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ankitgarg0312
Joined: 08 Feb 2008
Posts: 6
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 21 Aug 2008 13:34 opamp gain and offset |
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for a single supply opamp (single ended) :
How op amp gain affects systematic offset.
how can we decrease systematic offset in opamp design
Thanks
Ankit
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kwkam
Joined: 25 Feb 2002
Posts: 281
Helped: 11
Location: Somewhere on earth
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| 21 Aug 2008 16:17 opamp gain and offset |
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| opamp's open loop gain can save systematic offset. To reduce this offset, you have go inside the circuit and find where is the source of offset and correct.
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drDOC
Joined: 17 Jul 2008
Posts: 50
Helped: 6
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| 21 Aug 2008 16:21 opamp gain and offset |
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Just work differentially and as symmetric as possible.
When you go from a differential to single side stage you surely need a diode connection. Be sure that the other side of the circuit, which does not has the diode connection, is working on the same voltage as the diode connection.
From there one your systematic offset should be gone. And now you can minimize the stochastic offset by looking at mismatch, and healthy layout.
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ankitgarg0312
Joined: 08 Feb 2008
Posts: 6
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| 22 Aug 2008 5:09 Re: opamp gain and offset |
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" Be sure that the other side of the circuit, which does not has the diode connection, is working on the same voltage as the diode connection.
"
is there any other source of systematic offset other than this..
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rfsystem
Joined: 25 Feb 2002
Posts: 798
Helped: 85
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| 23 Aug 2008 17:33 Re: opamp gain and offset |
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Mostly the systematic offset comes at the stage where you convert from symmetric to asymmetric. Design the VDSAT of the active loads equal to the VDSAT of the output stage active device.
The you get a balanced active load voltage.
Did not try to make it extreme balanced. Mismatches are already imbalance.
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drDOC
Joined: 17 Jul 2008
Posts: 50
Helped: 6
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| 25 Aug 2008 10:28 Re: opamp gain and offset |
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| Quote: |
| is there any other source of systematic offset other than this.. |
Systematic stress due to layout causing systematic mismatch. So watch your layout!
Thermocouple effect due to a heat gradient on-chip. So watch where you place the power consuming output stage.
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ytliang
Joined: 04 Aug 2008
Posts: 61
Helped: 5
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| 27 Aug 2008 4:38 opamp gain and offset |
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How op amp gain affects systematic offset.
- the gain amplifies the offset
how can we decrease systematic offset in opamp design
- make your transistors larger (both W and L) to reduce the offset.
- use layout techniques to reduce the mismatch.
- use offset cancelation techniques such as switch capacitor etc...
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