JP3332408B2 - Automatic power control circuit - Google Patents

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 for a mobile device such as an automobile telephone or a portable telephone.
In particular, the present invention relates to an automatic power control circuit that controls transmission power to a specified level.

[0002]

2. Description of the Related Art In a mobile communication system such as an automobile telephone employing 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 restricted, different frequencies are allocated to adjacent cells and used, but the same frequency is allocated and used to distant cells where radio waves do not reach under normal conditions. However, even between distant cells, radio waves may reach depending on the location of the mobile device, the terrain, and the like. In this case, a mobile station using the same frequency in each cell causes radio wave interference.

[0003] Therefore, a circuit for switching the magnitude of transmission power in several steps is added to the transmission circuit of the mobile station, and the base station checks the electric field strength of the radio wave received from the mobile station and transmits / receives the signal to / from the mobile station. The mobile station determines an appropriate power level that is not necessary and is not too large, and instructs the mobile station, and the mobile station switches the transmission power to the specified power level. Further, the automatic power control circuit keeps the transmission power level constant at the switched power level.

The automatic power control circuit extracts a part of the transmission power, performs rectification detection, controls the amplification degree of the amplifier of the transmission circuit based on 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 varies depending on the temperature.

In order to solve this problem, conventionally, a bias power supply is connected to the anode of a diode to be rectified and detected via another diode and a resistor to compensate for a change in forward voltage drop due to the temperature of the diode to be rectified and detected. Like that. In another conventional technique, a part of the transmission power is taken out, amplified by a logarithmic amplifier, and then rectified and detected, and the dynamic range is compressed to reduce the influence of the temperature characteristics of the diode of the rectified detection circuit. Like that.

[0006]

The prior art described above is
An object of the present invention is to solve the problem that the temperature characteristics of the diode of the rectification detection circuit fluctuate transmission power. In the case of the related art in which the temperature characteristic of the rectification detection diode is compensated by another diode, unless the characteristics of the temperature compensation diode match the characteristics of the rectification detection diode, the temperature compensation effect is reduced. Therefore, a mobile device is manufactured by preparing a pair of diodes having uniform characteristics. However, preparing a pair of diodes having uniform characteristics is a factor that increases the manufacturing cost of the mobile device. Further, this prior art employs a configuration in which a part of transmission power is detected by a directional coupler or a capacitor, and a small voltage detected by the directional coupler or the capacitor is amplified by an amplifier. In consideration of portability, a mobile device preferably has a small hardware scale, while it is required to have a capability 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. However, conventionally, there is no such a consideration, and the desired control performance will be achieved by adding extra hardware. Circuit configuration.

In the case of the prior art in which the logarithmic amplifier is provided to compensate for the temperature characteristics of the rectifying and detecting diode, there is a problem that the hardware scale of the logarithmic amplifier is large. In addition, this prior art has a problem that the temperature characteristics of the logarithmic amplifier are not considered. Furthermore, the logarithmic amplifier compresses the linearity, so it is necessary to control with higher resolution, 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 limit.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic power control circuit having a novel configuration capable of ignoring fluctuations in transmission power without compensating for temperature characteristics of diodes and the like of a rectifying detection circuit.

[0009]

An object of the present invention is to provide a transmitter which amplifies a radio frequency signal to a required power level by a transmission power amplifier and emits the signal from an antenna, and controls the transmission power level to the required power level. in the automatic power control circuit, wherein a coupling circuit for taking out a part of the output of the transmission power amplifier, the output impedance proportional to the input impedance is configured as a large becomes, boosting an input signal voltage
An impedance converter that obtains an output signal voltage by applying a bias to the output signal of the impedance converter, and a rectifier for detecting the output signal of the impedance converter biased by the bias unit. And a circuit for comparing the required power level with the power level of the output signal of the detection circuit, controlling the amplification of the transmission power amplifier based on a difference between the two, and controlling the transmission power level to be constant at the required power level. This is achieved by providing means.

