JPH05291854A - Automatic power control circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To suppress the output fluctuation due to the temperature characteristics of the automatic power control circuit that maintains the transmission level of the transmitter at the command power level from the base station. [Structure] A part of the output of the transmission power amplifier 1 is connected to a coupling circuit
The signal extracted from the coupling circuit 2 is input to the impedance converter 4 whose output impedance is set to be larger than the input impedance, and the output voltage of the impedance converter 4 is amplified with respect to the input voltage. Then, the output signal of the impedance converter 4 is detected by the detection circuit 5, the difference between the output of the detection circuit 5 and the command power level is amplified by the error voltage amplifier 7, and the value of the transmission power amplifier 1 is detected by this value. Control the degree of amplification. Since the voltage signal is amplified by the input impedance before input to the detection circuit 5, the output fluctuation of the transmission power amplifier 1 due to the temperature characteristic of the diode used in the detection circuit 5 becomes a negligible value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission power control circuit used in mobile equipment such as automobile telephones and mobile telephones.
In particular, the present invention relates to an automatic power control circuit that constantly controls transmission power to a designated level.

[0002]

2. Description of the Related Art In a mobile communication system such as an automobile telephone adopting a cellular system, it is desirable to use a different frequency for each cell in order to prevent radio wave interference between mobile units. However, since the usable frequency band is limited, different frequencies are assigned to adjacent cells and used, but the same frequency is assigned to and used for distant cells that radio waves do not reach in a normal state. However, even between cells that are far apart, radio waves may arrive depending on the location of the mobile device, the topography, and other conditions. In this case, mobile stations using the same frequency in each cell will cause radio wave interference.

Therefore, a circuit for switching the magnitude of the transmission power in several steps is added to the transmission circuit of the mobile unit, and the base station examines the electric field strength of the radio wave received from the mobile unit and transmits / receives to / from the mobile unit. The mobile station switches the transmission power to the commanded power level by determining an appropriate power level that is necessary for the mobile station and is not too large. Furthermore, the automatic power control circuit is adapted to keep the transmission power level constant at the switched power level.

The automatic power control circuit takes out a part of the transmission power, rectifies and detects it, controls the amplification degree of the amplifier of the transmission circuit according to the magnitude of the obtained signal, and keeps the transmission power constant. is there. However, since the diode used in the rectification detection circuit has a temperature characteristic of about 2 mV / ° C., there is a problem that the transmission power fluctuates depending on the temperature.

In order to solve this problem, conventionally, a bias power supply is connected to the anode of a diode for rectification detection through another diode and a resistor to compensate for the change in forward voltage drop due to the temperature of the diode for rectification detection. I am trying. In another conventional technique, a part of the transmission power is taken out, amplified by a logarithmic amplifier and then rectified and detected, so that the dynamic range is compressed and the influence of the temperature characteristic of the diode of the rectification and detection circuit is reduced. I am trying.

[0006]

SUMMARY OF THE INVENTION The above-mentioned prior art is
The problem is that the temperature characteristic of the diode of the rectifying and detecting circuit gives fluctuations in transmission power. In the case of the prior art in which the temperature characteristic of the rectifying and detecting diode is compensated by another diode, the temperature compensating effect becomes small unless the characteristic of the temperature compensating diode is matched with the characteristic of the rectifying and detecting diode. Therefore, a pair of diodes with uniform characteristics is prepared to manufacture the mobile device. However, preparing diodes with uniform characteristics in pairs is a factor that increases the manufacturing cost of the mobile device. Further, in this conventional technique, a part of the transmission power is detected by the directional coupler or the capacitor, and the small voltage detected by the directional coupler or the capacitor is amplified by the amplifier. The mobile device preferably has a small hardware scale in consideration of portability, and on the other hand, it is required to have a performance of processing a small detection voltage and stably controlling a small transmission power. For this reason, it is necessary to design a circuit with a small hardware scale and excellent control performance from the beginning, but in the past there was no such consideration, and it would be possible to achieve the target control performance by adding extra hardware. The circuit configuration is as follows.

