We made a mistake not to cut out the plans on the PCB around the op- am. The op-am operates in non-invert mode with gain = 2 (Figure 4. in data sheet R1 = R2 = 1K) ... The problem now is a huge overshoot observed on the output
I know anything for this PCB will be the "band aid", but what is the feasible solution to fix it with out re-layout the board?
Require bandwidth is - 0.3dB ~ 70 MHz is enough
Thanks,
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Since the amplifier has plenty of output current try reducing the value of your feedback resistors to move the pole formed with the parasitic up in frequency.
The next step if that doesn't work is rework where you mount a small cap (1-2pF depending on parasitics) directly on top of the feedback resistor.
kevin
Since you only need 70 MHz, you could scale the feedback resistors, as Kevin suggests.
Or slap a small cap across Rf.
Or use a slower opamp.
-- John Larkin, President Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
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...The small feedback cap really help !
Remember in the old days I used to twist the tiny wires to make feedback cap and cut off the length to have right capacitance...and end up having no idea how many pf was it :-)
Thanks all,
How big a cap did you add? 1 pF maybe? We stock 0603's down to 0.2 pF.
The inverting node on these opamps has to be a very small PCB trace, and cutting out ground plane can help keep the C down.
-- John Larkin, President Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
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