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OPA2107 dual op-amp, voltage swing versus load, voltage swing versus supply voltage

Kenneth Aquino
Expert 1300 points
Other Parts Discussed in Thread: TL072, OPA2107, LM741, OPA1642

Hi,

The data sheet does not have plots of output voltage swing versus output load, nor output voltage swing versus supply voltage.  The output voltage swing is specified in the data sheet for a 2 kOhm load with +/-15 volt supplies.  The TL072 has such plots, for instance.  Would someone at TI please provide these OPA2107 plots to me?  Also on my wish list with regards to the OPA2107 is a schematic for the op-amp, again there exists one for the TL072, for example.

Regards,

Ken

  • 0
    TI__Genius 12325 points
    Kenneth,
    The output swing vs. output loading was not characterized on this part (it is 26 years old) so this information is not available. The output swing vs supply voltage can be determined (for a 2k load) from the +/-15V supply data. In that case, the output swing is specified as +/-12V, so the OPA2107 is able to reach within 3V of it's power supply rails. You can use this value for other supply voltages. I should point out that the open loop gain is only specified to withing 5V of the power supply rails, this is a much better indicator of the linear output swing range.

    TI is no longer providing simplified internal schematics for op amps. There is still one in the TL072 datasheet because this is an older, commodity device.
  • 0 in reply to John Caldwell
    Expert 1300 points
    Hi Joh+

    I'll have to dust off my Meyers and Gray "Analysis and Design of Analog Integrated Circuits" that I used in a course where we analyzed the insides of an LM741 op-amp a few years ago. I'm running the OPA2107 with +/- 5.6 volt rails, I'm sure a lot of audio designs are running down that low using this part too. Kind of a rhetorical question, but is my design ok (open loop gain-wise, for instance) with low supplies like that?

    Ken
  • 0 in reply to Kenneth Aquino
    TI__Genius 12325 points
    Ken,
    I wouldn't run an old part like the OPA2107 with supplies that low and expect to achieve low distortion since the open loop gain is only specified to within 5V of either supply. That gives you +/-0.6V of linear swing. A modern part like the OPA1642 is going to perform vastly superior in that type of application.
  • 0 in reply to John Caldwell
    TI__Genius 12325 points
    Maybe it would be best to take a step back and ask, what are you trying to do? Do you have a schematic of the circuit and any specific performance goals?
  • 0 in reply to John Caldwell
    Expert 1300 points
    I can send you a schematic. I'm using the OPA2107 in a two stage transimpedance amplifier (TIA) setup. It's a unique TIA where I avoid the the high resistor feedback noise by using a capacitor in the feedback (basically an integrator stage one followed by a differentiator stage 2). This was suggested by Ciofi in a paper he published. I can send you the paper too. It's for a space (outer-space) application. I really wanted to use the OPA1642, but management didn't want to use it simply because we had to buy the die for the OPA2107 and get it packaged in a ceramic pkg. Having already done that, we were reluctant to do the same for the OPA1642. Unfortunately, I didn't find the OPA1642 until after we had spent all the time and money on packaging the OPA2107. The current signals on the TIA are from a photodiode and the maximum signal is -60 dBm which is 1 nA, at 1 kHz. You will see though that I have to put a 1GOhm resistor in the first stage feedback in order to provide a path for the OPA2107 curernts. This extremely large value was chosen to minimize the current noise. The 1st stage could see 3 nADC, so that DC current flows through the 1G causing the output to go to 1G x 3nA = 3 volts.
    How do I add attacments:
    Design goals are:

    Less than 15 fA/rt-Hz noise referred to the input in a bandwidth from 910 to 990 Hz.
    Transimpedance from detector to output = 1.07 GOhm
    Signal levels of 10 pA RMS to 1000 pA RMS; DC offset of up to 3.5 nA DC.
  • 0 in reply to Kenneth Aquino
    TI__Genius 12325 points
    Attachments can be added by clicking the "use rich formatting" option at the lower right corner of the text box. First, hopefully you are AC coupling the photodiode, otherwise the dark current alone could force the OPA2107 outside of its linear region. Is it possible to raise the power supply voltages you are using for the OPA2107? This seems like the best option to ensure linear operation.
  • 0 in reply to John Caldwell
    Expert 1300 points
    I'm running the quadrant detector (Hamamatsu GS6841), similar to a photodiode, in photovoltaic mode with zero bias, so there is almost no dark current. There is however a well specified amount of DC light (not dark current per se) hitting the GS6841 which could cause as much as 3 nA to flow. Not possible to raise the supply voltages at this point. Sacrilege, but I have an LTSPICE version of this desgin, can I send that to you?

    Ken