Coupling high voltage to low voltage stages

[predator89]

I want to connect a high voltage output stage to low voltgae input stage of 2 stage op amp.
Can anyone suggest me which output stage topology would be better for this.

 

[AMS012]

Common source with a resistor load will give the maximum swing.

 

[predator89]

Common source with a resistor load will give the maximum swing.

But my main confusion is how would i connect the low voltage output to the high voltage mos transistors

 

[crutschow]

Need more info on what you are trying to do with the circuit.

 

[predator89]

Need more info on what you are trying to do with the circuit.

I am trying to build a high voltage amplifier. And i started with a low voltage input stage with supply of 3.3 V and want to connect it to high voltage output stage. So that i can get a swing of 0 to 40V AC for the input of 0 to 3 V AC.
So i have difficulty in deciding which topology to go for.

 

[crutschow]

So we're into the 20 question mode. :wink:
What is the output load?

 

[predator89]

What is the output load?

Its 1pf capacitance and 1M resistance.

 

[crutschow]

The frequency response required?

 

[predator89]

The frequency response required?

I need a gain of 10X .. and phase margin of 60 and GBW of 1 MHz.
My idea was to implement opamp and then try using negative feedback to control gain.

 

[crutschow]

GBW doesn't tell me the frequency response required at the output.
Don't tell me what you think you need, tell me what you actually need.

 

[Easy peasy]

You need a diff amp circuit to convert the high o/p voltage into something your low voltage opamp can deal with, search the net, plenty of examples...

 

[FlapJack]

I think you at least must give the input frequency, is it fixed or variable.

 

[Audioguru]

I do not think you want to connect a high voltage output stage to a low voltage input stage. That is saying it backwards.
I think you have an input stage that operates from a 3.3V supply and you want it to drive an output stage that has a much higher output voltage swing.

You said you want the input to be 0V to 3VAC but you did not say 3V RMS or 3V p-p. What is it?
You said you want an output swing of 40V but did not say 40V RMS or 40V p-p. What is it?

 

[d123]

Hi, possibly you can make use of or adapt this idea:

https://www.daycounter.com/Circuits/Voltage-Servo/Voltage-Servo.phtml