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JOHN35

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help
Jul 04^th, 2015, 5:54am

hi , i have designed two stage open loop comparator. i want to check for the offset voltage. i have made unity gain feedback configuration. is this the correct way to know the offset voltage. i have designed it in 65nm technology. power supply in 1.2 v, 0v (vss). i have given 500mv at noninverting termina. inverting terminal i have connected to output.

please help me. thanks in advance.

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sheldon

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Re: help
Reply #1 - Jul 4^th, 2015, 6:59pm

John,

In general, comparators behave differently than op amps. In this
case it might be better to perform a dc sweep and 0.495 -> 0.505
and see when the output voltage goes to the mid range of the
logic level at the output. Since you have not given much detail,
your comparator may have hysteresis so you will need to perform
the sweep in the opposite direction, 0.505 -> 0.495 then average
the results.

Sheldon

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JOHN35

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Re: help
Reply #2 - Jul 6^th, 2015, 3:13am

Thank you so much sheldon, actually i haven't used any external hysteresis network. and i got logic high value (VOH) approximatley 1.1 V . i didn't get full supply voltage. when i include two more stages i could get nearly 1.16 V.
i will tell my observations:
i have operated in the range of 480mV to 820mV

1st obs: when i maintain 1mV difference between two terminals i got high state >1V (actually it is not fixed as input changing it is changing that is why i have told >1V). low state as (<93mV)

2nd obs:for same dynamic range with 2mV difference between terminals VOH>1.12V VOL<42mV

3rd obs: for 3mV difference VOH>1.14V VOL<21mV

dynamic range : (820-480) 340mV

i am new to analog design. if i ask nonsense questions please forgive me. i am willing to learn the concepts. and i am very much thankful to the "DESIGNER'S GUIDE COMMUNITY" as it is spreading knowledge through out the world.

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