JPH09199963A - Transmission power control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission power control circuit which conducts open loop transmission power control and closed loop transmission power control with high accuracy. SOLUTION: A transmission power control circuit provided with a 1st variable gain control amplifier 9 varying a gain of an input signal with a control voltage is provided with a 2nd variable gain control amplifier 10 varying a gain of an output voltage of the 1st variable gain control amplifier 9 and an automatic power control circuit generating a control voltage to control the gain of the 2nd variable gain control amplifier 10 from a distributed transmission output. The automatic power control circuit is provided with at least a comparator circuit 17 outputting a difference between a transmission output and a reference value, a sample-and-hold circuit 18 sampling and holding the output of the comparator circuit 17. The sample-and-hold circuit 18 is selected to be a sampling state or a holding state in response to the transmission state to apply on/off control for the automatic power control circuit. The automatic power control circuit is set when the open loop transmission power control is in use and the automatic power control circuit is cleared when the closed loop power control is in use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a code division multiplexing system (CDMA system) used for digital mobile communication and the like.
The present invention relates to a transmission power control circuit of a transmitter, and in particular, enables a highly accurate transmission power control regardless of a transmission power control method.

[0002]

2. Description of the Related Art In a CDMA system, a signal that has been primary-modulated is second-modulated with a spreading code and transmitted, and the receiving side obtains the desired 1 The next modulated wave is extracted. In the process of the despreading, signals of other channels become noise.

In the downlink from the base station to the mobile station, the target signal wave and the other interference waves undergo the same variation on the propagation path and reach each mobile station. The relationship between the reception levels of the signal wave and the interference wave after spreading becomes constant. However, in the uplink from the mobile station to the base station, even if each mobile station transmits a signal wave with the same transmission power, since the distance from the mobile station to the base station and the propagation environment are different, each signal The reception level of the wave at the base station is different. Therefore, in order for the base station to correctly demodulate the respective signal waves by despreading, the reception levels of the respective signal waves must be equalized, and the mobile station needs highly accurate transmission power control.

The transmission power control methods include open-loop transmission power control in which the mobile station variably controls the transmission power by the mobile station according to the received electric field level of the received wave and base station based on the reception result. , Closed-loop transmission power control in which a control signal is sent to the mobile station to variably control the transmission power of the mobile station.

In the open loop transmission power control, a wide range of variable control is performed in which the transmission power is varied by, for example, 10 dB or more in one control so that a desired transmission power can be obtained. In this open loop transmission power control, it is necessary to perform control that guarantees the absolute value of the transmission power.

On the other hand, in the closed loop transmission power control, for example, adjustment to a desired transmission power is performed by relative variable control in a narrow range in which the transmission power is changed by 1 dB. In this closed loop transmission power control, it is necessary to perform control that guarantees the relative value of the transmission power.

As shown in FIG. 5, a transmission power control circuit of a conventional CDMA transmitter used for digital mobile communication or the like, as shown in FIG. 5, varies the gain of a signal input by an input terminal 1 for inputting a signal. Variable gain control amplifier 3
And an input terminal 5 for the control voltage of the variable gain control amplifier 3,
A high output amplifier 4 for amplifying the output signal of the variable gain control amplifier 3 and a signal output terminal 2 are provided.

In this transmission power control circuit, the gain of the signal input from the input terminal 1 is controlled by the variable gain control amplifier 3 according to the control voltage of the control voltage input terminal 5,
Then, it is amplified by the high output amplifier 4 and output from the output terminal 2. Regardless of whether the transmission power control method is closed loop transmission power control or open loop transmission power control, the gain of the variable gain control amplifier 3 is variably controlled by the control voltage input from the input terminal 5, thereby controlling the transmission power. Is performed.

[0009]

However, in the conventional transmission power control circuit, since the transmission power is controlled by only one variable gain control amplifier, the temperature condition and the power supply voltage condition are controlled during the open loop transmission power control. Due to such factors, the absolute value of the transmission power cannot be guaranteed. Also, during closed-loop control, in which the transmission power is controlled by the control signal from the base station, the transmission power is relatively variably controlled within a narrow range. There was a problem that the value could not be guaranteed.

The present invention solves these conventional problems, and in each of the open loop transmission power control and the closed loop transmission power control, the transmission power control circuit can perform the transmission power control with high accuracy. Is intended to provide.

