JPH06311194A - Circuit for compensating distortion of multivalue quadrature amplitude modulated wave - Google Patents

Abstract

PURPOSE:To fix the open loop transfer function of a feedback loop regardless of gain control of transmission power by permitting a control part to control a first attenuator so that the open loop transfer function of the feedback loop is always fixed in correspondence to the changing quantity when a second attenuator changes the gain of transmission power. CONSTITUTION:The second attenuator (ATT) 42 is provided for the input stage of AMP 3 of a circuit for compensating the distortion of a multivalued quadrature amplitude modulated wave to control the gain of transmission power. A control part (CT) 10 controlling feedback control use ATT 41 corresponding to the contents of changing control executed from the outside of this gain control use ATT 42 is provided to prevent the feedback loop from becoming unstable. Namely, when the attenuating quantity of ATT 42 is increased and transmission power from an output terminal 7 is reduced by external operation, CT 10 reduces the attenuation quantity of ATT 41 and increases a feedback quantity. When the attenuating quantity of ATT 42 is operated for reduction on the contaries, the attenuating quantity of the ATT 41 is increased and the feedback quantity is suppressed. Thus, control operation is executed so that the complete transfer function of feedback loop is always fixed regardless of the gain control of transmission power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilevel quadrature amplitude modulation wave distortion compensating circuit for compensating for non-linear distortion of a multilevel quadrature amplitude modulation wave transmitter for controlling gain of transmission power.

[0002]

2. Description of the Related Art In a transmitter that amplifies and transmits a multilevel quadrature amplitude modulated wave to a constant level, a negative feedback distortion compensating circuit is used to compensate the linear distortion generated in a power amplifier. Since direct feedback causes various difficult problems, a linear distortion compensation circuit shown in FIG. 3 is used, for example. This is called a Cartesian loop linearizer.

This Cartesian loop linearizer is a kind of modulation feedback in which a high frequency signal is once decomposed into a signal component in the base band and feedback is performed. And the quadrature signal component (that is, quadrature demodulation) and feed back to the input stage of the quadrature modulator, which is advantageous in that the circuit can be easily realized. Digital Modulation and Demodulation Technology "by Yoshihiko Akaiwa, published by Trikeps Co., Ltd., pp. 108-112. The outline of the operation will be described below with reference to FIG.

In FIG. 3, a quadrature modulator (MOD) 21 is provided.
Quadrature-modulates the transmission in-phase signal component and the transmission quadrature signal component applied to the input terminals 11 and 12 based on the local signal from the local oscillator 8 to form a quadrature amplitude modulation wave. This quadrature amplitude modulated wave is amplified to a proper level by the power amplifier (AMP) 3 and sent from the output terminal 7 to the transmission line.

In such a transmitter, 91 and 92 subtractors are provided at the respective input stages of the MOD 21, and the (first) attenuator (ATT) 41 and quadrature demodulator (DEM) 22 are provided in the feedback loop. And bottom filter (LPF: 6
1, 62) are provided.

That is, a part of the output signal of the AMP3 is taken out by a coupler, and the signal which is reduced to an appropriate level by the ATT41 is decomposed by the DEM22 into the in-phase signal component and the quadrature signal component based on the local signal from the oscillator 8 and the resulting signal component 61 and 6
The signal component in the base band is extracted through the LPF of 2 and
It is input to the subtractors 1 and 92 and fed back to the input stage of the MOD 21.

In this Cartesian loop linearizer, in order to obtain a good distortion compensation characteristic, it is necessary to make the frequency of the unity gain of the feedback loop as high as possible. For that purpose, it is necessary to obtain a sufficiently large amount of feedback. Need to

[0008]

By the way, in mobile communication, the transmission power of the mobile unit is appropriately adjusted according to the position of the mobile unit so that the base station can receive the transmission signal of the mobile unit in a good condition. There may be a need. In such a case, the gain control of the transmission power is performed only by adjusting the gain of the power amplifier. Therefore, in order to avoid the saturation, a (second) attenuator is provided in the input stage of the power amplifier and the input to the power amplifier is controlled. It will be adjusted.

