Pmod IA - low frequencies

[Giuliana]

Hi, Im doing a project about impedance analyzer so I decided to buy the Pmod IA. 

However, for low frequencies (1 - 3 kHz) I didnt receive the results I was expecting...I read in a  previous post that an oscillator acting as an external clock could solve this issue but I dont know how to do it. Also, Im not sure if adding this external clock, high frequencies would be affected too. If somebody has already experience and want to share the knowledge could be really helpful. 

Thanks! 

[JColvin]

Hi @Giuliana,

I have not personally done this but based on page 33 of the datasheet, https://www.analog.com/media/en/technical-documentation/data-sheets/AD5933.pdf, "To achieve system accuracy from the 0.1 kHz to 1 kHz range, the system clock needs to be scaled down from the 16.776 MHz nominal clock frequency to 500 kHz, typically. The clock scaling can be achieved digitally using an external direct digital synthesizer like the AD9834 as a programmable divider, which supplies a clock signal to MCLK and which can be controlled digitally by the nearby microprocessor.".

If you wanted to load (the currently unloaded) IC4 and provide your own external clock rather than having the Pmod IA use it's internal clock, you would need to install a 5.00 mm x 3.20mm oscillator in place of IC4 and a 0.1 uF ceramic capacitor for C7; depending on the oscillator chosen you may also need an additional load capacitor to put into C11. The Pmod IA schematic, https://reference.digilentinc.com/_media/reference/pmod/pmodia/pmodia_sch.pdf, offers some suggestions of different oscillators, those these are all 16.000 MHz oscillators and not slower ones that are suggested by the AD5933 datasheet.

Thanks,
JColvin