Q
I am having difficulty measuring capacitor impedances at low frequencies (200Hz)
My specifications are:
VDD = 3.3V
Capacitor 6.8nF
Rfeedback = 179K
Excitation frequency: 100Hz-200Hz
A
Assuming VDD = 3.3V,
Vp = 1.48+1 = 2.48V
ADC input voltage = Rfeedback/Runknown * Vp
Calibrating the system,
ADC input voltage = 179k/178.8k * Vp = 2.48V
With the cap (6.8nF @ 200Hz = 117k)
ADC input voltage = 179k / 117k * Vp = 3.79V
VDD is less than 3.79V, which is where the problem stems from.