Doherty bias circuit to dynamically compensate for process and environmental variations

• US 20040174213A1
• Filed: 03/12/2004
• Published: 09/09/2004
• Est. Priority Date: 09/10/2001
• Status: Active Grant

• Current Assignee: Philip H. Thompson
• Original Assignee: Philip H. Thompson
• Inventors: Thompson, Philip H.
• Granted Patent: US 6,917,246 B2
• Time in Patent Office: Days
• US Class Current: 330/124R
• CPC Class Codes: H03F 1/0288 using a main and one or several auxiliary peaking amplifiers whereby the load is connected to the main amplifier using an impedance inverter, e.g. Doherty amplifiers
• CPC Class Codes: H03F 1/30 Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters in differential amplifiers H03F3/45479

Abstract

The invention includes a Doherty power amplifier system having a Doherty power amplifier electrically connected to a Doherty bias circuit. The Doherty amplifier includes a carrier amplifier and peaking amplifier. The Doherty bias circuit includes a current mirror and a first node that works to maintain a constant current in the current mirror as a function of a base voltage at the first node. The base voltage that results in a constant current is passed from a current mirror circuit to the carrier amplifier. The base voltage is at least one of scaled and shifted to produce a second voltage at a second node by employing a scaling/level shifting circuit. The scaling/level shifting circuit includes an input electronically connected to the current mirror circuit. The second voltage is passed through a voltage buffer to the peaking amplifier. An effect of the invention is to generate bias voltages for a Doherty amplifier that dynamically adjust to compensate for manufacturing process and environmental changes.

Claims

1. A bias circuit to bias a Doherty amplifier having a carrier amplifier and peaking amplifier, the bias circuit comprising:

a current mirror circuit comprising an output electronically connected to the carrier amplifier;

a scaling/level shifting circuit comprising an input electronically connected to the current mirror circuit; and

a voltage buffer having an input electrically connected to the scaling/level shifting circuit and an output electrically connected to the peaking amplifier.

2. The bias circuit of claim 1, wherein the current mirror comprises a reference device that is electrically connected to the carrier amplifier to form a control current mirror.

3. The bias circuit of claim 1, wherein the current mirror comprises a reference device and a voltage follower having a low output impedance electrically connected to an input of the reference device.

4. The bias circuit of claim 3, wherein the reference device is electrically connected to the carrier amplifier to form a control current mirror.

5. The bias circuit of claim 1, wherein the current mirror comprises a voltage follower having a low output impedance electrically connected to the input of the scaling/level shifting circuit.

6. The bias circuit of claim 5, wherein the current mirror further comprises a reference device having an input electrically connected to the low output impedance of the voltage follower.

7. The bias circuit of claim 6, wherein the reference device is electrically connected to the carrier amplifier to form a control current mirror.

8. The bias circuit of claim 1, wherein the scaling/level shifting circuit further comprises at least two resistors disposed as a voltage divider.

9. The bias circuit of claim 1, wherein the scaling/level shifting circuit further comprises an amplifier having a voltage offset source as an input.

10. A Doherty power amplifier system comprising:

a Doherty amplifier having a carrier amplifier and peaking amplifier; and

a bias circuit comprising

a current mirror circuit comprising an output electronically connected to the carrier amplifier,

a scaling/level shifting circuit comprising an input electronically connected to the current mirror circuit, and

a voltage buffer having an input electrically connected to the scaling/level shifting circuit and an output electrically connected to the peaking amplifier.

11. The system of claim 10, wherein the current mirror comprises a reference device that is electrically connected to the carrier amplifier to form a control current mirror.

12. The system of claim 10, wherein the current mirror comprises a reference device and a voltage follower having a low output impedance electrically connected to an input of the reference device.

13. The system of claim 12, wherein the reference device is electrically connected to the carrier amplifier to form a control current mirror.

14. The system of claim 10, wherein the current mirror comprises a voltage follower having a low output impedance electrically connected to the input of the scaling/level shifting circuit.

15. The system of claim 14, wherein the current mirror further comprises a reference device having an input electrically connected to the low output impedance of the voltage follower.

16. The system of claim 15, wherein the reference device is electrically connected to the carrier amplifier to form a control current mirror.

17. The system of claim 10, wherein the scaling/level shifting circuit further comprises at least two resistors disposed as a voltage divider.

18. The system of claim 10, wherein the scaling/level shifting circuit further comprises an amplifier having a voltage offset source as an input.

19. A process to bias a Doherty amplifier having a carrier amplifier and peaking amplifier, the process comprising:

maintaining a constant current in a current mirror as a function of a base voltage at a first node;

passing the constant current from a current mirror circuit to the carrier amplifier;

at least one of scaling and shifting the base voltage to produce a second voltage at a second node by employing a scaling/level shifting circuit comprising an input electronically connected to the current mirror circuit; and

passing the second voltage through a voltage buffer to the peaking amplifier.

20. The process of claim 19, wherein passing the constant current from a current mirror circuit to the carrier amplifier includes mirroring the constant current through a control current mirror, wherein the control current mirror comprises a reference device within the current mirror that is electrically connected to the carrier amplifier.

21. A circuit, comprising:

a linear amplifier bias circuit comprising first means for adjusting for process variations and environmental variations; and

a non-linear amplifier bias circuit comprising second means for adjusting for process variations and environmental variations, wherein the second means for adjusting for process variations and environmental variations is a function of the first means for adjusting for process variations and environmental variations.

22. The circuit of claim 21, further comprising

a linear amplifier coupled to the linear amplifier bias circuit, wherein

the linear amplifier bias circuit comprises a reference device that is disposed in relation to the linear amplifier so as to comprise the first means for adjusting for process variations and environmental variations.

23. The circuit of claim 21, wherein the first means for adjusting for process variations and environmental variations comprises a current mirror.

24. The circuit of claim 21, wherein the first means for adjusting for process variations and environmental variations comprises means for producing a first voltage and the second means for adjusting for process variations and environmental variations includes means for producing a second voltage that is a function of the first voltage.

25. The circuit of claim 21, wherein the linear amplifier bias circuit comprises a voltage follower coupled to a reference device, the circuit further comprising:

a carrier amplifier coupled to the voltage follower.

26. The circuit of claim 25, wherein the non-linear amplifier bias circuit comprises a voltage buffer coupled to a scale/level shift circuit, the circuit further comprising:

a non-linear amplifier coupled to the voltage buffer, wherein the scale/level shift circuit is coupled to the voltage follower.

27. The circuit of claim 26, wherein the linear amplifier is configured to function as a carrier amplifier and the non-linear amplifier is configured to function as a peaking amplifier in a Doherty amplifier.

28. The circuit of claim 27, wherein the linear amplifier bias circuit is a class AB amplifier bias circuit and wherein the non-linear amplifier bias circuit is a class C amplifier bias circuit.