Back to results
US 4,366,443 AGranted
Television intermediate frequency amplifier
AssigneeRCA Corporation
InventorJack R. Harford
Life of this patent
Estimating the term…
Abstract
An I.F. amplifier system is provided in which gain control is accomplished by varying the A.C. impedances of variable impedance devices, which devices are coupled as load and emitter degeneration impedances for amplifying transistors. Variable D.C. gain control currents are applied to the variable impedance devices to vary their impedance. When coupled as collector loads, gain control is achieved by varying the load lines of the amplifiers. When coupled as emitter impedances, gain control is achieved through variable emitter degeneration. These two techniques of gain control are employed in respective different amplifying stages, which reduces the maximum amount of gain control current required at any particular point in the gain control process, thereby reducing the power consumption of the system.
Claims7
A television intermediate frequency amplifying system comprising:
- a first amplifying stage having a signal input and a signal output, and including a first amplifying transistor coupled in a common emitter configuration, a first resistor coupled between the collector of said first transistor and a source of supply potential and passing a first direct current therebetween, and means coupled in shunt with said first resistor and responsive to variations of a first gain control current for causing gain variations for said first amplifying stage opposite in sense as said first gain control current variations with negligible disturbance of the magnitude of said first direct current;
- and
- a second amplifying stage having a signal input coupled to the signal output of said first amplifying stage, and including a second amplifying transistor coupled in a common emitter configuration, a second resistor coupled between said emitter of said second transistor and a point of signal reference potential and passing a second direct current therebetween, and means coupled in shunt with said second resistor and responsive to variations of a second gain control current for causing gain variations for said second amplifying stage of the same sense as said second gain control current variations with negligible disturbance of the magnitude of said second direct current.
A television intermediate frequency amplifying system comprising:
- a plurality of gain controlled amplifying stages coupled in cascade, said stages including
- a first stage having a first amplifying transistor coupled in a common emitter amplifier configuration with a load impedance coupled in the collector circuit thereof, and a first variable impedance transistor having a base coupled to the collector of said first amplifying transistor and a base-to-emitter junction exhibiting an impedance effectively in shunt with said load impedance which varies as a function of a control current applied to the emitter of said first variable impedance transistor;
- a second stage having a second amplifying transistor coupled in a common emitter amplifier configuration and a second variable impedance transistor having a base coupled to the emitter of said second amplifying transistor and a base-to-emitter junction exhibiting an impedance which varies as a function of a control current applied to the emitter of said second variable impedance transistor;
- and
- a source of variable control current, including a first controlled current path coupled to the emitter of said first variable impedance transistor, and a second controlled current path coupled to the emitter of said second variable impedance transistor,
- wherein the gain of said first stage decreases with increasing current flow in said first controlled current path, and the gain of said second stage increases with increasing current flow in said second controlled current path.
3 more elements
A television intermediate frequency amplifying system comprising:
- a plurality of gain controlled amplifying stages coupled in cascade, said stages including
- a first stage having a first amplifying transistor coupled in a common emitter amplifier configuration with a load impedance coupled in the collector circuit thereof, and a first variable impedance transistor having a base coupled to the collector of said first amplifying transistor and a base-to-emitter junction exhibiting an impedance effectively in shunt with said load impedance which varies as a function of a control current applied to the emitter of said first variable impedance transistor;
- a second stage having a second amplifying transistor coupled in a common emitter amplifier configuration and a second variable impedance transistor having a base coupled to the emitter of said second amplifying transistor and a base-to-emitter junction exhibiting an impedance which varies as a function of a control current applied to the emitter of said second variable impedance transistor;
- a source of variable control current, including a first controlled current path coupled to the emitter of said first variable impedance transistor, and a second controlled current path coupled to the emitter of said second variable impedance transistor,
- wherein the gain of said first stage decreases with increasing current flow in said first controlled current path, and the gain of said second stage increases with increasing current flow in said second controlled current path;
- and
- a third gain controlled amplifying stage having a third amplifying transistor coupled in a common emitter configuration, the base of said third amplifying transistor being direct current coupled to the collector of said first amplifying transistor, and the collector of said third amplifying transistor being direct current coupled to the base of said second amplifying transistor, and a third variable impedance transistor having a base coupled to the collector of said third amplifying transistor and a base-to-emitter junction exhibiting an impedance which varies as a function of the control current applied to the emitter of said third variable impedance transistor,
- wherein said source of variable control current further includes a third controlled current path coupled to the emitter of said third variable impedance transistor, wherein the gain of said third stage decreases with increasing current flow in said third controlled current path.
5 more elements
A television intermediate frequency amplifying system comprising:
- a first amplifying stage including a first amplifying transistor coupled in a common emitter configuration, a first resistor coupled between said collector of said first transistor and a source of supply potential and passing a first direct current therebetween, means coupled in shunt with said first resistor and responsive to variations of a first gain control current for causing gain variations for said first amplifying stage opposite in sense as said first gain control current variations with negligible disturbance of the magnitude of said first direct current, and an emitter impedance which is substantially unvarying in response to variations in any gain control current, said emitter impedance being the exclusive emitter impedance of said first transistor;
- and
- a second amplifying stage coupled in cascade with said first amplifying stage, and including a second amplifying transistor coupled in a common emitter configuration, a second resistor coupled between said emitter of said second transistor and a point of signal reference potential and passing a second direct current therebetween, and means coupled in shunt with said second resistor and responsive to variations of a second gain control current for causing gain variations for said second amplifying stage of the same sense as said second gain control current variations with negligible disturbance of the magnitude of said second direct current.
Dependencies are inferred from the claim text.