Sampling threshold detector for direct monitoring of RF signals
View Patent ↗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 band to detect when a threshold is exceeded by a radio frequency (RF) signal, the sampling threshold detector comprising:
a clocked sampler configured to sample the RF signal at a sampling clock frequency (f SAMP ) based on a local oscillator frequency (f LO ) and to position kickback intermodulation products that are produced by operation of the sampler such that when the RF signal is mixed down to the baseband intermediate frequency (f IF ) the intermodulation products are out-of-band;
a passive attenuator configured to receive the RF signal, the passive attenuator allowing the detector 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 a static programmable threshold voltage therefrom and to provide the resulting signal to the clocked sampler as the RF signal to be sampled.
2. The sampling threshold detector of claim 1 wherein the clocked sampler is 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 the 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 filter provided before the continuous time pre-amplifier and configured to capture the peak of the RF signal within a particular frequency band.
7. The sampling threshold detector of claim 1 wherein the sampler comprises a single high bandwidth clocked sampler directly attached to the RF signal, enabling direct monitoring of the RF signal.
8. The sampling threshold detector of claim 1 wherein the clocked sampler provides a digitized output having a digital output value, the digital output value being based on whether or not the RF signal exceeds the threshold.
9. A method of sampling threshold detection comprising:
monitoring a radio frequency (RF) signal using a single high bandwidth clocked sampler;
selecting a sampling clock frequency (f SAMP ) based on a local oscillator frequency;
operating the single high bandwidth clocked sampler at the selected sampling clock frequency (f SAMP ) to position kickback intermodulation products that are produced by operation of the clocked sampler such that when the RF signal is mixed down to the baseband intermediate frequency (f IF ) the intermodulation products are out-of-band; and
receiving the RF signal to monitor higher voltages to provide a reverse path attenuation of noise generated by the single high bandwidth clocked sampler; and subtracting a static programmable threshold voltage to provide the resulting signal to the single high bandwidth clocked sampler as the RF signal to be sampled.
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 9 further comprising:
calculating at run-time intermodulation products for each signal to be received; and
selecting the sampling clock frequency additionally based on the intermodulation products calculated at run-time.
12. The method of claim 9 wherein the 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 (f SAMP ) is determined based on the local oscillator frequency (f LO ) and the 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 an acceptable operating range of the single high bandwidth 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:
capturing the peak of the RF signal within a particular frequency band.
17. 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.
18. The method of claim 9 wherein the single high bandwidth clocked sampler provides a digitized output having a digital output value, the digital output value being based on whether or not the RF signal exceeds the threshold.