At 71 Hz the impedance for 1 V applied gate Ubias increases to 1.00 kΩ while for -1 V Ubias remains at 1.35 kΩ. According to the explanations of the phase angle, the impedance Z of the circuit changes drastically in the capacitive-dominated region when a 1 V Ubias is applied, however, Z remains mostly constant over a wide frequency range when a -1 V gate Ubias is applied.