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Amplifier configuration and gain calculation

Vigneshwaran JN
Prodigy 140 points
Other Parts Discussed in Thread: LM48511

I have been designing a audio board using amplifier LM48511

Though the Amplifier (LM48511) selected is a differential amplifier, I need to use it in single ended configuration which is feasible as per Datasheet. I have provided the single ended audio signal in the inverting input through ac coupling capacitor and gin resistors and grounded the non inverting input after the gain resistors . Please confirm its correctness.

Also the gain calculation provided in Datasheet is with respect to differential mode.

AVD = 2 X RF /RIN

Though  In my design, I have been operating in single ended configuration, the amplifier operates differentially.

Please confirm if the same formula mentioned above can be used for single ended gain calculation or use the typical single ended gain formula which is AVD = -RF /RIN

  • 0
    TI__Guru**** 189401 points

    Hi,

    Based on my understanding of what you have posted, you are correct.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 140 points

    Thank You..

    But please provide more clarity on which gain formula to use. Either single ended gain formula or differential gain formula?

  • 0 in reply to Vigneshwaran JN
    Prodigy 140 points

    Hi,

    Please provide the gain formula to be used for the Gain calculation of the above mentioned circuit.

  • 0 in reply to Vigneshwaran JN
    TI__Genius 9175 points

    The gain equation should be RF/RIN for both single ended in and differential in (but this makes assumptions on how you are measuring the input and output voltages). The assumption is that you measure the input across the differential input legs and the output across the differential output legs.

    That is, the RF/RIN gain assumes that you are measuring voltage differentially in and differentially out. For a single ended input, there is no differential input voltage however the gain equation remains unchanged since, if you ground one of the input legs, the voltage from the ungrounded input leg to ground is still technically the voltage across the input pair.

    However if you are running differential in and measured the voltage on just one of the input legs with respect to ground and then measured the output voltage differentially across the output pair, you would find a gain of 2x RF/RIN which is how the gain is specified in the datasheet.

    Regards,

    Matt