Dynamic selection of local oscillator signal injection for image rejection in integrated receivers

• US 20060003722A1
• Filed: 06/30/2004
• Published: 01/05/2006
• Est. Priority Date: 06/30/2004
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Kasha, Dan B., Tuttle, G. Tyson, Kerth, Donald A.
• Granted Patent: US 7,272,374 B2
• Time in Patent Office: Days
• US Class Current: 455/285
• CPC Class Codes: H03J 1/0041 for frequency synthesis with counters or frequency dividers
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04B 1/28 the receiver comprising at least one semiconductor device having three or more electrodes

Abstract

A system and method are disclosed for dynamically selecting high-side injection or low-side injection of local oscillator mixing signals based upon an assessment of signal power within the input signal spectrum that could cause unwanted images in the processed signal. This image rejection assessment provides an advantageous basis upon which to make dynamic high-side versus low-side injection determinations.

Claims

1. A method for dynamically selecting high-side or low-side injection of local oscillator mixing signals to help reject images within a receiver, comprising:

providing a mixer configured to utilize a mixing signal to mix an input signal to a desired frequency;

receiving an RF signal spectrum including a plurality of channels;

identifying a channel within the RF signal spectrum to be tuned;

assessing signal power at one or more frequencies within the RF signal spectrum that are different from the frequency of the channel to be tuned;

selecting high-side injection or low-side injection for the mixing signal based upon the signal power assessment;

generating a high-side local oscillation (LO) signal if high-side injection is selected, and generating a low-side local oscillation (LO) signal if low-side injection is selected; and

mixing the RF signal spectrum with the local oscillation signal that was selected and generated so as to mix the channel to be tuned down to the desired frequency.

2. The method of claim 1, wherein the receiving, identifying, assessing, selecting, generating and mixing steps are performed within a single integrated circuit.

3. The method of claim 1, further comprising generating two phase shifted mixing signals for use by the mixer, the mixer operating to generate I and Q output signals.

4. The method of claim 1, wherein the identifying step is conducted before the assessing step.

5. The method of claim 4, wherein the identifying, assessing and selecting steps are conducted each time a channel is tuned.

6. The method of claim 4, wherein the assessing step comprises assessing signal power at a first frequency that would be as far from the high-side LO signal, if selected, as is the channel to be tuned and assessing signal power at a second frequency that would be as far from the low-side LO signal, if selected, as is the channel to be tuned.

7. The method of claim 1, wherein the assessing step is conducted before the identifying step.

8. The method of claim 7, wherein signal power within an RF signal spectrum of interest is assessed at a plurality of frequencies across the RF signal spectrum.

9. The method of claim 1, wherein the desired frequency is a low-IF frequency.

10. The method of claim 9, wherein the receiving, identifying, assessing, selecting, generating and mixing steps are performed within a single integrated circuit

11. The method of claim 9, wherein the desired frequency is a fixed low-IF frequency.

12. The method of claim 9, wherein the desired frequency is a variable low-IF frequency.

13. The method of claim 1, wherein the RF signal spectrum comprises an RF terrestrial audio broadcast spectrum.

14. An integrated receiver, comprising:

a mixer coupled to receive an RF signal spectrum and a mixing signal as inputs and having a mixed signal as an output, the RF signal spectrum comprising a plurality of channels;

local oscillator (LO) generation circuitry configured to provide an oscillation signal as an output, the oscillation signal being used to generate the mixing signal for the mixer;

conversion circuitry coupled to receive the mixed signal from the mixer and configured to output a digital signal;

digital-signal-processor (DSP) circuitry coupled to receive the digital signal from the conversion circuitry and configured to output a tuned digital signal, the DSP circuitry including signal power determination circuitry; and

control circuitry coupled to the DSP and to the LO generation circuitry, the control circuitry being configured to receive signals from the signal power determination circuitry, to receive a channel selection signal, to select high-side or low-side injection based upon a signal power assessment of one or more frequencies within the RF signal spectrum, and to control the LO generation circuitry to provide a high-side LO signal or a low-side LO signal depending upon the injection selection.

15. The integrated receiver of claim 14, further comprising quadrature generation circuitry configured to generate two phase shifted mixing signals for use by the mixer, the mixer operating to generate I and Q output signals.

16. The integrated receiver of claim 14, wherein the control circuitry is configured to conduct a signal power assessment after receiving the channel selection signal, and wherein the signal power assessment comprises assessing signal power at a first frequency that would be as far from a high-side LO signal, if selected, as is the channel to be tuned and assessing signal power at a second frequency that would be as far from a low-side LO signal, if selected, as is the channel to be tuned.

17. The integrated receiver of claim 16, wherein the control circuitry is configured to conduct a signal power assessment each time a channel is tuned.

18. The integrated receiver of claim 14, wherein the control circuitry is configured to conduct a signal power assessment before receiving the channel selection signal, and wherein the signal power assessment is configured to assess signal power at a plurality of frequencies across the RF signal spectrum.

19. The integrated receiver of claim 14, wherein the mixed signal is at low-IF frequency.

20. The integrated receiver of claim 19, wherein the desired frequency is a fixed low-IF frequency.

21. The integrated receiver of claim 19, wherein the desired frequency is a variable low-IF frequency.

22. The integrated receiver of claim 14, wherein the RF signal spectrum comprises an RF terrestrial audio broadcast spectrum.