JPH08102768A - Transmitter - Google Patents

Abstract

PURPOSE: To provide an inexpensive transmitter with low power consumption and small-sized constitution capable of being automatically controlled to an optimum operating point at all times and obtaining a stable distortion improving effect even when an output level varies. CONSTITUTION: A phase modulator 13, a variable attenuator 14, a high power amplifier 15, a directional coupler 16, a detector 17, an error amplifier 18 and an analog multiplier 20 constitute an envelope feedback loop. The analog multiplier 20 changes the size of modulation signals to be added to the phase modulator 13 by varying a gain by output signals from the error amplifier 18. The variable attenuator 14, the high power amplifier 15, the directional coupler 16, the detector 17, the error amplifier 18, an averaging circuit 22 and the error amplifier 23 constitute an operating point feedback loop. The envelope feedback loop controls the envelope of waves to be modulated so as to respectively match base band modulation signals and the envelope of the detected waves to be modulated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmitter, and more particularly to a transmitter that transmits a signal power-amplified by a power amplifier.

[0002]

2. Description of the Related Art In the field of mobile communications in the microwave band and mobile satellite communications, in order to cope with the rapid increase in the number of subscribers in recent years, effective use of finite frequency resources and reduction of the effect of distortion are required. From the balance of 4 phase modulation (QPSK) and π / 4
A narrow band linear modulation system such as shift QPSK is adopted as the modulation system of the modulator in the transmitter.

In such a transmitter, although a narrow band modulated wave can be transmitted, a strict linear operation is required for a power amplifier that amplifies the modulated wave in order to improve the spread of the spectrum. Therefore, conventionally, the power amplifier is required. The saturation output was increased and the linearity was improved.

Further, conventionally, even when a power amplifier having a non-linear phase characteristic is used, the spread of the spectrum is suppressed by using an automatic gain control (AGC) circuit and a phase modulation circuit as shown in FIG. Is also known (Japanese Patent Laid-Open No. 4-287457, entitled "Phase Compensation Method for Power Amplifier").

In this conventional transmitter, the input terminal 4
The modulated wave with little amplification distortion input via 1 is AGC
While being supplied to the circuit 42, the envelope detection circuit 46 performs envelope detection. The modulated wave output from the AGC circuit 42 is phase-modulated by the phase modulation circuit 43 and then supplied to the power amplifier 44 for power amplification. The output signal of the power amplifier 44 is output to the output terminal 45, while the envelope detection circuit 48
Is supplied to.

The differential amplifier 47 receives the envelope detection signal of the input modulated wave with less amplitude distortion input from the envelope detection circuit 46 and the power amplifier 44 input from the envelope detection circuit 48. The envelope detected signal of the modulated wave having the amplitude distortion generated at is compared with the signal of the difference A
It controls the gain of the GC circuit 42. As a result, amplitude distortion that occurs during amplification by the power amplifier 44 is suppressed.

Further, the output detection signal of the envelope detection circuit 46 is supplied to the phase modulation circuit 43, and the phase modulation circuit 43 controls so as to perform the phase modulation of the characteristic opposite to the phase characteristic of the power amplifier 44. Thereby, the phase distortion generated in the power amplifier 44 is suppressed, and the deterioration of the carrier power to noise power ratio (C / N) is reduced.

[0008]

However, by increasing the saturation output of the power amplifier or improving the linearity,
In the conventional transmitter that suppresses the spread of the spectrum, the price of the power amplifier becomes high, and a large heat dissipation mechanism is required due to the increase in power consumption, thus increasing the size of the entire device.

Further, in the conventional transmitter shown in FIG. 5, since the signal input to the input terminal 41 is a phase-modulated high frequency modulated wave, each of the input side and the output side of the power amplifier 44 is Envelope detection circuits 46 and 48 provided in
Requires an expensive high frequency detection circuit as
Since two phase modulation circuits are required, there is a problem such as high cost.

The present invention has been made in view of the above points,
It is an object of the present invention to provide an inexpensive transmitter with a low power consumption and a small structure.

Another object of the present invention is to provide a transmitter which is always automatically controlled to an optimum operating point and which can obtain a stable distortion improving effect even when the output level is varied.

[0012]

In order to achieve the above object, the present invention provides a modulator that linearly modulates a carrier wave with a modulation signal to output a modulated wave, and a modulator output the modulated wave as a control signal. A variable attenuator that outputs a signal attenuated according to, a power amplifier that power-amplifies the output signal of the variable attenuator and outputs to the transmission output unit, a detector that detects the envelope of the output signal of the power amplifier, An error signal generating means for generating and outputting an error signal between the signal obtained by full-wave rectifying the baseband signal and the output detection signal of the detector, and multiplying the output error signal of the error signal generating means with the baseband signal to obtain A configuration including a multiplier that supplies the obtained multiplication result to the modulator as a modulation signal, and an averaging circuit that outputs a signal obtained by averaging the output error signal of the error signal generating means to the variable attenuator as a control signal. With That.

