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Noise screening on LMC6081

Bob Daniels
Prodigy 10 points
Other Parts Discussed in Thread: LMC6081

To TI E2E,

We are using  the LMC6081 in a transimpedance configuration with a feedback resistor of 500M and feedback capacitor of 3pF. The sensor on the input is a silicon photo detector with a resopnsivity of 150V/microwatt @532nm, capacitance of 500 – 600pF and a  shunt resistance of 1GOhm. This is being made for us by the detector manufacture who wire bond the detector, LMC6081 die, resistor and capacitor and is mounted inside a TO-5 package with a glass window. We are having a low yield of passing units because of various noise failures.

The types of noise were getting are popcorn, dc jumping, drop outs and burst. The output signal level is in the hundreds of millivolts and the noise levels are around 30 to80 microvolts. Time scale is 30 minutes, sampling at 0.5 seconds. I can provide data plots if needed.

Do you know of any noise issues with the LMC6081? What type of noise test screening is done on the die at TI? Can you help provide some assistance in understanding the failure modes (likely causes and possible fixes).

Regards,

Bob Daniels

  • 0
    TI__Guru 55056 points
    Hello Bob,

    We do not do any specific noise screening for the standard LMC6xxx products. CMOS devices are not known for popcorn noise and we have not had any issues with popcorn on this process in the past. Production noise tests are VERY, VERY expensive and are not normally done unless there is a major issue.

    How long has this design been in production? What is the failure rate and volume? Was it always bad? Have you had any issues with packaged parts on a breadboard? Has *ANYTHING* changed in the production flow?

    I recently had a similar case where the popcorn noise was traced back to tiny 0201, high value SMT resistors. Don't assume it can only be the amplifier. Be suspicious of everything - even mechanical.

    Have you tried bread-boarding with the *exact* same components used in the module? The commercial LMC6081 bare die is the same as the die in the packaged parts, so bench testing with a packaged part should be comparable. Tiny SMT parts can be mounted on 0.1" headers with wire and plugged into a standard breadboard for testing (and swapping). If the failure rate is so high, then you should be able to duplicate the noise on the bench.

    If possible, please provide the schematic and a scope shot of the noise. The levels and edges of the popcorn noise can tall us a lot.

    I also assume you have ruled out common interference like nearby cell phones and WiFi - they can create packet "bursts" that can look random at slow speeds.

    Regards,