- 1) This Op Amp provides differential gain relative to a bias point assisted with input U1 which has more influence with a low value on summing point N and must match the summing point P on the + side to satisfy the 0V different on +/- input. Ideally this serves to balance the offsets in E1 to match E2&E3 initial levels.(factored by the loss/gain R ratios.
- 2) THe 2 diodes serve 1 purposes to make a half-wave rectifier Amp. For negative inputs on E1 relative to E2,E3 the output is positive with >100dB gain until D1 conducts and reduces inverting gain, lets call it Av-, to zero. E2,E3 offset remains at unity gain to output Ua, (relative to U1 bias point) So D1 rectifies negative inputs on E1
or in other words, OpAmp rectifies more positive inputs on E2,E3 summing point, P, the Positive input to output.
- 3) for negative swings on the output, Ua, D2, conducts with very little offset since the OA has a gain of>100dB and that is a much lower resistance than R6, so the signal gain from E1 to Ua is -R6/R1
So in short, (no pun intended) D1 blocks positive signals on P relative to N input sides and D2 selects R6 as the fixed gain ratio for negative signals on the P side relative to N.
So in short a negative precision half-wave rectifier with gain controlled by R6 and bias point set by U1. or E1 visa versa.
U2 is not used as a useful output.
That's it. After a while you dont need to do the equations and you can see the gain from familiarity.