JPH0558283B2 - - 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 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.

(Conventional technology and its problems) As a method to demodulate and feed back the amplifier output,
2nd International Conference on Radio Spectrum Survey Technics
Conference on Radio Spectrum Conservation
Techniques) There is a method announced on pages 44 to 49. FIG. 2 shows an example of the prior art.
Signals x, t, input from terminals 201 and 202
y and t are input to low frequency wave generators 230 and 235 through subtracters 201 and 215, respectively. The output of the low frequency wave generator 230 is multiplied by the carrier wave which is the output of the sine wave generator (oscillation angular frequency is ω _C ) 290 in the multiplier 240, and the output of the low frequency wave generator 235 and the phase shifter 295 are used to multiply the 90° phase. After the multiplier 245 multiplies the sine wave generator 290 output with the changed sine wave generator 290 output, the multiplier 240 and 245 outputs are added to the adder 2.
Add by 50. The output of adder 250 is at terminal 20
This is a signal that has been orthogonally modulated by the baseband signal input from No. 1,202. 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 inputted to multipliers 280 and 285 after adjusting the phase shift by phase shifter 275 . 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 sent to the terminal 201.
Subtract from the input signal from . Multiplier 280
Then, it is demodulated by multiplying it by the output of the sine wave generator whose phase has changed by 90 degrees, and the demodulated signal is sent to the subtracter 215.
is input to the terminal 202 and subtracted from the input signal from the terminal 202. The LPFs 230 and 235 are used to limit the band of the feedback circuit, and it is desirable that their characteristics be approximately equal. The phase shifter 275 is for preventing deterioration of the loop 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 the phase shifter 275 is not provided. At this time, if the output z _O (t) of the adder 250 is written as z _O (t) = x (t) cos ω _C t + y (t) sin ω _C t (1), the outputs of the adders 280 and 285 are G・R・x(t−Δτ) cosΔτω _C or G・R・y(t−Δτ) cosΔτω _C (2). Therefore, if 0 cosΔτω _C <1 (3), the round-trip gain equivalently decreases, and a sufficient distortion improvement characteristic cannot be obtained. Also, 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 problem described above can be avoided. However, such a circuit
When used in an FDM system, assuming that the delay of the amplifier has frequency characteristics, when the line is changed, 0<cos(Δτ'ω _C −Δθ)<1 (7) (Δτ' is the new delay), and the loop gain becomes deteriorates.

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; amplifying the quadrature modulator output; a power amplifier that outputs; an attenuator that receives a portion of the output of the power amplifier and attenuates the signal; a phase difference detector that receives the output of the quadrature modulator and the output of the attenuator and outputs a signal indicating a phase difference between the two; a circuit; a phase shifter that changes the phase of the output of the sine wave generator by a phase difference determined by the output of the phase difference detection circuit; and a phase shifter that changes the phase of the output of the sine wave generator and outputs it; A demodulation operation generates a third baseband signal corresponding to the first baseband signal and a fourth baseband signal corresponding to the second baseband signal; a quadrature demodulator that outputs baseband signals of No. 4 to the first and second subtracters, respectively; the first and second subtracters, the quadrature modulator, the power amplifier, the attenuator, and the quadrature demodulator; and a band-limiting circuit included in a one-circuit circuit consisting of a circuit.

(Example) Embodiments of the present invention will be described with reference to the drawings.

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

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.
A quadrature modulator 130 modulates the output of a sine wave generator 131 (angular frequency is ω _C ). The modulated signal is amplified by power amplifier 140 and transmitted. A portion of the output of the amplifier 140 is attenuated by an attenuator 145 and input to the orthogonal demodulator 135 . Orthogonal demodulator 13
5 is a sine wave generator 13 that has passed through a phase shifter 132;
1 output, demodulates the attenuator 145 output, and
and obtain a second baseband signal. These first and second baseband signals are input to subtracters 110 and 115, respectively.

