Precision emitter follower

• US 6,064,268 A
• Filed: 01/28/1999
• Issued: 05/16/2000
• Est. Priority Date: 01/28/1999
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: HP Inc.
• Inventors: Felps, Jimmie D
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHANH V
• Application Number:
  US09/239,418
• Time in Patent Office: 474 Days
• Field of Search: 330/288, 330/296, 330/311, 330/207, 330/298, 330/136
• US Class Current: 330/288
• CPC Class Codes: H03F 3/50 Amplifiers in which input is applied to, or output is derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower

Abstract

A first current source supplies current to the collector of an emitter follower stage and a sense transistor. The sense transistor programs a current mirror so that most of the base current required by the emitter follower transistor comes from the current mirror instead of the input. A second current source that requires more current that the first current source supplies is connected to the output of the emitter follower and sinks the current coming out of the emitter of the emitter follower and the collector current of a load transistor. The load transistor supplies the difference in current between the amount of current supplied by the first current source and the amount sunk by the second current source.

Claims

1. An amplifier, comprising:

an emitter follower transistor of a first conductivity type and having an input terminal, and first and second bias terminals;

a load transistor having a load output terminal, a supply terminal, and a control terminal;

a first constant current means, said first constant current means drawing a first fixed current from said second bias terminal and said load output terminal;

a sense transistor having a first sense terminal, a second sense terminal, and a sense output terminal;

a second constant current means, said second constant current means forcing a second fixed current through said sense transistor from said first sense terminal to said second sense terminal and into said first bias terminal, and wherein a difference in current between said first fixed current and said second fixed current causes said control terminal to control said load transistor to supply said difference in current to said first constant current means, and

a current mirror, said current mirror providing a duplicate current, said duplicate current being a duplicate of a sense current that flows into said sense output terminal, and wherein said duplicate current is provided to said input terminal.

2. The amplifier of claim 1 wherein said load transistor is of a second conductivity type.

3. The amplifier of claim 2 wherein said sense transistor is of said first conductivity type and wherein said sense transistor is matched to said emitter follower transistor.

4. The amplifier of claim 3 wherein said current mirror comprises a wilson current mirror.

5. The amplifier of claim 3 wherein the magnitude of the current through said first constant current means is larger than the magnitude of the current through said second constant current means.

6. The amplifier of claim 5 wherein the magnitude of the current through said first constant current means is approximately twice the magnitude of the current through said second constant current means.

7. An amplifier, comprising:

an emitter follower circuit having an input terminal, and first and second bias terminals;

a load circuit having a load output terminal and a supply terminal wherein said load output terminal supplies a load current from said supply terminal to said load output terminal that is controlled by a control terminal;

a first constant current circuit, said first constant current circuit drawing a first fixed current from said second bias terminal and said load output terminal;

a sense circuit having a first sense terminal, a second sense terminal, and a sense output terminal;

a second constant current circuit, said second constant current means forcing a second fixed current through said sense circuit from said first sense terminal to said second sense terminal and into said first bias terminal, and wherein said control terminal is connected to said first sense terminal, and,

a current mirror circuit said current mirror circuit providing a duplicate current, said duplicate current being a duplicate of a sense current that flows into said sense output terminal, and wherein said duplicate current is provided to said input terminal.

8. The amplifier of claim 7 wherein said sense circuit is matched to said emitter follower circuit.

9. The amplifier of claim 7 wherein said current mirror circuit comprises a wilson current mirror.

10. The amplifier of claim 9 wherein the magnitude of the current through said first constant current circuit is larger than the magnitude of the current through said second constant current circuit.

11. The amplifier of claim 10 wherein the magnitude of the current through said first constant current circuit is approximately twice the magnitude of the current through said second constant current circuit.