Further, according to the present invention, the full-wave rectification characteristic in the error signal generating means and the input signal power versus output detection voltage characteristic of the detector are characteristics which are close to each other.

[0014]

In the present invention, the feedback loop formed by the modulator, the variable attenuator, the power amplifier, the detector, the error signal generating means, and the multiplier constitutes an envelope feedback loop, and the baseband modulated signal and the modulated wave. The envelope is controlled to be the same as.

Further, in the present invention, the feedback loop including the variable attenuator, the power amplifier, the detector, the error signal generating means and the averaging circuit constitutes an operating point feedback loop, and the average of the output error signals of the error signal generating means is averaged. Control to minimize the value.

Further, according to the present invention, the full-wave rectification characteristic of the error signal generating means and the input signal power-output detection voltage characteristic of the detector are close to each other. It is possible to control so that the baseband modulation signal and the envelope of the modulated wave become the same more accurately.

[0017]

Next, an embodiment of the present invention will be described. FIG. 1 shows a block diagram of an embodiment of the present invention. As shown in the figure, this embodiment has an oscillator 11 and a buffer amplifier 1.
2, a phase modulator 13, a variable attenuator 14, a high power amplifier (HPA) 15, a directional coupler 16, a detector 17, an error amplifier 18, an analog multiplier 20, a waveform folding circuit (full-wave rectification circuit) 21, It is composed of an averaging circuit 22 and an error amplifier 23.

The oscillator 11 oscillates and outputs a carrier frequency of a predetermined frequency. The phase modulator 13 uses a predetermined phase modulation method, for example, BPSK (Binary Phase Sh).
ifKeying) modulation is performed. Variable attenuator 1
4 attenuates the input signal at an attenuation rate according to the output signal of the adder 28. The high power amplifier 15 amplifies an input signal with high efficiency. The detector 17 detects the envelope of the input signal.

Further, the phase modulator 13, the variable attenuator 14,
The first feedback loop including the high power amplifier 15, the directional coupler 16, the detector 17, the error amplifier 18, and the analog multiplier 20 constitutes an envelope feedback loop. Each circuit that constitutes this envelope feedback loop is designed to operate at a speed sufficiently higher (for example, 10 times or more) than the modulation signal speed for transmission (for example, 64 kbps). The analog multiplier 20 changes the gain in accordance with the output signal from the error amplifier 18, so that the phase modulator 13
It is provided to form an envelope feedback loop by changing the magnitude of the modulation signal applied to the.

Also, the variable attenuator 14 and the high power amplifier 1
5, directional coupler 16, detector 17, error amplifier 18,
The second feedback loop including the averaging circuit 22 and the error amplifier 23 constitutes an operating point feedback loop. This operating point feedback loop has the slowest operating speed among the constituent circuits (for example, the averaging circuit 22).
Alternatively, the operation speed of the error amplifier 23) is adjusted to operate at a speed sufficiently slower than the modulation signal speed (for example, 1/100 times or less).

Next, the operation of this embodiment will be described.
The high frequency signal oscillated and output by the oscillator 11 is input as a carrier wave to the phase modulator 13 via the buffer amplifier 12. On the other hand, the baseband signal a as shown in FIG. 2A, whose band is limited and the harmonic distortion is attenuated, is input from the input terminal 19. The baseband signal a is supplied to the analog multiplier 20, is multiplied by the output signal of the error amplifier 18 described later, and is then supplied to the phase modulator 13 as a modulation signal.

In the phase modulator 13, the phase of the carrier wave from the buffer amplifier 12 is 0 corresponding to the logical values "1" and "0" of the modulation signal input from the analog multiplier 20, respectively.
BPSK modulation at 180 ° and 180 ° is performed, and the obtained modulated wave having a constant amplitude is supplied to the variable attenuator 14. The variable attenuator 14 attenuates the input modulated wave at an attenuation rate according to the output signal of the error amplifier 23, which will be described later, and supplies it to the high power amplifier 15.

The modulated wave b having the waveform shown in FIG. 2B, which has been power-amplified by the high power amplifier 15 to a level required for transmission, is branched into two by the directional coupler 16, one of which is output to the output terminal 24. The signal is output, and the other is subjected to envelope detection by the detector 17 to obtain an envelope detection signal c shown in FIG. 2 (C), which is then supplied to the error amplifier 18. On the other hand, the baseband signal a from the input terminal 19 is the waveform folding circuit 2
1 for full-wave rectification.

