Sampling threshold detector for direct monitoring of RF signals
The peak level of a high frequency analog signal in an RF receiver is detected by a system which samples the signal and compares it against a static threshold, generating an above/below status. The system is implemented with a sampler of sufficient aperture bandwidth to capture the signal in question, operated at a clock frequency, dynamically chosen as a function of f LO (local oscillator frequency) and the desired f IF (intermediate frequency), to minimize in-band intermodulation products. The sampler produces kickback intermodulation products that are positioned out-of-band, or are of low enough power in-band so as to be inconsequential. Samples are taken for a statistically significant period of time, and the status is used to adapt the threshold to systematically determine the peak amplitude of the signal being observed.
1. A sampling threshold detector for monitoring a radio frequency (RF) signal in a receiver having a mixer for generating a baseband intermediate frequency (IF) signal from the RF signal, the IF signal having a band of interest, the detector comprising:
an input for receiving a threshold voltage value, the threshold voltage value for comparing to an amplitude of the RF signal;
a clocked sampler configured to sample the RF signal at a sampling clock frequency (f SAMP ) and to generate a status signal when the amplitude exceeds the threshold voltage value,
wherein the sampling clock frequency (f SAMP ) produces kickback intermodulation products at an output of the mixer, and the sampling clock frequency (f SAMP ) is chosen based on a local oscillator frequency (f LO ) of the mixer in order to position the kickback intermodulation products outside of the band of interest of the IF signal.
2. The sampling threshold detector of claim 1 wherein the clocked sampler comprises a single high bandwidth sampler.
3. The sampling threshold detector of claim 1 wherein the sampling clock frequency (f SAMP ) is determined based on the local oscillator frequency (f Lo) and a baseband intermediate frequency (f IF ).
4. The sampling threshold detector of claim 3 wherein the sampling clock frequency (f SAMP ) is determined according to f SAMP =f LO +N*f IF , where N is an integer that results in a positive sampling frequency within an acceptable operating range of the clocked sampler.
5. The sampling threshold detector of claim 1 further comprising a machine readable memory storing a set of candidate sampling clock frequency values from which the sampling clock frequency for the clocked sampler is selected.
6. The sampling threshold detector of claim 1 further comprising:
a passive attenuator configured to receive the RF signal to monitor higher voltages to provide a reverse path attenuation of noise generated by the clocked sampler; and
a continuous time pre-amplifier configured to receive the output of the passive attenuator and to subtract the threshold voltage value therefrom, wherein the threshold voltage value is provided by a static programmable threshold voltage, and to provide a resulting signal to the clocked sampler as the RF signal to be sampled.
7. The sampling threshold detector of claim 6 further comprising:
a filter provided before the continuous time pre-amplifier and configured to capture a peak of the RF signal within a particular frequency band.
8. The sampling threshold detector of claim 1 wherein the clocked sampler comprises a single high bandwidth sampler directly attached to the RF signal, enabling direct monitoring of the RF signal.
9. A method of sampling threshold detection comprising:
monitoring a radio frequency (RF) signal using a single high bandwidth clocked sampler in a receiver having a mixer for generating a baseband intermediate frequency (IF) signal from the RF signal, the IF signal having a band of interest;
selecting a sampling clock frequency (f SAMP ) based on a local oscillator frequency (f LO );
sampling an amplitude of the RF signal at the selected sampling clock frequency (f SAMP ); and
generating a status signal when the amplitude exceeds a threshold voltage value,
wherein the sampling clock frequency (f SAMP ) produces kickback intermodulation products at an output of the mixer, and selecting the sampling clock frequency (f SAMP ) comprises positioning the kickback intermodulation products outside the band of interest of the IF signal.
10. The method of claim 9 further comprising:
pre-calculating intermodulation products for each signal to be received; and
selecting the sampling clock frequency additionally based on the pre-calculated intermodulation products.
11. The method of claim 10 further comprising:
calculating at run-time intermodulation products for each signal to be received; and
selecting the sampling clock frequency additionally based on the pre-calculated intermodulation products.
12. The method of claim 9 wherein a final folded results of the kickback intermodulation products are positioned out of band, or are of low enough power in-band so as to be inconsequential.
13. The method of claim 9 wherein the sampling clock frequency is determined based on the local oscillator frequency (f LO ) and a baseband intermediate frequency (f IF ).
14. The method of claim 13 wherein the sampling clock frequency (f SAMP ) is determined according to f SAMP =f LO +N*f IF , where N is an integer that results in a positive sampling frequency within the acceptable operating range of the clocked sampler.
15. The method of claim 9 further comprising storing a set of candidate sampling clock frequency values from which the sampling clock frequency for the single high bandwidth clocked sampler is selected.
16. The method of claim 9 further comprising:
receiving the RF signal to monitor higher voltages to provide a reverse path attenuation of noise generated by the clocked sampler; and
subtracting the threshold voltage value from the RF signal, wherein the threshold voltage value is provided by a static programmable threshold voltage, to provide a resulting signal to the clocked sampler as the RF signal to be sampled.
17. The method of claim 9 further comprising: capturing a peak of the RF signal within a particular frequency band.
18. The method of claim 9 further comprising directly monitoring the RF signal by sampling the RF signal using the single high bandwidth clocked sampler directly attached to the RF signal.