In the case of the conventional technique for compensating the temperature characteristic of the diode for rectifying and detecting by providing the logarithmic amplifier, there is a problem that the hardware scale of the logarithmic amplifier is large. Further, this conventional technique also has a problem that the temperature characteristic of the logarithmic amplifier is not taken into consideration. Furthermore, since the logarithmic amplifier compresses linearity, control with higher resolution is required, and the temperature characteristic of the circuit that processes the signal detected by the directional coupler and the capacitor becomes a problem. I haven't. Furthermore, since the linearity of the logarithmic amplifier is limited, the control of the transmission power level is also limited by this limitation.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic power control circuit having a novel structure in which fluctuations in transmission power can be ignored without compensating for temperature characteristics of a diode or the like of a rectification detection circuit.

[0009]

The above object is used in a transmitter that amplifies a radio frequency signal to a required power level by a transmission power amplifier and emits it from an antenna, and controls the transmission power level to the required power level. In an automatic power control circuit, a coupling circuit for extracting a part of the output of the transmission power amplifier, and an impedance converter for inputting a part of the power extracted by the coupling, the output impedance of which is set to be larger than the input impedance. A bias means for applying a bias to the output signal of the impedance converter, a detection circuit for rectifying and detecting the output signal of the impedance converter biased by the bias means, a required power level and the detection circuit. The output power of the output signal is compared with the power level of the output signal to control the amplification degree of the transmission power amplifier. The transmit power level by providing a control means for controlling the constant required power level Te is achieved.

[0010]

The voltage of the output of the transmission power amplifier extracted by the coupling circuit becomes the value amplified by the impedance converter and is input to the detection circuit. Therefore, the temperature characteristic of the diode of the detection circuit becomes negligible, and the transmission power level is maintained substantially constant at the required power level regardless of temperature changes.

Here, when the influence of the frequency characteristics of the impedance converter or the like becomes a problem, data for correcting the frequency characteristics with respect to the commanded power level from the base station is stored in the memory, and the data of the detection circuit is stored. By using the data stored in the memory as the command power level to be compared with the output power level, it is possible to easily avoid the influence of the frequency characteristic of the impedance converter or the like.

Furthermore, when a directional coupler is used as the coupling circuit, the traveling wave coupling end output is input to the impedance converter, the reflected wave coupling end output is input to the bias means, and the resistance used for this bias means is changed. Use a value that works as a terminating resistor. Thereby, when the mechanism for converting the impedance is put in the directional coupler, it is not necessary to separately use the impedance converter.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a circuit diagram of a transmitter circuit of a mobile device including an automatic power control circuit according to a first embodiment of the present invention. At the input end of the transmission power amplifier 1 of the mobile device, a radio frequency signal (RF
Signal), the output end of the transmission power amplifier 1 is connected to the antenna filter 10, the antenna 11 is connected to the output end of the antenna filter 10, and the output signal of the transmission power amplifier 1 is emitted from the antenna to the air. The automatic power control circuit attached to the main loop of this transmitter circuit is
Directional coupler 2, bias means 3, impedance converter 4, half-wave rectification detection circuit 5, level control voltage generator 6, error voltage amplifier 7 as control means, and RO
It consists of M8.

The directional coupler 2 is provided in the middle of the transmission power amplifier 1 and the antenna filter 10 in the main loop, and the directional coupler 2 is used to output one of the output powers of the transmission power amplifier 1. Parts are taken out.

The bias means 3 superimposes a bias voltage on the output signal of the transmission power amplifier 1 extracted by the directional coupler 2. The bias means 3 includes a resistor 3a and a resistor 3b, and a voltage obtained by dividing the voltage (+ 5V) of the bias power supply B by these resistors {3b / (3a + 3b)} is used as the bias voltage. This voltage corrects the forward voltage drop of the diode 5a used in the detection circuit 5.
In addition, in this embodiment, the resistor 3b also functions as a terminating resistor.

