RF receivers and methods therefor
View Patent ↗Methods in intermediate frequency and direct conversion receivers for reducing pre-selection filter leakage and harmonic coupling to a programmable voltage controlled oscillator by mixing a receive signal at a mixer having a mixer injection frequency outside a pre-selection filter passband. In some applications, the mixer injection frequency is conditionally moved outside the pre-selection filter passband. In other applications, signal gain is increased to compensate for any loss resulting from shifting the mixer injection frequency outside the pre-selection passband.
1. A method in intermediate frequency and direct conversion receivers having a pre-selection filter passband, comprising:
mixing a receive signal at a mixer injection frequency outside the pre-selection filter passband,
the mixer injection frequency proportional to a first quantity divided by a second quantity,
the first quantity proportional to a difference between the receive signal frequency and an intermediate frequency, the second quantity proportional to a difference between unity and a quantity proportional to a reciprocal of a chopper divide ratio.
2. The method of claim 1 , chopping the receive signal at an input chopper before mixing, chopping the receive signal at an output chopper after mixing, the input and output choppers having a chopper frequency proportional to the mixer injection frequency divided by the chopper divide ratio.
3. The method of claim 1 , increasing a gain of the receive signal before mixing.
4. The method of claim 1 ,
measuring a condition of the receive signal,
mixing the receive signal at a mixer injection frequency proportional to a difference between the desired signal frequency and an intermediate frequency if the receive signal condition is below a predetermined threshold;
mixing the receive signal at a mixer injection frequency proportional to the first quantity divided by the second quantity if the receive signal condition is above the predetermined threshold.
5. A method in intermediate frequency and direct conversion receivers having a pre-selection filter passband (BW PSF ), comprising:
mixing a receive signal at a mixer having a mixer injection frequency (f LO ) proportional to (f RX −/+f IF )/(1−/+K LO /NL),
chopping the receive signal with a chopper having a chopper frequency (f CHOP ) proportional to (f LO /NL),
where (f RX ) is a frequency of the receive signal, (f IF ) is an intermediate frequency of the receiver, NL is a divide ratio of the chopper, (K LO ) is a VCO proportionality constant divide ratio.
6. The method of claim 5 , selecting the mixer injection frequency (f LO ) so that an absolute value of (f RX −f LO ) is greater than the preselection filter passband (BW PSF ).
7. The method of claim 5 , selecting the mixer injection frequency (f LO ) so that a VCO frequency, f VCO , is outside a bandwidth of receive signal harmonics.
8. The method of claim 5 ,
measuring a strength of the receive signal,
mixing the receive signal at the mixer having the mixer injection frequency (f LO ) proportional to (f RX −/+f IF )/(1+/−K LO /NL) when the receive signal strength is above a predetermined threshold;
mixing the receive signal at a mixer having a mixer injection frequency (f LO ) proportional to (f RX −/+f IF ) when the receive signal strength is below the predetermined threshold.
9. The method of claim 8 , chopping the receive signal at an input chopper before mixing, chopping the receive signal at an output chopper after mixing, the input and output choppers having a chopper frequency (f CHOP ) proportional to the mixer injection frequency divided by the chopper divide ratio (f LO /NL).
10. The method of claim 8 , increasing a gain of the receive signal before mixing if the receive signal gain is below a threshold.
11. A method in intermediate frequency and direct conversion receivers, comprising:
receiving a signal;
providing a mixer injection frequency by dividing a voltage controlled oscillator output by a frequency divide ratio,
the voltage controlled oscillator having a frequency outside a bandwidth of received signal harmonics;
mixing the received signal at a mixer injection frequency outside a bandwidth of a fundamental frequency of the received signal.
12. The method of claim 11 , dividing the voltage controlled oscillator output by a frequency divide ratio equal to one.
13. The method of claim 11 , mixing the received signal at a mixer injection frequency outside a channel bandwidth of the received signal.