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OPA1637: Advantage of FDA

Part Number: OPA1637
Other Parts Discussed in Thread: LME49720

Hello experts,

I got question about merit of OPA1637 (Fully Differential Amp) compared with differential output circuit made by LME49720 (dual ch amp).

If we use audio signal(20Hz~20kHz), do OPA1637 have merit compared with the differential output circuit made by LME49720?

Customer expect OPA1637 have advantage for noise, THD+N.

Could you give me some advise?

Also, I would appreciate if you would tell me other advantage of OPA1637.

Thanks and best regards,

Ryo Akashi

  • Hi Ryo,

    Thanks for reaching out. Both of these amplifiers are very similar in voltage noise, however we could see a different overall noise performance due to the large difference in current noise.  Since the OPA1637 is a super beta input amplifier it has highly reduced input referred current noise.  The current noise can be converted into voltage noise and may be your dominant noise source depending on the resistor values used. We would have to run a simulation on your system to know which one will have better performance.

    In regards, to your question about the advantages of the OPA1637 there are a couple. An FDA does fully differential in to fully differential out using one amplifier compared to a discrete solution that uses two.  For this reason you usually see much less power being used when going with an FDA over the discrete solution. 

    Below is a spec-spec comparison of the two devices.

    Specifications OPA1637 LME49720
    Num Channels 1 2
    Vs min (V) 3 5
    Vs max (V) 36 34
    GBW (MHz) 9.2 55
    Slew Rate (V/us) 15 20
    Vn (nV/rtHz) 3.7 2.7
    In (fA/rtHz) 300 1600
    Rail-to-Rail --- No
    Iq typ (mA) 0.95 5
    Isc typ (mA) 31 26
    Ibias max (pA) 2000 72000
    Operating Temperature (°C) -40 to 125 -40 to 85
    Additional Features Super-β input N/A
    Price (web $) 1.25 | 1ku 1.10 | 1ku

    Regards,

    Tyler Noyes 

  • Hello Tyler-san,

    Thank you for your reply.

    I understand OPA1637 have some advantages (power consumption, current noise)

    Also, thank you for sharing the comparison table.

    Thanks and best regards,

    Ryo Akashi