JPH0158888B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diode variable attenuation circuit, particularly an automatic output control system for maintaining a constant output by interposing an attenuation diode in an RF signal path. This is an improvement that compensates for the non-linearity between the two and makes the output constant with high precision despite input fluctuations.

Diode variable attenuators have been widely used in automatic output control systems. An example of this is
As shown in the figure. 1 is an oscillator, 2 is an attenuation diode,
3 is a power amplifier, 4 is a detection circuit, 5 is an output end, 6
is a detector, and 7 is a control circuit. The output of the power amplifier 3 is detected by a detector 6 via a detection circuit 4,
This detected output voltage is compared with a reference voltage in the control circuit 7, and a control current is applied to the attenuation diode 2 according to the difference signal to control the amount of attenuation of the attenuation diode 2, and a constant output is output to the output terminal 5. obtain. A specific example of the circuit configuration of the attenuation diode 2 is shown in FIGS. 2 and 3. 10 is an RF signal input end, 11 is an RF signal output end, 12 is an RF chain, 13 is a control current input end, and 14 and 15 are transformers. Further, a conventional control circuit 7 is shown in FIG. 20 is a detection output voltage input terminal connected to the detector 6, 21 is an operational amplifier, 22 is a reference voltage, 23, 24, 26, 27 are resistors, 25 is a PNP transistor, 28 is a control current output terminal, Vcc is the power terminal. The detection output voltage fluctuates due to fluctuations in the RF signal input, and a signal corresponding to the difference signal between the detection output voltage and the reference voltage 22 is obtained as the output of the operational amplifier 21.
The PNP transistor 25 is controlled and the control current is applied from the control current output terminal 28 to the attenuation diode 2 to adjust the amount of attenuation. In such a conventional control circuit 7, the control current of the attenuation diode 2 varies linearly with respect to the variation of the difference signal between the detection output voltage and the reference voltage 22, but the amount of attenuation with respect to the control current of the attenuation diode 2 is non-linear. Therefore, there is a problem that the output appearing at the output terminal 5 is not constant. That is, as shown in FIG. 5, the control current-attenuation characteristic of the attenuation diode 2 is nonlinear, and the attenuation of the attenuation diode 2 is suitable for input fluctuations in a signal region larger than the reference RF signal input. If the control current is to be varied, the attenuation amount of the attenuation diode 2 is too large for input fluctuations in a small signal region as shown by the broken line a in FIG.
It decreases as shown in Figure A. On the other hand, if the attenuation amount of the attenuation diode 2 appropriately changes the control current for input fluctuations in a signal region smaller than the reference RF signal input, then the input fluctuations in a large signal region as shown by the broken line b in Fig. 6. Attenuation diode 2
The amount of attenuation is still too large, making it impossible to keep the output at the output end 5 constant.

The present invention has been made in order to improve the problems of the prior art.The present invention has been made to improve the problem of the prior art. It is characterized by being configured to control a diode.
The present invention will be explained below with reference to the embodiment shown in FIG. In the figures, the same reference numerals as in other figures indicate the same members. That is, the operational amplifier 21 corresponds to a first circuit into which the detected output voltage of the detector and the reference voltage are input, and which generates a difference signal output corresponding to the difference signal between the detected output voltage and the reference voltage. A PNP transistor 25 is interposed between the power supply and the control input terminal,
This corresponds to a second circuit that sends a control output signal to the control input terminal in accordance with the difference signal. The output terminal of the operational amplifier 21 is connected to the first terminal via the resistor 24.
It is connected to the base of a PNP transistor 25, and the emitter of this first transistor 25 is connected to a resistor 26.
It is similar to the conventional control circuit shown in FIG. 4 that the collector is connected to the power supply terminal Vcc through the resistor 27 and the control current output terminal 28 through the resistor 27. The present invention provides such a conventional circuit with a third circuit between the power supply and the control input terminal that makes the control output signal have a non-linear relationship with respect to the difference signal, for example, a second circuit.
A PNP transistor 30 is inserted.
The emitter of the first PNP transistor 25 is further connected to the second PNP transistor 3 via a resistor 29.
The emitter of this second PNP transistor 30 is connected to the power supply terminal Vcc through a resistor 31, and the collector is connected to the control current output terminal 28 through a resistor 32.

