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Low Jitter I2S to PWM Processor for TAS5631B

Christopher K.
Intellectual 450 points
Other Parts Discussed in Thread: TAS5631B, TAS5631, TAS3308, TAS5518, TAS5558, TAS5548, TAS5630B, TAS5508C, TAS5086

Hello TI,

I'm currently developing an active PA system, where a custom TAS5631B PCB is used to power the Top Speakers. Unfortunately I am not very happy with the current audio performance. Since the Tweeter of the PA has a high efficiency factor and is directed via a horn even small amount of noise will become annoying.  In the current set-up I wanted to use a TAS3308 DSP with build in PWM Output to drive the TAS5631 power stage. Now this setup has an remarkable amount of high frequency noise which is really bugging me. The Problem is easy to find and hard to fight. As you can see there is quiet a lot of jitter on the PWM outputs of the TAS3308

Since the TAS3308 was set to NRND a while ago I can't expect much help from TI to reduce the jitter. Now if I use the TAS5518 PWM processor from the TAS5631EVM to drive my custom Amp board the noise is reduced to a non audible amount. Same shows the PWM signal of the 5518 which is almost jitter free

But this device is also set to NRND and would be a little to much in combination with the needed DSP. So I am looking for a simple IC which converts I2S signals from a DSP to a very low jitter PWM signal for the TAS5631. Any suggestions from your side how to procede and create a wonderful low noise active PA system?

Yours sincerely,

Christopher

  • 0
    TI__Mastermind 37045 points

    Hi Christopher,

    Our latest addition to the TAS55xx family is TAS5548 (with ASCR) and TAS5558 (preview). These are the latest and the best. You may want to check out the TAS5548 EVM which can be ordered from the e-store. 

     

    reg,

    Paul.

    Applications Engineer

    Dallas TX

     

     

  • 0 in reply to user5276421
    Intellectual 450 points

    Hello Paul,

    maybe you can advise something more "low tech". I definitely will go with DSP processor to handle the signal processing so all I need is a simple 2 channel I2S to PWM converter with good jitter performance. The processors you mentioned will work I think but on the same page there are a little bit oversized for the task given.

    best regards,

    Christopher

  • 0 in reply to Christopher K.
    TI__Guru**** 189399 points

    Hi, Christopher,

    Most of our modulators are target at multi-channel applications.

    The other thought I had is --> what if you LPF the PWM out of the 3308 and run that into the TAS5630B? I wonder if that would clean up your noise problem?

    -d2

  • 0 in reply to Don Dapkus
    Intellectual 450 points

    Hello Don,

    LPF for the PWM  is an option I still have to try out. In the layout of the DSP PCB I had already included empty pads for a 2nd order RC-Lowpass but since the noise is in in the audible range I fear that this measure will not help much. Therefore I'm looking proactive for an simple to use I2S to PWM interface.  While the TAS55xx ICs will without doubt have a good performance they are to complicated for this task. I could accept a multichannel solution but I don't want an IC with additional signal processing in it.

    best regards,

    Christopher

  • 0 in reply to Christopher K.
    TI__Expert 4320 points

    Christopher

    you also have the option to use the TAS5508C - pin to pin compatible with the TAS5518 and with same performance, it has BiQuads that can do the cross over you need.

    A smaller footprint option is the TAS5086, its a 6ch device with a small audio processor. It has a lower noise than the TAS3308 but not as good as the TAS5508C. then there is no BiQuads for cross-overs.

    rgds,

    Kim N Madsen