[0011]

Therefore, in the transmission power control circuit of the present invention, in addition to the first variable gain control amplifier for varying the gain of the input signal according to the control voltage, the first variable gain control amplifier is provided. And a second variable gain control amplifier for varying the gain of the output voltage and an automatic power control circuit for generating a control voltage for controlling the gain of the second variable gain control amplifier from the branched transmission output. The automatic power control circuit is controlled to be turned on / off according to the state of power control.

Therefore, in the open loop transmission power control, the automatic power control circuit is turned on, and in the closed loop transmission power control, the automatic power control circuit is turned off. , High-precision control becomes possible.

[0013]

A first aspect of the present invention is a transmission power control circuit including a first variable gain control amplifier for varying the gain of an input signal according to a control voltage. A second variable gain control amplifier that varies the gain of the output voltage of the gain control amplifier; and an automatic power control circuit that generates a control voltage for controlling the gain of the second variable gain control amplifier from the branched transmission output. The automatic power control circuit includes at least a comparison circuit that outputs the difference between the transmission output and the reference value, and a sample hold circuit that samples / holds the output of the comparison circuit. The automatic power control circuit is turned on / off by switching the hold circuit to sample or hold. Ensures absolute value of the transmission output to turn on the automatic power control circuit, also, when the closed loop transmission power control ensures the relative value of the transmission output to turn off the automatic power control circuit.

According to a second aspect of the present invention, the automatic power control circuit includes a detector for detecting the signal level of the branched transmission output, a low-pass filter for filtering the output voltage of the detector, and a low-pass filter. A second variable gain control amplifier including a comparison circuit for comparing the output voltage of the bandpass filter and the reference voltage and a sample hold circuit for sampling / holding the output voltage of the comparison circuit. The gain is controlled by an analog circuit to form an automatic power control circuit.

According to a third aspect of the present invention, the automatic power control circuit includes a detector for detecting the signal level of the branched transmission output, and an A / D converter for analog-digital converting the output voltage of the detector. , An averaging circuit for averaging the output data of the A / D converter, a comparison circuit for comparing the output data of the averaging circuit with reference data, a sample hold circuit for sampling / holding the output data of the comparison circuit, and a sample The output data of the hold circuit is composed of a D / A converter that performs digital-analog conversion, and the gain of the second variable gain control amplifier is controlled by the output voltage of the D / A converter. The main part of the power control circuit is digitized.

According to a fourth aspect of the present invention, there is provided error detection means for detecting an error between the output of the comparison circuit and the output of the sample hold circuit in the automatic power control circuit. When the error exceeds a predetermined value, the sample hold is performed. The circuit is configured to switch from hold to sample, and even in closed loop transmission power control, the absolute value of the transmission output can be guaranteed with a certain accuracy.

According to a fifth aspect of the present invention, the error detection means includes a second comparison circuit for outputting a difference between the output voltage of the comparison circuit in the automatic power control circuit and the output voltage of the sample hold circuit, and a second comparison circuit. Of the absolute value circuit that takes the absolute value of the output voltage of the comparison circuit of No. 3, and a third comparison circuit that outputs the difference between the output voltage of the absolute value circuit and the error reference voltage. It can be an error detecting means of the control circuit.

According to a sixth aspect of the present invention, the error detecting means outputs a difference between the output data of the comparison circuit and the output data of the sample hold circuit in the automatic power control circuit, and the output data of the difference circuit. It is composed of an absolute value circuit that takes the absolute value of and a comparator that outputs the difference data between the output data of the absolute value circuit and the error reference data, and can be the error detection means of the digitized automatic power control circuit. .

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) As shown in FIG. 1, the transmission power control circuit of the first embodiment controls the input terminal 6 to which a signal is input and the gain of the input signal in accordance with a control voltage 20. A variable gain control amplifier 9, and a variable gain control amplifier 10 that variably controls the gain of the output signal of the variable gain control amplifier 9 by the output voltage of a sample hold circuit 18 described later.
High power amplifier 11 for amplifying the output of the variable gain control amplifier 10.
And a distributor 12 for distributing the output signal of the high-power amplifier 11,
Output terminal 7 that outputs a transmission signal with controlled transmission power
And a detector 13 for detecting the output signal level of the distributor 12,
The low-pass filter 14 that filters the detection voltage of the detector 13, the level comparator 17 that compares the detection voltage 15 that is the output voltage of the low-pass filter 14 and the reference voltage 16, and the level comparator 17 A sample and hold circuit 18 that samples or holds the output signal of the control signal 19 according to a control signal 19, and a transmission state control signal input terminal 8 to which a transmission state control signal that specifies a control amount of transmission power is input
And sample and hold circuit 1 according to the transmission state control signal
8. A variable gain control amplifier 9 and a level comparator 17 are provided with a controller 21 for outputting a control signal and a reference voltage 16.

