modulator 1- The amplitude characteristic shows the filter characteristic as an elliptical function filter.

FIG. 6 shows the frequency-amplitude characteristic of the noise transfer function NTF (z) of the ΔΣ modulator 1 of the present embodiment shown in FIG. 5A and the frequency-amplitude characteristic of the noise transfer function NTF (z) shown in FIG. 5B. It is a figure comparing.
In FIG. 6, the solid line is a diagram showing the noise transfer function NTF (z) of the ΔΣ modulator 1 of the present embodiment shown in FIG. 5A, and the broken line is a diagram showing the noise transfer function NTF (z) shown in FIG. 5B. It is a diagram.

As shown in FIG. 6, in the frequency-amplitude characteristic by the noise transfer function NTF (z) shown in FIG. 5B, the amplitude in the band A between the first noise blocking band and the second noise blocking band exceeds 5 dB. It has become.
On the other hand, in the frequency-amplitude characteristic of the ΔΣ modulator 1 of the present embodiment, it can be seen that the amplitude in the band A is a value near 0 dB and is suppressed so as not to be larger than necessary.

As described above, according to the ΔΣ modulator 1 of the present embodiment, in the frequency-amplitude characteristic by the noise transfer function NTF (z), the pole point is in the band A between the first noise blocking band and the second noise blocking band. Two are provided, and by appropriately adjusting these pole points, it is possible to suppress the amplitude in the band A from becoming larger than necessary, and it is possible to obtain good frequency-amplitude characteristics.

〔others〕
It should be noted that the embodiments disclosed this time are exemplary in all respects and are not restrictive.
In the above embodiment, the _{ΔΣ modulator 1 capable of outputting an output signal including two RF signals U 1} and U 2 having different frequencies (adjacent frequencies) is shown, but includes a larger number of input signals having different frequencies. The same applies to a ΔΣ modulator capable of outputting an output signal, and good frequency-amplitude characteristics can be obtained.
That is, the first adder 5 can add three or more input signals, and the noise transfer function NTF (z) of the ΔΣ modulator 1 has a noise blocking band corresponding to the frequency of each input signal by the loop filter 6. Even when the frequency-amplitude characteristic is set to have, a good frequency-amplitude characteristic can be obtained by providing a pole between adjacent noise blocking bands.

In the above embodiment, in the frequency characteristic by the noise transfer function NTF (z) of the ΔΣ modulator 1, two pole points are provided in the band A (FIG. 4) between the first noise blocking band and the second noise blocking band. Although the case is illustrated, the number of poles provided in the band A may be one. Further, one or more zero points may be provided in the band A. Further, both poles and zeros may be provided in band A.

Further, in the above embodiment, the frequency characteristic of the ΔΣ modulator 1 is a filter characteristic as an elliptic function filter, but it may be a filter characteristic as a quasi-elliptic function filter.
Also in this case, at least one of the pole point and the zero point is provided in the band between the first noise blocking band and the second noise blocking band, whereby good frequency-amplitude characteristics can be obtained. can.

In the above embodiment, the case where the loop filter 6 is configured by connecting two filter circuits in parallel is illustrated, but a larger number of filter circuits may be used for the configuration. Further, a plurality of filter circuits may be connected in series to form the loop filter 6.

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 ΔΣ modulator 2a, 2b Input port 4 Output port 5 1st adder 6 Loop filter 7 2nd adder 8 Quantifier 9 Differential 10 Path 15 1st filter circuit 16 2nd filter circuit 18 3rd adder 19 Control unit 20 Branch unit 100 Transmitter 102, 103 Orthogonal modulator 104 Transmission path 105 1st bandpass filter 106 2nd bandpass filter

Claims (8)

It is a delta-sigma modulator,
A first adder that adds the first input signal and the second input signal whose frequencies are adjacent to each other,
With a loop filter,
A second adder that adds the output of the first adder and the output of the loop filter, and
A quantizer that generates quantized data based on the output of the second adder, and
A differential device that obtains a difference between a feedback signal that feeds back the output of the quantizer and the output of the first adder and gives the difference to the loop filter is provided.
The loop filter has a first pass band corresponding to the frequency of the first input signal and a second pass band corresponding to the frequency of the second input signal, and has a first pass in the frequency characteristics of the ΔΣ modulator. A ΔΣ modulator having a filter characteristic in which at least one of a pole point and a zero point is provided between a first noise blocking band corresponding to a band and a second noise blocking band corresponding to a second pass band. The ΔΣ modulator according to claim 1, wherein the frequency characteristic is a filter characteristic as an elliptic function filter or a quasi-elliptic function filter. The ΔΣ modulator according to claim 1 or 2, wherein the absolute value of the noise transfer function that determines the frequency characteristic is 2 or less. The ΔΣ modulator according to claim 3, wherein the absolute value of the noise transfer function is 1.5 or less. The frequency characteristic is a filter characteristic as an elliptic function filter or a quasi-elliptic function filter.
The ΔΣ modulator according to claim 1, wherein the absolute value of the noise transfer function is 1.5 or less. The ΔΣ modulator according to any one of claims 1 to 5.
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 a first input signal and a second input signal having adjacent frequencies.
A first adder that adds the first input signal and the second input signal, and
With a loop filter,
A second adder that adds the output of the first adder and the output of the loop filter, and
A quantizer that generates quantized data based on the output of the second adder, and
A differential device that obtains a difference between a feedback signal that feeds back the output of the quantizer and the output of the first adder and gives the difference to the loop filter is provided.
The loop filter has a first pass band corresponding to the frequency of the first input signal and a second pass band corresponding to the frequency of the second input signal, and has a first pass in the frequency characteristics of the ΔΣ modulator. A semiconductor integrated circuit having filter characteristics in which at least one of a pole point and a zero point is provided between a first noise blocking band corresponding to a band and a second noise blocking band corresponding to a second pass band. It is a computer program for causing a computer to execute a distortion compensation process of delta-sigma modulation performed on data representing the first input signal and the second input signal having adjacent frequencies.
The first addition step of adding the plurality of input signals to the computer,
A second addition step that adds the output of the first addition step and the output of the loop filter, and
A quantized data generation step that generates quantized data based on the output of the second addition step, and a quantized data generation step.
A difference step in which the difference between the feedback signal fed back from the output of the quantization data generation step and the output of the first addition step is obtained, and the difference is output to the loop filter.
Is a computer program that executes processing including
The loop filter has a first pass band corresponding to the frequency of the first input signal and a second pass band corresponding to the frequency of the second input signal, and has a first pass in the frequency characteristics of the ΔΣ modulator. A computer program having a filter characteristic in which at least one of a pole point and a zero point is provided between a first noise blocking band corresponding to a band and a second noise blocking band corresponding to a second pass band.

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