JPH08335837A - Agc circuit and transmitter using the agc circuit - Google Patents

Abstract

PURPOSE: To provide an AGC circuit of a transmitter which performs the parallel operation of power amplifier modules and can apply the AGC with no deterioration of characteristic despite the occurrence of failures of some power amplifier modules. CONSTITUTION: A transmitter consists of an exciting part 3 and power amplifier modules 4a to 4d. Then the couplers 5a to 5d are added to the transmitter to monitor the output of every amplifier module together with detectors 9a to 9d which detect the output of every coupler, a selection circuit 10 which selects the signal of the highest voltage among those outputs of detectors, a DC voltage amplifier 12, and a voltage control variable resistance attenuator 2. In a normal non-defective state, the transmission output is controlled by an amplifier module that has the highest output. If this module has a failure, the transmission output is controlled by the output of another non-defective amplifier module. Therefore, the output of the power amplifier module is never varied despite the occurrence of failures. Thus the characteristic of an AGC circuit is never deteriorated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AGC circuit and a transmitter using the same, and more particularly to an AGC circuit for maintaining a constant transmission output of a television transmitter and the like and a transmitter using the same.

[0002]

2. Description of the Related Art The most basic conventional AGC (Automatic Gain Control) circuit will be described with reference to FIG. In FIG. 2, the transmitted signal IN is transmitted as a transmission signal OUT via the excitation unit 3 and the power amplification unit 8. The exciter 3 comprises an exciter 1 and a variable resistance attenuator 2.

The power amplifier 8 is a distributor 6 for distributing the signal from the excitation unit 3 to a plurality of systems, and a plurality of power amplifiers 4a to 4d having a parallel connection configuration for amplifying the power of the distributed signals of the respective systems.
And a combiner 7 for combining these amplified outputs.

A combiner 5 is used to monitor this combined output.
The output of the coupler 5 is detected by the detector 9, and the voltage change is amplified by the DC amplifier 12 to generate a control voltage. By controlling the amount of attenuation of the variable resistance attenuator 2 according to this control voltage, negative feedback is applied and the transmission output becomes constant.

Here, the power amplification unit 8 has been made into a transistor in recent years, and is configured by providing a plurality of power amplification modules (4a-4d) in parallel in order to obtain required power and redundancy. Often. Furthermore, in order to minimize the manufacturing cost, the number of transistors used is minimized,
Moreover, in order to reduce power consumption, it is usual to use the transistor near the capacity limit.

In such a case, when one of the plurality of power amplification modules fails, the AGC circuit operates so as to keep the transmission output constant, so that the power amplification module per one operates. As described above, the power amplification module is used near the limit of its capability, and therefore various characteristics will deteriorate as the output increases.

For example, in the case of a television transmitter or a television relay broadcasting device, the linearity is deteriorated and the image quality is adversely affected. In particular, when video is amplified at the same time as audio, color intermodulation deteriorates, adversely affects image quality, and spurious occurs due to intermodulation, resulting in fatal deterioration of characteristics.

In order to prevent such characteristic deterioration, conventionally, an AGC circuit of the system shown in FIGS. 3 and 4 has been proposed. In FIGS. 3 and 4, the same parts as those in FIG. 2 are designated by the same reference numerals.

In FIG. 3, the AGC is applied only to the excitation unit 3. That is, the output of the exciting unit 3 is monitored by the coupler 5, the monitor output is detected by the detector 9, and the DC amplifier 12 detects and amplifies the voltage change to obtain the AGC control voltage. ing.
By doing so, even if a failure occurs in the power amplification module, it is the simplest method that can apply AGC without deteriorating the characteristics.

FIG. 4 is disclosed in Japanese Examined Patent Publication No. 3-48702, in which the outputs of the power amplification modules 4a to 4d are monitored by the couplers 5a to 5d, respectively, and the outputs of these monitors are referred to as reference voltages. Input to the controller 13 and input to the DC amplifier 12
The reference voltage of is controlled.

In this method, each power amplification module 4a
Inputting the failure detection output of 4d to the reference voltage control unit 13 through the couplers 5a to 5d, and when a failure occurs, the reference voltage is controlled so that the characteristics are not deteriorated to control the level of the amplification output. Is.

[0012]

In the configuration shown in FIG. 3, the power amplifying section 8 is not subjected to AGC, so that the output fluctuation of the power amplifying section directly leads to the fluctuation of the transmission output, so that the power amplifying section It is necessary to strictly suppress output fluctuations.

In the configuration shown in FIG. 4, it is necessary to add a failure detection function to each of the power amplification modules 4a-4d, and the reference voltage control circuit 1 for generating a reference voltage.
3 is required, which complicates the circuit. In particular, it is necessary to design the reference voltage control circuit 13 so that the value of the reference voltage is desired according to the failure detection signal from each of the power amplification modules 4a to 4d, which also complicates the circuit.

An object of the present invention is to use an AGC circuit having a simple structure in which even if one of the power amplification modules in parallel operation fails, there is no change in the control voltage so that the characteristic is not affected, and the AGC circuit is used. It is to provide a transmitter.

[0015]

The AGC circuit according to the present invention is an AGC circuit of a transmitter constituted by a plurality of power amplifying means connected in parallel with each other, and detects each output of the power amplifying means. And a control means for controlling the inputs of the plurality of power amplifying means in accordance with the selected output.

