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Design >> Analog Design >> Variable gain OPAMP noise problems
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Message started by jebasingh on Sep 19^th, 2009, 6:16am

Title: Variable gain OPAMP noise problems
Post by jebasingh on Sep 19^th, 2009, 6:16am

Hi,
i am using current feedback OPAMP THS3201 and the gain is varied using the N-channel JFET ( Voltage controlled resistor ). The input signal is a square wave with 100MHZ frequency and 1.8V amplitude and the gain varies from 1V/V to 10V/V . Like this 36 channels were there in my PCB
The problem is when i connected this circuit with power supply and started varying the JFET gate voltage noise picks up in the output and i am not getting the desired wave form......
It seems the power supply noise . i have used good filtering techniques in the PCB .....
can any one suggest me what can i do for the input power supply to reduce the noise.... the noise harmonics were in GHz and the amplitude is in 400mV.

Thanks
Jebasingh