Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

How to know delay in comparator

Status
Not open for further replies.

shanmei

Advanced Member level 1
Joined
Jul 26, 2006
Messages
430
Helped
8
Reputation
16
Reaction score
8
Trophy points
1,298
Location
USA
Activity points
4,496
As in the figure, how do we know the how much of the delay of the comparator? Or I just want to know the exact time where Vin reaches Vref.

Do you have any suggestion? Thanks. comp.png
 

Audioguru

Advanced Member level 5
Joined
Jan 19, 2008
Messages
9,437
Helped
2,150
Reputation
4,300
Reaction score
2,002
Trophy points
1,393
Location
Toronto area of Canada
Activity points
59,509
The datasheet for a comparator specifies the typical "response time" and even shows a graph of it. I looked at the LM339 and LM393 comparators datasheets.
 

dick_freebird

Advanced Member level 5
Joined
Mar 4, 2008
Messages
8,008
Helped
2,248
Reputation
4,506
Reaction score
2,250
Trophy points
1,393
Location
USA
Activity points
64,083
What datasheets tell you, and what the comparator really does,
diverge a lot depending on the input slew rate and overdrive
level. A very low overdrive (one that does not fully steer the
front end) blows out prop delay big-time. Usually the Tpd test
will be at a sensible minimum overdrive and you can count on
the comparator being faster if drivenfaster / harder. But with
a slow ramp as shown, your delay at low overdrive can end
up looking like an offset term and somewhat hysteretic (even
if DC hysteresis is nil).
 

Audioguru

Advanced Member level 5
Joined
Jan 19, 2008
Messages
9,437
Helped
2,150
Reputation
4,300
Reaction score
2,002
Trophy points
1,393
Location
Toronto area of Canada
Activity points
59,509
The graphs on the datasheets for the LM339 and LM393 comparators show 5mV, 20mV and 100mV override and the resulting different response times. It looks like the open collector output with a 5.1k load to +5.0V goes high (output transistor turns off) has about a 5 times longer response time than when it goes low.
 

D.A.(Tony)Stewart

Advanced Member level 5
Joined
Sep 26, 2007
Messages
7,096
Helped
1,727
Reputation
3,453
Reaction score
1,736
Trophy points
1,413
Location
Richmond Hill, ON, Canada
Activity points
52,022
but if you had to pay $1/picosecond Delay penalty charges, look how much you would save.
It's only ~$1/ps
vs $2.26 for 1.3ms or | $1.73Billion per picosecond.|:laugh:
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top