Need help in this circuit

[incol]

Hi all:
See the circuit. M1 and m3, m6 and m7 have the same size. When m1 and m3's gate voltage, amp's +input are all 1/2VCC, I want amp's output is also 1/2VCC. But I find that m6 and m7 is not match well, so there is a current go though m7 and R1 to amp's transistor, and VOUT= 1/2VCC- I*R1.So how to slove this problem with small change of the circuit?

Thanks very much!

 

[pmr9]

If u want amp's output to be 1/2VCC then no need of r feedback of amp.
Connect it in unitygain config.[/b]

 

[analog_prodigy]

If you want the output same as input, the gain should be 1. if u give unity gain negative feedback, the opamp works as buffer. u will get the output as input

 

[incol]

If u want amp's output to be 1/2VCC then no need of r feedback of amp.
Connect it in unitygain config.[/b]

I need the resistor R1 in my circuit, can it add some small circuit to solve this problem, not move the transistor or resistor in the circuit?
Thank you very much!

Added after 5 minutes:

If you want the output same as input, the gain should be 1. if u give unity gain negative feedback, the opamp works as buffer. u will get the output as input

Thank you very much, if move m1,m3,m6,m7, input is the same as output, but I need m1-m7 for another use, so can I use other methods to sove m6 and m7 mismatch. This mismatch will lead to output offset.

Thanks!!

 

[rajanarender_suram]

1)Try to keep a buffer between the node A and -ve terminal of OP-AMP.
2) Or You have to increase your R1 Too high, i dont know your constraint about R1(it should be much more than The resistance looking into the drain of M3)

 

[Fahmy]

what about setting the common mode level of node A to 0.5Vcc+IR such that the output comon mode will be at 0.5Vcc, does this work for your application?

 

[rajanarender_suram]

what about setting the common mode level of node A to 0.5Vcc+IR such that the output comon mode will be at 0.5Vcc, does this work for your application?

I dont think this works Fahmy , because input diff Voltage for Opamp becomes large so the output goes to Gnd.