JP4310476B2 - Modulation amplifier circuit - Google Patents

Description

  The present invention relates to a modulation amplifier circuit, and more particularly to a modulation amplifier circuit suitable for digital modulation signals such as QAM and OFDM signals, which modulates and amplifies signals without distortion and with high efficiency.

FIG. 2 is a block diagram showing a configuration of a conventional modulation and power amplification circuit. The output of the carrier signal oscillator 30 is input to a 90 ° phase shifter 31, and two carrier signals having a phase difference of 90 ° are generated. The respective carrier signals are amplitude and phase modulated based on the modulation signals I and Q by the modulators 33 and 34 and synthesized by the synthesis circuit 35. Then, the power is amplified by the linear amplifier 36 and output. Patent Document 1 below discloses an example of a conventional modulation and power amplification circuit as described above.
JP 05-260105 A

  In the conventional power amplifier circuit as described above, since the linear amplifier 36 needs to perform a class A operation with little distortion, the power efficiency is very poor at 1 to 10%, and particularly high power output can be obtained. There was a problem that it was difficult. Further, when trying to increase the power efficiency, there is a problem that distortion is generated due to the nonlinearity of the linear amplifier, and unnecessary radiation power (spurious) is increased.

  The object of the present invention is to solve the above-mentioned problems of the prior art, and particularly suitable for digital modulation signals such as QAM and OFDM signals, and capable of modulating and amplifying signals without distortion and with high efficiency. It is to provide an amplifier circuit.

  The modulation amplifier circuit of the present invention receives carrier signals and generates carrier signal phase shift means for generating two carrier signals having a phase difference of 180 degrees, and amplifies the carrier signals output from the carrier signal phase shift means. Two amplifying means, a synthesizing means for synthesizing and outputting the outputs of the two amplifying means, a positive modulation signal on one of the power supplies of the two amplifying means, and a negative modulation signal on the other, respectively. The main feature is that the modulation means for superimposing is provided.

  Further, in the modulation amplification circuit, the amplification means is composed of a grounded class C power amplification circuit using a transistor element, and the carrier signal is amplitude-modulated based on the output from the modulation means. is there. In the modulation amplification circuit described above, the synthesizing means is a Wilkinson hybrid circuit. In the modulation amplification circuit described above, the power supply voltage of the amplification means is set at the center of a region where the output power of the amplification means changes linearly with respect to a change in power supply voltage. is there.

  The modulation amplifier circuit of the present invention receives carrier signals and generates carrier signal phase shift means for generating two carrier signals having a phase difference of 180 degrees, and amplifies the carrier signals output from the carrier signal phase shift means. Two amplifying means, a synthesizing means for synthesizing and outputting the outputs of the two amplifying means, a positive modulation signal on one of the power supplies of the two amplifying means, and a negative modulation signal on the other, respectively. Two sets of modulation amplifying means comprising superimposing modulation means are further provided. Further, a carrier signal is input, two carrier signals having a phase difference of 90 degrees are generated, and output to the respective carrier signal phase shifting means. The main feature is also provided with phase shifting means and second synthesizing means for synthesizing the output signals of the two synthesizing means of the two sets of modulation amplification means.

  Since the modulation amplifier circuit of the present invention performs amplitude modulation by collector modulation in each amplifier of the final amplification stage, a class C amplifier can be used as the amplifier, and the conventional power efficiency is 1 to 10%. Has an effect of improving to 10 to 30%. In addition, it is possible to perform amplitude modulation and phase modulation by combining the outputs of two amplifiers that amplify the carrier whose phase is inverted by a coupler, and furthermore, two sets of modulation amplifier circuits using the two amplifiers of the present invention are used. By doing so, QAM is possible, and if primary modulation processing is performed, it is possible to cope with OFDM. Therefore, it is suitable for a wireless transmitter that performs digital communication.

  The modulation amplifier circuit of the present invention will be described below with reference to the drawings.

  Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a block diagram showing the configuration of the modulation amplifier circuit of the present invention. A carrier signal (100 MHz to several GHz) output from the carrier signal oscillator 10 is input to the 90 ° phase shifter 11, and two signals having a phase difference of 90 ° are output. The 90 ° phase shifter 11 can be constituted by a circuit network including, for example, a coil and a capacitor.

