Low IF mixer with improved selectivity performance

• US 20060141974A1
• Filed: 12/23/2004
• Published: 06/29/2006
• Est. Priority Date: 12/23/2004
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Mujtaba, Syed Aon, Campbell, Edward E.
• Granted Patent: US 7,424,278 B2
• Time in Patent Office: Days
• US Class Current: 455/318
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04B 2001/1045 Adjacent-channel interference

Abstract

A low IF mixer and method for down-converting a signal at a desired frequency are disclosed with improved selectivity performance. The energy of sidebands on each side of the desired frequency is evaluated; and a local oscillator frequency is selected based on the evaluation of the energy. Generally, the local oscillator frequency associated with the sideband having a lower energy is selected. The desired frequency may have a frequency of RF and the sidebands have a frequency of the desired frequency plus or minus an offset frequency (RF+IF or RF−IF). The signal at the desired frequency may be multiplied by the selected local oscillator frequency to down-convert the signal.

Claims

1. A method for down-converting a signal at a desired frequency, comprising the steps of:

evaluating an energy of sidebands on each side of said desired frequency; and

selecting a local oscillator frequency based on said evaluation of said energy.

2. The method of claim 1, wherein said selecting step further comprises the step of selecting a local oscillator frequency associated with said sideband having a lower energy.

3. The method of claim 1, wherein said desired frequency is RF and a first of said sidebands has a frequency of said desired frequency plus an offset frequency RF+IF.

4. The method of claim 1, wherein said desired frequency is RF and a second of said sidebands has a frequency of said desired frequency minus an offset frequency RF−

IF.

5. The method of claim 1, further comprising the step of multiplying said signal at a desired frequency by said selected local oscillator frequency.

6. The method of claim 5, further comprising the step of filtering said multiplied signal.

7. A low IF mixer, comprising:

a port for receiving a signal at a desired frequency;

a multiplier for multiplying said received signal at a desired frequency by a local oscillator frequency, wherein said local oscillator frequency is selected based on an evaluation of interference in sidebands on each side of said desired frequency.

8. The low IF mixer of claim 7, wherein said evaluation of interference comprises an evaluation of the energy in said sidebands on each side of said desired frequency.

9. The low IF mixer of claim 7, wherein said selected local oscillator frequency is associated with said sideband having a lower energy.

10. The low IF mixer of claim 7, wherein said desired frequency is RF and a first of said sidebands has a frequency of said desired frequency plus an offset frequency RF+IF.

11. The low IF mixer of claim 7, wherein said desired frequency is RF and a second of said sidebands has a frequency of said desired frequency minus an offset frequency RF−

IF.

12. The low IF mixer of claim 11, further comprising a filter that filters an output of said multiplier.

13. The low IF mixer of claim 12, wherein said filter is a complex low pass filter.

14. A receiver in a wireless network, comprising:

an antenna for receiving a signal at a desired frequency; and

a low IF mixer having a multiplier for multiplying said received signal at a desired frequency by a local oscillator frequency, wherein said local oscillator frequency is selected based on an evaluation of interference in sidebands on each side of said desired frequency.

15. The receiver of claim 14, wherein said evaluation of interference comprises an evaluation of the energy in said sidebands on each side of said desired frequency.

16. The receiver of claim 14, wherein said selected local oscillator frequency is associated with said sideband having a lower energy.

17. The receiver of claim 14, wherein said desired frequency is RF and a first of said sidebands has a frequency of said desired frequency plus an offset frequency RF+IF.

18. The receiver of claim 14, wherein said desired frequency is RF and a second of said sidebands has a frequency of said desired frequency minus an offset frequency RF−

IF.

19. The receiver of claim 18, further comprising a filter that filters an output of said multiplier.

20. The receiver of claim 19, wherein said filter is a complex low pass filter.