Propagation delay of cmos inverter

[steven23]

In CMOS inverter, what if clock time period is less than 2*propagation delay?? and how to fix it?

 

[BradtheRad]

The internal transistors/mosfets will be unable to switch fast enough to make the output to go fully hi or low.

The output will start to resemble a triangle wave hovering at a middle volt level.

The transistors/mosfets will spend a greater percentage of a cycle in linear mode. This will result in greater wasted current inside the device.

It will not necessarily ruin the device to do this.

 

[steven23]

thanks. it was useful. does it change the operating frequency of output signal??

 

[yadavvlsi]

Yes, Frequency is 1/(2*propagation delay).

 

[BradtheRad]

thanks. it was useful. does it change the operating frequency of output signal??

The output starts to resemble a triangle wave, of the same frequency as the input signal.

To fix it you need to use a faster device.

The usual advice is to have your signal pull the input to either zero V or supply V, as rapidly as possible. It may cause the internal switching to happen slightly faster.

 

[D.A.(Tony)Stewart]

If you need an inverter to run faster, normally you choose a family of CMOS or ECL that runs faster. GaAs runs fastest at GHz speeds. For normal HCT CMOS, you may read about the reasons for speed differences (**broken link removed**)
If you have more specific question , then ask with more details.