  Each carrier signal is input to two 180 ° phase shifters 12, and two signals having a phase difference of 180 ° are output. The 180 ° phase shifter 12 is configured by a differential transformer, for example. Alternatively, the differential output of the differential amplifier circuit may be used as a differential signal. The output signals of the respective 180 ° phase shifters 12 are input to the four amplifiers 13, respectively.

  FIG. 3 is a circuit diagram showing the configuration of the amplifier 13 of the present invention. This amplifier is a grounded-emitter amplifier circuit using a bipolar transistor 40, has an operating point deeper than the cutoff point of the collector current, and constitutes a class C power amplifier. The collector of the transistor 40 is connected to a power supply terminal 42 via a tuning circuit 41 tuned to the carrier frequency, and the power supply terminal 42 is connected to the modulation circuit 14. The collector is connected to one input terminal of the hybrid circuit 15 via the impedance matching circuit 43.

  FIG. 4 is a circuit diagram showing a configuration of the modulation circuit 14 of the present invention. The transmission data is input to, for example, a DSP (digital signal processor) 50, is subjected to known OFDM primary modulation processing by a program, and outputs I and Q digital signals. The D / A converter 51 converts the I and Q digital signals output from the DSP 50 into analog I and Q signals.

  The analog I and Q signals are respectively input to the amplifier 52 of the modulation circuit 14 and power amplified. The amplifier 52 is a general low-distortion power amplifier circuit for low and intermediate frequencies, and may be a class B push-pull amplifier. The output of each amplifier 52 is input to the primary winding of each modulation transformer 53. The midpoint of the secondary winding of the modulation transformer 53 is connected to a constant voltage power circuit 54 that outputs a voltage Vc. Accordingly, from both ends of the secondary winding, a voltage (positive voltage modulation signal + mI (+ mQ) is superimposed on one of the power sources (voltage Vc) and a negative voltage modulation signal -mI (-mQ) is superimposed on the other ( For example, Vc + mI) is output. Note that m is a coefficient determined by the output power of the amplifier 52 and the like.

FIG. 5 is an explanatory diagram showing the operating characteristics of the amplifier 13 of the present invention. This graph shows the relationship between the output voltage of the modulation circuit 14 applied to the power supply terminal 42 of the amplifier 13 and the high-frequency output power of the amplifier 13 when the input carrier power is constant. As shown in FIG. 5, there is a region (VL to Vh, a range indicated by a thick line) where the high-frequency output power changes linearly with respect to the change in the output voltage of the modulation circuit 14.
Therefore, in the present invention, the output voltage Vc of the constant voltage power supply circuit of the modulation circuit 14 is set to approximately the center of this linear region. Further, the output power of the amplifier 52 of the modulation circuit 14 is set so that the fluctuation range of the modulation signal Vc ± mI falls within this linear region.

  FIG. 6 is a circuit diagram illustrating a configuration example of a hybrid circuit. The hybrid circuit 15 (16) is a circuit that adds and synthesizes the outputs of the two amplifiers 13 and outputs the result. FIG. 6A shows the configuration of a Wilkinson hybrid circuit that can be used as the hybrid circuits 15 and 16. The microstrip line forms a transmission line of 70Ω / 4λ, and the signals input from port A and port B are added and output to port C.

When the input and output impedance of the hybrid circuit is 50Ω, the impedance of the 70Ω microstrip line is strictly √2 × 50Ω (about 70.7Ω). The microstrip line may be a coaxial cable having substantially the same characteristic impedance and the same electrical length.
FIG. 6B shows a configuration of a narrowband hybrid circuit in which the transmission line (microstrip line) of the Wilkinson hybrid circuit is replaced with a transformer.

  FIG. 7 is a circuit diagram showing another configuration example of the hybrid circuit. In this 4-port hybrid circuit, signals input from the four input ports J to M are added and output to the port N. Therefore, the two hybrid circuits 15 and the next-stage hybrid circuit 16 shown in FIG. 1 can be replaced with the hybrid circuit shown in FIG.

