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Old 26th September 2012, 01:48 AM   #1
WSJ is offline WSJ  United States
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Default Characterization and Testing Operational Amplifiers

Understanding DC characteristics, AC characteristics, settling time, slew rate and bandwidth for an Op-Amp and the limitations these parameters encounter in actual circuits is critical for audio equipment designers. This project will introduce designers to testing the properties of Op-Amps.

Here are a few Parameters that can be measured with the test fixture:

Vos - Input off set voltage.
+IB - Input bias current.
-IB - Input bias current.
IOS - Input offset current.
SR - Slew Rate
fp - Full power bandwidth.
AVol - Open loop DC voltage gain.
Xf - Unity gain bandwidth or gain bandwidth product.
CMRR - Common mode rejection ratio.
RL - The output driving a resistive load at the output.
CL - The output driving a capacitive load at the output.
CMR - Common mode range.

Additional tests can be added as needed.
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Last edited by WSJ; 26th September 2012 at 07:06 AM.
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Old 26th September 2012, 04:38 AM   #2
Frex is offline Frex  France
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Hello,

All of these parameters are already measured in the datasheet from manufacturer, why do you want to measure them again ? For sorting better parts in a lot of same ?
Regards.

FRex
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Old 26th September 2012, 06:25 PM   #3
WSJ is offline WSJ  United States
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Quote:
Originally Posted by Frex View Post
Hello,

All of these parameters are already measured in the datasheet from manufacturer, why do you want to measure them again ? For sorting better parts in a lot of same ?
Regards.

FRex
Production testing may not include all of the DC parameters and most likely none of the AC parameters. The AC characteristics and distortion vary form one device to the next and can be surprisingly different between manufactures. I have evaluated hundreds of Opamps and seen many fall short of the published performance. Who knows what Opamps are counterfeits? Once you have the test equipment to evaluate different Opamps you will be surprised at the variations.


Test Parameter Requirements vs Test Time

Not all devices are tested equally. Testing adds costs, so low cost components are rarely tested completely, whereas medical or high costs components (where reliability is important) are frequently tested.

But testing the device for all parameters may or may not be required depending on the device functionality and end user. For example if the device finds application in medical or life saving products then many of its parameters must be tested, and some of the parameters must be guaranteed. But deciding on the parameters to be tested is a complex decision based on cost vs yield.
Automatic test equipment - Wikipedia, the free encyclopedia


Production Testing Strategy

Characterization vs. High Volume Production
* It is not cost effective to extensively test all parameters in production
* Generally a shorter test list is sufficient to guarantee performance
* Key data sheet and predictive parametric items should be selected

AC versus DC testing
* Precision Opamps have a test list dominated by DC parameters
* High speed Opamps may have mostly AC parameters tested
* This presentation focuses on DC testing

http://users.ece.gatech.edu/rincon-m...h/fA_meter.pdf
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Old 27th September 2012, 01:54 AM   #4
WSJ is offline WSJ  United States
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Inside the Opamp test fixture
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Old 28th September 2012, 04:58 PM   #5
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Nice. Instrumentation engineering
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Last edited by OnAudio; 28th September 2012 at 05:03 PM.
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