At the transmission state control signal input terminal 8, a signal representing the received electric field strength is inputted as a transmission state control signal at the time of open loop transmission power control, and a base for designating the transmission power at the time of closed loop transmission power control. The control signal from the station is input as the transmission state control signal. Controller 21
Outputs a control voltage 20 for controlling the gain of the variable gain control amplifier 9 according to the transmission state control signal, and also outputs a reference voltage 16 according to the transmission power to be set to the level comparator 17. Furthermore, for the sample and hold circuit 18,
In open loop transmission power control, the sample state (the state in which the sample value of the input signal at that time is read and output) is entered, and in the closed loop transmission power control, the hold state (the sample value of the input signal stored in the past is stored. The control signal 19 is output so as to be in the output state).

Variable gain control amplifier 10, high power amplifier 11,
The feedback loop including the distributor 12, the detector 13, the low-pass filter 14, the level comparator 17, and the sample-hold circuit 18 constitutes an automatic power control circuit when the sample-hold circuit 18 is in the sample state. When the sample hold circuit 18 is in the hold state, the sample hold circuit 18
Output becomes a constant value and the automatic power control function is not exerted.

Next, the operation of this circuit will be described. First,
The signal input from the input terminal 6 is supplied to the variable gain control amplifier 9
Thus, the variable voltage is variably amplified according to the control voltage 20 output from the controller 21 and input to the variable gain control amplifier 10.

The controller 21 has a transmission state control signal input terminal 8
When the control signal input from is an open loop transmission power control signal, the sample hold circuit 18 is controlled by the control signal 19 so as to be a sample. As a result, the variable gain control amplifier 10, the high output amplifier 11, the divider 12, the detector 1
3, the automatic power control circuit composed of the low-pass filter 14, the level comparator 17, and the sample hold circuit 18 operates as follows.

The output signal of the variable gain control amplifier 10 is amplified by the high output amplifier 11, distributed by the distributor 12, detected by the detector 14, and filtered by the low-pass filter 14. The output voltage (detection voltage) 15 of the low-pass filter 14 is compared with the reference voltage 16 according to the transmission power in the level comparator 17, and the voltage corresponding to the difference between the detection voltage 15 and the reference voltage 16 is sampled. It is output to the hold circuit 18.

Sample hold circuit 18 in the sampled state
Sequentially outputs the analog value of the difference to the variable gain control amplifier 10 as a sample value, and the variable gain control amplifier 10
Amplifies the signal input from the variable gain control amplifier 9 according to the output of the sample hold circuit 18. As a result, the gain of the signal is varied so that the output level of the high power amplifier 11 becomes the required transmission power. That is, the transmission power from the output terminal 7 is always controlled to the required transmission power by this automatic power control circuit, and the absolute value of the transmission power is guaranteed.

On the other hand, when the control signal input from the transmission state control signal input terminal 8 is a closed loop transmission power control signal, the controller 21 controls the sample and hold circuit 18 to hold it by the control signal 19. Control.
In this case, the automatic power control circuit composed of the variable gain control amplifier 10, the high output amplifier 11, the divider 12, the detector 13, the low pass filter 14, the level comparator 17 and the sample hold circuit 18 is turned off, The variable gain control amplifier 10 is fixed to a constant gain. Therefore, the gain of the transmission power is relatively controlled only by the control according to the control voltage 20 in the variable gain control amplifier 9.

Therefore, during open loop transmission control,
The absolute value of the transmission power is guaranteed by the automatic power control circuit,
At the time of closed loop transmission control, the relative value of the transmission power is guaranteed by turning off the automatic power control circuit. In this way, this transmission power control circuit can perform highly accurate transmission power control in either transmission power control state.

(Second Embodiment) The transmission power control circuit of the second embodiment digitizes the processing in the automatic power control circuit.

As shown in FIG. 2, this transmission power control circuit averages the output data of the A / D converter 22 and the A / D converter 22 for analog-digital converting the detection voltage of the detector 13. Averaging circuit 23 and output data 24 of the averaging circuit 23
Circuit 26 for comparing the reference data 25 with the reference data 25, a sample hold circuit 27 for sampling or holding the output data of the comparison circuit 26, and a D / A converter for performing digital-analog conversion of the output data of the sample hold circuit 27.
28 and. Other configurations are the same as those of the first embodiment.

