# Preamplifier before latch stage in comparator circuit

Adding preamplifier based on simple inverter before latch stage can improve performance of comparator by decreasing offset voltage. Can anybody explain me how it works?

Best Regards

• Can you provide the source of the information in your question? I ask because, sometimes it can and sometimes it can make things work depending on component selection. Also, it isn't clear how any pre-amplifier can reduce the offset voltage of a comparator fed from the pre-amp. I can juggle a few reasons of course but better for you to explain the specifi problem where a pre-amp is a benefit. Commented Sep 21, 2015 at 18:36
• I am reading publication "Offset Voltage Analysis of Dynamic Latched Comparator" written by M. Choi, H. Jeon and Y. Kim. It can be found on IEEE or from Northeastern University. I'm developing in Cadence circuit without these inverters and I'm just wondering how to improve the circuit. I've found this publication, however I can't understand what advantages we have from inverters. Maybe I shouldn't use this architecture, stay with my humble double-tail latched comparator and use some simple techniques to improve performance. Commented Sep 21, 2015 at 19:15
• @VIPPER The link doesn't work for me. Is it possible that it's available only to the university affiliates? If so, could you add some excerpts to you text so that the rest of us understand your context? Commented Nov 24, 2018 at 3:36

## 1 Answer

The inverters provide gain, so the input referred offset is reduced by a factor equal to the gain. For e.g. if the latch has 10mV offset and the inverter has a gain of 10, then you can resolve an input as low as 1mV.

• Thanks for answer. Could provide some equations to prove that? Commented Sep 8, 2018 at 17:43
• Just substitute the numbers in my explanation above with variables and you’ll get your equation. It’s also mentioned in the paper you linked above on page 2. The amp-latch topology is the most basic comparator topology but it seems like you don’t know about it. So its better to go through good textbooks discussing comparators by Allen or K. Martin or Razavi and then it will be very clear
– eenn
Commented Sep 16, 2018 at 3:54