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Propagation delay time calculation for cmos inverter

Propagation delay time calculation for CMOS inverter

 

Question: How you will calculate propagation delay time for CMOS inverter?

Solution:

propagation delay time calculation for cmos inverter

 

Propagation delay (tp) measures the speed of output reaction to input change. It is the sum of fall propagation delay and rises propagation delay.

t_p=\frac12(\;t_{pf}+t_{pr})....................(i)

Where

tpf =Fall propagation delay which is defined as the time for output to fall by 50% or reference to input change by 50%

If the input is step change then

t_{pf}=\ln\left(2\right)\;\tau_n.............(ii)

And

tpr = Rise time propagation delay which is defined as the time for output to rise by 50% or reference to input change by 50%.

If the input is step change (ideal case) then

t_{pr}=\ln\left(2\right)\;\tau_p.............(iii)

Substituting the equation (ii) and (iii) in equation (i) we get

\begin{array}{l}t_p=\frac12\{\ln\left(2\right)\;\tau_n+\ln\left(2\right)\;\tau_p\}\\\\\;\;\;=\frac12\;\ln\left(2\right)\;(\tau_n+\tau_p)\\\\\;\;t_p=0.35\;\;(\tau_n+\tau_p)\\\\\\\end{array}

Which is the total propagation delay of CMOS inverter.

Propagation delay time calculation for CMOS inverter

 

Read: Power consumption of a mos inverter

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