JPH0923118A - Transmission circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output a signal with high phase accuracy at high power efficiency even in the case of using a power amplifier having a non-linear characteristic because a phase delay can be controlled by a phase difference signal and to simplify the constitution of this transmitting circuit by using a circuit including the phase delay in an orthogonal modulator. SOLUTION: A signal modulated by a digital modulator 1 is modulated to a carrier by an orthogonal modulator 2. The modulated carrier modulated by the modulator 2 is amplified by a power amplifier 4 through an amplifier 3 and the amplified carrier is outputted to an output terminal 6 through a power distributor 5. A reference signal 9 outputted from the modulator 1 is given to the input terminal of a phase comparator 10 and a part of the modulated carrier outputted from the distributor 5 is envelop-detected by a detector 7 and given to the input terminal of the comparator 10. A difference signal is generated from the two signals inputted to the comparator 10 and outputted from the comparator 10 and the voltage of the difference signal is amplified by a level conversion circuit 11 to control a phase delay 12 built in the modulator 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission circuit used in a transmission device such as a .pi. / 4 shift QPSK type radio.

[0002]

2. Description of the Related Art In a radio using a modulation system such as a .pi. / 4 shift QPSK system, a transmission output amplifier is required to have high linearity. However, the linear power amplifier has lower power supply efficiency than the saturated power amplifier. In particular, the deterioration of the power source efficiency is a serious problem in mobile wireless devices such as portable and vehicle-mounted batteries which use a battery as a power source. Therefore, even in a wireless device that uses a modulation method such as a π / 4 shift QPSK method, a distortion compensation technique that can improve power supply efficiency and maintain linearity by using a power amplifier in a state close to saturation is important.

FIG. 2 shows an example of a conventional π / 4 shift QP.
1 shows an amplitude compensation type transmission circuit used in a transmission device such as an SK system. The signal quadrature-modulated by the digital modulator 1 is modulated on the carrier wave by the quadrature modulator 2 and output. The modulated carrier wave modulated by the quadrature modulator 2 is amplified by the power amplifier 4 through the amplifier 3 and is output to the output terminal 6 through the power distributor 5. On the other hand, the digital modulator 1
The reference signal 9 output from the comparator 14 is applied to the input terminal of the comparator 14, and a part of the modulated carrier wave from the power distributor 5 is envelope-detected by the detection circuit 7 and then applied to the input terminal of the comparator 14. To be The two signals input to the comparator 14 output a difference signal between the two signals by the comparator 14 and control the amplifier 3 capable of variable gain.

Next, this operation will be described. Generally, the power amplifier 4 is non-linear as shown in the input / output characteristic of FIG. The comparator 14 compares the reference signal 9 output from the digital modulator 1 with a signal obtained by envelope-detecting the modulated carrier wave having the amplitude distortion generated by the power amplifier 4 by the wave detector 7,
The difference signal is generated. The difference signal output from the comparator 14 controls the amplifier 3 whose gain can be changed, so that the amplitude distortion is improved.

The process of compensating for the amplitude error will be described with reference to FIG. The axis of the figure shows the vector direction of the IQ signal, and the circle shows the miracle of the phase when the signal amplitude is constant. White circles indicate ideal points with no phase or amplitude error. The amplitude compensation type transmission circuit changes the gain of the amplifier 3 according to the amplitude difference signal to control the output amplitude as shown by the triangles. As a result, in the constellation of this transmission output wave, the variation during non-compensation as shown in FIG. 9 becomes constant as shown in FIG.

However, in the conventional technique shown in FIG. 2, although the amplitude distortion is improved, the amplitude distortion is generated at the same time as the phase distortion is generated as shown in FIG. If the determination is performed based on the phase during demodulation, there is a drawback that the modulation accuracy is not improved.

Other than the conventional technique shown in FIG. 2, there are JP-A-3-174810, JP-A-4-287457 and JP-A-3-255710.

[0008]

To construct an output circuit with high modulation accuracy, it is necessary to improve the phase characteristic. However, in the conventional amplitude type transmission circuit, the amplitude distortion is improved, but the phase distortion is not improved, and there is a problem that the modulation accuracy is not improved when the determination is performed based on the phase during demodulation.

An object of the present invention is to provide an output circuit with improved phase distortion and high modulation accuracy even when a power amplifier having a non-linear characteristic is used.

[0010]

In order to achieve the above object, the present invention compares the phase of a modulated carrier wave which is distorted by a reference signal and a power amplifier, and controls a phase delayer by the difference signal. As a result, a signal with good modulation accuracy is output.

