JPH04364602A - Feed forward interference circuit - Google Patents

Abstract

PURPOSE:To detect a pilot signal with high precision without being affected by noise. CONSTITUTION:A pilot signal of a single frequency from a pilot signal generator 35 is subject to phase modulation by using a PN code from a pseudo noise generator 51 at a phase modulator 43 to apply spread processing to the frequency and a spread output is injected to the input signal by a pilot injection circuit 36, its output is distributed to paths 25, 26 by a power distributer 24, outputs of the paths 25, 26 are synthesized by a power synthesizer 28 and part of its output is extracted by a pilot extract circuit 37. An output of a local oscillator 46 is phase-modulated by the PN code at a phase modulator 47 to implement frequency spread and its output applies frequency conversion to an output of the circuit 37 at a mixer 48 to attain inverse frequency spread and a level of a pilot signal of the single frequency component is detected from the output by the detector 38. A control circuit 39 controls a variable attenuator 29 and a variable phase shifter 30 in a control circuit 39 so that the detection level is zero.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] This invention relates to a feedforward interference circuit (also called an interferometric interference suppression circuit) represented by a distortion detection circuit and a removal circuit, which are basic circuits constituting a feedforward distortion compensation circuit. The present invention relates to a feedforward interference circuit that uses a pilot signal to detect the equilibrium state of the circuit.

0002

2. Description of the Related Art As an input/output nonlinear compensation method for amplifiers that is effective in high frequency bands such as microwave bands, there is a feedforward type distortion compensation circuit shown in FIG. ). A feedforward distortion compensation circuit basically consists of two interference circuits. One is a distortion detection circuit 3, and the other is a distortion removal circuit 4. The distortion detection circuit 3 is composed of a main amplifier signal transmission path 5 and a linear signal transmission path 6,
Further, the distortion removal circuit 4 includes a main signal transmission path 7 that linearly transmits the output signal of the main amplifier and a distortion injection path 8. Further, the signal transmission path 5 of the main amplifier is connected to the main amplifier 9
and a variable attenuator 10 and a variable phase shifter (generally a variable delay line is used) 11 that adjust the amplitude and phase transfer characteristics of this path 5, respectively, connected in series,
The linear signal transmission path 6 includes a delay line 12 and a phase inversion circuit 13.
It consists of a series connection with. The main signal transmission path 7 includes a delay line 14, and the distortion injection path 8 includes a variable attenuator 15.
It consists of a variable phase shifter 16 and an auxiliary amplifier 17 connected in series. Auxiliary amplifier 17 may include a phase inversion circuit. Here, since there is no large difference in characteristics, the variable attenuator 10 and the variable phase shifter 11 included in the distortion detection circuit 3 are connected to the linear signal transmission path 6 in the form of both or only one of them. In some cases, it is provided. Similarly, in the distortion removal circuit 4, the variable attenuator 15 and the variable phase shifter 16 may be provided in the main signal transmission path 7 depending on the case. The input terminal 1 is also coupled to the signal transmission path 5 and linear signal transmission path 6 of the main amplifier. A power divider 18, a power combiner/divider 19 that couples the distortion detection circuit 3 and the distortion removal circuit 4, the main signal transmission path 7, and the distortion injection path 8.
The power combiner 20 that couples the output terminal 2 with the output terminal 2 is a simple lossless power divider/power combiner configured with a transformer circuit, a directional coupler, and the like.

[0003] First, this operation will be explained. The input signal input to input terminal 1 is divided into two outputs by power divider 18 and supplied to paths 5 and 6, and both outputs of paths 5 and 6 are combined by power combiner/divider 19. be done. Here, the variable attenuator 10 and the variable phase shifter 11 included in the distortion detection circuit 3 are connected to the two signal transmission paths 5 and 6 with respect to the signal component output from the power combiner/divider 19 to the distortion injection path 8 side. The transmission characteristics of the two signals are adjusted so that the amplitude and delay amount are equal and the phases are opposite to each other. However, the opposite phase condition can be achieved by appropriately setting the amount of phase shift between the input and output terminals of the divider 18 and the power combiner/divider 19, or by using the input and output phase inversion characteristics of the main amplifier 9. Alternatively, as shown in FIG. 5, this can be achieved by inserting a phase inversion circuit with a short-circuit termination 22 at one terminal of the circulator 21 in either path 5 or 6. At this time, the transmission loss of the path from input terminal 1 to output terminal 2 via main amplifier signal transmission path 5, power combiner/divider 19, main signal transmission path 7 and power combiner 20 is minimized. The parameters of each circuit element are set so that the power gain and output of the main amplifier 9 do not decrease.

