# Help creating circuitry to measure phase difference of different waveforms up to 25MHz

Discussion in 'General Electronics Chat' started by c1rcu1ts, Jan 31, 2016.

1. ### c1rcu1ts Thread Starter Member

Oct 19, 2013
62
0
Hello, good day all.

I am attempting to build an impedance meter capable of conducting a frequency sweep of up to 25MHz on a DUT ( i have no clue what the Z is, but the physical property is a liquid). I intend on injecting a sine wave, a triangle wave and a square wave into the DUT; one at a time to characterize the DUT at the range of frequencies for each waveform. I will be using the AD5930 (the waveform generator IC) which has a peak to peak output of 0.56V, can output a maximum of 4mA and able to perform a frequency sweep up to 25MHz.

The set up i am going to use is the auto-balancing bridge method. More information could be found on http://cp.literature.agilent.com/litweb/pdf/5950-3000.pdf concerning the auto-balancing bridge from page 24 onwards (picture below shows the design). I can build the circuitry and I can use a diff amp to obtain the magnitude of the voltage. This would only yield the magnitude of the impedance of the DUT. My concern is developing the circuitry to measure the phase of the impedance of the DUT at the particular frequencies. Any help? any IC reccomendations?

Thank You.

2. ### dannyf Well-Known Member

Sep 13, 2015
1,810
362
Generally north of 1Mhz is fairly difficult.

Analog has some dedicated chips -> not going up to 25Mhz though. They have one fully integrated but you have to sign a NDA and they may not share it with you even then.

Most of the time, it is done through a synchronous detector -> producing a product of the two signals. But again, 25Mhz is very challenging.

there are ways to do it in software but that's typically beyond what a regular person can do.

You may dial back the goal to the point where it is doable for you and go up from there.

3. ### c1rcu1ts Thread Starter Member

Oct 19, 2013
62
0
Thanks danny, that was one of my options. I originally intended on using differential amplifiers to read Vx and Vr (according to the initial diagram) into the computer via ADCs (external from arduino) and an arduino MEGA 2560. The file type i was hoping to get it to be CSV so i could replot it. I read on the forums that the data points could be potentially time logged but i am not sure. I am therefore exploring options. Thanks again.