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LM124: Correct unity GBWP for 1V Amplitude

Sumin Sunilraj
Prodigy 10 points

Part Number: LM124

Tool/software:

I can see that you have provided typical value of unity GBWP  1.2MHZ & slew rate typical value is 0.5v/uS. For 1 V amplitude(Vpeak) sinewave is it possible for LM124 to give output without distortion/attenuation. I have calculated slew rate with this formula 2pi * F * A, in this case I will take gbwp(1.2MHZ) as F and 1V as A , I got around 7.54 V/uS. so I believe LM124 won't work as intended with 1 V amplitude(Vpeak) sinewave as intended, can you guys comment on this and give the correct unity gbwp

  • 0
    TI__Guru* 77501 points

    Hi Sumin,

    Sumin Sunilraj said:
    can you guys comment on this and give the correct unity gbwp

    You are referring to Full Power BW of the op amp. For slew rate of 0.5V/usec, LM124's max. output vs. frequency is approx. 79kHz, see the attached image for the calculation. 

    If you have other questions, please let us know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 10 points

    Hi Raymond,

    The full power BW of the LM124 opamp is 79kHz right, can you please provide some clarity on the test conditions for finding the unity gbw.Currently I'm using the below configurations. Vi I was giving some 100mV Amplitude (sinewave) with 1.2MHZ , is this the correct way to check the unity gbwp?

    Regards,

    Sumin S

  • 0 in reply to Sumin Sunilraj
    TI__Guru* 77501 points

    Hi Sumin, 

    Sumin Sunilraj said:
    I'm using the below configurations. Vi I was giving some 100mV Amplitude (sinewave) with 1.2MHZ , is this the correct way to check the unity gbwp

    The attached image in Figure 6-1 is shown a buffer configuration, so LM124 should work to buffer 100mVpk from input to output. 

    1.2MHz is a typical BW for the LM124, this is correct way to check the datasheet, but this is not the correct way to check the unity gain bandwidth (UGBW) for your application. 

    Your design product should have a design specification, where the design should say what is the max. operating frequency in your input signal. GBWP = Gain*Cutoff_frequency@-3dB, see the video below. You need to consider the design margin for your product.

    If your max. signal is operating at 1.2MHz, then you can not use LM124 for the application. It is likely that you need UGBW approx. 10MHz in order to meet the BW requirements. 

    If the application has max. operating frequency <100kHz, then you may use the LM124 as buffer for your design. 

    https://www.youtube.com/watch?v=vSidAFDshuk&t=67s

    Here is the additional video series about the GBWP topics. 

    https://www.ti.com/video/series/precision-labs/ti-precision-labs-op-amps.html?keyMatch=precision%20op%20amp%20video%20training&tisearch=universal_search

    If you have additional questions, please let me know. 

    Best,

    Raymond