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Reducing AD8309 RSSI baseline

Question asked by andyrobertson on Jul 23, 2014
Latest reply on Jul 24, 2014 by jdobler

On page 11 of the AD8309 datasheet,

The output has a minimum level of about 0.34 V (corresponding

to a noise power of –78 dBm, or 17 dB above the nominal intercept

of –95 dBm). This rather high baseline level ensures that the pulse

response remains unimpaired at very low inputs.

If I understand correctly, this is the equivalent of an RSSI squelch to keep it from banging around too much at extremely low levels. I'm considering using the AD8309's RSSI output as an input to a signal-cancellation circuit, which seeks to minimize the RSSI level of a 10MHz signal as much as possible. So, in my case, I want to see the noise floor at the RSSI output without being limited to 350mV or -78dBm by a squelch function. In my case, I'm not looking for pulses at extremely low levels. I'm looking for as much dynamic range of a filtered RSSI as I can get. The lower, the better. Is there any to adjust or disable this squelching behavior and cause RSSI baseline to work down to nearly zero volts? If so, how would I do it?

Also, is it possible to reduce the log amplifier's bandwidth from 500MHz to something less by using negative feedback capacitors, as might be done with some small integrator caps in a fully-differential amplifier?  I like the part, but it has way more frequency range than I think I need.  Again, I seek to minimize the level of a clean but very feeble signal