Designer’s Guide Community

chaojixin

Junior Member

Offline

Posts: 11
Shanghai

Can I design a hysteresis comparator which is used in integration ADC like this?
May 29^th, 2012, 2:29am

I set the W/L of M2 larger than M6 to make the hysteresis curve different from the common comparator.
but I use this comparator in integration ADC which Vi1 connect to a DC level and Vi2 to a ramp wave. Vi1 never near the start point of ramp wave.
Can I design the comparator like this in my case? what's the problem of it?

thanks!

Back to top

_Microsoft_Visio__002.jpg

IP Logged

loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: Can I design a hysteresis comparator which is used in integration ADC like this? Reply #1 - May 30^th, 2012, 1:12am Integration ADC have mostly stop being used. Consider a sigma-delta method, or a VCO counter structure. As a method to introduce hysteresis, the method and architecture will work, although there are other methods also.
Back to top	Jerry Twomey www.effectiveelectrons.com Read My Electronic Design Column Here Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical IP Logged

chaojixin Junior Member Offline Posts: 11 Shanghai	Re: Can I design a hysteresis comparator which is used in integration ADC like this? Reply #2 - May 30^th, 2012, 3:40am but in fact it is not a real 'hysteresis'. the real 'hysteresis' is like this. so I'm afraid such a comparator will be sensitive to noise
Back to top	_Microsoft_Visio_.jpg IP Logged

loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: Can I design a hysteresis comparator which is used in integration ADC like this? Reply #3 - Jun 3^rd, 2012, 2:55pm the circuit shown will give the desired hysterisis effect, when the sizes of the devices are widely mismatched. The original drawing of the response is incorrect, and the newer one is accurate, agreed.
Back to top	Jerry Twomey www.effectiveelectrons.com Read My Electronic Design Column Here Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical IP Logged

chaojixin

Junior Member

Offline

Posts: 11
Shanghai

Re: Can I design a hysteresis comparator which is used in integration ADC like this?
Reply #4 - Jun 4^th, 2012, 8:41pm

both drawing is correct. the curve in original drawing is made by setting W/L of M3 larger than M6 , and the newer one (ordinary case which has real hysteresis) is made by setting W/L of M3 smaller than M6.
my question is, does the comparator in original drawing has any drawback?

Back to top

IP Logged

loose-electron

Senior Fellow

Offline

Best Design Tool =
Capable Designers

Posts: 1638
San Diego California

Re: Can I design a hysteresis comparator which is used in integration ADC like this?
Reply #5 - Jun 10^th, 2012, 1:15pm

chaojixin wrote on Jun 4^th, 2012, 8:41pm:

both drawing is correct. the curve in original drawing is made by setting W/L of M3 larger than M6 , and the newer one (ordinary case which has real hysteresis) is made by setting W/L of M3 smaller than M6.
my question is, does the comparator in original drawing has any drawback?

It is only the inpput stage to a comparator.

You will probably need a second gain stage and an output buffer

Back to top

Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

IP Logged

pf66 New Member Offline Posts: 2	Re: Can I design a hysteresis comparator which is used in integration ADC like this? Reply #6 - Aug 13^th, 2012, 7:01am Dear Chaojixin, Your hysteresis plot will be sensitive to mismatch of M2/M6. Moreover, they are NMOS/PMOS and can not really be matched. Any special reason why not use high gain two-stage (with possible offset compensation/auto zero at first stage) ? Alex
Back to top	IP Logged