  Next, the operation will be described. Since the modulation operation of the I signal and the Q signal is the same, the modulation operation of the I signal will be described. The case of I = 1, 0, −1 will be described as the simplest case.

  First, when I = 0, the same voltage Vc is applied from the modulation circuit to the power supply terminal of each amplifier 13. Therefore, as shown in FIG. 5, the same power Pc is output from each amplifier 13. However, since the carrier signals inputted to the respective amplifiers have a phase difference of 180 °, they are added and synthesized by the hybrid circuit 15, so that they cancel each other and the output becomes zero.

  When I = 1, Vh (= Vc + m) and VL (= Vc-m) are applied to the power supply terminals of the respective amplifiers 13 from the modulation circuit. Therefore, as shown in FIG. 5, electric power Ph and PL are output from each amplifier 13. As a result of addition and synthesis by the hybrid circuit 15, the output becomes the difference between the two input powers (Ph−PL).

  In the case of I = −1, a voltage opposite to that in the case of I = 1 is applied to the power supply terminal of each amplifier 13 from the modulation circuit. Each amplifier 13 outputs powers PL and Ph. As a result of addition and synthesis by the hybrid circuit 15, the output becomes (PL−Ph), and the carrier of the same power is output in the opposite phase to the case of I = 1. Eventually, by appropriately setting Vc and m as described above, for example, signals of phase and output power proportional to I and Q can be obtained in the range of −1 ≦ I and Q ≦ 1.

  Although the embodiments have been described above, the following modifications may be considered in the present invention. In the embodiment, an example using a bipolar transistor has been disclosed. However, an FET, an integrated circuit (IC), or a vacuum tube can be used as an amplifier element for power amplification. A known linearizer that generates distortion of an amplifier by a DSP and applies it in reverse phase may be combined.

It is a block diagram which shows the structure of the modulation amplifier circuit of this invention. It is a block diagram which shows the structure of the conventional modulation and power amplification circuit. It is a circuit diagram which shows the structure of the amplifier 13 of this invention. It is a circuit diagram which shows the structure of the modulation circuit 14 of this invention. It is explanatory drawing which shows the operating characteristic of the amplifier 13 of this invention. It is a circuit diagram which shows the structural example of a hybrid circuit. It is a circuit diagram which shows the other structural example of a hybrid circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Carrier signal oscillator 11 90 degree phase shifter 12 180 degree phase shifter 13 Amplifier 14 Modulation circuit 15 Hybrid circuit 16 Hybrid circuit

Claims (5)

Carrier signal phase shifting means for inputting a carrier signal and generating two carrier signals having a phase difference of 180 degrees;
Two amplifying means for amplifying the respective carrier signals output from the carrier signal phase shifting means;
Combining means for combining and outputting the outputs of the two amplifying means;
A modulation amplification circuit comprising: modulation means for superimposing a positive modulation signal on one of the power supplies of the two amplification means and a negative modulation signal on the other.   2. The modulation amplifier circuit according to claim 1, wherein the amplifying means comprises a grounded class C power amplifier circuit using a transistor element, and amplitude-modulates a carrier signal based on an output from the modulating means. .   2. The modulation amplifier circuit according to claim 1, wherein the synthesizing means is a Wilkinson hybrid circuit.   2. The modulation amplifier circuit according to claim 1, wherein the voltage of the power source of the amplifying unit is set at the center of a region where the output power of the amplifying unit linearly changes with respect to the change of the power source voltage. . Carrier signal phase shifting means for inputting a carrier signal and generating two carrier signals having a phase difference of 180 degrees;
Two amplifying means for amplifying the respective carrier signals output from the carrier signal phase shifting means;
Combining means for combining and outputting the outputs of the two amplifying means;
Two sets of modulation amplification means comprising modulation means for superimposing a positive modulation signal on one of the power supplies of the two amplification means and a negative modulation signal on the other, respectively,
90 degree phase shifting means for inputting a carrier signal, generating two carrier signals having a phase difference of 90 degrees, and outputting the two carrier signals to the respective carrier signal phase shifting means;
A modulation amplification circuit comprising: second combining means for combining the output signals of the two combining means of the two sets of modulation amplifying means.

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