Since the distortion detection circuit 3 is configured in this way, the output of the terminal 19d on the path 8 side of the power combiner/divider 19 is linearly proportional to the input of the two signals on the two paths 5 and 6. The nonlinear components generated by the main amplifier 9 are detected as the difference component between the two signals. For this reason, this interference circuit is called a distortion detection circuit.

Next, the variable attenuator 15 and variable phase shifter 16 provided in the distortion injection path 8 are connected to a power combiner/divider 19.
The transfer functions of the two paths 7 and 8 from the terminal 19a connected to the main amplifier signal transmission path 5 to the output terminal 20c of the combiner 20 are equal in amplitude and delay amount and opposite in phase. is adjusted to Here, since the input signal of the distortion injection path 8 is the distortion component of the main amplifier 9 detected by the distortion detection circuit 3, the input signal of the distortion injection path 8 is the distortion component of the main amplifier 9 detected by the distortion detection circuit 3.
At the output terminal 20c of the feedforward amplifier, that is, the output terminal 2 of the feedforward amplifier, the distortion components generated by the same main amplifier 9 are injected into the output signal of the main amplifier 9 with opposite phases and equal amplitudes. Cancellation of distortion components is realized. The above is the operating principle of the feedforward amplifier.

As described above, a feedforward amplifier is composed of two interference circuits for signal cancellation and distortion cancellation, and these can in principle be modeled as a simple feedforward interference circuit as shown in FIG. As shown in the figure, this interference circuit includes a power divider 24 that divides the input signal of the input terminal 23 into two powers, two signal transmission paths 25 and 26 to which the divided outputs are supplied, and two signal transmission paths 25 and 26. The signal transmission path 25 consists of a variable attenuator 29, a variable phase shifter 30, an amplifier 31, and a power combiner 28 that combines the outputs of two signal transmission paths 25 and 26 and supplies the power to an output terminal 27. The transmission path 26 includes a delay line 32 and a phase inversion circuit 33. Here, the amplifier 31 corresponds to the main amplifier 9 in the case of the distortion detection circuit 3 and the auxiliary amplifier 17 in the case of the distortion removal circuit 4.

The optimum operation of this feedforward interference circuit is based on the two paths 25 and 2 that constitute it, as described above.
6 are balanced under the condition that the transfer functions of 6 have equal amplitude, equal delay characteristics, and are in opposite phases in phase relationship.This method is particularly useful as a method for detecting this balanced state and automatically setting the circuit to the optimal balanced state. There is a method using a pilot signal as described in Application No. 3-49688 "Feedforward Amplifier". The basic configuration of a circuit that implements this method is shown in FIG. The pilot signal from the pilot generator 35 is injected into the path 5 in a pilot injection circuit 36 installed in the circuit of the main amplifier 9. A pilot signal is extracted by a pilot extraction circuit 37 using a directional coupler etc. inserted on the output side of the power combiner 20, and the level of the extracted output is detected by a pilot level detection circuit 38 comprising a receiver etc. The signal is supplied to a control circuit 39 composed of a microcomputer or the like. Among the lines connecting circuit elements, solid lines mean signal lines, and broken lines mean data lines for control.

To explain this operation, the pilot signal is a continuous wave of a specific frequency, and the level of the pilot signal at the output terminal 2 is determined by using an amplitude detector or homodyne detector with narrow band characteristics as the pilot level detection circuit 38. is detected. If the two signal paths 7 and 8 constituting the distortion removal circuit 4 are in the above-mentioned optimal operating state, the level of the detected pilot signal will inevitably be zero. Therefore, while monitoring the output of the pilot level detection circuit 38 which is proportional to this level, for example, by applying a perturbation method, the set values of the variable attenuator 15 and the variable phase shifter 16 of the distortion removal circuit 4 are changed little by little. , by detecting the point where the output of the pilot level detection circuit 38 is minimum and setting it as the operating point, the optimum operating state of the distortion removal circuit 4 can be realized.

[0009] Such automatic control can be easily achieved using a microcomputer. Although the distortion removal circuit 4 has been described above, the distortion detection circuit 3 also includes a pilot injection circuit provided between the input terminal 1 and the power divider 18,
The pilot extraction circuit is connected to the output terminal 19d of the power combining/distributing circuit 19 and the variable attenuator 15 on the input side of the auxiliary amplifier 17.
A similar operation can be achieved by providing it between the two. That is, since the basic operations of these two circuits are the same, the circuit can be simplified and described using a basic feedforward interference circuit as shown in FIG.