To explain the operation of the present invention, when the detected output voltage is equal to the reference voltage 22, the first PNP transistor 25 is set so that an appropriately set control current flows through the control current output terminal 28.
Then, at the emitter voltage of the first PNP transistor 25 in this state, the second PNP transistor 30 is set to be in the OFF state. When the signal input becomes large and the detected output voltage becomes higher than the reference voltage 22, the impedance of the first PNP transistor 25 increases linearly in accordance with the difference signal between the detected output voltage and the reference voltage 22, reducing the control current. let As the impedance of the first PNP transistor 2 increases, the emitter voltage increases, and the second PNP transistor 30
Maintain OFF state. On the other hand, when the signal input becomes small and the detected output voltage becomes lower than the reference voltage 22, the impedance of the first PNP transistor 25 decreases linearly in proportion to the difference signal between the detected output voltage and the reference voltage 22. PNP transistor 2
5 is increased in accordance with the difference signal. Furthermore, this first PNP transistor 2
As the impedance of transistor 5 decreases, the emitter voltage also decreases, turning off the second PNP transistor 30.
From this state, a current flows to the control current output terminal 28 as an active region. Therefore, the current flowing to the control current output terminal 28 is connected to the first PNP transistor 25 and the second PNP transistor 25.
The current flowing through both the PNP transistor 30 and the PNP transistor 30 is added, and the increase in the control current becomes larger than the variation in the difference signal when the detected output voltage becomes higher than the reference voltage 22. Therefore, in the region where the detection output voltage is higher than the reference voltage, that is, in the region where the signal input is large, the difference signal-control current characteristic is shown by the broken line a in FIG. Take the difference signal-control current characteristics of
The non-linear attenuation characteristic of the attenuation diode 2 can be compensated for, and the output signal voltage can be kept constant with high precision even with fluctuations in the signal input as shown in FIG. 7b.

In the above embodiment, the characteristics of the collector current of the first PNP transistor 25 and the difference signal are set as shown by the broken line a in FIG. The current is added, but in the region where the detected output voltage is lower than the reference voltage 22, the characteristics of the collector current of the first PNP transistor 25 and the difference signal are set as shown by the broken line b in Fig. 6, and the detected output voltage is set as the reference voltage. In a region higher than the voltage 22, a current may be added to the collector current from another transistor or the like to form a characteristic as shown by the broken line a.

As is clear from the above explanation, according to the present invention, since the control current has a non-linear relationship with respect to the difference signal between the detection output voltage and the reference voltage, the amount of attenuation according to the signal input is obtained with
The output signal voltage can be kept constant with high precision in response to fluctuations in the signal input.

[Brief explanation of drawings]

Figure 1 is a block circuit diagram using a diode variable attenuator for automatic output control, etc. Figures 2 and 3 are specific circuit configuration diagrams of the attenuation diode.
The figure is a conventional control circuit diagram for controlling an attenuation diode, and Fig. 5 is a control current-attenuation characteristic diagram of an attenuation diode, where A is a diagram showing the entire characteristic range, and B is a diagram used as an attenuator. FIG. 6 is a characteristic diagram for explaining the operation of the conventional circuit and the present invention. FIG. 7 is a signal input-output signal voltage characteristic diagram, and A is a characteristic diagram of the conventional circuit. B is according to the invention. FIG. 8 is a circuit diagram showing an embodiment of a control circuit used in the present invention. 2... Attenuation diode, 6... Detector, 7...
...Control circuit, 22...Reference voltage, 25...First
PNP transistor, 30... second PNP transistor.

Claims (1)

[Claims] 1. An attenuating diode interposed in a signal path and having a control input terminal, a detector for detecting an output signal of the attenuating diode, a detected output voltage of the detector, and a reference voltage. a first circuit that is input and generates a difference signal output corresponding to the difference signal between the detected output voltage and the reference voltage;
A second circuit includes a first transistor interposed between a power source and the control input terminal, and transmits a control output signal to the control input terminal when the difference signal is input to its base. The diode variable attenuator includes a second transistor interposed between the power supply and the control input terminal, the base of which is connected to the second circuit, and the control output according to the state of the second circuit. A diode variable attenuation circuit characterized by comprising a third circuit that brings a signal into a non-linear relationship with respect to the difference signal. 2 The above first circuit has one input as the detector output,
is an operational amplifier whose other input is a reference voltage;
Claim 1, wherein the first and second transistors are PNP transistors, and the base of the second transistor is connected to the emitter side of the first transistor via a resistor. Diode variable attenuation circuit as described. 3. The diode variable attenuation circuit according to claim 2, wherein the diode variable attenuation circuit is connected to a control input terminal of the attenuation diode so as to match the collector currents of the first and second PNP transistors.