Title: Gain-controlled amplifier

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Claims: What is claimed is:

1. An amplifier in which the ratio of the amplifier output signal to the amplifier input signal is responsive to a control signal, said amplifier comprising:

a first terminal for application of a direct reference potential;

a second terminal for application of an input signal potential having a quiescent value substantially equal to said reference potential;

a third terminal for supplying said output signal;

a load direct coupled to said third terminal;

a first transistor of a first conductivity type, having base, emitter and collector electrodes, said collector electrode being connected to said third terminal and said emitter electrode being connected to said second terminal;

a first controlled current source responsive to a control signal for supplying a first controlled current;

first diode means connected between said first terminal and said first controlled current source and poled for easy conduction of said first controlled current, said first diode means responding to the flow of said first controlled current therethrough to develop a substantially direct offset potential between said first terminal and said first transistor base electrode, which offset potential controls the flow of collector current in said first transistor; and

a second controlled current source responsive to said control signal for supplying a second controlled current to said third terminal to counteract changes in the quiescent component of said first transistor collector current as supplied to said load.

2. An amplifier as set forth in claim 1 having:

second and third transistors, each having a base and an emitter and a collector electrode, their respective collector electrodes being connected respectively to said first transistor base electrode and to said first transistor collector electrode;

means for similarly and adjustably biasing the base electrodes of said third and said fourth transistors with respect to their emitter electrodes using said control signal, to implement said first and said second controlled current sources, respectively.

3. An amplifier as set forth in claim 2 wherein said second and said third transistors are of said first conductivity type, the respective emitter electrodes of each of said second and said third transistors are similarly connected to said first terminal, the respective base electrodes of said second and said third transistors are connected to receive said control signal, a first resistor and a second resistor have their first ends connected respectively to said first transistor base electrode and to said second transistor collector electrode and have respective second ends, and a fourth terminal for application of an operating potential has the second ends of said first and said second resistors connected thereto.

4. An amplifier as set forth in claim 3 having:

means for connecting each of said second and said third transistors in current mirror amplifier configuration.

5. An amplifier as set forth in claim 2 wherein said second and said third transistors are of a second conductivity type complementary to said first conductivity type, a fifth terminal has the respective base electrodes of said second and third transistors connected thereto to receive said control signal; and

a fourth terminal for application of an operating potential has the emitter electrodes of said second and third transistors similarly connected to it.

6. An amplifier as set forth in claim 5 having:

means for connecting each of said second and said third transistors in current mirror amplifier configuration.

7. An amplifier as set forth in claim 1 having:

a fourth terminal for application of an operating potential;

a second transistor of said first conductivity type, said third transistor having a base electrode connected to the same end of said first diode means as is said first transistor base electrode, said third transistor having an emitter electrode connected to said first terminal and having a collector electrode; and

current mirror amplifier means having an input terminal to which the collector electrode of said third transistor is connected, having a common terminal connected to said fourth terminal, and having an output terminal connected to said third terminal.

8. An amplifier as set forth in claim 1 wherein said second controlled current source includes:

a fourth terminal for application of an operating potential; and

current mirror amplifier means being included in said second controlled current source having an input terminal between which and said first transistor base electrode said first controlled current source is connected and having an output terminal connected to said third terminal.

9. An amplifier as set forth in claim 1 wherein said diode means is provided by:

a further transistor having an emitter electrode connected to said first terminal, having a collector electrode connected to said first controlled current source, and having a base electrode, the base electrodes of said first and said further transistors each having said further transistor collector electrode direct coupled thereto.

10. A circuit for controlling the gain of a common-base transistor amplifier comprising a transistor having emitter and collector and base electrodes, a base-emitter junction between said base and emitter electrodes, said emitter electrode being direct current conductively coupled through an input signal source to a terminal at a reference potential, and said collector electrode being coupled through a load to an operating voltage terminal, said circuit comprising:

diode means coupled between said base electrode and said terminal at said reference potential in the forward direction relative to said base-emitter junction of said transistor;

means for supplying a quiescent current in the forward direction to said diode means to establish a quiescent forward voltage thereacross;

means for applying a constant proportion of said quiescent forward voltage across the base-emitter junction of said transistor whereby at a quiescent current level to establish a given quiescent forward voltage across said diode means for application across the base-emitter junction of said transistor, a given value of quiescent collector current flows through said transistor and a corresponding given value of quiescent voltage exists at the collector electrode of said transistor;

means responsive to a control signal for changing the amount of current flow through said diode means and correspondingly changing the forward bias voltage across said base-emitter junction, whereby the flow of said collector current changes; and

means coupled to said collector electrode and also responsive to said control signal for maintaining the quiescent voltage at said collector electrode at said given value notwithstanding said change in the flow of said collector current.

11. A circuit as set forth in claim 10, wherein the last-named means comprises a current path connected between said collector electrode and one of said terminals and means responsive to said control signal for controlling the impedance of said path to control the current flow through said path to maintain the quiescent voltage at said collector electrode at said given value.

12. A circuit as set forth in claim 11, wherein said current path comprises the emitter-to-collector path of a second transistor.

13. A circuit as set forth in claim 12, wherein said second transistor is of the same conductivity type as said first transistor and is connected at its emitter electrode to said terminal at said reference potential and at its collector electrode to the collector electrode of the first mentioned transistor.

14. A circuit as set forth in claim 12, wherein said second transistor is of a conductivity type complementary to that of the first mentioned transistor and is connected at its emitter electrode to said operating voltage terminal and at its collector electrode to the collector electrode of the first mentioned transistor.

15. A circuit as set forth in claim 10, further including a signal source and wherein the coupling of said emitter electrode to said terminal at said reference potential is via said signal source.

Other info:

Inventors: Hall, James Robert (Canoga Park, CA, US)

Application Number: 520791
Filing Date: 1974-11-04
Publication_date: 1976-04-13
Assignee: RCA Corporation (New York, NY)
Primary Class(es): 330/285 330/288
Other Classes:
US Patent Ref:

3828266

Aug, 1974

Okada et al.

330/29.

Other Refs:
Primary Examiner: Mullins, James B.
Assistant Examiner:
Attorney: Christoffersen; H., Cohen; S., Limberg; A. L.