Then, there is no problem when the transmission power is increased, but there is a problem that when the transmission power is decreased, the feedback amount is reduced and the non-linear distortion increases. Especially MCA
When it is necessary to control the power gain of up to 20 dB as in a (multi-carrier access) system,
There is a problem that the open loop transfer function of the feedback loop becomes unstable immediately.

The present invention has been made in order to meet such a conventional demand, and an object thereof is to provide a loop transfer function of a feedback loop in a transmitter of a multilevel quadrature amplitude modulation wave for gain control of transmission power. It is an object of the present invention to provide a multi-valued quadrature amplitude modulation wave distortion compensation circuit which can always be made constant regardless of the power gain control and can stably perform the original distortion compensation operation.

[0011]

In order to achieve the above object, a multilevel quadrature amplitude modulation wave distortion compensation circuit of the present invention has the following configuration. That is, the multi-valued quadrature amplitude modulation wave distortion compensation circuit of the present invention, after a certain amount of the output signal of the amplifier for power amplification of the quadrature amplitude modulation wave formed by the quadrature modulator is appropriately attenuated by the first attenuator, A multi-valued quadrature amplitude modulation wave distortion compensating circuit for decomposing into an in-phase signal component and a quadrature signal component of a base band and feeding back to the input stage of the quadrature modulator; A second attenuator; and a control unit for controlling the attenuation amount of the first attenuator according to the change of the attenuation amount of the second attenuator.

[0012]

Next, the operation of the multilevel quadrature amplitude modulation wave distortion compensation circuit of the present invention constructed as described above will be described. In the present invention,
When the gain of the transmission power is changed by operating the second attenuator, the controller attenuates the first attenuator so that the open loop transfer function of the feedback loop is always constant according to the change amount. Control the amount.

Therefore, as in the MCA system, a maximum of 20
Even if it is necessary to control the power gain as much as dB, the open loop transfer function of the feedback loop is stabilized, so that it is possible to construct a mobile communication system that performs such a large gain control of the transmission power.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a multilevel quadrature amplitude modulation wave distortion compensation circuit according to an embodiment of the present invention. This multilevel quadrature amplitude modulation wave distortion compensating circuit is used when a transmitter capable of gain control of transmission power by providing a (second) attenuator (ATT) 42 at the input stage of AMP3 in the circuit shown in FIG. , A control unit (C which controls the feedback amount controlling ATT 41 in accordance with the contents of the change control of the gain controlling ATT 42 not shown).
T) 10 is provided to prevent the feedback loop from becoming unstable.

Specifically, when the attenuation amount of the ATT 42 increases and the transmission power from the output terminal 7 decreases due to an external operation, the CT 10 reduces the attenuation amount of the ATT 41 to increase the feedback amount, and vice versa. When the attenuation amount of the ATT42 is reduced, the attenuation amount of the ATT41 is increased and the feedback amount is suppressed, so that the loop transfer function of the feedback loop is always constant regardless of the gain control of the transmission power. Take action.

Next, FIG. 2 shows a concrete application example in which the multilevel quadrature amplitude modulation wave distortion compensation circuit of the present invention is applied to the transmitter of the above-mentioned MCA system. In FIG. 2, a synthesizer (SYN) 122 generates a signal having a carrier frequency based on the local signal from the local oscillator 8, and the MOD 21
And give to DEM22. Synthesizer (SYN) 121
Generates the frequency of the channel used for transmission based on the local signal from the local oscillator 8 and supplies it to the multipliers 111 and 112.

In the MCA system, it is necessary to ensure frequency stability. Therefore, in the MCA system developed by the present applicant, an unmodulated signal is transmitted in the preamble section of the transmission signal, and the oscillation frequency and the like can be corrected in this preamble section.

