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Design >> Analog Design >> Limiting Amplifier output voltage
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Message started by aaron_do on Dec 12^th, 2008, 12:05am

Title: Limiting Amplifier output voltage
Post by aaron_do on Dec 12^th, 2008, 12:05am

Hi all,

In a limiting amplifier + RSSI, the limiting amplifier has a certain output swing, for example 1 V pk-pk. After each limiting stage, there is a peak detector. So my question is, does the peak detector need to have a "linear" output up to an input voltage of 1 V pk-pk. I put linear in "" because i know we're actually looking at the DC output versus AC input. My thinking is that the RSSI detection range will be low if the peak detectors don't work up to the full output swing of the limiting amplifiers.

Part 2... Its difficult to get a "linear" peak detector up to 1 Vpk-pk input, so what are the implications of have a lower limiting output, 0.5 V pk-pk for example...

thanks,
Aaron

Title: Re: Limiting Amplifier output voltage
Post by ACWWong on Dec 12^th, 2008, 12:27am

It has to be "linear" enough over a majority of the output swing, just sufficient such that when the detector signal outputs for all the stages are summed together, its give sufficient piecewise "linearity" over the full signal range of interest.
Part 2: i guess the implication is more cascaded gain stages...
cheers
aw

Title: Re: Limiting Amplifier output voltage
Post by rf-design on Dec 15^th, 2008, 2:12pm

If the topic is "limiting amp" + "RSSI" that means that the overall function should be log(amplitude). Because the total functions is composed of single segments each segment is at its best also a log-function. But log-dectection is tied in some manner to nonlinearities of the device the detection voltages would be in some Vt or Vdsat-range.