Automatic gain control circuit

Claim 2

An automatic gain control circuit adapted to compensate for variation in the strength of a received signal and to quickly return to normal operation and when variation is of short duration, said automatic gain control circuit comprising: means for rectifying said received signal, at least two capacitor-charging circuits having different time constants and being connected with the output of said rectifying means for producing a control signal responsive to said variations of the received signal, variable impedance means, means connecting said variable impedance means with the input of said rectifying means for controlling the proportion of said received signal being acted upon by said rectifying means in accordance with the impedance of said variable impedance means, and means connecting said variable impedance means with said capacitor-charging circuits for varying said impedance as a function of said control signal.

Claim 3

An automatic gain control circuit according to claim 1; in which one of said capacitor-charging circuits has a small time constant for charging a first capacitor of relatively small capacity and another of said capacitor-charging circuits has a large time constant for charging a second capacitor of relatively large capacity, said capacitor-charging circuits are connected to each other so that, when said variation of the received signal is of short duration to terminate before said second capacitor of said other capacitor-charging circuit is substantially charged, the charge on said first capacitor of said one capacitor-charging circuit is discharged, at least in part, to said second capacitor.

Claim 4

An automatic gain control circuit according to claim 2; further comprising means activated in response to the discharging of said first capacitor to said second capacitor for quickly completing the discharging of said first capacitor.

Claim 5

An automatic gain control circuit according to claim 3; in which said means for quickly completing the discharging of said first capacitor includes a transistor rendered conductive in response to said discharging of said first capacitor to said second capacitor.

Claim 6

An automatic gain control circuit according to claim 2; in which said means connecting said variable impedance means with said capacitor-charging circuits has a relatively large input impedance through which the charges on said first and second capacitors are relatively slowly discharged upon the termination of a variable in received signal strength which is of sufficient duration to achieve substantially complete charging of said first and second capacitors.

Claim 7

An automatic gain control circuit according to claim 2; in which said means for rectifying the received signal includes at least one diode.

Claim 8

An automatic gain control circuit according to claim 6; in which said one diode is connected to said one capacitor-charging circuit, said means for rectifying the received signal includes another diode, and said other diode is connected to said other capacitor-charging circuit.

Claim 9

An automatic gain control circuit according to claim 7; in which said other capacitor charging circuit includes a resistor connected between said other diode and said second capacitor for determining said large time constant for charging of said second capacitor, and a resistor is connected between said capacitor-charging circuits for determining the rate at which said charge on the first capacitor is discharged, at least in part, to said second capacitor.

Claim 10

An automatic gain control circuit according to claim 8; in which a resistor is connected between said one diode and said first capacitor for determining said small time constant for charging of said first capacitor.

Claim 11

An automatic gain control circuit according to claim 2; in which a parallel circuit of a unidirectional element and a resistor is connected betweeN said rectifying means and said one capacitor-charging circuit with said unidirectional element conducting in the direction toward said first capacitor and said resistor determines the rate at which said charge on the first capacitor is discharged, at least in part, to said second capacitor when said variation of the received signal is of short duration.

Claim 12

An automatic gain control circuit according to claim 10; in which an additional resistor is connected between said unidirectional element and said first capacitor for determining said small time constant.

Claim 13

An automatic gain control circuit according to claim 11; in which said additional resistor is connected in series with said parallel circuit of the unidirectional element and the first mentioned resistor.

Claim 14

An automatic gain control circuit according to claim 11; in which said additional resistor is connected in series with said unidirectional element in said parallel circuit.

Claim 15

An automatic gain control circuit according to claim 1; in which said means connecting said variable impedance means with said capacitor-charging circuits includes an amplifier transistor receiving said control signal and having a relatively high input impedance so that when said variation of the received signal is of relatively long duration to complete the charging of said first and second capacitors within said relatively long duration, the charges on said capacitors are discharged to said transistor at a slow rate on termination of said variation.

Claim 16

An automatic gain control circuit comprising: a transmission line for transmitting a signal from one end to the other end of said line, a signal shunt path connected with said transmission line and including variable impedance means for varying the preparation of said signal passing through said shunt path, and thereby controlling the gain of said signal, in accordance with the impedance of said variable impedance means, rectifying means connected with said transmission line for providing a rectified signal that varies with the strength of said signal being transmitted by said line, control means having a connection receiving said rectified signal from said rectifying means for varying the impedance of said variable impedance means as a function of the potential applied to said control means by said connection, first and second capacitor-charging circuits including first and second capacitors, respectively, and being connected with said connection between said rectifying means and said control means for the charging of said capacitors with said rectified signal, said first and second capacitor-charging circuits having relatively small and large time constants, respectively, for the charging of their respective capacitors so that, when the level of the signal received by said transmission line is increased for a short period during which said second capacitor is only incompletely charged by the corresponding rectified signal, said first capacitor discharges, at least in part, to said second capacitor for quickly restoring said potential applied to said control means to the value of said rectified signal then received from said rectifying means, and said control means having a relatively large input impedance through which said first and second capacitors discharge relatively slowly after said level of the received signal has been increased for a relatively long period during which both capacitors are fully charged, thereby to delay the return of said potential to the value of the rectified signal then received from said rectifying means.

