Driving analog data convertor AD7823 with an op-amp

Hello,

I'm interested in using an op-amp to drive an AD7823 data convertor.

Maximum gain required is about ~30, since I can use a ref voltage as low as 1.2V on the AD7823. Required bandwidth operation is 100KHz.

I have no requirements on the op-amp except that the supply range should be between 3v to 5v. However, I do prefer to use a single supply op-amp. I'm not sure whether I should choose an op-amp with a differential output, which according to my understanding, will be more accurate (Will the AD7823 be able to work with it?) or a single ended output with a common ground to the ADC Vin- input?

After reading some application notes I became a little bit confused with all the configurations out there and would appreciate some help...

Thanks in advance,

regards,

Eyal

  • Hi-

    I have moved this question to the ADC Drivers community.  Someone here should be able to assist you.

    Thanks,

    AndyR

    EngineerZone Community Manager 

  • Thank you Dan,

    My main concern about using a single ended op-amp is noise or cross talk from other ground loops using the same ground reference point. Are there any differential-output amplifiers you can recommend that will work well with the AD7823?

    Eyal

  • 0
    •  Analog Employees 
    on Oct 10, 2012 5:33 AM over 8 years ago

    Hello Eyal,

    On the question of using a single-ended vs. a differential-output amplifier, it generally depends on the level of precision you are trying to obtain. Since the AD7823 is an 8-bit ADC, it's LSB size with a  1.2V reference, one-half of an LSB is 2.3mV and its SINAD is 48 dB, so you won’t have any issues finding an amp that meets the noise/precision limits of the ADC.

    Below is a list of op amps that you may want to consider, depending on your total set of application requirements. Since the AD7823 is a low-power ADC, I focused on quoting some low-power op amps for you.

    Please let us know if you have any further questions.

    Best regards,

    Dan

    Part
    Number
    Special Features Amps
    per
    Package
    Feedback
    Type
    Temp Range Vsupply
    Span
    (Min)
    (V)
    Vsupply
    Span
    (Max)
    (V)
    Iq
    per
    Amplifier
    Rail-to-Rail
    In
    CMRR @ Min Gain
    (dB)
    Ib Vos @ Min Gain Rail-to-Rail
    Out
    Vnoise Density
    @ Min Gain (RTI)
    Vnoise
    0.1-10 Hz
    Bandwidth Slew
    Rate
    Stable
    Close-Loop
    Gain
    (Min)
    (V/V)
    Budgetary
    Price
    (USD)
    AD8601 1 Voltage -40 to 125°C 2.7 6 1.2 mA Yes -80 200 fA 500 uV Yes 18 nV/rtHz 6 V/us 1 0.36
    AD8602 2 Voltage -40 to 125°C 2.7 6 1.2 mA Yes -80 200 fA 500 uV Yes 18 nV/rtHz 6 V/us 1 0.44
    AD8604 4 Voltage -40 to 125°C 2.7 6 1.2 mA Yes -80 200 fA 500 uV Yes 18 nV/rtHz 6 V/us 1 0.90
    AD8605 1 Voltage -40 to 125°C 2.7 6 1.2 mA Yes -100 200 fA 20 uV Yes 6.5 nV/rtHz 2.3 uV p-p 5 V/us 1 0.68
    AD8606 2 Voltage -40 to 125°C 2.7 6 1.2 mA Yes -100 200 fA 20 uV Yes 6.5 nV/rtHz 2.3 uV p-p 5 V/us 1 1.19
    AD8608 4 Voltage -40 to 125°C 2.7 6 1.2 mA Yes -100 200 fA 20 uV Yes 6.5 nV/rtHz 2.3 uV p-p 5 V/us 1 1.58
    AD8615 1 Voltage -40 to 125°C 2.7 6 1.7 mA Yes -100 200 fA 80 uV Yes 7 nV/rtHz 2.4 uV p-p 12 V/us 1 0.76
    AD8616 2 Voltage -40 to 125°C 2.7 6 2 mA Yes -100 200 fA 23 uV Yes 6 nV/rtHz 2.4 uV p-p 12 V/us 1 1.29
    AD8618 4 Voltage -40 to 125°C 2.7 6 2 mA Yes -100 200 fA 23 uV Yes 6 nV/rtHz 2.4 uV p-p 12 V/us 1 2.29
    AD8657 Micro Power, Precision, RRIO 2 Voltage -40 to 125°C 2.7 18 22 uA Yes -95 20 pA 350 uV Yes 50 nV/rtHz 5 uV p-p 70 mV/us 1 0.95
  • Eyal, I think we need to know a little more about your application, in particular your input signal source. In particular:

    A) What is the signal range (positive and negative) and impedance?

    B) What is the signal referenced to i.e. is it floating, is it ground referenced or does it have a large offset.

    The large LSB step size of an 8 bit converter should help you, so you need to focus on ensuring that the error sources for the amplifier are managed.