OPA857: OPA857

Prodigy 20 points

Replies: 5

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Part Number: OPA857

Good Afternoon,

The Transimpedance gain error is 1% typical and 15% maximum. I understand that the 15% take into account all the variability within a production wafer and very wafers.

What kind of typical variation can we expect to have on this parameter for a wafer ?

Best Regards,

Michel Tremblay

5 Replies

  • Hello Michel,

       If you mean the variation in the parameter for the OPA857-DIE, it would be very similar. There are some certain stresses caused by packaging; however, it would not change this parameter drastically. 

    Thank you,

    Sima

  • In reply to SimaJalaleddine:

    Good Morning,

    Thank You for the answer  but it is not what I am asking.

    The Data Sheet specifies a Transimpedance Gain variation of typical 1%

    with a maximum 15% which is very high compare to the 1% typical.

    On any given wafer, what is the range of value of this specific parameter

    that we can expect ?

    A 15% variation for this parameter seems to be very high taking into account

    The fact that it should be controlled by a resistor.

    Best Regards,

    Michel Tremblay

  • In reply to Tremblay Michel:

    Hello Michel,

       The max/typical specs are based on the Gaussian distribution. Within +/- one standard deviation, about 68 percent of the device population will have a value at typical or lower. There will never be a device greater than the max specification. The 15% variation for the parameter is explained in the OPA857 datasheet: "Note that the 2-kΩ internal resistance used for the V-to-I conversion is not trimmed and can vary ±15% with process. Therefore, the source must be capable of sourcing both dc and ac voltages to make sure that the output voltage swing is compliant with the class-A output stage of the TIA block. Any change in the test circuit configuration (such as gain change) requires a new calibration of the internal V-to-I converter."

    Thank you,

    Sima

  • In reply to SimaJalaleddine:

    Thank you for your answer. I understand that the gain variation of +/- 15% applies only when used in the ' Test Mode ' without a photodiode.

    If the OPA857 is used with a photodiode in normal use, what is the gain range that we can expect on the Transimpedance gain of 18.2 KOhms and 4.5 Kohms

    assuming the load is as specified ?

  • In reply to Tremblay Michel:

    Hello Michel,

       I believe the same concept would be applied; which would mean the internal resistors that set the transimpedance gain and Rout are not trimmed. This is the reason you would see the same 15% variance, but instead in the transimpedance gain. 

    Thank you,

    Sima