I implemented the following circuit on a pcb board. The goal of the circuit is to measure the capacitance of C1 and C2 in a differential way. C4 and C5 are the guards of C1 and C2. The comparator TL3016 is used as a Schmitt trigger creating an oscillation at around 5MHz. The voltage sources V1 and V3 are in the circuit to get the oscillation going in LTspice for the 1st few milliseconds.
I measured the jitter of the output of TL3016 with a PLL circuit at 10kHz bandwidth to be around 30ppm. I calculated the expected jitter based on the expected noise and slew rate to be 100 times smaller. What am I doing wrong? It would be great if you good give me some new insights.
Note that when measuring the signals with a scope I noticed that the dutycycle is not 50% of the oscillation signal, but more like 30%.
Many thanks, Chris