0010

[Problems to be Solved by the Invention] Conventionally, as a pilot signal processing method in such an automatic adjustment circuit, a method using a simple single frequency pilot has been used, and while this method has the advantage of a simple circuit configuration, The optimal operating point is when the detection level of the pilot signal is minimum, so in order to increase the detection sensitivity, it is necessary to increase the power level of the pilot signal to be injected. When interference signals such as leaked radio waves and noise are mixed in, errors occur in the detection level, making it impossible to achieve highly accurate control operations.

An object of the present invention is to provide a feedforward interference circuit that is less susceptible to interference such as noise and enables pilot detection with high detection sensitivity.

0012

According to the present invention, a pilot signal is injected after being spread in its frequency spectrum by a modulating means, and a detected signal is inversely spread in its frequency spectrum by a demodulating means to extract the pilot signal. Spread spectrum is performed by a direct frequency spread method, a frequency hopping method, a chirp method, and a hybrid method combining these methods.

In this way, the power level of the pilot signal injected into the feedforward interference circuit can be dramatically increased without increasing the power level per frequency bandwidth, and the resistance to interference such as noise can be increased. Better pilot detection can be achieved.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the present invention applied to a basic model of a feedforward interference circuit, and parts corresponding to those in FIG. 8 are given the same reference numerals. In this example, a direct frequency spread method is applied as a pilot signal modulation/demodulation method, but the same operation and effect can be expected even if a frequency hopping method, a chirp method, or a hybrid method using a combination of these methods is used. Pilot generator 3
The pilot signal from 5 is frequency-spread by the modulator 41 and supplied to the pilot injection circuit 36. The extracted output of the pilot extraction circuit 37 is subjected to inverse frequency spreading in the demodulation section 42 and is supplied to the pilot level detection circuit 38. The modulation section 41 includes a phase modulator 43 (this uses a two-phase modulator or a four-phase modulator, but an amplitude modulator can be used as well),
It is composed of a bandpass filter 44. The demodulator 42 also includes a bandpass filter 45, a local oscillator 46, a phase modulator 47,
It is composed of a mixer 48 and a pilot band filter 49. Further, a PN signal from a pseudo-noise code (PN) generator 51 is injected into a modulation section 41 and a demodulation section 42, respectively, and a phase adjuster 52 is added to synchronize both injected PN signals. This operation will be explained below with reference to the spectrum diagram shown in FIG.

First, the pilot generator 35 generates a continuous wave pilot signal having a frequency fP and a level of L1 dB/Hz as shown in FIG. 2A, and inputs this to the phase modulator 43. The phase modulator 43 phase-modulates the pilot signal with the PN signal, so that a signal SP with a spread spectrum is obtained as shown in FIG. 2B. In this case, for example, if the speed of the PN signal is 500 kbps and the level is 0 dB,
If the conversion gain of the phase modulator 43 is 0 dB, the level per Hz of the frequency-spread pilot signal SP is ideally reduced by 50 dB or more with respect to L1. Conversely, if the level per Hz of the pilot that can be input to the interference circuit can be set to a constant value, 500 kbps
By frequency-spreading the continuous wave pilot signal using the PN signal, its power can be dispersed, so the original pilot signal level can be increased by 50 dB or more.

Next, the signal SP' shown in FIG. 2C, whose level distribution is changed by the feedforward interference circuit and whose frequency components are the same as the signal SP, is input to the demodulator 42, so that the signal SP' shown in FIG. Correlation detection using the PN signal reproduces a pilot signal of frequency fP' as shown in FIG. 2D. This pilot signal is input to a pilot level detector 38 and its power level is specified. The pilot level detector 38 can be configured using a tuned receiver or the like similar to the detector described in FIG. 7, so the pilot level can be accurately detected using this. Here, fP' is the oscillation frequency fP of the pilot generator 35
and the oscillation frequency of the local oscillator 46, and the passing frequency of the pilot band filter 49 and the tuning frequency of the pilot level detector 38 are made to match this frequency.

[0017] By doing so, the pilot signal injection level can be equivalently increased without changing the power per frequency band, so the pilot detection sensitivity can be greatly increased. Furthermore, as is well known, this correlation demodulation process for pilot signals converges the power of the spread pilot, but conversely, it spreads the power for interference waves that have no correlation with the PN signal. This has the effect of increasing pilot signal detection accuracy. Therefore, even when the balance between the two paths of the feedforward interference circuit is extremely good and the level of the pilot signal at the output end of the power combiner 28 decreases, it is possible to perform reliable level detection with few errors. It is.

