JPH0558282B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) In wireless communications, the relationship between the linearity of a power amplifier in a transmitter and the power supply efficiency is always a problem. If an amplifier with high power supply efficiency is used, nonlinear distortion will increase. When performing high-density digital transmission, linear modulation methods such as 4-phase PSK and 16-value QAM are used, but signals modulated by such modulation methods inevitably suffer from transmission spectrum degradation due to the nonlinearity of the amplifier. To compensate for such deterioration, distortion suppression using a negative feedback amplifier circuit is one of the methods commonly used. As one method for obtaining a high loop gain especially for signals in a high frequency band, a method is known in which the output of a power amplifier is demodulated and fed back in the form of a baseband signal.

The present invention relates to a negative feedback amplifier that demodulates the output of such a power amplifier and feeds it back in the form of a baseband signal.

(Prior art and its problems) As a method to demodulate and feed back the amplifier output,
2nd International Conference on Radio Spectrum Convergence Technics
Conferenceon Radio Spectrum Conversion
There is a method published in ``Techniques''. FIG. 2 shows an example of the prior art. Signals x, t, y, and t inputted from terminals 201 and 202 are inputted to low-frequency wave generators 230 and 235 through subtracters 201 and 215, respectively. The carrier wave which is the output of the low range wave generator 230 and the output of the sine wave generator 290 (the angular frequency is multiplied by ω _C in the multiplier 240, and the phase is changed by 90° between the output of the low range wave generator 235 and the phase shifter 295) The output of the sine wave generator 290 and the multiplier 24
After multiplication by 5, multipliers 240 and 24
The five outputs are added by an adder 250. adder 250
The output is a signal that has been orthogonally modulated by the baseband signals input from terminals 201 and 202. The output of the adder 250 is amplified by an amplifier 260 with a gain of G and is transmitted from the terminal 203. A transmission signal that receives a portion of the output of amplifier 260 and is attenuated by attenuator 270 having an attenuation amount R is input into multipliers 280 and 285 after its phase is adjusted by phase shifter 257 . The multiplier 285 demodulates the signal by multiplying it by the output of the sine wave generator 290, and the demodulated signal is input to the subtracter 210 and subtracted from the input signal from the terminal 201. The multiplier 280 demodulates the signal by multiplying it by the 90° phase-shifted sine wave generator output, and the demodulated signal is input to the subtracter 215 and subtracted from the input signal from the terminal 202. The low frequency wave generators 230 and 235 are used to limit the band of the feedback circuit, and it is desirable that the two characteristics are approximately equal. Furthermore, the phase shifter 275 is provided to prevent deterioration of the round-trip gain due to delay. For example, assume that the delay from the input of the amplifier 260 to the output of the attenuator 270 is Δτ, and that there is no phase shifter. At this time, the output of adder 250 z _O
If (t) is written as z _O (t) = x (t) cosω _C t + y (t) sinω _C t (1), the output of multipliers 280 and 285 is G・R・x(t−Δτ) cosΔτω _C or G・R・y(t−Δτ) cosΔτω _C (2). Therefore, if 0cosΔτω _C <1 (3), the feedback path gain will equivalently decrease, and distortion improvement characteristics will not be sufficiently obtained, and the gain seen from the input and output of the circuit will increase, causing further distortion. Become.

When cosΔτω _C <0 (4), positive feedback occurs and the circuit oscillates. Therefore, the phase shifter 275 is used to shift the phase of the attenuator output by Δθ
When the multipliers _{280 and} 285 are moved by Therefore, if Δθ is determined so that Δτω _C −Δθ=2nπ (6), the problems described above can be avoided. However, such a circuit
If it is used in a transmitter for an FDM system and the delay of the amplifier 260 has frequency characteristics, the loop gain will vary depending on the line.

Therefore, an object of the present invention is to prevent such deterioration of the open circuit gain.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a negative feedback amplifier which receives first and second baseband signals as inputs; first and second subtracters each receiving two baseband signals; a quadrature modulator receiving the first and second subtracter outputs and a sine wave generator output;
a power amplifier that amplifies and outputs the orthogonal modulation output; an attenuator that receives a portion of the output of the power amplifier and attenuates the signal; an output of the sine wave generator circuit by a phase determined by the control circuit output; a phase shifter that changes the phase of the output signal; and a demodulation operation performed upon receiving the output of the phase shifter and the output of the attenuator;
a third baseband signal corresponding to the baseband signal of the second baseband signal and a fourth baseband signal corresponding to the second baseband signal; and a quadrature demodulator that outputs the signals to the quadrature demodulator and a second subtracter; a band-limiting circuit included in a one-circuit circuit including first and second subtracters, the quadrature modulator, the power amplifier, the quadrature demodulator, and the attenuation circuit; The method is characterized in that the amount of phase change of the phase shifter is determined so that the circuit output has a maximum value.