In the impedance converter 4, the bias means 3 is taken out from the main loop by the directional coupler 2.
The signal to which the bias voltage is applied is input by. The input impedance of the impedance converter 4 is a value that matches the output impedance of the directional coupler 2 to the impedance converter 4 side, and is about 50 ohms in this embodiment. The output impedance of the impedance converter 4 is about 1250 ohms in this embodiment. Therefore, the impedance converter 4 of this embodiment functions to increase the voltage of the input signal by about 5 times on the output side. The impedance converter 4 can be configured by a microstrip line or discrete components such as the inductor 4a and the capacitor 4b. When using a directional coupler having an impedance conversion mechanism, the impedance converter 4 becomes unnecessary.

The output signal of the impedance converter 4 is input to the half-wave rectification detection circuit 5. Half-wave rectification detection circuit 5
Is a diode 5a provided in the forward direction in this embodiment.
And a resistor 5b and a capacitor 5c connected in parallel between the output of the diode 5a and the ground, but the configuration may be different. Alternatively, a full-wave rectifier circuit may be used.

The output side of the error voltage amplifier 7 is connected to the control terminal for controlling the amplification degree of the transmission power amplifier 1. The error voltage amplifier 7 amplifies and outputs a difference between two input signals, one input terminal is connected to the output terminal of the half-wave rectification detection circuit 5, and the other input terminal is level-controlled. The output terminal of the voltage generator 6 is connected. A Tx ON / OFF signal is input to the control terminal of the error voltage amplifier 7,
The output of the error voltage amplifier 7 is turned on / off. When Tx is on, the error voltage amplifier 7 outputs a signal corresponding to the difference between the two input signals, and when Tx is off, the output is invalidated and the bias to the transmission power amplifier 1 is set to zero. As a result, the high frequency output of the transmission power amplifier 1 is cut off.

The level control voltage generator 6 is easily realized by a D / A converter and generates a voltage corresponding to the data output from the ROM 8 and outputs it to the error voltage amplifier 7. .. The ROM 8 stores data corresponding to the power level instructed by the base station,
Data for canceling the frequency characteristics of the impedance converter 4 and the filter 10 at each power level and correction data corresponding to each transmission power level are stored in advance, and the data according to the command from the base station generates the level control voltage. Output to the container 6. In addition, if the mobile device does not need to consider the frequency characteristics of the impedance converter 4 and the like,
By omitting the ROM 8 and directly inputting the power level based on the command from the base station to the level control generator 6, the cost can be reduced.

In the automatic power control circuit having the above configuration, when the RF signal is input to the transmission power amplifier 1, the transmission power amplifier 1 amplifies the RF signal with the amplification degree designated by the input signal to the control terminal, Output. In the connection path between the transmission power amplifier 1 and the antenna filter 10, a traveling wave toward the antenna and a reflected wave from the antenna exist,
Part of the traveling wave and the reflected wave enters the automatic power control circuit side through the directional coupler 2. Of these, the reflected wave is consumed by the terminating resistor 3b of the bias means 3, and only part of the traveling wave is input to the impedance converter 4.
Now, it is assumed that the output power of the transmission power amplifier 1 fluctuates for some reason. A part of this output power is taken out by the directional coupler 2 and detected by the half-wave rectification detection circuit 5, which becomes one input of the error voltage amplifier 7 as an RF output correlation voltage. The error voltage amplifier 7 compares this RF output correlation voltage with the power level commanded by the base station, amplifies the difference, and inputs it to the control terminal of the transmission power amplifier 1. As a result, if the transmission power level becomes higher than the command power level, the amplification degree becomes smaller, and if the transmission power level becomes lower than the command power level, the amplification degree becomes large and the transmission power level is kept constant at the command power level. It

When the temperature changes, the diode 5 of the detection circuit 5
Even if the characteristic of a changes, the detection circuit 5 of the automatic power control circuit according to the present embodiment outputs the RF output correlation voltage to which the influence of temperature can be ignored to the error voltage amplifier 7. The reason is that the impedance converter 4 is provided and the detection circuit 5 is provided.
This is because the input voltage to the circuit is approximately five times as large in this embodiment. The traveling wave component of the RF signal amplified by the transmission power amplifier 1 is extracted by the directional coupler 2 at a constant ratio. This power is, for example, about 0.14V at the lowest output
rms, about 1.4 Vrms at maximum output (rms
Indicates the effective value. ). When this power is input to the impedance converter 4 having an input impedance of 50 ohms and an output impedance of 1250 ohms, the voltage value on the output side becomes about 5 times, and about 0.7 Vrms at the minimum output,
The maximum output is about 7.0 Vrms.

