# Three stage feedback amplifier

In the following circuit, in order to obtain negative feedback, shouldn't we need A2 to be positive? Also, is the correct feedback topology current-current?

• "shouldn't we need A2 to be positive?" --- According to the specs given, $G_m$ for $A_2$ is positive. I'm not sure what the $-/+$ on the $A_2$ symbol means but, regardless, the transconductance (ratio of output current to input voltage) is positive so, I assume, if the input voltage increases, the output current increases. Is that what you mean by "need A2 to be positive"? Commented Jun 21, 2017 at 0:22
• @HalHollis What I meant was rather that since the overall loop gain had to be positive for a negative feedback (unless I'm mistaken), I think the sign of A2 should be positive too. I was asked to determine its sign so that negative feedback is enabled. However, online I see that it's actually a two-stage op amp with gain unit and buffer at the end and that the sign of the gain of the middle stage (normally a CS) is usually NEGATIVE! What do you think? Commented Jun 21, 2017 at 6:33
• Anyone? Should I close this thread or is there still a chance to get some help? Commented Jun 21, 2017 at 15:26
• For this example, A2 should be positive.
– G36
Commented Jun 21, 2017 at 17:31
• @G36 According to what rationale? Why should it be positive, as I supposed myself? Commented Jun 21, 2017 at 17:36