Electronics > Beginners
Programmable gain amplifier amp vs variable gain amplifier
ricko_uk:
Thank you David,
could you please explain the Gilber cell and FET approach? Or suggest where I could find examples? I googled it but nothing came up that seemed like what you mentioned.
Thank you :)
unitedatoms:
No difference. Except if precision resistors are included (in pin selectable chips), then thermal drifts are better matched and datasheet has specs for drifts, and price wise, precision resistors can have significant cost.
David Hess:
--- Quote from: ricko_uk on January 02, 2020, 04:28:44 am ---could you please explain the Gilber cell and FET approach? Or suggest where I could find examples? I googled it but nothing came up that seemed like what you mentioned.
--- End quote ---
There should be lots of examples of the Gilbert cell online. Tektronix called that configuration the paraphase amplifier:
https://en.wikipedia.org/wiki/Gilbert_cell
Examples using FETs are not as common. The FET is used as a variable resistor but the trick is using a pair of matched FETs so the resistance of the first FET is measured to control the gate voltage and then the same gate voltage is applied to the second FET.
ricko_uk:
Thank you all!! :) :)
TimFox:
There are also “multiplying DACs”, such as the ADI AD55xx series, where an external signal input replaces the DC reference in a normal DAC. This allows a digital word to determine the gain from that input, typically through an op amp current to voltage amplifier. With an appropriate choice of DAC and supply voltages, this works with an AC analog input signal.
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