Opportunistic intermediate frequency selection for communication receivers

1. A method of selecting an intermediate frequency, comprising the steps of:

measuring a power of a signal on a first channel;

measuring a power of a signal on a lower channel adjacent the first channel;

measuring a power of a signal on an upper channel adjacent the first channel;

measuring an in channel interference on the first channel at a first intermediate frequency;

measuring an adjacent channel interference on the first channel, at a second intermediate frequency; and

selecting the intermediate frequency with the best signal quality, wherein a signal on the first channel is time multiplexed having inactive and active time slices, and wherein the step of selecting is performed during an inactive time slice.

2. A method as in claim 1 , wherein the second intermediate frequency is produced by mixing a radio frequency (RF) signal with a local oscillator signal having a frequency between a frequency of the first channel and a frequency of one of a lower and an upper adjacent channel.

3. A method as in claim 1 , comprising measuring flicker noise and direct current (DC) offset of an unused channel.

4. A method of selecting an intermediate frequency, comprising the steps of:

measuring an in channel interference on a first channel at a first intermediate frequency;

measuring a first adjacent channel interference on the first channel at a second intermediate frequency; wherein the second intermediate frequency is produced by mixing a radio frequency (RF) signal with a local oscillator signal having a frequency between a frequency of the first channel and a frequency of a lower adjacent channel;

measuring a second adjacent channel interference on the first channel at a third intermediate frequency; wherein the third intermediate frequency is produced by mixing the radio frequency (RF) signal with a local oscillator signal having a frequency between a frequency of the first channel and a frequency of an upper adjacent channel; and

selecting the intermediate frequency with the best signal quality.

5. A circuit, comprising:

a select circuit arranged to produce a select signal in response to an in channel interference and an adjacent channel interference measurements on a first channel at a respective plurality of intermediate frequencies of zero or between a desired channel and one of the upper and lower adjacent channels;

a local oscillator circuit coupled to receive the select signal, the local oscillator circuit producing a selected local oscillator signal in response to the select signal;

a mixer circuit coupled to receive a radio frequency (RF) signal and the selected local oscillator signal, the mixer circuit producing a selected intermediate frequency signal in response to the radio frequency signal and the selected local oscillator signal; and

a measurement circuit comprising an automatic gain control (AGC) circuit arranged to measure a signal-to-interference plus noise (SINR) ratio on the first channel and apply a resulting signal to the select circuit, wherein the resulting signal is one of a noise and a strength signal.

6. A wireless receiver, comprising:

an antenna;

a radio frequency (RF) amplifier coupled to the antenna;

a mixer circuit coupled to receive a radio frequency (RF) signal from the RF amplifier, the mixer circuit producing a selected intermediate frequency signal in response to the radio frequency signal and a selected local oscillator signal, wherein a frequency of the selected intermediate frequency signal is zero or between a desired channel and one of the upper and lower adjacent channels;

a local oscillator circuit coupled to receive a select signal, the local oscillator producing a selected local oscillator signal in response to the select signal;

a select circuit arranged to produce the select signal in response to in channel interference and adjacent channel interference measurements on a first channel at a respective plurality of intermediate frequencies;

a first measurement circuit arranged to measure noise on the first channel and produce a noise signal, the first measurement circuit applying the noise signal to the select circuit; and

a second measurement circuit arranged to measure signal strength on the first channel and produce a signal strength signal, the second measurement circuit applying the signal strength signal to the select circuit.

7. A circuit as in claim 6 , wherein the noise signal and the signal strength signal comprise the signal quality measurements.