JPH0318108A - Transmission power control circuit - Google Patents

Abstract

PURPOSE:To eliminate an excessive output at the time inputting a signal and turning on a power source and to maintain the quality of a line by adding the output of a constant voltage to the output of a DC amplifier in opposite- polarity relation by an adder at all times, and increasing the attenuation quantity of a variable attenuator by a constant value. CONSTITUTION:A detector 4 detects the output level and the DC amplifier amplifies the difference from a reference value to obtain an output V1. The adding circuit 6 adds this output V1 and the output V2 of the constant voltage circuit 7 in opposite-polarity relation at all times. Namely, this addition is opposite-polarity subtraction for increasing the attenuation quantity of the variable attenuator 2 by the constant value. Therefore, even when the difference between the output V2 of the constant voltage circuit 7 and the output V1 of the DC amplifier 5 is minimum, the attenuator 2 provides an input signal with the corresponding attenuation quantity to hold the constant output level. A temperature compensating circuit 8 which decreases an output current in case of a temperature rise is provided on the output side of the constant voltage circuit 7 to maintain the control range of the level irrelevantly to temperature variation.

Description

[Detailed Description of the Invention] [Summary] Regarding a circuit for controlling transmission power in a digital multiplex radio device, the output of a power amplifier is detected by a wave detector, and a DC amplifier having a time constant generates a difference from a reference value. In a transmission power control circuit that controls a variable attenuator to control the gain of the power amplifier, the purpose is to prevent the transmission output level from becoming transiently excessive due to turning on/off of an input signal or turning on the power. The output of the constant voltage circuit is always added to the output of the DC amplifier with the opposite polarity using an adder circuit, so that the amount of attenuation of the variable attenuator is increased by a constant value. [Industrial Field of Application] The present invention relates to a transmission power control circuit, and particularly to a circuit for controlling transmission power in a digital multiplex radio device. In recent digital wireless communication systems, the modulation method has become multilevel (1611AM→64QA→256QAM).
As a result, there is a need to reduce the amount of distortion caused by amplifiers used in wireless equipment and eliminate adverse effects on adjacent channels. Therefore, in order to suppress distortion, a transmission power control circuit that performs ALC (automatic level control) to keep the transmission output level below a certain value is required.

[Prior art 1] Figure 4 shows a conventional transmission power control circuit.
is a preamplifier RN that amplifies the input signal (modulated wave), 2 is a variable attenuator that variably attenuates the output of the preamplifier 1, 3 is a power amplifier that amplifies the output of the variable attenuator 2, and 4 is a power A detector that detects the output of the amplifier 3 into a direct voltage;
Elle! a voltage r1 that generates a differential voltage by comparing it with the voltage, and provides a sufficient time constant to follow the AMJffc component of the modulation spectrum so that the transmission level does not fluctuate;
It is a direct current amplifier having r4 and a capacitor C, and the amount of attenuation of the variable attenuator 2 increases in proportion to the output voltage (current) of the direct current amplifier 5 (see FIG. 5).

In such a transmission power control circuit, the detector 4 detects the transmission output level, and the base f1! created by the resistor r3 is detected. By comparing the voltage (voltage for making the transmission output level below a certain value) and the detected DC voltage of the detector 4 input via the resistor r5 in the DC amplifier 5, a differential output is generated, and a variable output voltage is generated. The gain of the amplifier 3 is controlled by ALC operation so that the attenuator 2 is controlled to keep the transmission output level from the power amplifier 2S3 constant.

[Problem to be Solved by the Invention 1] In such a conventional transmission power control circuit, as shown in FIG.
As shown in , when the human input signal is off, the DC 1 width switch 5
The negative output current of variable attenuator 2 is minimized, which causes variable attenuator 2
Since the amount of attenuation becomes the minimum, the gain of the filter 3 becomes the maximum.

In this state, when the human input signal is turned on as shown in the figure (a), due to the time constant of the DC amplifier 235, it cannot immediately follow the ALC operation for the input signal level, and as shown in the figure (a).
As shown in I)), excessive output due to transient overshoot occurs. This phenomenon also occurs when the power is turned on with a signal applied.

As a result, as shown in FIG. 7, the transmission level increases, causing errors in adjacent channels or the own channel, resulting in deterioration of line quality.

Therefore, in the present invention, the output of a power amplifier is detected by a wave detector, and a difference from a base value is generated by a DC amplifier having a time constant to control the variable attenuation 23 and the gain of the power amplifier. In a control circuit, the purpose is to prevent the transmitter from becoming over-output due to turning on/off of a human input signal or turning on the power.

[Means for solving the problem] In order to achieve the above object, the transmission power control circuit according to the present invention uses a DC amplifier 5 as shown in principle in FIG.
The output of the constant voltage circuit 7 is always added to the output of the variable attenuator 2 with the opposite polarity using an adder circuit, so that the attenuation scale of the variable attenuator 2 is increased by a fixed value.

Further, in the present invention, as shown by the dotted line in FIG. 1, a temperature compensation circuit 8 may be further provided on the output side of the constant voltage circuit 7 to reduce the output voltage of the constant voltage circuit 7 when the temperature rises.

[Function 1] The transmission power control circuit of the present invention shown in FIG. 1 will be explained with reference to FIG.

In the present invention, a constant voltage/A value is always added to the output of the DC I intensifier 5 by the constant voltage circuit 7 in the adder circuit 6. In this case, the "addition" is an attenuation performed in the opposite polarity so as to increase the amount of attenuation of the variable attenuator 2 by the constant value. Therefore, even when the difference 1v2 - 11 between the output v2 of the constant voltage circuit 7 and the output 1 of the DC amplifier 2x5 is the minimum, the variable attenuator 2 provides an attenuation amount corresponding to the difference to the input signal.

