When the Input Frequency Changes If the input frequency increased above its unmodulated value, the phase of Va would fall below 90° due to the parallel tuned circuit becoming increasingly capacitive. The phasor representing vi (and V2) would move clockwise as shown in Figure 121. This would result in a larger total voltage being applied across D1 and a reduced voltage across D2. Since the capacitor C1 would now charge to a higher voltage, the final output from the circuit would be a positive voltage.