rlc meter with opamp

Thread Starter


Joined Jan 1, 2008
i want a circuit of " rlc meter " that designed with op-amp .
i need this circuit for my homework .
please help me . . . .
thanks . . .


Joined Apr 20, 2004
You could probably figure this out but thinking of the response of a component to a frequency sweep.

R - no change

L - impedance increases with frequency

C - impedance drops with frequency

The hard part is comparing the reference frequency amplitude with the signal that has been applied to the component being measured. Probably some serious calibration issues there, which might account for the healthy price of LCR instruments - a used low-end meter goes for almost $2000.00. I imagine you'll find some computing power in there besides the odd op amp.


Joined Dec 21, 2007
There's a ridiculous component made by Analog Devices, the AD8302, which measures the amplitude and phase difference between two signals and outputs proportional voltages. It doesn't sound like you're at the point of being able to integrate this part into an RLC measurement system, and it's also not an opamp. I think making an RLC meter with only opamps and passive components would be pretty tough and would probably not make a very good meter in the end. The AD5933 gives a 12-bit complex impedance measurement through a frequency sweep, from which RLC can be extracted. If I needed to make an RLC meter, I'd start with that puppy. It has a lot of trickery that would save a crap-ton of time. Must you use /only/ opamps for the RLC meter?!


Joined Nov 9, 2007
Since this is the homework help forum I assume you are studying Op Amps.
Their main characteristic is that they are controlled by using suitable components in their feedback loops.

Look at Beenthere's comments and choose suitable impedances instead of the simple resistors given in your course. Will the same impedance do for all of L, R, and C or do you need switched ones?

There have been number of commercial LCR meters based on this principle.