The error amplifier 18 generates and outputs an error signal between the envelope detection signal c from the detector 17 and the full-wave rectified signal d as shown in FIG. It is supplied to the analog multiplier 20. This error signal is indicated by e in FIG. Therefore, in the analog multiplier 20 of the envelope feedback loop, the error amplifier 1
8 is a signal obtained by multiplying the error signal e obtained by 8 and the baseband modulation signal a from the input terminal 19, and the phase modulator 1
In 3, the carrier wave is phase-modulated.

Here, the detector 17 has the input signal power versus output detected voltage characteristic as shown in FIG. As can be seen from the figure, since the detector 17 normally uses a diode, its input signal power-output detection voltage characteristic shows not a linear characteristic but a non-linear characteristic corresponding to the diode characteristic.

On the other hand, since the input voltage of the folding circuit 21 corresponds to the amplitude of the input voltage of the detector 17, the input voltage-output voltage characteristic of the folding circuit 21 is as shown in FIG.
The characteristic is set to correspond to the input signal power-output detection voltage characteristic of the detector 17. As a result, the baseband modulation signal and the detector 17 are generated by the envelope feedback loop.
The envelope is controlled so that the envelopes of the modulated waves detected by are coincident with each other.

In the present embodiment, the error amplifier 18 described above is used.
2 is also supplied to the averaging circuit 22, where it is averaged (integrated) to be a signal as shown by f in FIG. It is supplied to the attenuator 14 as a control signal. Therefore, the operating point feedback loop for controlling the variable attenuator 14 averages the error in the output envelope detection signal c of the detector 17 and controls it so as to minimize it.

As described above, according to this embodiment, the amplitude distortion generated in the high power amplifier 15 can be improved by the envelope feedback loop, and the output error signal of the error amplifier 18 can be corrected by the operating point feedback loop. Can be minimized. The modulated wave output from the output terminal 24 is transmitted via a transmission output unit (not shown).

The present invention is not limited to the above embodiment, and for example, a linear modulation system such as a four-phase phase modulation (QPSK) system or an amplitude modulation system is adopted as the modulation system of the modulator. Is also possible in principle.

[0030]

As described above, according to the present invention,
The envelope feedback loop formed by the modulator, the variable attenuator, the power amplifier, the detector, the error signal generating means and the multiplier controls the baseband modulated signal and the envelope of the modulated wave to be the same. Therefore, the amplitude distortion generated in the power amplifier can be improved.

Further, according to the present invention, the operating point feedback loop including the variable attenuator, the power amplifier, the detector, the error signal generating means and the averaging circuit minimizes the average value of the output error signals of the error signal generating means. Since it is controlled so that it is always controlled to the optimum operating point, a stable distortion improving effect can be obtained even when the output level is changed.

As described above, according to the present invention, it is possible to relax the standard of the saturation output and linearity of the power amplifier by the distortion improving effect as compared with the related art, and most of the circuits can be integrated. It is possible to have a low-cost, low-power-consumption and small-sized configuration as compared with the conventional one.

Further, according to the present invention, the full-wave rectification characteristic in the error signal generating means and the input signal power versus output detection voltage characteristic of the detector are characteristics which are close to each other, whereby the envelope curve described above is obtained. The feedback loop makes the baseband modulated signal and the envelope of the modulated wave the same more accurately, so that amplitude distortion generated in the power amplifier can be significantly suppressed.

[Brief description of drawings]

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

FIG. 2 is a time chart for explaining the operation of FIG.

3 is a diagram showing an example of input signal power vs. output detected voltage characteristics of the detector of FIG.

FIG. 4 is a diagram showing an example of input voltage-output voltage characteristics of the folding circuit of FIG.

FIG. 5 is a block diagram of an example of the related art.

[Explanation of symbols]

 13 phase modulator 14 variable attenuator 15 high power amplifier 17 detector 18, 23 error amplifier 19 modulation signal input terminal 20 analog multiplier 21 waveform folding circuit 22 averaging circuit

Claims (2)

[Claims] 1. A modulator for linearly modulating a carrier wave with a modulation signal to output a modulated wave, and a variable attenuator for outputting a signal obtained by attenuating the modulated wave output from the modulator according to a control signal, A power amplifier that amplifies the output signal of the variable attenuator and outputs it to the transmission output unit, a detector that detects the envelope of the output signal of the power amplifier, a signal that is a full-wave rectified baseband signal, and the detector. Error signal generating means for generating and outputting an error signal with the output detection signal, and multiplying the output error signal of the error signal generating means with the baseband signal, and the obtained multiplication result to the modulator. And a averaging circuit that outputs a signal obtained by averaging the output error signal of the error signal generating means to the variable attenuator as the control signal. 2. The transmission according to claim 1, wherein the full-wave rectification characteristic of the error signal generating means and the input signal power versus output detection voltage characteristic of the detector are characteristics which are close to each other. vessel.