Why is threshold voltage negative in PMOS?
Typically, threshold voltage is the Vgs voltage required to start forming the channel referred to as channel inversion. In case of PMOS, the bulk/substrate and the source terminals are connected to Vdd. With reference to the source terminal, if you start reducing your gate voltage from Vdd (exactly opposite to NMOS where you start your gate voltage from zero) to a point where you observe the channel inversion, at this point if you calculate Vgs and source being at the higher potential, you get a negative value. This is why you have a negative value of Vth for a PMOS. With a similar argument, you will see that NMOS will have a positive Vth.
How to Calculate Overdrive Voltage of PMOS?
Overdrive Voltage of PMOS calculator uses Effective Voltage = Voltage between Gate and Source-modulus(Threshold Voltage) to calculate the Effective Voltage, The Overdrive voltage of PMOS formula is defined as the voltage between transistor gate and source (VGS) in excess of the threshold voltage (VTH) where VTH is defined as the minimum voltage required between gate and source to turn the transistor on (allow it to conduct electricity). Effective Voltage is denoted by Vov symbol.
How to calculate Overdrive Voltage of PMOS using this online calculator? To use this online calculator for Overdrive Voltage of PMOS, enter Voltage between Gate and Source (VGS) & Threshold Voltage (VT) and hit the calculate button. Here is how the Overdrive Voltage of PMOS calculation can be explained with given input values -> 2.16 = 2.86-modulus(0.7).