1. AD8622 need dual power supply, if you only use positive power supply, the noise is very big. And AD8622 noise is very huge, you should select another one.
2. The power supply need Tan capacitor to filter.
3. The grounded system are not good. For power supply and OpAmp, grounded is very important. You vias is too few.
4. You can use ADISimpll free software to simulate before you do it.
I made the connections short, added dual supply, but it didn't made much differenc e (maybe a little). SO I have to change the OPAMP.ADA4841, single power with very low noise.
My calculations show you have an open loop bandwidth of 50 KHz and a phae margin of 78 degrees. So it should be stable.
are you sure you do not have any more R-C components in the schematic? My calculations show you have an open loop bandwidth of 50 KHz and a phae margin of 78 degrees. So it should be stable.
If you had additional series R and shunt C components, either in front of the op amp, or between the op amp and vco, they would add more phase shift and maybe make it unstable.
If not, I would make sure there are good bypass capacitors on the voltage supply lines right next to the op amp. modern op amps, with their huge bandwidths, LOVE to oscillate.
BTW, it is a really good idea to have perhaps a 220 ohm resistor between the op amp output and the VCO tune port, to protect the varactor from blowing up.
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