Claim 17

An automatic gain control circuit comprising: a transmission line for transmitting a signal from one end to the other end of said line, a signal shunt path connected with said transmission line and including variable impedance means for varying the preparation of said signal passing through said shunt path, and thereby controlling the gain of said signal, in accordance with the impedance of said variable impedance means, rectifying means connected with said transmission line for providing a rectified signal that varies with the strength of said signal being transmitted by said line, control means having a connection receiving said rectified signal from said rectifying means for varying the impedance of said variable impedance means as a function of the potential applied to said control means by said connection, first and second capacitor-charging circuits including first and second capacitors, respectively, and being connected with said connection between said rectifying means and said control means for the charging of said capacitors with said rectified signal, said first and second capacitor-charging circuits having relatively small and large time constants, respectively, for the charging of their respective capacitors so that, when the level of the signal received by said transmission line is increased for a short period during which said second capacitor is only incompletely charged by the corresponding rectified signal, said first capacitor discharges, at least in part, to said second capacitor for quickly restoring said potential applied to said control means to the value of said rectified signal then received from said rectifying means, and said control means having a relatively large input impedance through which said first and second capacitors discharge relatively slowly after said level of the received signal has been increased for a relatively long period during which both capacitors are fully charged, thereby to delay the return of said potential to the value of the rectified signal then received from said rectifying means.

Claim 18

An automatic gain control circuit according to claim 15; in which said variable impedance means includes a transistor having its base connected with said control means and its collector-emitter interposed in said signal shunt path for varying the impedance in said path as a function of the potential applied to said base.

Claim 19

An automatic gain control circuit comprising: a transmission line for Transmitting a signal from one end to the other end of said line, a line amplifier interposed in said transmission line, a first diode connected to said transmission line between said amplifier and said other end of the line, a first time constant circuit connected to the output side of said first diode, a parallel circuit of a second diode and a resistor also connected to said output side of said first diode, a second time constant circuit connected to said parallel circuit and having a time constant that is shorter than the time constant of said first time constant circuit, and a variable impedance element connected to said transmission line and having a control electrode connected with said second time constant circuit to control the impedance of said variable impedance element in response to the time duration of an input signal of a predetermined voltage supplied to said transmission line.

Claim 20

An automatic gain control circuit comprising: a transmission line for Transmitting a signal from one end to the other end of said line, a line amplifier interposed in said transmission line, a first diode connected to said transmission line between said amplifier and said other end of the line, a first time constant circuit connected to the output side of said first diode, a parallel circuit of a second diode and a resistor also connected to said output side of said first diode, a second time constant circuit connected to said parallel circuit and having a time constant that is shorter than the time constant of said first time constant circuit, and a variable impedance element connected to said transmission line and having a control electrode connected with said second time constant circuit to control the impedance of said variable impedance element in response to the time duration of an input signal of a predetermined voltage supplied to said transmission line.

Claim 21

An automatic gain control circuit according to claim 17; in which a second resistor is connected in series with said parallel circuit.

Claim 22

An automatic gain control circuit comprising: a transmission line for transmitting a signal from one end to the other end of said line, a line amplifier interposed in said transmission line, first and second diodes connected to said transmission line between said line amplifier and said other end of the line, a first time constant circuit connected to the output side of said first diode, a second time constant circuit connected to the output side of said second diode and having an attack time that is shorter than the attack time of said first time constant circuit, a resistance element connected between said first and second time constant circuits, and a variable impedance element connected to said transmission line and having a control electrode connected to said second time constant circuit to control the impedance of said variable impedance element in response to the terminal voltage of said second time constant circuit.

Claim 23

An automatic gain control circuit comprising: a transmission line for transmitting a signal from one end to the other end of said line, a line amplifier interposed in said transmission line, first and second diodes connected to said transmission line between said line amplifier and said other end of the line, a first time constant circuit connected to the output side of said first diode, a second time constant circuit connected to the output side of said second diode and having an attack time that is shorter than the attack time of said first time constant circuit, a resistance element connected between said first and second time constant circuits, and a variable impedance element connected to said transmission line and having a control electrode connected to said second time constant circuit to control the impedance of said variable impedance element in response to the terminal voltage of said second time constant circuit.