(Operation) The effective value or complex amplitude average value of the orthogonal demodulator output baseband signal is known from the input signal power and the gain design values of each part of the negative feedback circuit. Therefore, it is possible to determine the complex amplitude average value of the output of the orthogonal demodulator and determine the amount of phase change of the phase shifter so that the determined value becomes a known desired value. As a result, the designed round-trip gain is always obtained.

(Example) The present invention will be described in detail below using the figures.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In this embodiment, digital signals are input from terminals 101 and 102, each of which is band-limited so that there is no intersymbol interference. For example, when transmitting a signal using 4-phase PSK, the waveform will be as shown in FIG. 4a.

The signal input from the terminal 101 is sent to the subtracter 110
The signal input from the terminal 102 is input to the subtracter 115. The outputs of subtracter 110 and subtracter 115 are input to quadrature modulator 130 through low-pass filters 120 and 125, respectively.
The quadrature modulator 130 modulates the output of the sine wave generator 131. The modulated signal is sent to a power amplifier 140
is amplified and transmitted. A part of the output of the amplifier 140 is attenuated by an attenuator 145 and sent to the quadrature demodulator 135.
Enter. The orthogonal demodulator 135 includes a phase shifter 132
The output of the attenuator 145 is demodulated using the output of the sine wave generator 131 that has passed through the sine wave generator 131 to obtain first and second baseband signals. Each baseband signal is input to subtracters 110 and 115. On the other hand, demodulator 1
35 output is also input to an amplitude calculation circuit 150 which calculates the average complex amplitude of the demodulated signal. For example, when the input signal is a digital signal, its average complex amplitude is proportional to the complex amplitude at the signal points shown in FIG. 3 using four-phase PSK as an example. FIG. 4a shows an example of the output of the orthogonal demodulator 135 when transmitting the signal points shown in FIG. 3. The signal in FIG. 4a may be sampled at the timing indicated by the arrow, and the complex amplitude at the sample point may be output. Amplitude calculation circuit 15
An example of 0 is shown in FIG. The quadrature demodulator outputs are input to sample circuits 510 and 520, respectively;
It is sampled at the rising edge of the pulse input from the terminal 503. The timing of the input signal from the terminal 503 is as shown in FIG. 4b, and the relationship between this signal and the output of the demodulator 135 is shown in FIGS. 4a and 4b. The signals sampled by sample circuits 510 and 520 are sent to square circuits 530 and 54, respectively.
The signals are squared by 0 and added by an adder 550. The output of adder 550 is the square value of the complex amplitude. From equation (5), the output of the amplitude calculation circuit 150 is G ² · R ² · (x ² (t-Δτ) + y ² (t-Δτ)) cos ² [
ω _C
Δτ−Δθ〕 (7) If the amplitude of the signal point in FIG. 3 is r, the value of equation (7) at the sampling time is r ² cos ² [ω _C Δτ−Δθ] (8). In the control circuit 160, the amplitude calculation circuit 150 output expressed by equation (8) and the desired output r ²
A control signal is output for determining the amount of phase change of the phase shifter 132 so that cos ² [ω _C Δτ−Δθ]=1 (9).

An example of the control circuit 150 is shown in FIG. The output of the amplitude calculation circuit 140 is input from the terminal 601. Formula (8)
The signal from terminal 601 is applied to comparator 610, which generates a counting pulse when the value of the input signal indicated by is less than the required value ^r2 , and which does not generate when it is equal. Further, the signal from the terminal 601 is input to a delay line 620 and a subtracter 630. In the subtracter 630, the terminal 6 is input from the output of the delay line 620, which is the previous input.
Subtract the signal from 01. The switch 640 receives the pulse that is the output of the comparator 610, and if the output of the subtracter 630 is positive, it decreases the count value of the counter 650 by 1, and if the output of the subtracter 630 is negative, it increases the count value of the counter 650 by 1. Outputs pulses. Upon receiving the output of the counter 650, a digital to analog converter 660 obtains a DC voltage. This DC voltage is applied to the phase shifter 132 to change the amount of phase change in the phase shifter. Note that it is also possible to set the reference voltage in the comparator 610 as low as ^0.9r2 instead of ^r2 . As the phase shifter 132,
The desired operation can be obtained by using a hybrid ring circuit and a circuit including a varactor diode as shown in FIG.

