Reply to thread

Hi,

* a capacitor in parallel with a resistor.

* 1MOhms ... 30MOhms

* 1kHz, 500mV

What

* accuracy

* precision

* resolution

do you expect? (In numbers please)

I guess my approach would be to use a "dual, simultaneous sampling ADC" to measure V and I.

Maybe with let´s say 32x oversampling. This means you need a sampling frequency of 32 x 1kHz.

Best if it is synchronous to your 1kHz. Not only frequency synchronous, but also phase synchronous. Maybe you could use a PLL to generate the 32x sampling clock from the 1kHz clock. Often the DDS outputs a digital signal that can help you with this.

A microcontroler needs to read the digital signal and mathematically perform the quadrature encoding.

So you get amplitude and phase angle of both signals ...

Indeed, since 1kHz is a rather low frequency ...

.. instead of using a DDS I´d rather use an STM32 microcontroller that is able to feed a DAC to generate the 1kHz. This way you are perfectly synchronous.

so the hardware is like this:

* uC --> DAC --> reconstruction filter --> shunt --> DUT

* DUT_voltage --> (maybe filter) --> ADC1 --> uC

* shunt voltage (DUT current) --> amplifier --> (identical filter as above) --> ADC2 --> uC

Using interenal ADCs maybe even internal DACs the hardware is rather simple.

Using internal DMA data transfer to/from the ADC and DACs the timing is perfect, while the processing time is relaxed

You will find software (parts) doing the math for you

Klaus