Forums

I2C noise into the audio signals

Started by Unknown December 9, 2013
We have TDA7719 audio processor and OLED display connected to the same I2C =
bus as I2C slaves. Both the devices are driven by MCU which is I2C master. =
After TDA7719 is initialized with I2C for input selection and volume, it st=
arts working. The MCU keeps refreshing the display by continuously writing =
data to the display through the same I2C bus. This I2C noise is getting cou=
pled into the audio signals and I can hear the rhythmic noise from the spea=
kers proportionate to the display refreshing. If the display is paused the =
noise also pauses.=20

What could be the issue? Appreciate any help.

Both MCU and TDA7719 are powered by separate regulators. Input to the TDA i=
s from MCU which has built in DAC. Problem in the audio source from MCU+DAC=
 is already ruled out as direct connection to the amplifier bypassing TDA i=
s outputting clean audio output.

Thanks
markj
On Mon, 9 Dec 2013 08:05:59 -0800 (PST), markjsunil@gmail.com wrote:

>We have TDA7719 audio processor and OLED display connected to the same I2C bus as I2C slaves. Both the devices are driven by MCU which is I2C master. After TDA7719 is initialized with I2C for input selection and volume, it starts working. The MCU keeps refreshing the display by continuously writing data to the display through the same I2C bus. This I2C noise is getting coupled into the audio signals and I can hear the rhythmic noise from the speakers proportionate to the display refreshing. If the display is paused the noise also pauses. > >What could be the issue? Appreciate any help. > >Both MCU and TDA7719 are powered by separate regulators. Input to the TDA is from MCU which has built in DAC. Problem in the audio source from MCU+DAC is already ruled out as direct connection to the amplifier bypassing TDA is outputting clean audio output. > >Thanks >markj
Do you have any opamps after the TDA? -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Mon, 09 Dec 2013 09:05:59 -0700, <markjsunil@gmail.com> wrote:

