JPS644689B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic transmission output control circuit (hereinafter abbreviated as ALC circuit) of a wireless transmitter.

FIG. 1 shows an example of an ALC circuit of a conventional wireless transmitter.

In the conventional ALC circuit, as shown in FIG. The partially extracted transmission output signal is rectified and input to the inverting input terminal of the error amplifier 1 via the resistor 3. On the other hand, a voltage dividing circuit constituted by resistors 4, 5, and 6 divides the stabilized voltage applied to the terminal 15 to form a reference voltage, which is applied to the non-inverting input side of the error amplifier 1. Add to. The error amplifier 1 compares the rectified signal with the reference voltage and amplifies the difference. The output of the error amplifier is connected to the power supply circuit of the power amplifier 12.

Next, when changing the transmission power, it is sufficient to change the reference voltage. In this example, a variable resistor is used as the resistor 5 to change the transmission power by changing the reference voltage. I'm letting you do it.

However, when such an ALC circuit changes the transmission power over a wide range, especially when stably controlling up to an extremely low transmission power, the voltage detected by the diode 9 becomes a very small value or becomes impossible to detect. , there was a drawback that it became uncontrollable.

On the other hand, when the transmission output power is small, it is possible to increase the size of the capacitor 11 so as to increase the detection voltage, but when the transmission output power is relatively large, the detection voltage becomes extremely large and the power supply voltage The power amplifier 12 is difficult to control, and a portion of the transmission output is often consumed by the detection circuit, which has the drawback of adversely affecting the power amplifier 12.

Furthermore, as a method to overcome the above drawbacks, a method has been proposed in which a variable capacitance diode is used for the capacitor 11 to change the capacitance value, but this method has the drawbacks of requiring a large number of circuit components and being expensive.

The present invention has been made to eliminate the above-mentioned drawbacks, and therefore, an object of the present invention is to provide a novel ALC circuit that has good controllability over a wide range of transmission output power and has a small number of parts. There is a particular thing.

In order to achieve the above object, according to the present invention
The ALC circuit consists of the first,
A bias is applied from a connection point between the second resistor and the third resistor of the voltage dividing circuit including the second and third resistors through the fourth resistor, and a bias is applied to the first voltage dividing circuit of the voltage dividing circuit. A connection point between the resistor and the second resistor is grounded through a fifth resistor, and the reference voltage and the bias voltage are simultaneously changed by changing the resistance value of the fifth resistor. It is configured as follows.

According to the configuration of the present invention, the reference voltage is changed depending on the magnitude of the transmission output, and at the same time, the reverse bias voltage applied to the detection diode is changed at the same ratio as the change in the reference voltage, thereby changing the detection efficiency. Control can be performed stably over a wide range of transmission output power.

Hereinafter, the present invention will be explained in more detail with reference to the drawings, with regard to preferred embodiments thereof.

FIG. 2 is a circuit diagram showing an embodiment of the ALC circuit according to the present invention. In the figure, the same reference numerals used in FIG. 1 are the same as the corresponding reference numerals in FIG. 1.

The present invention uses a diode 9 for detecting a transmitted output signal.
The detection efficiency is changed by changing the reverse bias voltage applied to the diode 9. The amount of change in the reverse bias voltage is made proportionally equal to the amount of change in the reference voltage. In this embodiment, for this purpose, a part of the voltage dividing circuit of resistors 4, 5, and 6 that creates the reference voltage, and a connection point between resistors 5 and 6, are connected to resistor 1.
A reverse bias voltage is applied to the cathode side of the diode 9 through the diode 8. Further, the connection point between the resistor 4 and the resistor 5 of the voltage dividing circuit is grounded via a resistor 16.

Now, if the transmission output is large, the resistor 5
Because it is necessary to increase the potential difference between both ends of
The resistance value of the resistor 16 is varied to increase it. In that case, the potential at the connection point between the resistor 5 and the resistor 6 increases, thereby applying a higher reverse bias voltage to the cathode of the diode 9 via the resistor 18. Therefore, the detection efficiency of the diode 9 is deteriorated, and the detection voltage is lowered compared to the case where the reverse bias voltage is not applied. Moreover, the transmission power amplifier 12
It also reduces the impact on

On the other hand, in order to lower the transmission power, it is necessary to reduce the potential difference between both ends of the resistor 5, and the resistance value of the resistor 16 is varied to reduce it. At that time, the potential at the connection point between the resistor 5 and the resistance value 6 drops, and the reverse bias voltage applied to the cathode of the diode 9 is smaller than when the transmission output is large, and the diode 9 The detection efficiency increases and a detection voltage sufficient for control can be obtained.

FIG. 3 is a block diagram showing another embodiment of the present invention, in which a switch element 17 is connected to the ground side terminal of the resistor 16 shown in FIG. 2 to be grounded. The main application of this embodiment can be applied to power down circuits used in automobile telephones and the like in recent years.

During operation, if power-down is not performed, the switch element 17 is left in an open state,
Power setting is performed using the variable resistor shown in the figure as the resistor 5. When powering down, the switch element 17 is closed and the operation explained in FIG. 2 is performed to reduce the transmission output power. Incidentally, the reason why a variable resistor is used as the resistor 16 is to arbitrarily set the power down.

FIG. 4 is a block diagram showing still another embodiment of the present invention, in which resistors 19 and 20 are added so that a slight forward bias can be applied to the diode 9 shown in FIG. 2 when setting a lower transmission power. The other operations are the same as the embodiment shown in FIG.

According to the present invention, as described above, the number of parts is small and a wide transmission output voltage range can be stably controlled.

Although the present invention has been described above with respect to various preferred embodiments thereof, these are merely illustrative, and it goes without saying that the present invention is not limited only to the embodiments described herein.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a conventional transmission output automatic control circuit, FIG. 2 is a circuit configuration diagram showing an embodiment of the transmission output automatic control circuit according to the present invention, and FIGS.
The figure is a circuit configuration diagram showing another embodiment of the present invention. 1...Error amplifier, 12...Transmission output amplifier,
13...Antenna.

Claims (1)

[Claims] 1 A diode for detecting the transmission output signal of a wireless transmitter, a stabilizing voltage circuit for creating a reference voltage source, and a first, second and third circuit for dividing the stabilized voltage to form a reference voltage. In an automatic transmission output control circuit having a voltage dividing circuit including a third resistor and an error amplifier that compares and amplifies the detected voltage detected by the diode and the reference voltage,
The first and second electrodes are connected to the detection output side end of the diode.
A bias is applied from a connection point between the second resistor and the third resistor of a voltage dividing circuit including a third resistor through a fourth resistor, and a bias is applied between the first resistor and the third resistor. The connection point of the second resistor is grounded through a fifth resistor, and the reference voltage and the bias voltage are changed simultaneously by varying the resistance value of the fifth resistor. Transmission output automatic control circuit.