I need to implement a log amplifier. Currently I'm doing it using a diode in the negative feedback loop but it only really gives me the log response close to the zero input, with the amps output quickly becoming proportional to the input (around 0.2V). Is there a way to make this logarithmic region span the entire length of the 0-5V input domain?
Use two resistors to reduce the input range of 5 volts to 0.2 volts.
Try the circuit of a "transdiode" (a "reversed" transistor connected in the negative feedback loop of an op-amp).