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REF200: The current source REF200 simulates PMT to test TIA and fails.

Xander
Prodigy 20 points
Part Number: REF200
Other Parts Discussed in Thread: LOG200

Tool/software:

Hello, engineers from Texas Instruments,
We are planning to test the logarithmic amplifier, but the REF200 we are using cannot simulate the PMT (-100uA-0uA). When it enters the current mirror, the current direction is changed through the series ammeter to become positive 2mA-3mA. As shown in the figure, the red part should normally display -100uA to 0uA. I am confused about this, please help me.

The log200 chip is in our plan. Currently, we use this circuit to simulate our system design and calibrate the optical system.

  • 0
    TI__Expert 5690 points

    Hello,

    Thanks for including a schematic with the question. Looking at your schematic and block diagram, I cannot tell where the ammeter is measuring. Where is the current being measured in the schematic? I also notice that two of your resistors are variable resistors. What resistance values are they being used at?

    Thanks,

    Jackson

  • 0
    Prodigy 20 points

    Hello, Jackson

    I used an ammeter with a measurement range of +-700uA in series between the current source and the amplifier circuit, right at the position of the red circle, so I got the result that the current was changed.

    I used the current source in the third picture to simulate the -100uA to 0uA current output of the PMT module. The purpose of the sliding resistor is to adjust the negative current output. I need to make current values ​​like -90uA, -80uA, and -50uA to calculate the voltage value of the logarithmic amplifier output to confirm the performance of the TIA circuit we designed.

    The positive current output on the right side of the current source circuit has been confirmed and can be used in the linear amplifier circuit for testing. The current problem is that the negative direction cannot be driven. The reason is being sought. I hope to find a stable means to confirm the input and output of the logarithmic amplifier and the related performance of the current reversal circuit.
    For the PMT simulation circuit on the left side of the circuit, I planned to adjust the current output by changing the resistance value of R1, but I found that the logarithmic amplifier or the current inversion part seemed to have a bias current effect on the input, as high as about 3mA, causing the -100uA I designed to disappear completely.

    I don’t know if this test method is feasible for logarithmic amplifiers. I hope you can give some suggestions here.

  • 0
    Prodigy 20 points

    The PMT module we use is the H10720 from Hamamatsu Electronics, and the main parameter used is the current output.

    Thanks，

    Xander

  • 0 in reply to Xander
    TI__Expert 5690 points

    Hi Xander,

    Thanks for the additional details. I'm not noticing anything wrong with your schematic where the REF200 is used. When you vary the resistance on R2, does the current measured in the ammeter stay constant or vary as the resistance changes?

    Can you measure the voltage drop across R2 like so and let me know what you find?

    Also, if you were to change R1 to 10kΩ, what is the current that you are measuring on the ammeter?

    Thanks,

    Jackson