| Contd... |
| Due to the symmetry of the CMOS circuit the rise time can be similarly obtained as; |
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| For equally sized n and p transistors (where βn=2βp) tf=tr |
| Thus the fall time is faster than the rise time primarily due to different carrier mobilites
associated with the p and n devices thus if we want tf=tr we need to make βn/βp =1.
This implies that the channel width for the p-device must be increased to approximately 2 to 3
times that of the n-device. |
| The propagation delays if calculated as indicated before turn out to be, |
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If we consider the rise time and fall time of the input signal as well, as shown in the fig 16.35 we have,
These are the rms values for the propagation delays. |
| Figure 16.35: Rise and Fall time graph of Output w.r.t Input |
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