In this transmission power control circuit, when the control signal input from the transmission state control signal input terminal 8 is an open loop transmission power control signal, the controller 21 controls the control signal.
19, the sample hold circuit 27 is maintained in the sample state. At this time, it comprises a variable gain control amplifier 10, a high output amplifier 11, a divider 12, a detector 13, an A / D converter 22, an averaging circuit 23, a comparison circuit 26, a sample hold 27 and a D / A converter 28. The automatic power control circuit operates as follows.

The output signal of the variable gain control amplifier 10 is amplified by the high output amplifier 11, distributed by the distributor 12, detected by the detector 13, converted into digital data by the A / D converter 22, and averaged. The averaging circuit 23 averages. The output data 24 of the averaging circuit 23 is compared with the reference data 25 corresponding to the transmission power by the comparison circuit 26, and the digital data corresponding to the difference is output to the sample hold circuit 27. The sample-hold circuit 27 in the sampled state sequentially outputs the sampled values of the input digital data, and D
The / A converter 28 converts the digital data output from the sample hold circuit 27 into an analog signal and outputs the analog signal to the variable gain control amplifier 10.

The variable gain control amplifier 10 amplifies the signal input from the variable gain control amplifier 9 according to the output of the D / A converter 28. As a result, the gain of the signal is varied so that the output level of the high power amplifier 11 becomes the required transmission power.
That is, the transmission power from the output terminal 7 is always controlled to the required transmission power by this automatic power control circuit, and the absolute value of the transmission power is guaranteed.

When the control signal input from the transmission state control signal input terminal 8 is a closed loop transmission power control signal, this transmission power control circuit performs the same operation as in the first embodiment.

In this transmission power control circuit, the sample hold circuit holds the sample value as digital data. In the sample hold circuit of the first embodiment, the analog voltage is held by the capacitor in the circuit, but there is a drawback that the voltage cannot be held for a long time because the capacitor discharges. On the other hand, in the sample hold circuit of the second embodiment, since the digital value is held, it can be held for a long time.

(Third Embodiment) The transmission power control circuit according to the third embodiment is capable of guaranteeing the absolute value of the transmission power during closed loop transmission control within a certain range.

This transmission power control circuit, as shown in FIG. 3, has an output voltage of the level comparator 17 and a sample hold circuit.
Equipped with a comparator 29 for comparing with the output voltage of 18, an absolute value circuit 30 for taking the absolute value of the comparator 29, and a comparator 32 for comparing the output voltage of the comparator 29 with the error reference voltage 32. ing. Other configurations are the same as those of the first embodiment.

In this transmission power control circuit, when the control signal input from the transmission state control signal input terminal 8 is an open loop transmission power control signal, the controller 21 controls the sample hold circuit 18 by the control signal 19. Keep in sample condition. Therefore, the output voltage of the level comparator 17 and the output voltage of the sample hold circuit 18 become equal, and the comparator 29,
The error detection circuit including the absolute value circuit 30 and the comparator 31 does not operate. At this time, the variable gain control amplifier 10, the high output amplifier
11, distributor 12, detector 13, low-pass filter 14, level comparator
The automatic power control circuit composed of 17 and the sample hold circuit 18 performs the same operation as in the first embodiment, and guarantees the absolute value of the transmission power during open loop transmission power control.

On the other hand, when the control signal input from the transmission state control signal input terminal 8 is a closed loop transmission power control signal, the controller 21 uses the control signal 19 to cause the sample hold circuit 18 to initially It is controlled so that it is in the hold state. In this state, the variable gain control amplifier 10 is fixed at a constant gain, and the transmission power is relatively controlled only by the control according to the control voltage 20 of the variable gain control amplifier 9.

During this period, the comparator 29 connected to the automatic power control circuit compares the output voltage V1 of the level comparator 17 with the output voltage V2 of the sample hold circuit 18, and outputs the difference as the output voltage V3 to the absolute value circuit 30. Output to. Absolute value circuit 30
Is the absolute value of this output voltage V3 | V3 | = | V2-V1
Is output to the comparison circuit 31, and the comparison circuit 31 outputs this | V3 |
The difference | V3 | -Verr between the error reference voltage Verr and the error reference voltage Verr is output to the controller 21. The controller 21 determines this difference | V3 |-
When Verr exceeds a certain value, the control signal 19 causes the sample-hold circuit 18 that holds the voltage to transit to the sample state.

