25-08-2017, 09:32 PM
DC Characteristics of a CMOS Inverter
DC Characteristics.ppt (Size: 272.5 KB / Downloads: 586)
A complementary CMOS inverter consists of a p-type and an n-type device connected in series.
The DC transfer characteristics of the inverter are a function of the output voltage (Vout) with respect to the input voltage (Vin).
The MOS device first order Shockley equations describing the transistors in cut-off, linear and saturation modes can be used to generate the transfer characteristics of a CMOS inverter.
Plotting these equations for both the n- and p-type devices produces the traces below.
DC Characteristics of a CMOS Inveter
The DC transfer characteristic curve is determined by plotting the common points of Vgs intersection after taking the absolute value of the p-device IV curves, reflecting them about the x-axis and superimposing them on the n-device IV curves.
We basically solve for Vin(n-type) = Vin(p-type) and Ids(n-type)=Ids(p-type)
The desired switching point must be designed to be 50 % of magnitude of the supply voltage i.e. VDD/2.
Analysis of the superimposed n-type and p-type IV curves results in five regions in which the inverter operates.