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THS4531: Ouput of amplifier obtained.

Shifali N
Expert 2225 points

Part Number: THS4531
Other Parts Discussed in Thread: OPA1637, OPA1632

Hi,

I am using THS4531 in my design for differential audio input amplifier. I have attached the signal flow in the attached block diagram. I will be giving differential input audio using mobile phone. And output is connected to speaker. I have few queries regarding Audio.

1. Is the audio input sourced by my Phone balanced audio?

2. Since the input is balanced, the positive and negative data will be out of phase by 180. But they will have similar amplitude. Hence wont the output of amplifier be 0. As Vout of differential amplifier is Vout=Gain(V+-V-).

3. What is the formula used to calculate the Vout+ and Vout- in differential amplifierAudio signal flow.pptx

4. My requirement is Mono Balanced Audio. So I am connecting Audio input in my board to Phone using TRS jack. Currently I have connected Tip to positive, Ring to negative and ground to sleeve. Since TRS can also be used as stereo left and right channel, how will the differential amplifier THS4531 come to know whether the data received is balanced or stereo left and right channels.

5. Do you have any document which explains the working of differential amplifier.

  • 0
    TI__Mastermind 23226 points

    1. No, usually there is both a right channel and a left channel for stereo(scopic) 3D audio effects, which are both "single-ended" signals.

    2. Only the difference will be amplified. If the two signals are the same amplitude and phase, the output will be 0V.

    3.  The difference between the outputs will be (input x gain), and their average will be the output common mode voltage setting. The difference can be negative even when both outputs are positive.

    4. The amplifier won't know. It will only amplify signals a signal that is applied differentially, and cancel out a signal that is common to both inputs.

    5.  Here is an application note you may find helpful. https://www.ti.com/lit/an/sboa331/sboa331.pdf

    Maybe a better solution is to just use one channel (left or right) and convert it into a differential output. https://www.ti.com/lit/an/sboa332/sboa332.pdf 

  • 0
    TI__Mastermind 32415 points

    Hello Shifali,

      Also, to add a comment on TRS connectors. Balanced vs unbalanced audio will depend on if you have a two conductor or three conductor phone connector. This is described in detail at this link. 

      General information on FDAs can be found here. We also have audio FDAs such as the OPA1632 and OPA1637. 

    Thank you,

    Sima