Hi,
I have a number of questions.
we want to design an ac ckt which generates a freq of 8khz
Q1. What waveform do you require, sine,square, etc.
ac current at 28mV
Q2. A current is measured in amps. milliamps, not millivolts.
and we want to measure the output voltage
Q3. The output voltage from what/where ?
varying the load from 6kohm to 6Mohm.
Q4. Where is the load connected?
first used a instrumentation amplifier but the variation in the output voltage was only from 6kohm to 40kohm.
Q5. A voltage variation is not measured in resistance units.
we dont know how to modify the ckt so that the output will vary from 6kohm to 6Mohm.
Q6. What output and what is varying, what circuit ?
As you can see, as stated by Nigel, your request dosn't make any sense.
There are many members who would like to help, but we don't understand the question.
Quite often, a simple diagram, incuded in your written reply will help us to see what you are trying to do.
Regards
EricG