Can I use an OP77 ultra low noise opamp on a single power supply?

Discussion in 'The Projects Forum' started by Spottymaldoon, Jun 10, 2016.

  1. Spottymaldoon

    Thread Starter Member

    Dec 4, 2015
    I am working on a trace gas analyzer that requires an extremely high gain, low noise input stage and I have had very good results using Analog Devices' OP77 with a huge feedback resistor (10G ohm) and a gain of 1000. My input is DC and always positive.

    Up until now I have powered this with ±5V. Can this device operate on +5V power alone and, if so, what is the disadvantage?

    If this can't be done can you recommend an alternative device?
  2. wayneh


    Sep 9, 2010
    It's fine. All op amps operate on a single supply: They have two power pins with a ∆V across them. As long as the inputs stay within the common mode range, it works. Some op-amps have a CMR that includes both power rails. That's called "rail-to-rail". Some have a CMR that includes only one of the power rails. Those are called"single supply". Op-amps that cannot sense at either rail are often called "dual supply".
  3. bertus


    Apr 5, 2008

    The OP77 will not work for rail to rail.
    If you want rail to rail functionality, have a look at the following table.
    There is given I/O for rail-to-rail in and output and O for output rail-to-rail only.


    Also have a look at appendix A of the attached PDF for single supply circuits.

    ronv likes this.
  4. Spottymaldoon

    Thread Starter Member

    Dec 4, 2015
    Weyneh and Bertus, thanks for your prompt and useful replies - I don't need rail to rail as I have flexibility on my V+. I plan to connect the OP77 output directly to a 16 bit AD converter which has a nominal 0-6V input range
  5. SgtWookie


    Jul 17, 2007
    The OP77's output cannot get within about 1 volt of the negative rail, even with an output load impedance > 10k. If you absolutely have to use a single supply rail, the OP77 will not be suitable unless it's output will always exceed about 1.5v.
  6. crutschow


    Mar 14, 2008
    What voltage swing do you need from the output op amp?
    Does it need to go down to zero volts?
  7. Spottymaldoon

    Thread Starter Member

    Dec 4, 2015
    SgtWookie and Cutschow, thank you for your inputs which are both sensible and useful. The nature of this type of measurement is that there is a moderate dc background level with the signal I am measuring which, so I hope, will translate to at least 1.5V of the total signal - a background that I'd need to remove in any case. The OP77, for all its limitations, seems a unique device with respect to its low noise, high intrinsic gain and high input impedance and I have used its predecessors with great success in the past with dual supplies. Of the multiple powered systems in the instrument, only the electrometer needs ± supply and so I'm hoping to eliminate that. However the proof of the pudding will come shortly when I run the thing up after almost a year of machining and building a set of circuits which are all new to me - I have had wonderful help here at All About Circuits: especially with a novel UHF driver which powers a special electrodeless lamp (photoionization) - I couldn't be more grateful for all you guys' help.
  8. Lestraveled

    Well-Known Member

    May 19, 2014
    Have you considered using a switched capacitor negative voltage converter like an LTC1144? This chip and two capacitors will give you a negative voltage almost equal to the positive supply at low currents. They are very convenient. There are a lot of these type chips around. Google,"switched capacitor voltage converter".
    wayneh likes this.
  9. Spottymaldoon

    Thread Starter Member

    Dec 4, 2015
    Lestraveled - no I hadn't and confess these devices are new to me. It could be a very good way to go but I need to check on the potential interference from the device's switching frequency with my super-sensitive opamp config - both through the supply rail and by radiation. Thanks for the idea.