How to design small hysteresis schmitter trig

[andy2000a]

schmitter circuit

I use CMOS circuit design & layout & simulation
have hysteresis schmitter equation ..

but my design range is small VH =3.55 VL= 3.45

and I use hspice sim find have large differnec on my circuit

 

[goodboy_pl]

schmitter op amp

theoritically, the hystersis loop is determined by the W/L of transistors and can be calculated but the small loop u need is very small and I think it will be process dependent!

maybe u need to change the architecture of your system or the idea behind it!

BEST!

 

[andy2000a]

schmitter trigger, single power op amp

but in single power OPA design
if my design range is Vh=2.55 Vl=2.45 ..

the OPA positive feedback resistor have large ration ..
I don't think OPA positiove feedback is good architecture ..
and schemitter is bad architecture ..

have any good architerure for hystersis circuit ?

 

[artem]

schmitter trigger

Schmitt trigger levels will vary dependend on power , because of feedback supplied from OPA or any other IC output - which is directly depndent on Vcc .
The simplest is to make stable power or put zener diode with resistor on OPA otuput and then use this fixed output to connect schmitt feedback resistor .

In addition you can set trigger detection point independently - 2 diodes and 2 feedback resistors will be needed .

or you can use 2 comparators (one per threshold ) and decoding logic but input noise could be a problem - capsitors will be necessary but transient time will be decreased .

 

[andy2000a]

no zener diode can be use in CMOS design ..
and I find main problem is my circuit act as power_on reset detect ..
and schmitt trig can work well if Vcc is "fix"
but my circuit have Vcc ramp up ..

I also use 1 Comp but hysteresis volt 100mv is too small . I think
　maybe I need 2 comparator for work ..

or anyone can provide a power_on_reset circuit with hysteresis circuit for reference ..

 

[joskin]

If you just apply the schmitter trig in Power-On-Reset circuit,Why you need to design so small hysteresis range 100mv?
I think 40% of supply voltage is ok.

 

[andy2000a]

sorry ..
I am a designer .. not define spec. ..
I also think don't need so small
but define speci not by me ..

by the way .. have anyone design a comparator with hysteresis ?
maybe this comparator can met my speci ..

 

[kevinwang123]

you can use one type comparator with hysteresis(use positive feedback).you can
adjust the W/L ratio to get the hysteresis you need.
you can find the comparator structure in any book that introduce comparator and opamp.hope this help you!

 

[huangjw]

maybe your simulating list's sweep interstep is large