As a result, the sample hold circuit 18 of the automatic power control circuit sequentially changes the analog value of the voltage corresponding to the difference between the detection voltage 15 output from the level comparator 17 and the reference voltage 16 as the sample value. Output to the gain control amplifier 10, and the variable gain control amplifier 10 outputs the variable gain control amplifier 9
The signal input from the amplifier is amplified according to the output of the sample hold circuit 18. Therefore, the output level of the high-power amplifier 11 has a variable signal gain so that the required transmission power is obtained under the control of the automatic power control circuit.

Further, the controller 21 shifts the sample hold circuit 18 to the hold state when the difference | V3 | -Verr output from the comparator 31 becomes a certain value or less.

Thus, in this transmission power control circuit,
Even in closed-loop transmission power control, if the transmission power deviates considerably from the reference voltage, the absolute value of the transmission power can be controlled within a certain range by controlling the transmission power to the required value. Can be guaranteed.

Therefore, the transmission power control circuit guarantees the absolute value of the transmission power by the automatic power control circuit during the open loop transmission control, and guarantees the relative value of the transmission power during the closed loop transmission control. It guarantees absolute accuracy within a certain range and enables highly accurate transmission power control in either transmission power control state.

(Embodiment 4) The transmission power control circuit of the fourth embodiment digitally processes the operation of the third embodiment.

As shown in FIG. 4, this transmission power control circuit, in the digitized automatic power control circuit of the second embodiment, calculates the difference between the output data of the comparison circuit 26 and the output data of the sample hold circuit 27. Difference circuit 33
And an absolute value circuit 34 that takes the absolute value of the output of the difference circuit 33,
A comparator 35 for comparing the output data of the absolute value circuit 34 and the error reference data 35 is provided. Other configurations are second
There is no difference from the embodiment.

In this transmission power control circuit, when the control signal input from the transmission state control signal input terminal 8 is an open loop transmission power control signal, the controller 21 controls the sample hold circuit 27 by the control signal 19. Keep in sample condition. At this time, the output data of the difference circuit 33 becomes 0,
The absolute value circuit 34 and the comparator 35 do not operate, and the variable gain control amplifier 10, the high output amplifier 11, the distributor 12, the detector 13, the A / D converter 22, the averaging circuit 23, the comparison circuit 26, the sample hold. The automatic power control circuit composed of the circuit 27 and the D / A converter 28 performs the same operation as that of the second embodiment, and guarantees the absolute value of the transmission power during the open loop transmission power control.

On the other hand, when the control signal input from the transmission state control signal input terminal 8 is a closed loop transmission power control signal, the controller 21 uses the control signal 19 to cause the sample hold circuit 27 to initially set It is controlled so that it is in the hold state.

Difference circuit 33 connected to the automatic power control circuit
Compares the output data D1 of the comparison circuit 26 with the output data D2 of the sample hold circuit 27 and outputs the difference to the absolute value circuit 34 as output data D3. Absolute value circuit 34
Is the absolute value of this output data D3 | D3 | = | D2-D
1 | is output to the comparison circuit 35, and the comparison circuit 35 outputs this | D3.
The difference between | and the error reference data 36 is output to the controller 21.
When this difference exceeds a certain value, the controller 21 causes the control signal 19 to cause the sample-hold circuit 27 that holds the digital value to transition to the sample state.

Further, the controller 21 shifts the sample hold circuit 27 to the hold state when the difference data output from the comparator 35 becomes a certain value or less.

When the sample hold circuit 27 transits to the sample state, the variable gain control amplifier 10, the high output amplifier 11,
Distributor 12, detector 13, A / D converter 22, averaging circuit 23,
Comparison circuit 26, sample hold circuit 27 and D / A converter
The automatic power control circuit composed of 28 operates, and the variable gain control amplifier 10 amplifies the signal input from the variable gain control amplifier 9 according to the output of the D / A converter 28. Therefore, even during closed-loop transmission power control, when the transmission power deviates considerably from the reference voltage, control is performed to bring the transmission power to the required value, and the absolute value of the transmission power is within a certain range of accuracy. Guaranteed.

Therefore, the transmission power control circuit guarantees the absolute value of the transmission power by the automatic power control circuit during the open loop transmission control, and guarantees the relative value of the transmission power during the closed loop transmission control. It guarantees absolute accuracy within a certain range and enables highly accurate transmission power control in either transmission power control state.

