I have used the follow structure to reverse input signal polarity .
I have used TINA-9 to simulate this circuit, it can work as I want.
But I am wondering should I put a buffer between two OPA277s since the input resistance of second OPA277 is only 1K.
Another way is to increase the input resistance of second OPA277 but increasing the input resistance of second OPA277 will increase the noise.
Please let me know any your suggestions.
David,
The circuit you have shown is probably okay. The load that R4 makes on U1 is greater than might be ideal for very highest DC accuracy. Don't expect U1 to swing as close to the rail as its specifications would suggest. See the output swing characteristics in the lower-right of page 7 of the data sheet. Linearity and offset voltage may be degraded somewhat with this load but it may not matter in your application. Note that in your circuit, U2 has the same output drive issues as U1. U2 must supply the current that flows in R5. This is the same current that flows in R4. If U2 is sourcing this current then U2 must sink the same current.
I don't understand the purpose of R3 and R6. The 10 ohm value is not so low that it would create a stability problem but I see no purpose in them.
You may want to consider the circuit shown below which uses only one op amp and provides the desired output polarity.
In this circuit, U1 must drive a 2k-ohm load, (R1+R2).
Regards, Bruce.
