Is it possible to create distorsion to the output with a to fast variation of Vgain ? See picture.
CH1 = output
CH2 = reception
CH3 = Vgain
What you are seeing is the variation in offset voltage of the AD8331. Here is a TPC from the datasheet that illustratres the offset variations as a function of VGAIN voltage:
The TPC shows a variation of +/- 20 mV over the entire gain range, but the AD8331 is actually tested to the limits in the spec table, +50mV to -50 mV at VGAIN = 0.5V. You are seeing a variation of about +/-100 mV over the entire gain range for VOS over the entire range of VGAIN.
You could try reducing your ramp speed or moving a HPF corner at the output of the signal chain above your ramp speed.
Also, the AD8332, which is a dual of the AD8331, does screen out Vos greater than +/-50mV over the entire gain range so you could expect a slightly lower Vos variation over the gain range.
Would either of these suggestions fix your problem?
Thanks for the answer.
2011/10/28 prb <firstname.lastname@example.org>
** Analog Devices EngineerZone <http://ez.analog.com/index.jspa> AD8331 - TGC problem reply fromprb <http://ez.analog.com/people/prb> in Amplifiers - View the fulldiscussion <http://ez.analog.com/message/35373#35373>
Analog Devices EngineerZone <http://ez.analog.com/index.jspa> AD8331 - TGC problem reply from
prb <http://ez.analog.com/people/prb> in Amplifiers - View the full
Retrieving data ...