> We have TDA7719 audio processor and OLED display connected to the same > I2C bus as I2C slaves. Both the devices are driven by MCU which is I2C > master. After TDA7719 is initialized with I2C for input selection and > volume, it starts working. The MCU keeps refreshing the display by > continuously writing data to the display through the same I2C bus. This > I2C noise is getting coupled into the audio signals and I can hear the > rhythmic noise from the speakers proportionate to the display > refreshing. If the display is paused the noise also pauses. > > What could be the issue? Appreciate any help. > > Both MCU and TDA7719 are powered by separate regulators. Input to the > TDA is from MCU which has built in DAC. Problem in the audio source from > MCU+DAC is already ruled out as direct connection to the amplifier > bypassing TDA is outputting clean audio output. > > Thanks > markj
wow, a FUN project! Do you know the magnitude of the sound? Are you hearing 60dB down, or 80dB down? Could be 'GND' noise coupling in. The 'exra' demand of the power could be shifting the gnds out from under your audio stuff. If you provide an email address I can send a .zip file to, I'll send you a sample of the results of a PCB Layout Tool I created to solve those EXACT problems. [gmail accounts seem to reject a .zip file and never tell anyone] The tool was created during the design of seismic monitoring electronics and the gnd noise was kept to less tha 1/4 LSB. Also did a lot of work to make ALL the power filters lossy over their WHOLE bandwidth, even into the GHz ranges. We're talking about a filter that looks like a huge series resistance and a short to gnd. A lot of people don't notice that most of the filters 'recommended' by the mfgr actually go into high impedance at certain spectral locations. That translates to having absolutely NO bypass at those tones. For example, bypass down to 0.1 ohm great!, but most of those filters at some frequency suddenly go to 10 and even 100 ohms. No problem *if* you have no frequencies there, but a big problem if you do! Put a scope probe on your power and you'll see 'ringy' waveforms, that's the effect. Another place to look is magnetic fields coupling across traces. MagFields are INSIDIOUS! Your scope will barely show them, yet they can induce audible stuff everywhere. then there's the AM modulated HF that gets rectified somewhere, too. I'm probably preaching to the choir on all this. Right now, I'd go forthe GND shifting.
On Monday, December 9, 2013 9:45:23 PM UTC+5:30, John Larkin wrote:
> On Mon, 9 Dec 2013 08:05:59 -0800 (PST), markjsunil@gmail.com wrote: >=20 >=20 >=20 > >We have TDA7719 audio processor and OLED display connected to the same I=
2C bus as I2C slaves. Both the devices are driven by MCU which is I2C maste= r. After TDA7719 is initialized with I2C for input selection and volume, it= starts working. The MCU keeps refreshing the display by continuously writi= ng data to the display through the same I2C bus. This I2C noise is getting = coupled into the audio signals and I can hear the rhythmic noise from the s= peakers proportionate to the display refreshing. If the display is paused t= he noise also pauses.=20
>=20 > > >=20 > >What could be the issue? Appreciate any help. >=20 > > >=20 > >Both MCU and TDA7719 are powered by separate regulators. Input to the TD=
A is from MCU which has built in DAC. Problem in the audio source from MCU+= DAC is already ruled out as direct connection to the amplifier bypassing TD= A is outputting clean audio output.
>=20 > > >=20 > >Thanks >=20 > >markj >=20 >=20 >=20 > Do you have any opamps after the TDA? >=20 >=20 >=20 >=20 >=20 > --=20 >=20 >=20 >=20 > John Larkin Highland Technology Inc >=20 > www.highlandtechnology.com jlarkin at highlandtechnology dot com =20 >=20 >=20 >=20 > Precision electronic instrumentation >=20 > Picosecond-resolution Digital Delay and Pulse generators >=20 > Custom timing and laser controllers >=20 > Photonics and fiberoptic TTL data links >=20 > VME analog, thermocouple, LVDT, synchro, tachometer >=20 > Multichannel arbitrary waveform generators
No John. Output of TDA is fed to TPA3110D2 amplifier.
On Monday, December 9, 2013 11:28:48 AM UTC-5, Robert Macy wrote:
> On Mon, 09 Dec 2013 09:05:59 -0700, <markjsunil@gmail.com> wrote: > > > We have TDA7719 audio processor and OLED display connected to the same > > I2C bus as I2C slaves. Both the devices are driven by MCU which is I2C > > master. After TDA7719 is initialized with I2C for input selection and > > volume, it starts working. The MCU keeps refreshing the display by > > continuously writing data to the display through the same I2C bus. This > > I2C noise is getting coupled into the audio signals and I can hear the > > rhythmic noise from the speakers proportionate to the display > > refreshing. If the display is paused the noise also pauses. >> > > What could be the issue? Appreciate any help. > > > > Both MCU and TDA7719 are powered by separate regulators. Input to the > > > TDA is from MCU which has built in DAC. Problem in the audio source from > > > MCU+DAC is already ruled out as direct connection to the amplifier > > > bypassing TDA is outputting clean audio output. > > > > Thanks > > markj > > wow, a FUN project! > > Do you know the magnitude of the sound? Are you hearing 60dB down, or > 80dB down? Could be 'GND' noise coupling