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Switching Output of Operational Amp

Question asked by ts1984atct on Nov 28, 2011
Latest reply on Jan 31, 2016 by Jovan.Eps

I am using AD8055 as an inverting amplifier in a set-up similar to Fig. 35(I used 1k instead of 402 Ohm).

What I need to do is switch on/off the output of the amplifier.

 

First, I put a switch ADG451 to the output of the op-amp, then it made a huge spike (roughly 1V) when the switch turns on. (This seems a well-known phenomena. Could you explain why it happens?)

 

Next, I put the switch parallel to the feedback resistor, so that when the switch is on,

the amplifier would work as a gain-0 amplifier.

However, the op-amp oscillates around 100 MHz when the switch is on.

It was not clear how this can happen.

I also tried AD844 instead of AD8055, in which case AD844 oscillates at 25MHz.

If I put OP27 instead, it works well, although the circuit is not fast enough to my purpose. 

The circuit is on a PCB board, and AD8055 and ADG451 are DIP packages,

which is one of my concern.

However, just putting ADG451 into the feedback loop seems fine,

because if I put another resistor(1k) in series with the switch (G=-1 with the switch on),

the circuit works well without any oscillation.

 

Is there any trick I can use to solve this problem?

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