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ADC081S021: ADC081 and OPA615

Harun Tetik
Prodigy 130 points
Part Number: ADC081S021
Other Parts Discussed in Thread: OPA615

Hi,

I want to build a circuit like the one below. There is an analog output of transimpedance amplifier. The amplitude of signal is between 0-3.3V, and the pulse width 10 ns. I want to use this analog signal on ADC and comparator input. My goal is to get the maximum value of the analog signal.

This is my simulation result. The green signal is analog voltage and the blue signal is comparator output.

How can i read the maximum value of analog signal with using comparator output?  Is sample and hold ADC appropriate for this operation? Or can i handle it with OPA615?

Thanks for helps.

  • 0
    TI__Mastermind 24940 points

    Hello

    I will need to take a deeper look at this, please allow a time to get my own simulations built and analyzed.

    To answer your questions, the ADC will be needed to read the analog input and convert it to the master device.

    The CS signal controls internal switch for begin hold mode. At the falling edge of CS, the Sample and Hold switch, that connects the analog input to the ADC, is opened. That means that the analog input voltage at the input channel when CS has a falling edge is the voltage level that will be converted.

    From your simulation, the circuit will not capture the max point of the analog input, but actually the instance after.

    Thus you want the falling edge of CS to be at the max analog input.

     

    If you are only interested in capturing the max point, have you considered monitoring ADCs

    For example the ADS7038 can monitor an analog input for a trigger voltage. The ADC will not output or convert until the analog input crosses the trigger voltage it is programmed to monitor for. Say 2.75V, once the analog input crosses this threshold, the ADC will start converting and output the measurement.

     

    Regards

    Cynthia

     

  • 0 in reply to Cynthia
    Prodigy 130 points

    Hello,

    Thank you for your help. 

    Cynthia said:
    From your simulation, the circuit will not capture the max point of the analog input, but actually the instance after.

    Yes, you are right. I am trying to handle it. If you have suggestions, let me know.

    Cynthia said:
    If you are only interested in capturing the max point, have you considered monitoring ADCs

    Yes, i am only interested in capturing the maximum value. But it can be millivolts.

    Cynthia said:
    I will need to take a deeper look at this, please allow a time to get my own simulations built and analyzed.

    I am waiting for your simulations.

    This is my spice simulation. Maybe it can help you.

    Best regards.

  • 0 in reply to Harun Tetik
    TI__Mastermind 24940 points

    Hello,

    In the meantime, I strongly recommend looking at the ADS7038,

    This device has a feature that will greatly simplify what you are trying to achieve.

    This device can hold the maximum and minimum of the data input of each channel. The max value will be stored in a register and will remain there until a new higher input is measured. This feature is further explained starting on page 20 of the datasheet 

    Regards

    Cynthia