BIASING NETWORK FOR TRANSISTORS

• US 3,708,756 A
• Filed: 05/12/1971
• Issued: 01/02/1973
• Est. Priority Date: 05/12/1971
• Status: Expired due to Term

• Current Assignee: Lyle A. Fajen
• Original Assignee: Lyle A. Fajen
• Inventors: Fajen, Lyle A.
• Primary Examiner(s): Lake, Roy
• Assistant Examiner(s): Mullins, James B.
• Application Number:
  US05/142,699
• Time in Patent Office: 601 Days
• Field of Search: 330/22,40,29
• US Class Current: 330/296
• CPC Class Codes: H03F 1/0261 with control of the polarisation voltage or current, e.g. gliding Class A
• CPC Class Codes: H03F 3/245 with semiconductor devices only
• CPC Class Codes: H03G 1/0005 Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal
• CPC Class Codes: H03G 3/3042 in modulators, frequency-changers, transmitters or power amplifiers transmission power control in bidirectional transmission systems H04W52/04

Abstract

A biasing network for an RF transistor amplifier is provided wherein the bias varies smoothly and continuously from a value below turn on giving class B operation at low power inputs, to a lower valve giving class C operation at higher power levels, and finally, to a point where the DC dynamic impedance between the base and the emitter of the amplifier is extremely low, promoting maximum transistor gain and efficiency. Linear amplification at RF frequencies over the full range of power inputs is achieved.

Claims

1. A bias circuit for an RF transistor amplifier wherein such amplifier has an emitter, a base and a collector and operates in the class B and class C ranges comprising means for applying a positive voltage level bias below the turn-on value of such transistor to said base at zero RF power input to such transistor, and transistor means for varying said bias voltage level from said positive below turn-on voltage level at zero power RF power input to a negative voltage level at a relatively low percentage of RF power input and to a still lower negative voltage level at a higher percentage RF power input, said transistor means having an emitter, a base and a collector, and said transistor means being controlled in response to the voltage on its base in accordance with the RF power input to the base of said amplifier.

2. A bias circuit according to claim 1 wherein the base voltage of said transistor means is supplied by a circuit comprising an RF diode.

3. A bias circuit according to claim 2 wherein said RF diode is a hot carrier diode.

4. A bias circuit according to claim 2 wherein the base voltage circuit includes a resistor divider network.

5. A bias circuit for an RF transistor amplifier wherein such amplifier has an emitter, a base and a collector and operates in the class B and class C ranges comprising circuit means for applying a positive voltage level bias below the turn-on value of such transistor to said base at zero RF power input to such transistor, said circuit means including a resistor connected from the base of said transistor to the emitter thereof and a constant current diode connected from said base to a source of DC voltage, and transistor means connected across said resistor for varying said bias voltage level from said positive below turn-on voltage level at zero power RF power input to a negative voltage level at a relatively low percentage RF power input and to a still lower negative voltage level at higher percentage RF power inputs.

6. A bias circuit according to claim 5 wherein said circuit means further includes a voltage limiting resistor for said constant current diode.

7. A bias circuit according to claim 6 wherein said circuit means further includes an RF inductor and a Q lowering ferrite member.

8. A bias circuit according to claim 5 wherein the transistor means includes an emitter connected to said resistor at the terminal thereof connected to the base of said transistor amplifier, a collector connected to the emitter of said transistor amplifier and a base connected to a control circuit.

9. A bias circuit according to claim 8 wherein the control circuit comprises a resistor connected across the base and collector of the transistor means, an RF diode and a resistor connected to the base of said transistor means and the base of amplifier transistor.