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OPA207: OPA207 Spice model issue

Part Number: OPA207
Other Parts Discussed in Thread: OPA1692, OPA1641

Hi,

I'm having some problem with the OPA207 PSpice model in LTSpice (sorry, I can't use TINA as I only have a Mac).  The model is giving me what looks like incorrect noise figures.

In the case of an isolated amp, non-inverting, unity gain, +ve terminal grounded, LTSpice is giving me 8.47nV/rtHz vs 7.5nV/rtHz in the datasheet

In the case of the above but with a 64k source impedance, LTSpice is giving me 59.86nV/rtHz versus a calculated value of 35.24nV/rtHz

If I change the opamp to an OPA1692, LTSPice and a calculated value strongly agree - 40.3nV/rtHz for LTSpice vs 40.39nV/rtHz calculated

I know it is not your responsibility to respond to LTSpice issues but I'm wondering if there is an issue in the model.  I can't cross-check on TINA unfortunately.

Andy advice would be welcome.


REgards,

ac

  • Hi Andrew,

    Could you post the  OPA207 LTSpice model over E2E and I will compare it with Tina noise model? You realized that not all Ti's macro model features are used or compatible with LTSpice simulation. You may have to apply some sort of noise correction in order to make them identical. 

    Best,

    Raymond

  • Hi Raymond,

    Thanks for the reply. What exactly do you want me to send? The model is from the TI site - SBOMAJ1A.zip and I used the OPA207.lib in that package.

    Do you need me to send the circuit that I used in LTSpice?

    Regards,

    AC

  • Hi Andrew,

    Please send me the noise circuit in LTSpice. I will compare them on my end.  

    Best,

    Raymond

  • Attached

    Input Stage.asc.txt
    Version 4
    SHEET 1 984 716
    WIRE 544 144 352 144
    WIRE 352 240 352 144
    WIRE 400 240 352 240
    WIRE 544 256 544 144
    WIRE 544 256 464 256
    WIRE 608 256 544 256
    WIRE -64 272 -112 272
    WIRE 64 272 16 272
    WIRE 400 272 64 272
    WIRE -112 304 -112 272
    WIRE 544 384 352 384
    WIRE -112 416 -112 384
    WIRE -112 416 -160 416
    WIRE -112 432 -112 416
    WIRE 64 432 64 272
    WIRE 352 480 352 384
    WIRE 400 480 352 480
    WIRE 544 496 544 384
    WIRE 544 496 464 496
    WIRE 608 496 544 496
    WIRE 400 512 352 512
    WIRE -288 528 -288 496
    WIRE -288 528 -352 528
    WIRE -160 544 -160 416
    WIRE -112 544 -112 512
    WIRE -112 544 -160 544
    WIRE 352 544 352 512
    WIRE -352 560 -352 528
    WIRE -288 560 -288 528
    WIRE -112 560 -112 544
    WIRE -112 656 -112 640
    WIRE 64 656 64 512
    WIRE 352 656 352 624
    FLAG -112 656 0
    FLAG -352 560 0
    FLAG -288 416 Vcc
    FLAG -288 640 Vee
    FLAG 64 656 0
    FLAG 432 224 Vcc
    FLAG 432 288 Vee
    FLAG 608 256 Out1
    FLAG 432 464 Vcc
    FLAG 432 528 Vee
    FLAG 352 656 0
    FLAG 608 496 Out2
    SYMBOL voltage -112 544 R0
    SYMATTR InstName V1
    SYMATTR Value 1
    SYMBOL voltage -288 544 R0
    SYMATTR InstName V2
    SYMATTR Value 15
    SYMBOL voltage -288 400 R0
    SYMATTR InstName V3
    SYMATTR Value 15
    SYMBOL res 32 256 R90
    WINDOW 0 0 56 VBottom 2
    WINDOW 3 32 56 VTop 2
    SYMATTR InstName R1
    SYMATTR Value 122k
    SYMBOL res 80 528 R180
    WINDOW 0 36 76 Left 2
    WINDOW 3 36 40 Left 2
    SYMATTR InstName R2
    SYMATTR Value 128k
    SYMBOL res -128 288 R0
    SYMATTR InstName R3
    SYMATTR Value 6k
    SYMBOL ind -128 416 R0
    SYMATTR InstName L1
    SYMATTR Value 5
    SYMBOL Opamps/opamp2 432 192 R0
    SYMATTR InstName U1
    SYMATTR Value OPA207
    SYMBOL voltage 352 528 R0
    SYMATTR InstName V4
    SYMATTR Value 1
    SYMBOL Opamps/opamp2 432 432 R0
    SYMATTR InstName U2
    SYMATTR Value OPA207
    TEXT -504 96 Left 2 !.temp 25
    TEXT -56 32 Left 2 !.include OPA207.lib
    TEXT -56 64 Left 2 !.include OPA1692.lib
    TEXT -504 64 Left 2 !.noise V(Out2) V4 oct 100 10 12k
    TEXT -504 32 Left 2 ;.noise V(Out1) V1 oct 100 10 12k
    

  • Hi Andrew,

    I run the comparison, and both simulation indicated that they are very similar. Sorry, I did not fix the proper noise density spectrum units. The datasheet is specified as typical, but the simulation is shown that both sets of data are comparable. 

    Best,

    Raymond

  • Hi Raymond,

    Many thanks for taking the time to run those sims. I understand that the data sheet gives typical values.  However, running the same sim with OPA1641 and OPA1692 gives essentially identical results between model and data sheet so I would expect OPA207 model to be pretty close to the data sheet.

    The difference between model and data sheet is around 1nV/rtHz for input noise voltage. If you include a source resistance - I have a 64k source resistance - and work out the calculated vs. simulated input noise current then you can see a bigger difference between model and data sheet.  For example, the model gives 60nV/rtHz vs a calculated value of 49.75nV/rtHz.  If you then take the model value and work backwards to find the input noise current it comes out at 0.77pA/rtHz vs a data sheet value of 0.18pA/rtHz.  So it looks to me that there is a discrepancy between model and data sheet.

    Having said all that, I don't want you to spend your time responding to this thread.  The OPA207 is not the best choice for a high source impedance anyway so I'll either use a JFET input opamp or a discrete JFET stage.  I can still use the OPA207 effectively in subsequent stages as long as the source impedance is low(ish).

    Happy to mark this thread as "answered"

    Regards,

    ac

  • Hi Andrew,

    keep in mind that the noise data of datasheet are only typicals which can widely vary from chip to chip.

    Many years ago we had to screen all of our NE5534 for the use in a professional audio application. We had to hand select the NE5534 for ultra low noise because we found that even many of the NE5534A (low noise version of the NE5534) showed too much noise. We had three groups, one group containing the lowest noise devices for the use in high gain microphone amplifier stages, another group with noisier devices for high gain but less demanding amplifier stages and a third group for low gain amplifier stages. 5% of all screened NE5534 fell in the lowest noise group, 50...70% fell in the second group and about 30% fell in the third group. 10...30% of the devices, depending on the batch, couldn't be used at all and would be better placed in the dustbin.

    Kai