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.
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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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-mora//research/fA_meter.pdf
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