[0011]

An embodiment of the present invention will be described below with reference to FIG.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The I signal and Q signal which are signals modulated by a digital modulator 1 are input to a quadrature modulator 2. Inside the quadrature modulator 2, the carrier wave output from the oscillator 13 is divided into two, one of which is modulated by the I signal, and the other is modulated by the Q signal of the carrier whose phase is delayed by about 90 degrees by the phase delay unit 12. To do. Carrier waves modulated by IQ signals are orthogonally combined by addition and output. The modulated carrier quadrature-modulated by the quadrature modulator 2 is an amplifier 3
Is amplified by the power amplifier 4 and is output to the output terminal 6 via the power distributor 5. On the other hand, the reference signal 9 output from the digital modulator 1 is given to the input terminal of the phase comparator 10, and a part of the modulated carrier wave from the power divider 5 is envelope-detected by the detector 7 and then the phase is detected. It is given to the input terminal of the comparator 10. The two signals input to the phase comparator 10 are output as a difference signal of the two signals by the phase comparator 10, voltage-amplified by the level conversion circuit 11, and the phase delay device 12 in the quadrature modulator 2 is controlled. .

Next, this operation will be described. Generally, in the power amplifier 4, as shown in the input / output characteristics of FIG. 3, when the input amplitude increases, the output amplitude becomes non-linear and a phase delay occurs. Therefore, the detection signal output from the detector 7 has amplitude information proportional to the phase. The phase comparator 10 detects the reference signal 9 output from the digital modulator 1 and the detector 7
Phase comparison of the detection signal proportional to the output phase,
The difference signal is generated. Since the phase delay device 12 capable of adjusting the voltage is controlled by the difference signal, the phase distortion is improved.

The phase delay device 1 in the quadrature modulator 2 is shown in FIG.
The process of controlling 2 and compensating for the phase error will be described. The axis of the figure shows the vector direction of the IQ signal, and the circle shows the miracle of the phase when the signal amplitude is constant. White circles indicate ideal points with no phase or amplitude error. In general, demodulation by a modulation method such as π / 4 shift QPSK method is determined by the phase position at the determination time by phase division. When there is no output compensating circuit, the output signal becomes the position of a black dot due to the distortion of the power amplifier 4 and deviates from the phase determination range. However, the output correction circuit according to the present invention controls the phase of the carrier wave of the Q signal by the phase difference signal, and controls the output phase as indicated by the triangle by changing the phase axis of the Q signal. In the constellation of this transmission output wave, the variation during non-compensation as shown in FIG. 9 becomes constant as shown in FIG.

In this embodiment, the phase delay device is a phase delay device inside the quadrature modulator, but it does not have to be inside the quadrature modulator. For example, the phase of the carrier wave input to the quadrature modulator is phased. You may control using a delay device. Further, the phase of the modulated carrier wave output to the quadrature modulator may be controlled by using a phase delay device. Further, although the description has been given with respect to the phase delay device for the Q signal, it is not particularly required to be the Q signal and IQ may be reversed.

[0016]

According to the present invention, since the phase delay device can be controlled by the phase difference signal, even when a power amplifier having a nonlinear characteristic is used, a signal with high power efficiency and high phase accuracy is output. You can Furthermore, since the circuit in which the phase delay device is incorporated in the quadrature modulator is used, the configuration can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram of a phase compensation type transmission circuit showing an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of an amplitude compensation type transmission circuit.

FIG. 3 is an output characteristic diagram of a general high output power amplifier.

FIG. 4 is an explanatory diagram of an example showing the operation of the phase compensation type transmission circuit of the present invention.

FIG. 5 is an explanatory diagram of an example showing an operation of an amplitude compensation type transmission circuit.

FIG. 6 is an explanatory diagram of an output constellation without compensation.

FIG. 7 is an explanatory diagram of an output constellation of the phase compensation type transmission circuit of the present invention.

FIG. 8 is an explanatory diagram of an output constellation of an amplitude compensation type transmission circuit.

[Explanation of symbols]

1 ... Digital modulator, 2 ... Quadrature modulator, 3 ... Amplifier,
4 ... Power amplifier, 5 ... Power distributor, 6 ... Output terminal, 7 ...
Detector, 8 ... Detected signal, 9 ... Reference signal, 10 ... Phase comparator, 11 ... Level converter, 12 ... Phase delayer, 13 ... Oscillator.

Claims (1)

[Claims] 1. A digital modulator, a quadrature modulator for modulating a carrier wave with the output of the digital modulator, a power amplifier for amplifying a modulation signal, and a detection signal of an output modulation signal of the power amplifier and a reference signal are compared. In the transmission circuit having means for compensating the non-linear distortion of the power amplifier by controlling the modulated signal with the difference signal, the phase delay in the quadrature modulator is caused by the difference signal between the output modulation signal of the power amplifier and the reference signal. A transmission circuit characterized by controlling the phase of a container.