Method and system for a transmitter loft cancellation scheme that maintains IQ balance

• US 8,364,100 B2
• Filed: 06/03/2010
• Issued: 01/29/2013
• Est. Priority Date: 12/06/2006
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Pan, Meng-An
• Primary Examiner(s): PHU, SANH D
• Application Number:
  US12/792,905
• Publication Number:
  US 20100311366A1
• Time in Patent Office: 971 Days
• Field of Search: 455/114.2, 455/333, 455/284, 455/285, 455/264, 455/315, 455/293, 455/295
• US Class Current: 455/114.2
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver

Abstract

Methods and systems for a transmitter LOFT cancellation scheme that maintains IQ balance are disclosed. Aspects of one method may include providing current compensation to both differential inputs of a mixer for each of I and Q channels. An initial current compensation of X units may be provided, followed by subsequent compensation as needed. The initial compensation may be provided to each differential input of the mixers used for I and Q channels. The subsequent current compensation for the I channel may be independent of the subsequent current compensation for the Q channel. Subsequent current compensation to a first differential input for a mixer may be increased by Y units while decreasing current compensation to the second differential input of the mixer by Y units. In this manner, the DC common mode level for the mixer may remain the same at the initial DC compensation current of X units for both mixers.

Claims

1. A method for processing signals, the method comprising:

increasing, in a transmitter, a current supplied to a first differential input of a fully differential mixer for an I (in-phase component) channel by a direct current (DC) compensation current amount;

decreasing, in the transmitter, a current supplied to a second differential input of the fully differential mixer for the I channel by the DC compensation current amount; and

independently adjusting a current supplied to a first differential input of a fully differential mixer for a Q (quadrature component) channel and independently adjusting a current supplied to a second differential input of the fully differential mixer for the Q channel.

2. The method according to claim 1, comprising adjusting the current supplied to the first differential input of the fully differential mixer for the Q channel according to a DC common mode current amount and adjusting the current supplied to the second differential input of the fully differential mixer for the Q channel according to the DC common mode current amount.

3. The method according to claim 2, comprising adjusting the current supplied to the first differential input of the fully differential mixer for the I channel according to the DC common mode current amount and adjusting the current supplied to the second differential input of the fully differential mixer for the I channel according to the DC common mode current amount.

4. The method according to claim 3, wherein the DC common mode current amount is variable.

5. The method according to claim 3, wherein the DC compensation current amount is variable.

6. The method according to claim 1, wherein the DC compensation current amount is a first DC compensation current amount, wherein the method further comprises increasing the current supplied to the first differential input of the fully differential mixer for the Q channel by a second DC compensation current amount and decreasing the current supplied to the second differential input of the fully differential mixer for the Q channel by the second DC compensation current amount.

7. A machine-readable storage having stored thereon, a computer program having at least one code section for processing signals, the at least one code section being executable by a machine for causing the machine to:

increase, in a transmitter, a current supplied to a first differential input of a fully differential mixer for a Q (quadrature component) channel by a direct current (DC) compensation current amount; and

decrease a current supplied to a second differential input of the fully differential mixer for the Q channel by the DC compensation current amount, thereby maintaining a DC common mode level of the Q channel.

8. The machine-readable storage according to claim 7, wherein the DC compensation current amount is variable.

9. The machine-readable storage according to claim 7, wherein the DC compensation current amount is a first DC compensation current amount, wherein the at least one code section comprises:

code for increasing a current supplied to a first differential input of a fully differential mixer for an I (in-phase component) channel by a second DC compensation current amount; and

code for decreasing a current supplied to a second differential input of the fully differential mixer for the I channel by the second DC compensation current amount, thereby maintaining a DC common mode level of the I channel.

13. The machine-readable storage according to claim 9, wherein the at least one code section comprises:

code for adjusting the current supplied to the first differential input of the fully differential mixer for the Q channel according to a DC common mode current amount; and

code for adjusting the current supplied to the second differential input of the fully differential mixer for the Q channel according to the DC common mode current amount.

14. The system according to claim 9, wherein the at least one code section comprises:

code for adjusting the current supplied to the first differential input of the fully differential mixer for the I channel according to a DC common mode current amount; and

code for adjusting the current supplied to the second differential input of the fully differential mixer for the I channel according to the DC common mode current amount.

15. The machine-readable storage according to claim 9, wherein the at least one code section comprises code for maintaining the DC common mode level of the I channel and maintaining the DC common mode level of the Q channel, where the DC common mode level of the I channel is equal to the DC common mode level of the Q channel.

16. The machine-readable storage according to claim 14, wherein the DC common mode current current amount is variable.

10. A system for processing signals, the system comprising:

a first current source that enables adjustment in a transmitter of a current supplied to a first differential input of a fully differential mixer for an I (in-phase component) channel, the first current source being configured to increase the current to the first differential input of the fully differential mixer for the I channel according to a direct current (DC) compensation current amount;

a second current source that enables adjustment in the transmitter of a current supplied to a second differential input of the fully differential mixer for the I channel, the second current source being configured to decrease the current to the second differential input of the fully differential mixer for the I channel according to the DC compensation current amount, thereby maintaining a DC common mode level of the I channel.

11. The system according to claim 10, wherein the DC compensation current amount is variable.

12. The system according to claim 10, wherein the DC compensation current amount is a first DC compensation current amount, wherein the system further comprises:

a third current source that enables increasing a current supplied to a first differential input of a fully differential mixer for a Q (quadrature component) channel by a second DC compensation current amount; and

a fourth current source that enables decreasing a current compensation to a second differential input of the fully differential mixer for the Q channel by the second DC compensation current amount, thereby maintaining a DC common mode level of the Q channel.

17. The system according to claim 12, wherein the first current source is further enabled to increase the current supplied to the first differential input of the fully differential mixer for the I channel by a DC common mode current amount;

and

wherein the second current source is further enabled to increase the current supplied to the second differential input of the fully differential mixer for the I channel by the DC common mode current amount, without introducing a difference in DC common mode level between the I channel and the Q channel.

18. The system according to claim 17, wherein the DC common mode current amount is variable.

19. The system according to claim 17, wherein the third current source is further enabled to increase the current supplied to the first differential input of the fully differential mixer for the Q channel by the DC common mode current amount;

and

wherein the fourth current source is further enabled to increase the current supplied to the second differential input of the fully differential mixer for the Q channel by the DC common mode current amount, without introducing a difference in a DC common mode level between the I channel and the Q channel.

20. The system according to claim 12, wherein the DC common mode level of the I channel is equal to the DC common mode level of the Q channel.