The phase change amount Δθ of the phase shifter 132 is controlled so as to cancel the phase change due to the delay Δτ from the output of the quadrature modulator 130 to the input of the quadrature demodulator 135.
In order to control the amount of phase change Δθ in the phase shifter 132 in this manner, the phase difference detection circuit 150 receives the output of the quadrature modulator 130 and the input of the quadrature demodulator 135, and controls a signal indicating the phase difference between the two. It is output to the phase shifter 132 as a signal.

FIG. 3 is a circuit diagram showing a specific example of the phase difference detection circuit 150 in the embodiment of FIG. 1. This phase difference detection circuit 150 includes amplitude limiters 304 and 305.
It is constructed using a double balance mixer. The input of the terminal 301 in FIG.
If there are 5 inputs, the input signal can be written as cos{ω _C (t+Δτ)+φ(t+Δτ)}, and the input from the terminal 302 is sent to the quadrature modulator 13.
When the output is 0, the input signal can be written as cos {ω _C t+φ(t)}. Then, the signal output from the terminal 303 becomes a component indicating the frequency difference after multiplying the two. The output signal is cos (ω _C Δτ + φ (t + Δτ) − φ (t)), and since the change in φ (t) is sufficiently slow compared to the change in ω _C , φ (t + Δτ) − φ (t) = 0 Therefore, the output signal can be regarded as cos(ω _C Δτ)(φ(t)
represents the phase component of the modulated signal).

FIG. 4 is a circuit diagram showing a specific example of the phase shifter 132 in the embodiment of FIG. This phase shifter 132
It is composed of a phase shifter 410 using variable caps 411 and 412 and a voltage converter 420. Voltage converter 42
0 receives a voltage of cos (Δτω _C ), controls the phase shifter 410 according to the voltage-capacitance characteristics of the variable caps 411 and 412, and
The amount of phase change at 0 is set to cos ^-1 (Δτω _C ). In Fig. 4, λ is the wavelength of the input sine wave, and Z _O is the input/output impedance of the circuit.

The embodiments of the present invention have been described above. In FIG. 1, reduction filters 120 and 125 are provided as band-limiting elements of the loop circuit between the subtracter 110 and the quadrature modulator 130, and between the subtracter 115 and the quadrature modulator 130, respectively. It may be provided between the orthogonal demodulator 135 and the first subtracter 110 and between the orthogonal demodulator 135 and the second subtracter 115, or a band wave generator may be provided in place of the reduction wave generator in a round circuit. It may be provided between the orthogonal modulator 130 and the orthogonal demodulator 135.

Further, the present invention is not limited to this embodiment, and it goes without saying that various modifications and changes can be made within the scope of the present invention.

(Effects of the Invention) As described above, according to the present invention, it is possible to provide a negative feedback amplifier in which the loop gain does not deteriorate even when the transmission frequency changes, and the distortion improvement characteristics do not deteriorate.

[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 circuit diagram showing a specific example of the phase difference detection circuit in the embodiment shown in FIG. 1, and FIG. 4 is a circuit diagram showing a specific example of the phase shifter in the embodiment shown in FIG. 101, 102, 201, 202... Input terminal, 103, 203... Output terminal, 110, 11
5,210,215...Subtractor, 120,12
5,230,235...Low range wave generator, 140,2
60...power amplifier, 145,270...attenuator, 131,290...sine wave generator, 132,
275, 295... Phase shifter, 130... Quadrature modulator, 135... Quadrature demodulator, 150... Phase difference detection circuit, 250... Adder, 240, 245, 2
80,285... Multiplier.

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;
a phase difference detection circuit that receives the output of the quadrature modulator and the output of the attenuator and outputs a signal indicating a phase difference between the two; an output of the sine wave generator by a phase difference determined by the output of the phase difference detection 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; a band-limiting circuit that is included in a round circuit that includes the first and second subtracters, the orthogonal modulator, the power amplifier, the attenuator, and the orthogonal demodulator; Feedback amplifier.