JPS5837142Y2 - automatic gain control device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an automatic gain control device, and in particular, it is designed to cancel the alternating current components of the positive direction output signal and the negative direction output signal taken out from the detection output stage, and to improve the distortion factor. The present invention relates to an automatic gain control device.

Conventionally, various technologies have been provided for circuits that perform automatic gain control by applying a reverse AGC signal to the high frequency amplification stage and intermediate frequency amplification stage in transistor receivers and the like. In this case, the gain of each amplification stage cannot be made zero, and therefore distortion tends to increase when a large input signal is applied.

For this purpose, in addition to the detection diode connected after the intermediate frequency stage, an automatic gain control transistor is connected between the emitter of the automatic gain control transistor constituting the intermediate frequency amplification stage and the base of the high frequency amplification stage. Automatic gain control devices have been proposed that supply an AGC signal that reduces the emitter current to the latter stage of the intermediate frequency circuit and increases the emitter current to the high frequency stage, but these devices have complicated circuit configurations. In particular, it is not desirable to improve the distortion rate in the low frequency range of audio signals.

The present invention has been made in view of the above, and the object of the present invention is to provide a forward AGC line and a forward AGC line connected to the output side of the intermediate frequency stage via forward and reverse diodes, respectively. A new automatic gain control device in which a capacitor is connected between the reverse AGC lines to cancel out the alternating current of the detected output signal obtained through each of the diodes, thereby greatly improving the distortion factor. is to provide.

An embodiment of the present invention will be specifically described below with reference to the drawings.

1 is an intermediate frequency transformer of an intermediate frequency amplification stage connected to a frequency conversion circuit (not shown), and one end is grounded on the secondary side of the intermediate frequency transformer 1 via a reverse diode 2 for detection. A smoothing capacitor 3 is connected thereto, and the output side of the diode 2 is connected via a series resistor 4 to a low frequency amplification stage which receives a detection output.

Reference numerals 5 and 6 denote a smoothing capacitor and a resistor connected in parallel to the capacitor 3, respectively.

Further, a capacitor 8 whose one end is grounded is connected to the secondary side through a forward diode 7 for detection, and a series resistor 9 is connected to the output side of this diode door. A level meter driven by the detection output is connected.

10.11 is a smoothing capacitor and a resistor connected in parallel to the capacitor 8.

On the other hand, on the output side of the diodes 2 and 7, a resistor 14 forming a reverse AGC line A and a forward AGC line B is connected via a signal detection resistor 12, 13, respectively.
．． Capacitor 15 and resistor 16. Integrating circuits each consisting of a capacitor 17 are connected, and a capacitor 18 of the polarity shown is connected between the midpoint of the connection between the resistors 12 and 14 and the midpoint of the connection between the resistors 13 and 16.

In a circuit having such a configuration, the signal obtained at the intermediate frequency stage is transmitted to the diode 2. Through the capacitor 3 and resistor 4, a detected output signal of the negative component of the waveform as shown in the figure is obtained, and this is supplied to the low frequency circuit. A detected output signal of the positive direction component of the waveform is supplied to a level meter.

At the same time, these detected output signals of positive and negative direction components are supplied to the capacitor 18 via the resistors 12 and 13, where the alternating current components of the two audio signals having the same phase and insulation level cancel each other out. The reverse AGC signal and the forward AGC signal, each having equal positive and negative DC levels, are supplied to the high frequency circuit and the frequency conversion circuit through the above-mentioned integration circuits, respectively, and are used to control the active control elements of each circuit to control the transistor receiver system. A
It becomes like trying to control GC.

In particular, in order to improve the distortion rate in the low frequency range, the time constant of the integrating circuit was selected to be large, thereby eliminating the delay in automatic gain control, and eliminating the delay in automatic gain control, which was caused by the large time constant of the integrating circuit, and eliminating the delay in metering due to high gain and large current during tuning. This has the advantage of being able to prevent a run-out.

As explained above, according to the present invention, a forward diode and a reverse diode for detection are connected in parallel to the intermediate frequency amplification stage, an integrating circuit is connected to each of these diodes, and a circuit is connected between the output sides of the two diodes. The AC component of the positive direction output signal from the forward direction diode and the negative direction output signal from the reverse direction diode is canceled out in the above condenser, and the reverse AGC is connected from each of the above integration circuits. By obtaining the signal and the forward AGC signal, rapid automatic gain control can be realized with a simple configuration without deteriorating the distortion rate in the low frequency range, which is extremely useful in practical use.

[Brief explanation of drawings]

The drawing is a circuit diagram showing an embodiment of an automatic gain control device according to the present invention. 1...Intermediate frequency transformer, 2...Reverse diode, 3...Forward diode, 14
．． 15... Resistor and capacitor forming an integrating circuit, 16.17... Resistor and capacitor forming an integrating circuit, 18... Capacitor for canceling alternating current components.

Claims (1)

[Scope of utility model registration request] It consists of a detection forward diode and a reverse diode connected in parallel to the intermediate frequency amplification stage, an integrating circuit connected to both of these diodes, and a capacitor connected between the output sides of both of the diodes. The alternating current components of the positive direction output signal from the diode and the negative direction output signal from the reverse direction diode are canceled in the above capacitor, and the reverse AG is connected from each of the above integration circuits.
An automatic gain control device characterized in that it is configured to obtain a C signal and a forward AGC signal.