I was performing some experiments to get used to opamps. I constructed separately a log and an antilog circuits.I then connected them simultaneously but the output was not equivalent to the input as i expected. Why is this? how can I resolve it ?

i tried adding another opamp in between as a buffer, but that still did not work.

http://i1261.photobucket.com/albums/ii583/Adam_Sant/aaaa.jpg

 

Simply because the log and antilog circuits are modelled after the diode equation which uses the diode's reverse bias saturation current. This is different from one diode to the next.
Hence your antilog circuit is not an exact inverse of your log circuit.

 

ow ok thanks. i derived the equations using the tracking property and now i understand better. So is there any alteration i can make to make the circuit to give me vin=vout? thanks