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lionelgreenstreet
Joined: 25 Sep 2008
Posts: 15
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 02 Oct 2008 13:12 Measure output range in opamp |
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If i want to measure the output range of an opamp in spice, there is a simple and accurate way to do it?
thanks in advance
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charkyriak
Joined: 05 Sep 2008
Posts: 8
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| 02 Oct 2008 16:15 Measure output range in opamp |
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The most common measurement for output range is 1dB compression point.....
maybe run a transient with large input signal and check where your output compresses....
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mpig09
Joined: 26 Aug 2005
Posts: 123
Helped: 6
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| 04 Oct 2008 16:08 Re: Measure output range in opamp |
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Dear lionelgreenstreet:
1.Try to hand calculate.
2.Input a big sine wave, to look the output swing.
mpig
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rfsystem
Joined: 25 Feb 2002
Posts: 797
Helped: 85
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| 04 Oct 2008 22:28 Re: Measure output range in opamp |
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Ok sometimes methods change but for 40 years th output range is measure by a specified decrease a performance number of an opamp.
The most typical is the DC-gain. So simply sweep the input DC while observing the AC gain at a low frequency. That could also be done a different loads.
If you want to make a quick, less accurate guess simply sweep DC in a noninverting buffer configuration and look at the input voltage difference.
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lionelgreenstreet
Joined: 25 Sep 2008
Posts: 15
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| 05 Oct 2008 10:05 Re: Measure output range in opamp |
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Thanks all for the answer
| Quote: |
| If you want to make a quick, less accurate guess simply sweep DC in a noninverting buffer configuration and look at the input voltage difference |
I've found in Allen's book a similar way to calculate output range of opamp: dc sweep of an opamp in inverting configuration done by two resistor with gain |-R2/R1|>1. (R2 is the resistor between Vout and Vin-)
I have some doubts about this configuration:
1)-R2/R1 is used greater than one to distiunguish icmr calculation (that is done by a dc sweep in buffer configuration):why limitations are done only by output stage in inverting configuration?
2) I have used this configuration to measure output range, later i've measured saturation range of all output mosfet: i've obtained two different ranges (first is larger than second):inverting method is useful or not?
thanks for the help
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Sadegh.j
Joined: 29 Nov 2006
Posts: 702
Helped: 32
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| 05 Oct 2008 21:45 Re: Measure output range in opamp |
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| Use Avanwave, increase the input amplitude and wait for the output to become nonlinear
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saro_k_82
Joined: 17 May 2007
Posts: 84
Helped: 14
Location: India
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| 06 Oct 2008 4:34 Re: Measure output range in opamp |
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| lionelgreenstreet wrote: |
I have some doubts about this configuration:
1)-R2/R1 is used greater than one to distiunguish icmr calculation (that is done by a dc sweep in buffer configuration):why limitations are done only by output stage in inverting configuration?
2) I have used this configuration to measure output range, later i've measured saturation range of all output mosfet: i've obtained two different ranges (first is larger than second):inverting method is useful or not?
thanks for the help |
1. The inverting configuration does not stress the input stage for linearity. The ICM is set and does not vary with the input voltage. So this is ideal for testing the output stage non-linearity (even with a gain of 1 or lower)
2. Even after the output mosfets moved out of saturation, the OL gain of the amp may be high and this prevents the non-linearity to some extent. This is the reason why manufacturers normally specify the output range with a definite load and within a gain limit (say within a CL gain of 5)
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