how to choose speed of cmos comparator

[abeybaby]

how can one choose speed of comparator if the input signal frequency is mentioned.. does it depend on sample frequency or what? and how to choose sampling frequency also.. i think it depends on nyquist rate.. but how much speed of comparator can be taken?

 

[Miguel Gaspar]

I recomend you that calculate the theorical output wave of the comparator under the given input signal. The transition time of the comparator must be very small, usually 1/10, the period. That is why you must calculate it and draw it.

If you need any more info. let me know.

 

[abeybaby]

i.e. almost 10times the input frequency i guess...
but why its 10 factor??

 

[Jim cage]

It depends on the architecture. for Flash ADC, you need much higher speed for the comperator with relation to the sampling frequency. This is due to charging/discharging of the capacitance of the comperators by the input signal (for 10bit flash you will have large resistor string with conjunction of the comperator capacitance). a rule of thumb that I am familiar is 10*fs.