FIG. 2 is a block diagram of an automatic power control circuit according to the second embodiment of the present invention. The present embodiment is an automatic power control circuit attached to a transmission circuit provided with an isolator 9 in the main loop. In this case, since only a traveling wave exists in the main loop, the power flowing in the main loop by the capacitor 2 '. Is taking out a part of. And
As the resistor 3b of the bias means 3, it is not necessary to have the function of a terminating resistor, so a resistor of 1K ohm order is used (in the first embodiment, which functions as a terminating resistor, 1
A resistance of 00 ohm order is used. ). The rest of the configuration is the same as that of the first embodiment, and the operation thereof is also the same.
Data for collectively correcting the temperature characteristics of the isolator 9 is stored in the OM 8.

In the above embodiment, one of the required power levels prepared in multiple stages is determined as the transmission power level based on the command from the base station, but the mobile unit itself receives the received electric field. It goes without saying that the present invention can also be applied to a device that detects a signal and determines the transmission power level according to the detected value.

[0024]

According to the present invention, since the input voltage to the detection circuit is increased by passing through the impedance converter, the temperature characteristic of the diode of the detection circuit can be ignored and the automatic power independent of the temperature can be obtained. It becomes possible to obtain a control circuit.

[Brief description of drawings]

FIG. 1 is a transmission circuit diagram of a mobile device including an automatic power control circuit according to a first embodiment of the present invention.

FIG. 2 is a transmitter circuit diagram of a mobile device including an automatic power control circuit according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... Transmission power amplifier, 2 ... Directional coupler, 2 '... Coupling circuit (capacitor), 3 ... Bias means, 4 ... Impedance converter, 5 ... Detection circuit, 6 ... Level control voltage generator, 7 ... Error voltage Amplifier (control means), 8 ... ROM.

Claims (6)

[Claims] 1. An automatic power control circuit for use in a transmitter for amplifying a radio frequency signal to a required power level by a transmission power amplifier and emitting from an antenna, wherein the automatic power control circuit constantly controls the transmission power level to the required power level. A coupling circuit for extracting a part of the output of the power amplifier, an impedance converter having a large output impedance with respect to the input impedance and receiving a part of the power extracted by the coupling circuit, and an impedance converter for the impedance converter. Bias means for applying a bias to the output signal, a detection circuit for rectifying and detecting the output signal of the impedance converter biased by the bias means, the required power level and the power level of the output signal of the detection circuit The transmission power level is controlled by controlling the amplification degree of the transmission power amplifier based on the difference between An automatic power control circuit comprising: control means for controlling the power level to the required power level. 2. The receiving power level according to claim 1, wherein one of a plurality of power levels prepared as the required power level is determined based on a command from the base station, or the reception level detected by the local station. An automatic power control circuit characterized in that it is determined by its own station based on an electric field. 3. The memory according to claim 1, further comprising a memory storing data in which a frequency characteristic of the impedance converter is corrected with respect to a required power level, and the data read from the memory is given to the control means as a required power level. Automatic power control circuit characterized by. 4. When the transmission power amplifier and the antenna are connected without using an isolator according to any one of claims 1 to 3, a directional coupler is used as the coupling circuit, and An automatic power control circuit characterized in that a resistor used as a bias means also has a function of a terminating resistor that absorbs reflected power from an antenna. 5. The data according to claim 1, wherein when the output of the transmission power amplifier is connected to the antenna via the isolator and the filter, data for collectively correcting the frequency characteristics of the impedance converter, the isolator and the filter is stored in the memory. Then, the data read out from the memory is applied to the control means as a required power level. 6. The structure according to claim 4, wherein the input / output impedance of the directional coupler is different without using a separate impedance converter, and has a conversion function of substantially increasing the impedance of the coupling output end. An automatic power control circuit characterized by using a set.