Linearity enhanced amplifier

• US 20050264365A1
• Filed: 05/26/2005
• Published: 12/01/2005
• Est. Priority Date: 05/28/2004
• Status: Abandoned Application

• Current Assignee: TriQuint Semiconductor Incorporated (Qorvo, Inc.)
• Original Assignee: TriQuint Semiconductor Incorporated (Qorvo, Inc.)
• Inventors: Takahashi, Greg
• Application Number:
  US11/140,132
• Publication Number:
  US 20050264365A1
• Time in Patent Office: Days
• US Class Current: 330/296
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence

Abstract

An amplifier circuit according to one embodiment of the present invention comprises an amplifier transistor configured to amplify an input signal received at a terminal of the amplifier transistor, and a bias circuit having a bias transistor forming a current mirror with the amplifier transistor for stabilizing a bias operating point for the amplifier transistor, a buffer transistor coupled to the bias transistor and to the amplifier transistor, and a current source coupled to the buffer transistor and configured to generate a temperature-dependent current for injection into the buffer transistor. The buffer transistor improves linearity of the amplifier transistor by creating a predistortion of the input signal, and the current source injects the temperature-dependent current into the buffer transistor to adjust the extent of predistortion and to compensate for undesirable effects caused by variations in ambient conditions.

Claims

1. An amplifier bias circuit for use with an amplifier transistor receiving an input signal, comprising:

a current buffer configured to provide DC bias control of the amplifier transistor and to improve linearity of the amplifier transistor by creating a predistortion of the input signal; and

a current source configured to generate a current for injection into the current buffer to adjust the extent of predistortion and to compensate for effects caused by variations in ambient conditions.

2. The amplifier bias circuit of claim 1, further comprising a bias transistor coupled with the amplifier transistor in a current mirror arrangement.

3. The amplifier bias circuit of claim 2, wherein the current buffer is configured to provide DC bias control of the amplifier transistor by producing a first base current for the bias transistor and a second base current for the amplifier transistor.

4. The amplifier bias circuit of claim 2, wherein a first base of the bias transistor is coupled to a second base of the amplifier transistor through first and second resistors, and a terminal of the buffer transistor is coupled to a circuit node between the first and second resistor.

5. The amplifier bias circuit of claim 4, wherein the first resistor is coupled to the first base and the second resistor is coupled to the second base, a resistance value of the first resistor being substantially larger than that of the second resistor.

6. The amplifier bias circuit of claim 1, wherein the current generated by the current source increases with decreasing ambient temperature.

7. The amplifier bias circuit of claim 1, wherein the current source comprises a proportional-to-absolute-temperature (PTAT) cell.

8. The amplifier bias circuit of claim 7, wherein the current source further comprises a mirror transistor and a current source transistor, the PTAT cell driving the mirror transistor and the mirror transistor controlling the current source transistor.

9. The amplifier bias circuit of claim 1, wherein the current source comprises a plurality of resistors, and wherein the current generated by the current source depends on ratios of the resistance values associated with the plurality of resistors.

10. The amplifier bias circuit of claim 9, wherein the current generated by the current source has a dependency on temperature, and a degree of the dependency can be changed by changing ratios of the resistance values associated with the plurality of resistors.

11. An amplifier circuit, comprising:

an amplifier transistor configured to amplify an input signal received at a terminal of the amplifier transistor;

a bias transistor forming a current mirror with the amplifier transistor for stabilizing a bias operating point for the amplifier transistor;

a buffer transistor coupled to the bias transistor and to the amplifier transistor, and configured to provide base currents to the amplifier transistor and the bias transistor; and

a current source coupled to the buffer transistor and configured to generate a temperature dependent current for injection into the buffer transistor.

12. The amplifier circuit of claim 11, wherein the buffer transistor is configured to create a predistortion of the input signal that cancels a distortion generated by the amplifier transistor.

13. The amplifier circuit of claim 11, wherein the current source is configured to generate a temperature dependent current that adjusts the predistortion created by the buffer transistor.

14. The amplifier circuit of claim 11, further comprising a first resistor coupled to the bias transistor and a second resistor coupled to the first resistor and to the amplifier transistor, a resistance value of the first resistor being substantially larger than that of the second resistor.

15. The amplifier circuit of claim 11, wherein the current generated by the current source increases with decreasing ambient temperature.

16. The amplifier circuit of claim 11, wherein the current source comprises a proportional-to-absolute-temperature (PTAT) cell.

17. The amplifier circuit of claim 16, wherein the current source further comprises a mirror transistor and a current source transistor, the PTAT cell driving the mirror transistor and the mirror transistor controlling the current source transistor.

18. The amplifier circuit of claim 11, wherein the current source comprises a plurality of resistors, and wherein the current generated by the current source depends on ratios of the resistance values associated with the plurality of resistors.

19. The amplifier circuit of claim 18, wherein the current generated by the current source has a dependency on temperature, and a degree of the dependency can be changed by changing ratios of the resistance values associated with the plurality of resistors.

20. A method for improving a linearity of an amplifier circuit including an amplifier transistor, comprising:

generating a reference current through a bias transistor coupled to the amplifier transistor in a current mirror arrangement;

generating first and second base currents using a buffer transistor coupled to the bias and amplifier transistors, the first base current being provided to the bias transistor and the second base current being provided to the amplifier transistor; and

generating a temperature-dependent current for injection into the buffer transistor to adjust a differential conductance associated with the buffer transistor.