Power amplifier control driver having over-current protection and linear control

• US 20040198301A1
• Filed: 12/06/2002
• Published: 10/07/2004
• Est. Priority Date: 12/06/2002
• Status: Active Grant

• Current Assignee: Skyworks Solutions Incorporated
• Original Assignee: Skyworks Solutions Incorporated
• Inventors: Rozenblit, Dmitriy, Damgaard, Morten, Domino, William J.
• Granted Patent: US 6,950,636 B2
• Time in Patent Office: Days
• US Class Current: 455/343.1
• CPC Class Codes: H03G 3/004 Control by varying the supply voltage
• CPC Class Codes: H03G 3/3042 in modulators, frequency-changers, transmitters or power amplifiers transmission power control in bidirectional transmission systems H04W52/04
• CPC Class Codes: H04B 1/0466 Fault detection or indication H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/0416 having gain or transmission power control

Abstract

A linear power control loop for a power amplifier is disclosed. Embodiments of the invention linearly control the power amplifier output, prevent the power amplifier from failure induced by excessive supply current by reducing power amplifier bias current, and provide a mechanism to detect whether the power amplifier is operating in a saturation condition.

Claims

1. A linear power control loop for a power amplifier, comprising:

a detector for providing a direct current (DC) baseband signal representing an output of a power amplifier;

a comparator for comparing the DC baseband signal to a reference signal and generating an error signal;

a filter; and

a power amplifier control current driver for linearly controlling the output of the power amplifier.

2. The power control loop of claim 1, wherein the power amplifier control current driver comprises:

a power control transistor responsive to the error signal and configured to add a supplemental current to the error signal, wherein the output of the power amplifier remains proportional to the error signal.

3. The power control loop of claim 2, further comprising an over-current protection circuit coupled to the power control transistor.

4. The power control loop of claim 3, wherein the over-current protection circuit comprises a protection transistor responsive to a power amplifier supply signal, where the protection transistor reduces current to the power control transistor when the power amplifier supply signal reaches a predetermined level.

5. The power control loop of claim 4, further comprising a diode configured to bias the protection transistor.

6. The power control loop of claim 5, further comprising a saturation detection transistor coupled to the protection transistor, where the saturation detection transistor is responsive to a voltage signal at the protection transistor and provides a logic signal when the voltage signal drops below a predetermined level.

7. A method for operating a linear power control loop for a power amplifier, comprising:

providing a direct current (DC) baseband signal representing an output of a power amplifier to a comparator;

comparing the DC baseband signal to a reference signal;

generating an error signal; and

linearly controlling the output of a power amplifier using a power amplifier control current driver.

8. The method of claim 7, further comprising:

adding a supplemental current to the error signal, whereby the output of the power amplifier remains proportional to the error signal.

9. The method of claim 8, further comprising using a transistor to provide over-current protection to the power control transistor.

10. The method of claim 9, wherein the transistor is responsive to a power amplifier supply signal, and where the transistor reduces current to a power control transistor when the power amplifier supply signal reaches a predetermined level.

11. The method of claim 10, further comprising using a diode to bias the transistor.

12. The method of claim 11, further comprising:

determining when the transistor enters a saturation mode; and

providing a logic signal when the transistor enters the saturation mode.

13. A system for linearly controlling output power in a portable cellular transceiver, comprising:

a power amplifier responsive to a power supply signal;

a detector for providing a direct current (DC) baseband signal representing an output of the power amplifier;

a comparator for comparing the DC baseband signal to a reference signal and generating an error signal;

a filter; and

a power amplifier control current driver for linearly controlling the output of the power amplifier.

14. The system of claim 13, wherein the power amplifier control current driver comprises:

a power control transistor responsive to the error signal and configured to add a supplemental current to the error signal, wherein the output of the power amplifier remains proportional to the error signal.

15. The system of claim 14, further comprising an over-current protection circuit coupled to the power control transistor.

16. The system of claim 15, wherein the over-current protection circuit comprises a protection transistor responsive to a power amplifier supply signal, where the protection transistor reduces current to the power control transistor when the power amplifier supply signal reaches a predetermined level.

17. The system of claim 16, further comprising a diode configured to bias the protection transistor.

18. The system of claim 17, further comprising a saturation detection transistor coupled to the protection transistor, where the saturation detection transistor is responsive to a voltage signal at the protection transistor and provides a logic signal when the voltage signal drops below a predetermined level.