That is, a phase error detector (PD) 5 is provided,
MOD21 output and DEM2 in the preamble section
The output frequency of the local oscillator 8, SYN 121, 122, etc. can be adjusted so that the phase difference between the two outputs is detected and the correction circuit (not shown) makes the phase difference zero.

By the way, when a non-modulated signal is transmitted in the preamble section of the transmission signal, M is transmitted in the preamble section.
The modulation operation is stopped in the OD21 so that the carrier signal is output as it is. In order to correct the oscillation frequency and the like in this preamble section, the output amplitude of the unmodulated preamble signal must be highly accurate. It is desired to be constant.

However, since the unmodulated preamble signal is not subjected to phase modulation, it becomes an open loop in the preamble portion and a level difference occurs between it and the data portion.
Therefore, when the conventional distortion compensation circuit shown in FIG. 3 is used, it is difficult to keep the output amplitude of the unmodulated preamble signal constant with high accuracy.

On the other hand, in the present invention, since the control unit 10 controls the loop transfer function of the feedback loop so that it is always constant, the output amplitude of the signal in the preamble section can be made constant with high accuracy. The corrective action can be surely performed.

The controller 10 controls the AT as described above.
The attenuation amount of the ATT 41 is controlled according to the attenuation amount of T42. In this MCA system, gain control of transmission power on the mobile side is performed by the following two methods. The first is a method in which the mobile body that receives the transmission signal of the base station determines the power value to be transmitted from the output terminal 7 from the value of the received power (open.
Loop power control). Second, the base station transmits a signal containing the transmission power control value of the mobile unit from its reception power value,
This is a method (closed loop power control) for determining the power value sent from the output terminal 7 by the mobile unit based on the transmission power control value.

[0023]

As described above, in the multilevel quadrature amplitude modulation wave distortion compensation circuit of the present invention, when the gain of the transmission power is changed by operating the second attenuator, the control unit changes the gain. Depending on the amount, the amount of attenuation of the first attenuator is controlled so that the open loop transfer function of the feedback loop is always constant. Therefore, it is necessary to control the maximum power gain of 20 dB as in the MCA system. Even in some cases, the loop transfer function of the feedback loop has the effect of being stabilized. Therefore, there is also an effect that it is possible to construct a mobile communication system that performs such a large gain control of transmission power.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a multilevel quadrature amplitude modulation wave distortion compensation circuit according to an embodiment of the present invention.

FIG. 2 is a configuration block diagram when a multilevel quadrature amplitude modulation wave distortion compensation circuit of the present invention is applied to an MCA system.

FIG. 3 is a configuration block diagram of a conventional multilevel quadrature amplitude modulation wave distortion compensation circuit.

[Explanation of symbols]

 3 Power Amplifier (AMP) 5 Phase Difference Detector (PD) 7 Output Terminal 8 Local Oscillator 10 Control Section 11 Input Terminal 12 Input Terminal 21 Quadrature Modulator (MOD) 22 Quadrature Demodulator (DEM) 41 Attenuator (ATT) 42 Attenuator (ATT) 61 Low-pass filter (LPF) 62 Low-pass filter (LPF) 63 Band-pass filter (BPF) 64 Band-pass filter (BPF) 91 Subtractor 92 Subtractor 111 Multiplier 112 Multiplier 121 Synthesizer (SYN) 122 Synthesizer (SYN)

Claims (1)

[Claims] 1. A baseband in-phase signal component and a quadrature signal component after appropriately attenuating a part of an output signal of an amplifier for power-amplifying a quadrature amplitude modulation wave formed by a quadrature modulator by a first attenuator. A multi-valued quadrature amplitude modulation wave distortion compensating circuit which is decomposed into the input signal and is fed back to the input stage of the quadrature modulator; a second attenuator for gain control of transmission power is provided in the input stage of the power amplifier; A multi-valued quadrature amplitude modulation wave distortion compensation circuit, comprising: a control unit that controls the attenuation amount of the first attenuator according to the change of the attenuation amount of the second attenuator.