Power supply modulator using op-amp and BJT -Output is not coming properly at 1Mhz
I have no idea what a &quot;supply modulator&quot; is but if the load has decoupling capacitors on it, then the voltage slew rate will be pretty low.
Besides that, the opamp has a slew rate of 6.5V/µs, so it will need 300ns to swing 2V (from 1.6V to 3.6V). It has to swing twice per period, so with 1MHz square wave the best you can hope is 300ns ramp up, 200ns constant, 300ns ramp down, 200ns constant. If that's not okay, you need an opamp with higher slew rate.
Also using the BJT as a saturated switch will be slow. You should wire the opamp as an adder instead, and add a constant DC to your input square wave.