JP2001285385A - Transmission equipment - Google Patents

Abstract

(57) [PROBLEMS] To further reduce power consumption of a transmission power amplifier when a modulation method is switched in a digital transmission device. When a modulation method is switched, a gate voltage of an FET inside a transmission power amplifier is set in accordance with the selected modulation method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to power saving of a transmission power amplifier in a digital transmission device.

[0002]

2. Description of the Related Art FIG.
FIG. 1 is a diagram showing a conventional transmission power amplifier and a peripheral circuit thereof generally used. Here, reference numeral 1 denotes a modulation circuit, which is set to switch a modulation method by SW4, modulates an input signal by the set modulation method, and outputs the modulated signal. The modulation signal of the modulation method selected by SW4 is input from the modulation circuit 1 to the IFAGC circuit 2, the gain is automatically controlled in the intermediate frequency (IF) band, and the transmission power amplifier 3 (hereinafter referred to as PA). The power is amplified and output to the subsequent stage. In that case, in a digital transmission device,
In order to use the operating point of PA3 in a linear operating range, P3
The signal input level to A3 must be constant. Therefore, a part of the output of the PA 3 is taken out, converted into a DC voltage by the detector 5, returned to the IFAGC circuit 2, and
A comparison is made with the DC voltage set to the specified output power at V7.

Then, the amount of attenuation of the attenuator 6 is changed by the error voltage obtained by the comparison, and P
The input level of A3 is fixed. Here, even if the modulation method is switched by SW4, the bias voltage from the PA voltage control circuit 10 'to PA3, that is, the gate voltage applied to a field effect transistor (hereinafter referred to as FET) inside PA3 is a PA bias voltage setting volume. 11 is set. The FET inside PA3
Is closely related to the saturation point of the FET, and in order to use it in a linear range, it is generally +
It is necessary to operate at a fixed voltage of 10V.

[0004]

However, in a circuit configuration as in the prior art, the power consumption of the PA does not change even when the modulation method is switched. That is, the operating point of the transmission power amplifier in the digital transmission device needs to be set in a linear range.
The modulation point is set so as to be optimal for a mode requiring the most linearity among the modulation methods, and the operating point cannot be appropriately switched in accordance with the modulation method.

Therefore, even if the modulation scheme of the transmission power amplifier is changed, the power consumption of the transmission power amplifier cannot be reduced. An object of the present invention is to make it possible to switch the operating point of a transmission power amplifier for each modulation scheme, and to reduce power consumption while maintaining the linearity required for that scheme.

[0006]

According to the circuit configuration of the present invention, when the modulation system is switched, the bias voltage (hereinafter referred to as gate voltage) of a transistor used inside the PA, for example, an FET, is controlled. Provide a circuit. As a result of providing this circuit, even if the modulation method is switched, depending on the modulation method, there is no problem in reducing the drain current flowing through the FET by changing the FET gate voltage. Can be reduced, and the power consumption of the PA can be reduced.

Further, the setting of the operating point for each modulation method of the transmission power amplifier can be set according to the gate voltage of the FET inside the transmission power amplifier. Thereby, the power consumption can be further reduced by further reducing the drain current of the FET without lowering the saturation point of the transmission power amplifier. The setting of the transmission power amplifier for each modulation method is performed by inputting the set value of the gate voltage of the FET inside the transmission power amplifier into the ROM. The set value in the ROM is read out in conjunction with the setting of the SW for setting the modulation method.

[0008]

FIG. 1 shows an embodiment of the present invention.
The difference from the above-described prior art shown in FIG. 2 is that when the modulation method is switched by SW4, the gate voltage of the FET used in PA3 can be controlled by the voltage control circuit 10. For example, if the modulation method is Quadrature Ph
case Shift Keying (hereinafter referred to as QPSK) and 16 Quadrature Amplitude
When switching with e Modulation (hereinafter referred to as 16QAM), QPSK is phase modulation, while
16QAM has information in the amplitude direction based on QPSK to increase the band efficiency. In the case of 16QAM, the frequency utilization rate is twice as high as that of QPSK.

In 16QAM, information is also provided in the amplitude direction, so that the operating point of PA3 is within a linear range,
It is desirable that the operating point of A3 be used at a point 6 to 8 dB lower than the saturation point. On the other hand, since QPSK is phase modulation, the operating point of PA can be used at a point 4 to 6 dB lower than the saturation point as compared with 16QAM.

Therefore, when switching from 16 QAM to QPSK, the difference is 2 dB. In this case, in consideration of the third-order intermodulation distortion (hereinafter referred to as IM3), if the output is the same, 4 dB is improved. In general, when the gate voltage of the FET used in PA3 is controlled and the drain current is halved, the degradation of IM3 becomes 3 dB. Therefore, QPS
In K, IM3 is almost the same even when the drain current is reduced by half compared to 16QAM.

In the voltage control circuit 10, RO
M8, which controls the gate voltage of the FET in conjunction with SW4. Further, by using the ROM 8, even if the number of switching of the output power is increased, it is possible to cope without changing the circuit. In the voltage setting by the ROM 8, by providing a voltage setting SW 9 inside the voltage control circuit 10, each setting data is stored according to the modulation method.

[0012]

As described above, according to the present invention, the voltage control circuit 10 can set the gate voltage used in the PA for each modulation method and determine the drain current. , Can be set in consideration of characteristics. In other words, the power consumption of the PA can be changed for each modulation method. Therefore, the power consumption of the PA can be set to be smaller in QPSK than in the setting of 16QAM.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a block configuration of a transmission power amplifier in a digital transmission device according to the present invention.

FIG. 2 is a diagram showing an example of a block configuration of a transmission power amplifier in a conventional digital transmission device.

[Explanation of symbols]

1: modulation circuit, 2: IFAGC circuit, 3: transmission power amplifier (PA), 4: transmission power switching SW, 5: detector,
6: attenuator, 7: volume for setting specified output power, 8:
ROM, 9: output power switching SW, 10, 10 ': PA voltage control circuit, 11: PA bias voltage setting volume.

Claims (1)

[Claims] 1. A transmission apparatus having a transmission power amplifier for selecting one of a plurality of modulation schemes and amplifying a transmission signal modulated by the selected modulation scheme, the transmission apparatus comprising: Wherein the operating point of the transistor of the transmission power amplifier is switched.