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Power supply with arbitrary voltage waveform and variable series resistance
duak:
Nihial,
I am not a SPICE user and can't comment on the simulation. If I understand the SPICE schematic I think it is basically correct. I would first connect the drain of M2 to VCC to allow M2 some drain to source voltage. Looking at the data sheets for the amplifiers, I see they both have unity gain bandwidths of about 4.5 MHz. I think this is likely to be unstable. To solve this I would add a series resistor of 10K between U4 IN- and vout_1. I would then add a capacitor between U4 IN- and U4 OUT to meet U4's need to have less than 180 degrees of phase shift at its unity gain frequency. I would start with 100 pF and see if the circuit is more stable. Decreasing the value to will increase the bandwidth but make it less stable. You may also have to increase the value of R8 - try 100R.
Please note that varying U2's gain will also change its bandwidth. Higher gains mean lower bandwidth. As I said before, U2 could be replaced with a multiplier like the AD734 that has a bandwidth that does not change as the output resistance control input is varied.
Let us know what you find.
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