Fast Rail to Rail CMOS comparator without clocks

[viperpaki007]

Hi,

I am trying to design fast rail to rail CMOS comparator with out clock signal. Can anybody refer some circuit.

regards

 

[KlausST]

Hi,

why designing your own?
why not using ready to buy?

many manufacturers have such comparators.

Klaus

 

[viperpaki007]

iIam designing an integrated comparator for custom IC design. Comparator will be part of a big integrated circuit. Therefore, i cannot use comparator from some manufacturer.

 

[erikl]

See e.g. R. Jacob Baker's book: CMOS Circuit Design, Layout, and Simulation, Volume 1, figures 27.8 and 27.9 (pp. 914-915).

 

[AMSA84]

Hi erikl,

This circuit that you have referenced is a generic one? Is the most common fast comparator?

There is any other topology that doesn't need a pre-amplifier?

Regards.

 

[Dominik Przyborowski]

The comparator is a bridge between analog and digital circuit so it need preamplifier to prepare signal for digital backend of circuit.

 

[AMSA84]

Hi Dominik,

Thanks. However, maybe I have questioned in a wrong way.

What I meant to ask was if there is any architecture where the pre-amplifier is part of the positive feedback circuit, that is, instead of having the differential pair as a first stage, lets say, and then the positive fdbck as a second, can we have that positive feedback for example as a load for the differential pair?

If it is possible, what's the nome of such circuit?

In my case the fast comparator is to be used to compare a sawtooth wave with a reference that will vary very slowly.

Hope made myself more clear.

Thanks in advance.

 

[D.A.(Tony)Stewart]

Positive feedback used for hysteresis. this is the % of output swing and ratio of feedback resistors to the midpoint of swing. This is how Schmitt trigger inputs are made, ranging from 1% for small and 30% for common CMOS gates.

Avalanche switching diodes are even faster. But normally you only use hysteresis to prevent glitches from input noise near threshold, not increase slew rate of output.