[0010]

The output voltage of the transmission power amplifier taken out by the coupling circuit is converted into the input signal voltage by the impedance converter.
It becomes a boosted value and is input to the detection circuit. For this reason,
The temperature characteristic of the diode of the detection circuit becomes negligible, and the transmission power level is kept constant at a predetermined power level regardless of the temperature change.

Here, when the influence of the frequency characteristics of the impedance converter and the like becomes a problem, data for correcting the frequency characteristics with respect to the command power level from the base station is stored in a 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, the influence of the frequency characteristics of the impedance converter and the like can be easily avoided.

Further, when a directional coupler is used as a coupling circuit, the output of the traveling wave coupling terminal is input to the impedance converter, the output of the reflected wave coupling terminal is input to the bias means, and the resistance of the resistor used for the bias means is adjusted. Use a value that functions as a terminating resistor. Accordingly, when a mechanism for converting impedance is provided in the directional coupler, it is not necessary to use a separate impedance converter.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a transmission circuit of a mobile device including an automatic power control circuit according to a first embodiment of the present invention. A radio frequency signal (RF) is input to the input terminal of the transmission power amplifier 1 of the mobile device.
Signal) is input, 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 transmission circuit,
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, RO
M8.

The directional coupler 2 is provided in the main loop between the transmission power amplifier 1 and the antenna filter 10, and the directional coupler 2 controls the output power of the transmission power amplifier 1 by one. The part is 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 sets a voltage obtained by dividing the voltage (+ 5V) of the bias power supply B by these resistors (3b / (3a + 3b)) as a bias voltage. This voltage corrects the forward voltage drop of the diode 5a used in the detection circuit 5.
In this embodiment, the resistor 3b also functions as a terminating resistor.

The impedance converter 4 has a bias means 3 which is taken out of the main loop by the directional coupler 2 and
, A signal to which a bias voltage is applied is input. 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 ohm in this embodiment. Therefore, the impedance converter 4 of the present embodiment functions to increase the voltage of the input signal by about 5 times on the output side. Incidentally, the impedance converter 4 can be constituted by a microstrip line, or can be constituted by discrete components such as an inductor 4a and a capacitor 4b. When a directional coupler incorporating an impedance conversion mechanism is used, the impedance converter 4 is 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. Further, a full-wave rectifier circuit may be used.

The output side of the error voltage amplifier 7 is connected to a control terminal for controlling the amplification of the transmission power amplifier 1. The error voltage amplifier 7 amplifies the difference between the two input signals and outputs the amplified signal. One input terminal is connected to the output terminal of the half-wave rectification detection circuit 5, and the other input terminal is connected to a level control circuit. The output terminal of the voltage generator 6 is connected. A Tx on / off signal is input to a 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, its output is invalidated and the bias to the transmission power amplifier 1 is set to 0. As a result, the high-frequency output of the transmission power amplifier 1 is turned off.

The level control voltage generator 6 is easily realized by a D / A converter, generates a voltage corresponding to data output from the ROM 8, and outputs the voltage to the error voltage amplifier 7. . The ROM 8 contains data corresponding to the power level commanded from the base station,
At each power level, data for canceling the frequency characteristics of the impedance converter 4 and the filter 10 and correction data corresponding to each transmission power level are stored in advance, and data according to a command from the base station is used to generate a level control voltage. Output to the container 6. If the mobile device does not need to consider the frequency characteristics of the impedance converter 4 or 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 according to the above configuration, when an RF signal is input to the transmission power amplifier 1, the transmission power amplifier 1 amplifies the RF signal with an amplification specified by an input signal to its 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.
Some of the traveling wave and the reflected wave enter the automatic power control circuit through the directional coupler 2. Of these, the reflected wave is consumed by the terminating resistor 3b of the bias means 3, and only a 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 the RF output correlation voltage with a power level commanded by the base station, amplifies the difference, and inputs the difference to the control terminal of the transmission power amplifier 1. Thereby, the amplification decreases when the transmission power level becomes higher than the command power level, and increases when the transmission power level becomes lower than the command power level, and the transmission power level is kept constant at the command power level. You.

