in fig 1 we see that there are 2 diodes between the 2 input ,and these for protect the input of OPAMP so it will never the difference between 2 input be more than .7v ,my question is why we connect no inverting input to 10k to ground and not connected direct to ground? and also in the second OPAMP we connect the 2 diodes after 47k? so why this and in fig 2 we connect 200k parallel with .01uf ,so is this low pass filter and how can I chose the value of 200k and .01uf
It would be helpful if you would provide more information about what you are building? it's not at all clear from the schematic.
If the inverting and non-inverting inputs of the opamp have similar resistance paths for DC bias current the effect of DC offset drift will be reduced.
Can you read more? You've been told that it is to minimize the effect of DC offset drift related to the DC bias currents. So go look into the effects of DC bias currents in opamps.
