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TLV9052: Amplifier + Comparator

Part Number: TLV9052
Other Parts Discussed in Thread: TINA-TI

Hi Team,

I am using  TLV9052 Dual Opamp as Amplifier and Comparator.

This is a very cost-sensitive system so each and every component matters to us.

If you see my Amplifier Circuit it is not biased properly. Negative half-cycles will not be available. We are not interested in negative half-cycles that is why Amplifier is not biased for negative half cycles.

My amplifier gain is 50.9 and the Bandwidth of TLV9052 is 5Mhz .So according to my Calculation Closed-loop Bandwidth is 100Khz.(5Mhz/50.9). Please correct me If I am wrong.

During the simulation, I can see that Upto 3Khz it is working fine after that Amplifier is not doing any amplification .

May I know why it is happening like this.

Please find the TINA-TI file and O/P waveforms attached.

OP_ Waveforms.pdf

AMP_TLV9052_GAIN_50.9 - Copy.TSC



  • Former Member
    0 Former Member

    Hello Hari,

    You are correct about the negative half cycles and the bandwidth.

    What will your input signal look like?  I cannot tell the magnitude of the input signal from the attached PDF.

    With such a high gain and such a low VCC, any input voltage approaching 36mV, including just the bias voltage for the amplifier, will rail the output.

    Please let me know what your input signal will look like including magnitude and offset.



  • Hi Daniel,

    Thank you very much.

    I attached TINA Simulation file also in the above mail.

    You can see I/P waveform in the TINA simulation file.



  • Former Member
    0 Former Member in reply to Hari T O0

    Hi Hari,

    I cannot see the input signal amplitude because of the y-axis scaling on the plot.  See below.

    Depending on what the input signal is, the amplifier might be doing the correct amplification.  What's happening is that C3 cuts out all the DC biasing and forces the amplifier to depend on the input signal to put it in the proper input common mode range.  So on the negative half cycle, the amplifier will see a negative input voltage and the ampifier will rail to the negative supply.  This I believe is clear to both of us.

    When the amplifier swings high, we expect to see the half wave output.  In the file you sent me, the input signal has a magnitude of 1.12mV.  If we gain this up by 50.9V/V, that gives us an expected output of 57mV.  Remember, however, that we are also gaining up the offset of the amplifier.  The offset of the TLV9052 is typically 33uV.  Multiply this by 50.9V/V and you get some additional offset giving us an expected output around 74mV, which is almost exactly what you'll get in simulation if you remove the comparator portion of the circuit.

    Now you'll notice that the half wave signal is not very sinusoidal.  You have to remember that when the amplifier tries to pull the output past the supply rail, it will go into overload recovery.  Basically, when the amplifier's output tries to leave the rail again it will have a delay before it does so.  The delay is especially bad when you try to make a small overload of the output.  So, the op amp is being overloaded and then rapidly trying to recover.

    The biggest issue, however, is that you're trying to amplify a signal with an input of 1.12mV amplitude with an amplifier that has a an offset of 330uV.  This is quite significant relative to the input signal.  If you also consider that, for a real world part, the offset could be negative and has a maximum data sheet spec of 1.6mV, then for such a case the offset would completely overwhelm your input signal and the op amp output would never leave the negative rail.

    In short, I think the application will need to be rethought.



  • Former Member
    0 Former Member in reply to Former Member

    Hi Hari,

    Since we have not heard back from you, I will assume the issue has been resolved and close this thread.

    If you still need assistance, you can post again here.  After some time, the thread will lock and you will then have to create a new one to revitalize the question.



  • Hi Hari,

    why not doing it this way?



  • Hi Kai,

    Thank you very much.(Kai Rockss...)

    I will study this circuit and will contact you to clear my questions.

    Let me ask you another Question

    I have a microphone with 1.1V DC and at 70dBSPL sound it will have an output peak of 1.12mv.

    So total voltage at the output of the MIC at 70dBSPL is 1.1V+1.12mV = 1.10112V.

    Is it possible to compare this value (1.10112V) with a reference voltage without using any Amplifier.

    My understanding is it is not possible to compare directly.So I amplified the 1.12mV and compared with a refrence voltage.

    May I know your thoughts about the same.