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,
. in
"Adequate power supply bypassing can be critical when optimizing the performance of a high frequency circuit. Inductance in the power supply leads can form resonant circuits that produce peaking in the amplifier=E2=80=99s response. In addition, if large current transients must be delivered to the load, then bypass capacitors (typically greater than 1 =CE=BCF) will be required to provide the best settling time and lowest distortion. A parallel combination of
4.7 =CE=BCF and 0.1 =CE=BCF is recommended. Some brands of electrolytic capacitors will require a small series damping resistor =E2=89=884.7 =CE=A9= for optimum results."n
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.
in
...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.
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