The transmitter according to the present invention comprises an attenuator for controlling the attenuation of a transmitted signal, a distributor for distributing the output of the attenuator into a plurality of systems, and a plurality of power amplifiers for amplifying the power of the distributed output. Means, selecting means for detecting each output of the power amplifying means and selecting the maximum detected output, control means for performing attenuation control of the attenuating means according to the selected output, and each amplifying means for the power amplifying means And a synthesizing unit for synthesizing and transmitting the outputs.

[0017]

The detected outputs of the power amplifiers in parallel operation are supplied to the comparing section for comparing with the AGC reference voltage via the respective diodes. As a result, an AGC loop is formed by the output of the power amplifier that normally has the highest output level. In this case, if the characteristics of the power amplifiers are set to be substantially the same, the outputs are set to be substantially the same, so that the AGC loop operates stably.

When a failure occurs in this power amplifier and the detection output decreases, the AGC loop is automatically switched to another power amplifier, and the remaining AGC loop is not formed and the level changes. It will not happen and the characteristics will not deteriorate.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, and the same parts as those in FIGS.

Excitation unit 3 and a plurality of power amplification modules 4
In the transmitter configured by the power amplification unit 8 configured by a to 4d, each power amplification module 4
There are provided couplers 5a to 5d for monitoring the outputs of a to 4d and detectors 9a to 9d for detecting the outputs of the couplers 5a to 5d and converting the output levels into voltages. , A voltage is generated according to the output of each power amplification module.

The selection circuit 10 selects the output having the highest voltage from the outputs of the respective detectors and supplies the selected voltage to the DC voltage amplifier 12. Here, the selection circuit 10
Is for selecting the signal with the highest voltage among the plurality of inputs, the diodes 11a to 11a as shown in FIG.
It can be constructed by supplying a detection output to each anode of d and commonly connecting each cathode.

The DC voltage amplifier 10 amplifies the voltage change of the output of the selection circuit 10 and gives the control voltage to the variable resistance attenuator 2 in the excitation unit 3, and all the power amplification modules 4a-4d.
On the other hand, the output of the power amplification module having the largest output at that time is controlled to be constant.

First, the operation of the circuit of this embodiment when all the power amplification modules are normal will be described. In this case, the output of the transmitter is controlled by the output of the power amplifier module with the highest output. Normally, when operating the power amplification modules in parallel, the output of each power module is set to be the same as much as possible in order to minimize the combined loss. Further, although the main cause of the output fluctuation of the power amplification unit is due to the temperature change, the output fluctuation of each power amplification module having the same configuration changes substantially in the same manner with respect to the temperature change. Therefore, the AGC circuit of this embodiment functions to stabilize the transmission output.

Next, the operation when one (or two or more) of the power amplification modules operating in parallel fails will be described. The failed power amplification module
The power amplifier module with the largest output (AGC)
If it is the power amplifier module involved in the control), the AGC control will be taken by the power amplifier module having the next highest output.

As described above, each power amplification module is set to have the same output as much as possible, so that the control voltage hardly changes. Therefore, the output of each power amplification module hardly changes, and the characteristics hardly change.

If the failed power amplification module is not the power amplification module involved in the AGC control, the control voltage does not change at all, so there is no change in the characteristics.

[0028]

According to the present invention, by selecting the output with the highest voltage from the outputs of the respective detectors, even if one of the power amplification modules operating in parallel fails, the control voltage Does not change, there is an effect that AGC can be applied with a simple structure without adversely affecting the characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a conventional AGC circuit.

FIG. 3 is a block diagram showing another example of a conventional AGC circuit.

FIG. 4 is a block diagram showing still another example of a conventional AGC circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exciter 2 Variable resistance attenuator 3 Excitation part 4a-4d Power amplification module 5a-5d Combiner 6 Distributor 7 Combiner 8 Power amplification part 9a-9d Detector 10 Selection circuit 11a-11d Diode 12 DC amplifier

Claims (5)

[Claims] 1. An AGC circuit of a transmitter constituted by a plurality of power amplifying means connected in parallel to each other, and selecting means for detecting each output of the power amplifying means and selecting a maximum detected output. An AGC circuit including: a control unit that controls inputs of the plurality of power amplification units according to the selected output. 2. The AGC according to claim 1, wherein the selecting means has a plurality of diodes each having the detection output as an anode input and having a cathode commonly connected.
circuit. 3. The control means includes direct current amplification means for direct current amplification of the selected output to derive a control voltage, and variable attenuation means for performing attenuation control of the inputs of the plurality of power amplification means in accordance with the control voltage. The AGC circuit according to claim 1, further comprising: 4. An attenuator for controlling the attenuation of a transmitted signal, a distributor for distributing the output of the attenuator to a plurality of systems, a plurality of power amplifiers for amplifying the power of the distributed output, and the power. A selection unit that detects each output of the amplification unit and selects the maximum detection output, a control unit that controls the attenuation of the attenuation unit according to this selection output, and a combined output of the power amplification unit are combined. A transmitter comprising a synthesizing means for transmitting. 5. The transmitter according to claim 4, wherein the selection means has a plurality of diodes each of which has an anode input for each of the detection outputs and whose cathodes are commonly connected.