The above explanation has been about the operation when the present invention is applied to the basic model of the feedforward interference circuit, but as mentioned above, this feedforward interference circuit has a distortion detection circuit and a distortion Since the basic operation is exactly the same as that of the removal circuit, it can be used as an automatic adjustment circuit for two interference circuits that constitute a feedforward amplifier. In this case, the control operation that is exactly the same as that explained with reference to Fig. 7 can be used, and it is also possible to detect the pilot signal with significantly higher accuracy than before and which is less susceptible to the effects of various interference waves. Become. Therefore, it is possible to perform automatic adjustment for setting the optimum operating point of distortion compensation in the feedforward amplifier and highly stabilizing the amplification operation with high accuracy and reliability.

FIG. 3 shows that a pilot signal is generated in a modulation section,
An example will be shown in which the pilot signal is frequency-spread using a frequency hopping method. In the modulation section 53 of this circuit, the oscillation frequency of the frequency synthesizer 54 is controlled by the output of the PN generator 51 to obtain a frequency-spread pilot signal. Since the bandpass filter 44 is inserted to remove unnecessary harmonic components from the frequency synthesizer output, it can be deleted if the level thereof is small. On the demodulator 42 side, a bandpass filter 45 separates the pilot signal from the output signal of the feedforward interference circuit, and then a mixer 48 performs frequency mixing on the output of the frequency synthesizer 55 and this pilot signal. At this time, the modulation section 53 and the demodulation section 4
The frequency hopping frequency of the oscillation frequency of each of the frequency synthesizers 54 and 55 is the same as that of the PN generator 5.
1 output and are completely synchronized by the phase adjuster 52, so by giving an offset to the oscillation frequencies of these two frequency synthesizers, the power level of the pilot signal input to the demodulator 42 is proportional to the power level of the pilot signal input to the demodulator 42. Continuous waves with offset frequencies can be detected. By detecting this level with the level detector 38, the same effect as the method using the direct frequency spread method shown in FIG. 1 can be achieved. Similarly, it is possible to use the chirp method or a hybrid method that uses a combination of these methods for frequency spreading, but these configurations are described in, for example, "
Latest spread spectrum communication method: R. C. Dixon, Tateno, Kataoka, Iida, translated by Jatec Publishing, 1978. It is the same as in , so it saves effort.

In the configuration described above, a signal subjected to frequency spreading processing is directly used as a pilot signal. Furthermore, once a frequency-spread signal is generated, it is frequency-converted and injected into a feedforward interference circuit, and the demodulation side uses the same local carrier wave as that used on the modulation side to generate a signal based on the frequency of the pilot signal. It is also possible to apply a configuration in which the signal is returned and demodulated, but since such a configuration is often used in various communication device circuits, a detailed explanation will be omitted.

[0021]

[Effect of the invention] As explained above, with this invention,
It is possible to perform pilot detection with high precision and high reliability to detect the optimum operating point of the feedforward interference circuit, so by applying it to the automatic adjustment circuit of the feedforward amplifier, it is possible to perform feedforward with extremely excellent linearity. The present invention can be applied as a method to improve the performance of linear amplifiers used in wireless communication, broadcasting, etc., as well as wired communication repeaters, audio equipment, etc.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the invention using a direct frequency spread method.

FIG. 2 is a diagram showing a pilot spectrum for explaining the operation of the embodiment in FIG. 1;

FIG. 3 is a block diagram showing main parts of an embodiment of the present invention using a frequency hopping method.

FIG. 4 is a block diagram showing an example of the basic configuration of a feedforward distortion compensation circuit.

FIG. 5 is a diagram showing a phase inversion circuit using a circulator.

FIG. 6 is a block diagram showing the basic configuration of a feedforward interference circuit.

FIG. 7 is a block diagram showing a configuration example of a conventional automatic adjustment circuit for a feedforward amplifier using a pilot.

FIG. 8 is a block diagram showing an example of the basic configuration of a conventional automatic adjustment circuit simplified as a feedforward interference circuit.

Claims (1)

[Claims] Claim 1: Distributing means for distributing an input signal into two, two paths to which the two distributed signals are respectively supplied, and a combining means for combining the outputs of these two paths and outputting a signal. and means for adjusting the transmission characteristics of the two paths, the feedforward is configured to inject a pilot signal into the input side of the distribution means and detect the pilot signal on the output side of the combination means. A feed characterized in that the interference circuit is provided with modulation means for frequency-spreading the pilot signal injected on the input side, and demodulation means for frequency-despreading the signal and demodulating the pilot signal on the output side. Forward interference circuit.