The device under test is a resistor and capacitor paralleled. The impedance (the resistor and the capacitor are time varied), the result is gotten from the lock-in amplifier, i.e.
R = √ (X 2 + Y 2 )
Θ=arctan(Y/X)
The input signal is sin(wt+Θsig),
The reference oscillators r X (t)=sin(2?f ref...