AD7124-4 Pseudodifferential

Good day,

I use from a Pseudodifferential opamp architecture at the inputs of ADC. It means that the inputs comming from the Sensor will be amplifier at gain=50 and shifted by 1.5V and finally goes to AIN_P.

On the other hand, 1.5V also is connected to AIN_N.

My Question: is it possible to remove the final amplifier stage and instead, use from the internal PGA of AD7124?

I already did this for differential configuration but for the Pseudodifferential I have no idea how to shift the level by 1.5V for internal PGA.

Thank you for your time and considerations.

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  • Hi, 

    I have few clarifications. Can you share what is your sensor, its specs and its output range? If you can share more info esp. the expected output voltage range from the sensor then that would be great. 

    Thanks,

    Jellenie

  • Hi,

    It's good to note that for Impedance matching purposes I already used from the ADA4528-2 as unity gain amplifier between the sensor output and amplifier inputs.

    So the signals comming to the amplifier indicated in the figure are already buffered. 

    Don't worry about the 20R resistors.

    Thank you.

  • Hi, 

    Apologies. I missed this one. 

    If the bridge is also supplied using single supply. Then I suspect that the common mode is positive? So I am not sure why do you need to shift it by 1.5V? If the output voltage at Senor P and Sensor N is positive and is within the ADC input voltage range then you do not need an external amplifier. 

    And one more thing, I would also suggest to configure your system in a ratiometric configuration wherein the reference and excitation voltage used are the same. Please see this reference circuit you can use this as a reference, It uses different product but the same scheme/approach can be use. CN0102 Circuit Note | Analog Devices though AD7124 can only operate up to 3.6V so 3.3V excitation can be use. 

    Thanks,

    Jellenie

Reply
  • Hi, 

    Apologies. I missed this one. 

    If the bridge is also supplied using single supply. Then I suspect that the common mode is positive? So I am not sure why do you need to shift it by 1.5V? If the output voltage at Senor P and Sensor N is positive and is within the ADC input voltage range then you do not need an external amplifier. 

    And one more thing, I would also suggest to configure your system in a ratiometric configuration wherein the reference and excitation voltage used are the same. Please see this reference circuit you can use this as a reference, It uses different product but the same scheme/approach can be use. CN0102 Circuit Note | Analog Devices though AD7124 can only operate up to 3.6V so 3.3V excitation can be use. 

    Thanks,

    Jellenie

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