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Digitally Tunable Capacitor Characterization using an Impedance Analyzer

Question asked by GuiXZatS on Feb 17, 2017

Dear All,


I am characterizing a digitally tunable capacitor (DTC) using HP 4294A high precision Impedance Analyser (40 Hz to 140 MHz).

I want to characterise the DTC as a floating capacitor (series configuration) and with one terminal connected to ground (shunt configuration). The capacitance that can be programmed in the DTC ranges from around 2 pF to 200 pF with an equivalent series resistance from 0.5 Ohm to 5 Ohm.


  1. In series configuration, we discover that be must connect the DTC ground with the 4294A frame to have good results. If we does not connect the DTC ground with the 4394A frame, the wave form Capacitance vs Frequency has a huge ringing (more than 10 pF of ringing). Could anyone explain why it is needed to connect the DTC gnd to the instrument frame? Are the obtained results using this configuration correct?
  2. To measure the DTC in shunt configuration, we must ground (DCT ground) one of the DCT capacitor sides but, as explained in point 1, be have huge ringing in the Capacitance vs frequency curve. We suspect that connecting the DTC ground to the 4294A frame we can remove that ring (as we did in point 1) but, in such a configuration, we are grounding (connecting to the 4394A frame) one side of the instrument terminals: The high side or the Low side and measurements are bad. It is any way to measure the DTC in this configuration?
  3. Any hint to characterise DTC will be really appreciated.


Thanks is advance for your support