US 4,307,348 A · Automatic gain control circuit

Abstract

An A.G.C. circuit is disclosed having two modulators connected in series to modulate an input signal and an amplifier for amplifying the output of the second modulator and applying it to an output terminal. A detector detects the output of the amplifier and an integrator compares the detected level with a reference so as to produce a control signal dependent on the error. The control signal is applied to the first modulator through an impedance path having an impedance which decreases with increasing frequency, and is applied to the same modulator through an impedance path having an impedance which increases with increasing frequency. In this way, the first modulator performs modulation primarily dependent on the A.C. component of the control signal and a second modulator performs modulation primarily dependent on its D.C. components of the control signal. Therefore, changes in the gain of the amplifier, or in the level of the input signal, which tend to alter the upper limit of the loop bandwidth of the circuit, are substantially offset by the effect of the resultant change in the gain of the second modulator.

Claims7

Dependent claims

An automatic gain control circuit arrangement for producing an output signal which is dependent on an input signal and whose mean level has a desired value, comprising

means defining a signal path having an input for receiving the input signal and an output at which is produced the output signal, the signal path including control means controllable to vary the level of the signal in the signal path and amplifying means for amplifying the signal in the signal path, and
detecting means connected to sense the level of the signal in the signal path after its level has been varied by the control means and amplified by the amplifying means, and operative in response to variations of the sensed level from the desired value to produce a control signal dependent on the variations and which adjusts the control means in a sense such that it offsets the said variations,
the control means comprising one part primarily responsive to the alternating component of the control signal and another part primarily responsive to the D.C. components of the control signal whereby changes in the gain of the amplifying means or in the level of the input signal which tend to alter the upper limit of the loop bandwidth of the circuit arrangement are substantially offset by the effect of the resultant change in the gain of the said other part of the control means.

Dependencies are inferred from the claim text.

Automatic gain control circuit

Life of this patent

Automatic gain control circuit

Life of this patent

Abstract

Claims7