Attenuation circuit

Claim 2

An attenuation circuit for attenuating an input signal, comprising: receiving a variable-impedance means having a first terminal for receiving an input signal to be attenuated, a second terminal, and a control terminal; bypass circuit means having a first connection to the first terminal of the variable-impedance means, and a control signal connection; and control signal source means adapted to apply a control signal to the control terminal of the variable-impedance means and to the control signal connection of the bypass circuit means; said variable-impedance means being operable in response to the control signal at the control terminal thereof to establish an impedance between its first and second terminals having a value related to the value of the control signal whereby an input signal at the first terminal of the variable-impedance means is attenuated by the variable-impedance means by an amount related to the value of the impedance between its first and second terminals; and said bypass circuit means being operable in response to the control signal at the control signal connection thereof to bypass a portion of the input signal at the first terminal of the variable-impedance means away from the first terminal thereby to attenuate the input signal by a predetermined amount, said amount being related to the value of the control signal; whereby said input signal at the first terminal of the variableimpedance means is attenuated by a total amount determined by the combined amounts of attenuation provided by the variableimpedance means and by the bypass circuit means, the resulting attenuated input signal occurring at the second terminal of the variable-impedance means.

Claim 3

An attenuation circuit for attenuating an input signal, comprising: variable-impedance means having a first terminal for receiVing an input signal to be attenuated, a second terminal, and a control terminal; a source of reference potential; transistor means coupled to the first terminal of the variable-impedance means and to the source of reference potential and including a control connection, said transistor means being adapted to operate in a conducting condition when a gating signal is present at the control connection thereof; circuit means coupled to the control connection of the transistor means and including a control signal connection; control signal source means adapted to apply a control signal to the control terminal of the variable-impedance means and to the control signal connection of the circuit means; said variable-impedance means being operable in response to the control signal at the control terminal thereof to establish an impedance between its first and second terminals having a value related to the value of the control signal whereby an input signal at the first terminal of the variable-impedance means is attenuated by the variable-attenuation means by an amount related to the value of the impedance between its first and second terminals; and said circuit means being operable in response to the control signal at the control signal connection thereof to produce a gating signal at the control connection of the transistor means having a value related to the value of the control signal, said gating signal causing the transistor means to operate in its conducting condition and to bypass a portion of the input signal at the first terminal of the variable-impedance means to the source of reference potential thereby to attenuate the input signal by a predetermined amount, said amount being related to the degree of conduction in the transistor means as established by the value of the gating signal; whereby said input signal at the first terminal of the variable-impedance means is attenuated by a total amount determined by the combined amounts of attenuation provided by the variable-impedance means and by the transistor means and the circuit means, the resulting attenuated input signal occurring at the second terminal of the variable-impedance means.

Claim 4

An attenuation circuit for attenuating an input signal, comprising: variable-impedance means having a first terminal for receiVing an input signal to be attenuated, a second terminal, and a control terminal; a source of reference potential; transistor means coupled to the first terminal of the variable-impedance means and to the source of reference potential and including a control connection, said transistor means being adapted to operate in a conducting condition when a gating signal is present at the control connection thereof; circuit means coupled to the control connection of the transistor means and including a control signal connection; control signal source means adapted to apply a control signal to the control terminal of the variable-impedance means and to the control signal connection of the circuit means; said variable-impedance means being operable in response to the control signal at the control terminal thereof to establish an impedance between its first and second terminals having a value related to the value of the control signal whereby an input signal at the first terminal of the variable-impedance means is attenuated by the variable-attenuation means by an amount related to the value of the impedance between its first and second terminals; and said circuit means being operable in response to the control signal at the control signal connection thereof to produce a gating signal at the control connection of the transistor means having a value related to the value of the control signal, said gating signal causing the transistor means to operate in its conducting condition and to bypass a portion of the input signal at the first terminal of the variable-impedance means to the source of reference potential thereby to attenuate the input signal by a predetermined amount, said amount being related to the degree of conduction in the transistor means as established by the value of the gating signal; whereby said input signal at the first terminal of the variable-impedance means is attenuated by a total amount determined by the combined amounts of attenuation provided by the variable-impedance means and by the transistor means and the circuit means, the resulting attenuated input signal occurring at the second terminal of the variable-impedance means.

Claim 5

An attenuation circuit in accordance with claim 2 wherein the transistor means includes: a transistor having base, collector, and emitter, the base being coupled to the control connection, the collector being coupled to the first terminal of the variable-impedance means, and the emitter being coupled to the source of reference potential.

Claim 6

An attenuation circuit in accordance with claim 2 wherein the circuit means includes a voltage-divider circuit coupled to the control connection of the transistor means and to the source of reference potential.

Claim 7

An attenuation circuit in accordance with claim 4 wherein the circuit means further includes a Darlington circuit coupled to the voltage divider circuit and to the control signal connection.

Claim 8

An attenuation circuit in accordance with claim 2 wherein the transistor means includes: a field effect transistor having a first electrode, a second electrode, and a gate electrode, the first electrode being coupled to the first terminal of the variable-impedance means, the second electrode being coupled to the source of reference potential, and the gate electrode being coupled to the control connection.

Claim 9

An attenuation circuit in accordance with claim 6 wherein: the first and second electrodes of the field effect transistor are drain and source electrodes, respectively.

Claim 10

An attenuation circuit in accordance with claim 2 wherein the transistor means includes: first and second transistors each having base, collector, and emitter, the bases of the first and second transistors being coupled to each other and to the control connection, the collector of the first transistor and the emitter of the second transistor being coupled to each other and to the first terminal of the variable-impedance means, and the emitter of the first Transistor and the collector of the second transistor being coupled to each other and to the source of reference potential.

Claim 11

An attenuation circuit in accordance with claim 1 wherein the variable-impedance means includes: a field effect transistor having a first electrode, a second electrode, and a gate electrode, the first electrode being coupled to the first terminal, the second electrode being coupled to the second terminal, and the gate electrode being coupled to the control terminal.

Claim 12

An attenuation circuit in accordance with claim 9 wherein: the first and second electrodes of the field effect transistor are drain and source electrodes, respectively.

Claim 13

An attenuation circuit in accordance with claim 1 wherein the variable-impedance means includes: first and second transistors each having base, collector, and emitter, the bases of the first and second transistors being coupled to each other and to the control terminal, the collector of the first transistor and the emitter of the second transistor being coupled to each other and to the first terminal, and the emitter of the first transistor and the collector of the second transistor being coupled to each other and to the second terminal.

Claim 14

An attenuation circuit in accordance with claim 1 wherein the variable-impedance means includes: a photoresponsive resistance device coupled between the first and second terminals; and a light source coupled to the control terminal and adapted to produce a light output for controlling the value of resistance of the photoresponsive resistance device.