Further, in the sample hold circuit of this circuit, since the sample value is held as digital data, it can be held for a long time.

[0054]

As is apparent from the above description, the transmission power control circuit of the present invention performs on / off switching of the automatic power control according to the transmission power control state, and thus the CDM.
Highly accurate transmission power control can be performed in both transmission power control states of the open loop transmission power control and the closed loop transmission power control of the A system transmitter.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a transmission power control circuit according to a first embodiment of the present invention,

FIG. 2 is a circuit configuration diagram showing a transmission power control circuit according to a second embodiment of the present invention,

FIG. 3 is a circuit configuration diagram showing a transmission power control circuit according to a third embodiment of the present invention,

FIG. 4 is a circuit configuration diagram showing a transmission power control circuit according to a fourth embodiment of the present invention,

FIG. 5 is a circuit configuration diagram showing a conventional transmission power control circuit.

[Explanation of symbols]

 1, 6 Input terminal 2, 7 Output terminal 3, 9, 10 Variable gain control amplifier 4, 11 High output amplifier 5 Control voltage input terminal 8 Transmission state control signal input terminal 12 Distributor 13 Detector 14 Low-pass filter 15 Detection voltage 16 Reference voltage 17 Level comparator 18 Sample and hold circuit 19 Control signal 20 Control voltage 21 Controller 22 A / D converter 23 Averaging circuit 24 Output data 25 Reference data 26 Comparison circuit 27 Sample and hold circuit 28 D / A conversion 29, 31 Comparator 30, 34, 35 Absolute value circuit 32 Error reference voltage 33 Difference circuit 36 Error reference data

Claims (6)

[Claims] 1. A transmission power control circuit including a first variable gain control amplifier for varying the gain of an input signal according to a control voltage, wherein a second variable gain control circuit for varying the gain of an output voltage of the first variable gain control amplifier. Variable gain control amplifier, and an automatic power control circuit for generating a control voltage for controlling the gain of the second variable gain control amplifier from the branched transmission output, the automatic power control circuit, at least, A comparison circuit that outputs the difference between the transmission output and the reference value, and a sample hold circuit that samples / holds the output of the comparison circuit, and by switching the sample hold circuit to sample or hold according to the transmission state, A transmission power control circuit for performing on / off control of the automatic power control circuit. 2. The automatic power control circuit includes a detector that detects a signal level of a branched transmission output, a low-pass filter that filters an output voltage of the detector, and a low-pass filter of the low-pass filter. It comprises a comparison circuit for comparing an output voltage with a reference voltage, and a sample hold circuit for sampling / holding the output voltage of the comparison circuit. The output voltage of the sample hold circuit controls the gain of the second variable gain control amplifier. The transmission power control circuit according to claim 1, which is controlled. 3. A detector for detecting the signal level of a branched transmission output by the automatic power control circuit, an A / D converter for analog-digital converting the output voltage of the detector, and the A / D conversion. Circuit for averaging the output data of the sampler, a comparison circuit for comparing the output data of the averaging circuit with reference data, a sample hold circuit for sampling / holding the output data of the comparison circuit, and the sample hold circuit And a D / A converter for digital-analog converting the output data of the second variable gain control amplifier, wherein the output voltage of the D / A converter controls the gain of the second variable gain control amplifier. The transmission power control circuit described. 4. An error detecting means for detecting an error between the output of the comparison circuit and the output of the sample hold circuit in the automatic power control circuit is provided, and the sample hold circuit is held when the error exceeds a predetermined value. The transmission power control circuit according to claim 1, wherein the transmission power control circuit is switched from a sample to a sample. 5. A second comparison circuit, wherein the error detection means outputs a difference between an output voltage of the comparison circuit and an output voltage of the sample hold circuit in the automatic power control circuit, and the second comparison circuit. 5. The transmission according to claim 4, further comprising: an absolute value circuit that takes an absolute value of the output voltage of the second comparison circuit, and a third comparison circuit that outputs a difference between the output voltage of the absolute value circuit and an error reference voltage. Power control circuit. 6. A difference circuit for outputting a difference between the output data of the comparison circuit and the output data of the sample hold circuit in the automatic power control circuit, and the absolute value of the output data of the difference circuit. 5. The transmission power control circuit according to claim 4, wherein the transmission power control circuit comprises an absolute value circuit and a comparator that outputs difference data between output data of the absolute value circuit and error reference data.