In this case, the amount of attenuation of the variable attenuator 2 by the constant voltage circuit 7 should be set so that it does not fall below the allowable ALC range of the power booster 3, as shown in FIG. ．． Therefore, as shown in FIG. 6(a), even when the input signal is off, a constant current is applied from the constant voltage circuit 7 to the variable attenuator 2, and the input signal is passed to the power amplifier 3 in an attenuated form. The maximum gain of the power amplifier 3 is suppressed as shown in Fig. 2, and even if the input signal changes from off to on, excessive output as shown in Fig. 2) is suppressed. In this way, if the variable attenuator 2 has a fixed amount of attenuation from the beginning, overpower can be heard, but if the gain of the power amplifier 3 decreases as shown by the dotted line in Figure 2 due to an increase in the ambient temperature, the transmission will be interrupted. Output P. ．． , the permissible range of ALC becomes narrower. Therefore, in the present invention, as shown by the dotted line in FIG. 1, a temperature compensation circuit 8 is provided on the output side of the constant voltage circuit 7, so that when the temperature rises, the output voltage of the constant voltage circuit 7 decreases. This prevents the gain of power amplifier 3 from decreasing. [Embodiment] FIG. 3 shows an embodiment of the transmission power control circuit according to the present invention. In this embodiment, the adder circuit 6 has an input resistance "
6. An operational amplifier 61 for adding the output J of the DC amplifier 5 and the output of the constant voltage circuit 7 via r9, an operational amplifier 62 for polarity inversion, and resistors rlO to rl3 for adjusting the gains of these operational amplifiers. The constant voltage circuit 7 includes a Zener diode ZD and a resistor ``8'' for providing a constant voltage, and a circuit for applying the constant voltage from the Zener diode ZD to the adder circuit 6 via resistors r7 and ``9''. The temperature compensation circuit 8 is composed of a series diode. The other configurations are the same as the conventional example.

In the operation of such a transmission power control circuit, the DC amplifier 5 compares the reference voltage obtained by dividing the voltage of the resistor r3 with the DC output voltage of the power amplifier 3 detected by the detector 4, and calculates the difference between the voltage divided by the resistor r3 and the DC output voltage of the power amplifier 3. When outputting with a time constant of 1, a constant voltage from the buffer 70 is added in the operational amplifier 61.

In this case, the output voltage Vl of the DC amplifier 5 is one-polarity in order to suppress the output of the detector 4 below the reference voltage, but the constant voltage v2 from the constant voltage circuit 7 is ten-polarity, and the detector 4
Even when the output is “0” and Vl is at its maximum, V
Since the constant voltage output ■2 is set so that there is a relationship of 2>Vl, the variable attenuator 2 receives V2-V via the adder circuit 6.
A current based on the voltage of l flows, and there is no input signal and the detector 4
Even when the output of is "0", an amount of attenuation proportional to the voltage of V2-Vl is given.

Therefore, when the transmission output level is high and the output voltage of the detector 4 becomes high, Vt becomes low, so ■2-Vl becomes large, and the variable attenuator 2 applies a larger amount of attenuation (smaller gain) to the input signal. In addition, in order to prevent the gain of the power amplifier 3 from decreasing due to temperature rise, which narrows the allowable range of ALC, the constant voltage The diode series body of the temperature compensation circuit 8 connected to the output side of the circuit 7 decreases the forward voltage drop when the temperature rises, thereby reducing the output of the constant voltage circuit 7.

As a result, V2-V1 decreases and the amount of attenuation of the variable attenuator 2 also decreases, making it possible to maintain the same maximum gain regardless of the temperature rise, as shown in FIG. [Effects of the Invention] As explained above, according to the transmission power control circuit according to the present invention, the output of the constant voltage circuit is always added to the output of the direct amplifier with the opposite polarity in the adder circuit, thereby adjusting the attenuation amount of the variable attenuator. By increasing the input signal by a certain value, it is possible to prevent over-output when the input signal is turned on/off or when the power is turned on with the signal turned on, and the line quality can be maintained. .

Furthermore, if a temperature compensation circuit is further provided on the output side of the constant voltage circuit to reduce the output current of the constant voltage circuit when the temperature rises, it is possible to maintain the ALC control range regardless of temperature fluctuations. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the principle of a transmission power control circuit according to the present invention, FIG. 2 is a graph diagram for explaining the operation of the present invention, and FIG. 3 is an illustration of a transmission power control circuit according to the present invention. FIG. 4 is a diagram showing a transmission power control circuit according to a conventional example. FIG. 5 is a characteristic graph of a variable attenuator. FIG. 6 is an operating waveform diagram of excessive output in a conventional example. is a diagram showing the influence of excessive output on other channels. In FIG. 1, 2... variable attenuator, 3... power amplifier, 4... detector, 5... DC amplifier, 6... addition circuit, 7... constant voltage circuit, 8 ...Temperature ll# compensation circuit. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) The output of the power amplifier (3) is detected by the detector (4), and the DC amplifier (5) having a time constant generates a difference from the reference value to control the variable attenuator (2) to control the output power. Amplifier (3)
In the transmission power control circuit that controls the gain of the variable attenuator (2), the output of the constant voltage circuit (7) is always added to the output of the DC amplifier (5) with opposite polarity in the adder circuit (6). A transmission power control circuit characterized in that the amount of attenuation is increased by a certain value. (2) A temperature compensation circuit (8) is further provided on the output side of the constant voltage circuit (7) to reduce the output current of the constant voltage circuit (7) when the temperature rises. transmission power control circuit.