Hello!
Please refer to the attached screendump from LTSpice. I am viewing the (0.8V peak to peak, 30 MHz sinusoidal AC) voltage before and after it is passed through a series combination of 340R resistor & 47pF capacitor, and then I measure the phase difference between the two voltages (labelled IN & OUT in the circuit), as follows:
Denote the times of the two sets of two consecutive peak voltages (of input & output waveforms) thus: T_in1, T_in2 and T_out1, T_out2 Then the phase difference Phi is given in degrees by:
180 x (1  [(T_out2  T_in1) / (T_in2  T_in1) ])
Eyeballing the curves (the double entendre just struck me!), I estimated these times as follows:
T_in1 = 83.57504 uS T_in2 = 83.60839 uS and T_out2 = 83.60688 uS
from which I calculate the phase difference to be 8.15 degrees. Noting that the voltage and current AC waveforms are in phase across the resistors, I am trying to reconcile this measured phase difference with that given by the phasor diagram formula:
Phase difference = Arc Tan (impedance of capacitor / total circuit resistance) which in this case translates to arctan  (112.8758 / 362)  = arctan (0.31181) = 17.32 degrees.
Please tell me what I am doing wrong. Many thanks!
Please refer to the attached screendump from LTSpice. I am viewing the (0.8V peak to peak, 30 MHz sinusoidal AC) voltage before and after it is passed through a series combination of 340R resistor & 47pF capacitor, and then I measure the phase difference between the two voltages (labelled IN & OUT in the circuit), as follows:
Denote the times of the two sets of two consecutive peak voltages (of input & output waveforms) thus: T_in1, T_in2 and T_out1, T_out2 Then the phase difference Phi is given in degrees by:
180 x (1  [(T_out2  T_in1) / (T_in2  T_in1) ])
Eyeballing the curves (the double entendre just struck me!), I estimated these times as follows:
T_in1 = 83.57504 uS T_in2 = 83.60839 uS and T_out2 = 83.60688 uS
from which I calculate the phase difference to be 8.15 degrees. Noting that the voltage and current AC waveforms are in phase across the resistors, I am trying to reconcile this measured phase difference with that given by the phasor diagram formula:
Phase difference = Arc Tan (impedance of capacitor / total circuit resistance) which in this case translates to arctan  (112.8758 / 362)  = arctan (0.31181) = 17.32 degrees.
Please tell me what I am doing wrong. Many thanks!
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