When the temperature changes, the diode 5 of the detection circuit 5
Even when the characteristic a changes, the detection circuit 5 of the automatic power control circuit according to the present embodiment outputs an RF output correlation voltage that can ignore the influence of temperature to the error voltage amplifier 7. The reason is that the impedance converter 4 is provided and the detection circuit 5
This is because the input voltage to the input is approximately five times 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 0.14 V at the lowest output
rms, about 1.4 Vrms at the maximum output (rms
Indicates an 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 at the output side becomes about 5 times, and at the time of the minimum output, about 0.7 Vrms.
It becomes about 7.0 Vrms at the time of the maximum output.

FIG. 2 is a configuration diagram of an automatic power control circuit according to a 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 through the main loop by the capacitor 2 ' I have taken out a part of. And
As the resistor 3b of the biasing means 3, it is not necessary to have the function of a terminating resistor, so a resistor of the order of 1K ohm is used (in the first embodiment functioning as a terminating resistor, 1
A resistance of the order of 00 ohms is used. ). The other configuration is the same as that of the first embodiment and the operation is the same.
The OM 8 stores data for collectively correcting the temperature characteristics of the isolator 9.

In the above-described embodiment, one of the required power levels prepared in a plurality of stages is determined as the transmission power level based on a command from the base station. It is needless to say that the present invention can also be applied to a system in which the transmission power level is determined 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 characteristics of the diode of the detection circuit can be ignored, and the automatic power independent of the temperature can be ignored. A control circuit can be obtained.

[Brief description of the 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 transmission circuit diagram of a mobile device provided with an automatic power control circuit according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION 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.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-187820 (JP, A) JP-A-64-27323 (JP, A) JP-A-1-138806 (JP, A) JP-A-4- 100428 (JP, A) JP-A-1-293017 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03G 3/20-3/34

Claims (6)

(57) [Claims] 1. An automatic power control circuit, which is used in a transmitter that amplifies a radio frequency signal to a required power level by a transmission power amplifier and emits the signal from an antenna, and controls the transmission power level to the required power level. configured and coupling circuit for taking out a part of the output of the power amplifier, and the ratio to the input impedance is the output impedance becomes large
An impedance converter that boosts an input signal voltage to obtain an output signal voltage, a bias unit that applies a bias to an output signal of the impedance converter, and a bias is applied by the bias unit. A detection circuit for rectifying and detecting the output signal of the impedance converter, and comparing the required power level with the power level of the output signal of the detection circuit; Control means for controlling the power level to the required power level at a constant level. 2. The reception power according to claim 1, wherein one of the power levels prepared in a plurality of stages is determined based on a command from a base station, or the reception level detected by the own station is used as the required power level. An automatic power control circuit characterized in that it is determined at its own station by an electric field. 3. The control device according to claim 1, further comprising a memory storing data obtained by correcting frequency characteristics of the impedance converter with respect to a required power level, and providing data read from the memory as the required power level to the control unit. An automatic power control circuit characterized by the following. 4. The method according to claim 1, wherein when the transmission power amplifier and the antenna are connected without using an isolator, a directional coupler is used as the coupling circuit. An automatic power control circuit characterized in that a resistor used for a bias means also has a function of a terminating resistor for absorbing reflected power from an antenna. 5. The memory according to claim 1, wherein when an output of the transmission power amplifier is connected to an antenna via an isolator and a filter, data for collectively correcting frequency characteristics of the impedance converter, the isolator and the filter is stored in a memory. An automatic power control circuit for providing data read from the memory to the control means as a required power level. 6. The directional coupler according to claim 4, wherein the input and output impedances of the directional couplers are different from each other without using an additional impedance converter, and the directional coupler has a conversion function of substantially increasing the impedance of the coupling output terminal. An automatic power control circuit, characterized in that the automatic power control circuit is used.