The present invention falls within the category of non-feedback control circuits, and such circuits inherently have the problem of unstable control. In order to avoid this problem, the band of the signal that goes around the circuit is limited to a circuit consisting of subtracters 110 and 115, a quadrature modulator 130, a power amplifier 140, an attenuator 145, and a quadrature demodulator 135. It is a well-known fact that it is necessary to provide a circuit (filter) to In the present invention, the low-pass filter is replaced by a subtracter 110 and a quadrature modulator 1.
30 and between the subtracter 115 and the quadrature modulator 1
30, but it can also be placed elsewhere. For example, when using a low-pass filter, the same effect can be obtained by placing the low-pass filter between orthogonal demodulator 135 and subtracter 110 and between orthogonal demodulator 135 and subtracter 115. is obtained.

On the other hand, in the present invention, since the purpose is to remove distortion around the center frequency of the amplifier output, the center frequency becomes the oscillation frequency of the oscillator 131 instead of a low-pass filter as a band limiting circuit of the loop circuit. A similar effect can be obtained by using a bandpass filter. In this case, a bandpass filter is provided somewhere between the orthogonal modulator 130 and the orthogonal demodulator 135 in the loop circuit.

The embodiments have been described above with reference to the figures, but
It goes without saying that the present invention is not limited to this embodiment, and that various changes can be made within the scope of the claims.

(Effects of the Invention) As described above, according to the present invention, a negative feedback amplifier can be obtained in which deterioration of the open loop gain due to delay in a power amplifier or the like is prevented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figure 2 is a block diagram showing a conventional negative feedback amplifier.
3 is a diagram showing the phase of the signal transmitted by the input signal of the embodiment of FIG. 1, FIG. 4 is a diagram showing an example of the input signal of the embodiment of FIG. 1, and FIG. 6 is a block diagram showing an example of the control circuit in the embodiment of FIG. 1; FIG. 7 is a block diagram showing an example of the phase shifter in the embodiment of FIG. 1. . 101, 102, 201, 202, 501, 5
02,503...Input terminal, 110,115,2
10,215,630...Subtractor, 120,1
25,230,235...Low range wave generator, 130...
...Quadrature modulator, 140,260...Power amplifier,
145,270...attenuator, 135...orthogonal demodulator, 132,275,295...phase shifter, 13
1,290...Sine wave generator, 240,245,
280,285...multiplier, 510,520...
...sample circuit, 530,540...square circuit,
250, 550... Adder, 160... Control circuit, 620... Delay circuit, 610... Comparator, 5
04, 602...Output terminal, 640...Switch, 650...Counter, 660...Digital-to-analog converter.

Claims (1)

[Claims] 1 With the first and second baseband signals as input:
first and second subtracters receiving the inputted first and second baseband signals, respectively; a quadrature modulator receiving the first and second subtracter outputs and the sine wave generator output; a power amplifier that amplifies and outputs the output of the quadrature modulator; an attenuator that receives a portion of the output of the power amplifier and attenuates the signal; and an output of the sine wave generator circuit by a phase determined by the output of the control circuit. a third baseband signal corresponding to the first baseband signal by a demodulation operation performed in response to the phase shifter output and the attenuator output; a quadrature demodulator that generates a fourth baseband signal corresponding to the second baseband signal and outputs the third and fourth baseband signals to the first and second subtracters, respectively; an amplitude calculation circuit that receives the third and fourth baseband signals that are the outputs of the orthogonal demodulator and calculates the average value of their complex amplitudes; the first and second subtracters, the orthogonal modulator, and the power A band-limiting circuit included in a loop circuit including an amplifier, the orthogonal demodulator, and the attenuator:
A negative feedback amplifier, wherein the control circuit determines the amount of phase change of the phase shifter so that the output of the amplitude calculation circuit becomes a maximum value.