How does this circuit operate?

[gingerjiang]

hi all

i have a circuit which operation isn't clear
sine wave Q1 is ac coupled to pmos M's gate through cap C1
when Q1's amplitude is increased, M's gate dc potential is increased too
this is the circuit's function, but i don't understand it's operation, anyone can give me a detailed explainment?

 

[pfd001]

circuit's operation

what's the input and output

 

[gingerjiang]

Re: circuit's operation

what's the input and output

input is Q1, and output is the gate of pmos M

 

[huojinsi]

Re: circuit's operation

gingerjiang wrote:
input is Q1, and output is the gate of pmos M

Is it right?

 

[gingerjiang]

Re: circuit's operation

the circuit's operation is from Vittoz, E.'s paper
CMOS analog integrated circuits based on weak inversion operations

 

[sk1105]

Re: circuit's operation

When input amplitude increases, to keep the constant current, so increase the gate voltage of PMOS. It's the basic idea of Vittoz's amplitude detector. You can check his classic paper.