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MPY634: How to improve "Input offset voltage" problem?

Prodigy 20 points

Replies: 3

Views: 63

Part Number: MPY634

Dear Sir, 

We are looking for a Multiplexer such as AD633 and MPY634.

As a test result, we have a trouble in input Vos...

we need a precision accurate Vout for next amplifier, if there exists any offset that would be amplified on next stage even it seems minor...

Is there any multiplexer TI solution that Vos <3mV?  

  • Hello Alice,

    The AD633 and MPY634 are 4-quadrant analog multipliers, which provides a much different function than a multiplexer. It is not clear if you are seeking a lower offset multiplier, or a multiplexer consisting of analog switches (for example TMUX1112)?

    Assuming you are looking for a lower offset analog multiplier the only analog multiplier device that TI still produces is the MPY634. All others have been discontinued. Therefore, we have no other device to suggest that provides that same function. The MPY634 datasheet does show in FIGURE 2, Basic Multiplier Connection, how a potentiometer can be added to the X2 input to adjust and reduce the offset. That circuit requires the addition of a few extra resistors and a potentiometer, and a manual adjustment. That isn't necessarily convenient, but it is an option for lower offset.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • In reply to Thomas Kuehl:

    Hello Thomas, 

    Yes, you got me. sorry I'm not English native speaker, I confused  "Multiplexer" with "Multiplier".But you are really smart, your answer hit the spot!

    As long as AD633 has the same optional trim for error source, we have already tried it on AD633 before, but the result was still not fulfilling.

    So, may I ask... do you have any further solution or related documents of MPY634 user-trimming circuitry test report...

    Thank you very much

    Best regard

  • In reply to Alice Meng:

    Hi Alice,

    You did just fine with your English; multiplexer and multiplier are quite similar in their spelling and could be easily confused when English is not one's first language.

    The MPY634 is a legacy analog function circuit. Burr-Brown introduced the product more than 30 years ago. Many analog multiplier functions have moved to digital methods of multiplication which is why the analog methods are less common today.

    There isn't a TI/Burr-Brown application note that specifically addresses user offset trimming. It is fairly straightforward as the MPY634 datasheet indicates. You would simply set the MPY634 with zero volts on the X1 and Y1 inputs (see datasheet Fig. 2) and adjust the potentiometer until Vout is as close to zero volts as possible.

    There is one applications note on the MPY634, but it doesn't really talk about adjusting the offset. However, it does provide further explanation of how the analog multiplier functions and provides a couple of applications circuits. Here's a link to that note:

    http://www.ti.com/lit/an/sbfa006/sbfa006.pdf

    Regards, Thomas

    Precision Amplifiers Applications Engineering