in. The 'exra' demand of the > power could be shifting the gnds out from under your audio stuff. > If you provide an email address I can send a .zip file to, I'll send you a > sample of the results of a PCB Layout Tool I created to solve those EXACT > problems. [gmail accounts seem to reject a .zip file and never tell > anyone] The tool was created during the design of seismic monitoring > electronics and the gnd noise was kept to less tha 1/4 LSB. Also did a lot > of work to make ALL the power filters lossy over their WHOLE bandwidth, > even into the GHz ranges. We're talking about a filter that looks like a > huge series resistance and a short to gnd. A lot of people don't notice > that most of the filters 'recommended' by the mfgr actually go into high > impedance at certain spectral locations. That translates to having > absolutely NO bypass at those tones. For example, bypass down to 0.1 ohm > > great!, but most of those filters at some frequency suddenly go to 10 and > > even 100 ohms. No problem *if* you have no frequencies there, but a big > > problem if you do! Put a scope probe on your power and you'll see 'ringy' > waveforms, that's the effect. > Another place to look is magnetic fields coupling across traces. MagFields > > are INSIDIOUS! Your scope will barely show them, yet they can induce > > audible stuff everywhere. > > then there's the AM modulated HF that gets rectified somewhere, too. > > I'm probably preaching to the choir on all this. Right now, I'd go forthe > GND shifting.
Isn't the obvious path via the I2C wires? I was wondering if the I2C speed could be slowed down (for the audio IC).. and then add some RC filters on the I2C input wires. Then see if that reduced the interference. (or is that a silly idea?) I guess the first job is to figure out how it's getting in. George H.
On Monday, December 9, 2013 9:58:48 PM UTC+5:30, Robert Macy wrote:
> On Mon, 09 Dec 2013 09:05:59 -0700, <markjsunil@gmail.com> wrote: > > > > > We have TDA7719 audio processor and OLED display connected to the same > > > I2C bus as I2C slaves. Both the devices are driven by MCU which is I2C > > > master. After TDA7719 is initialized with I2C for input selection and > > > volume, it starts working. The MCU keeps refreshing the display by > > > continuously writing data to the display through the same I2C bus. This > > > I2C noise is getting coupled into the audio signals and I can hear the > > > rhythmic noise from the speakers proportionate to the display > > > refreshing. If the display is paused the noise also pauses. > > > > > > What could be the issue? Appreciate any help. > > > > > > Both MCU and TDA7719 are powered by separate regulators. Input to the > > > TDA is from MCU which has built in DAC. Problem in the audio source from > > > MCU+DAC is already ruled out as direct connection to the amplifier > > > bypassing TDA is outputting clean audio output. > > > > > > Thanks > > > markj > > > > wow, a FUN project! > > > > Do you know the magnitude of the sound? Are you hearing 60dB down, or > > 80dB down? Could be 'GND' noise coupling in. The 'exra' demand of the > > power could be shifting the gnds out from under your audio stuff. > > > > If you provide an email address I can send a .zip file to, I'll send you a > > sample of the results of a PCB Layout Tool I created to solve those EXACT > > problems. [gmail accounts seem to reject a .zip file and never tell > > anyone] The tool was created during the design of seismic monitoring > > electronics and the gnd noise was kept to less tha 1/4 LSB. Also did a lot > > of work to make ALL the power filters lossy over their WHOLE bandwidth, > > even into the GHz ranges. We're talking about a filter that looks like a > > huge series resistance and a short to gnd. A lot of people don't notice > > that most of the filters 'recommended' by the mfgr actually go into high > > impedance at certain spectral locations. That translates to having > > absolutely NO bypass at those tones. For example, bypass down to 0.1 ohm > > great!, but most of those filters at some frequency suddenly go to 10 and > > even 100 ohms. No problem *if* you have no frequencies there, but a big > > problem if you do! Put a scope probe on your power and you'll see 'ringy' > > waveforms, that's the effect. > > > > Another place to look is magnetic fields coupling across traces. MagFields > > are INSIDIOUS! Your scope will barely show them, yet they can induce > > audible stuff everywhere. > > > > then there's the AM modulated HF that gets rectified somewhere, too. > > > > I'm probably preaching to the choir on all this. Right now, I'd go forthe > > GND shifting.
You can send the zip to markjsunil at live dot com The power supply should be OK as LM317L SOT89 pack can supply 100ma and TDA7719 max current is 35ma.
On Mon, 9 Dec 2013 09:10:41 -0800 (PST), markjsunil@gmail.com wrote:

>On Monday, December 9, 2013 9:45:23 PM UTC+5:30, John Larkin wrote: >> On Mon, 9 Dec 2013 08:05:59 -0800 (PST), markjsunil@gmail.com wrote: >> >> >> >> >We have TDA7719 audio processor and OLED display connected to the same I2C bus as I2C slaves. Both the devices are driven by MCU which is I2C master. After TDA7719 is initialized with I2C for input selection and volume, it starts working. The MCU keeps refreshing the display by continuously writing data to the display through the same I2C bus. This I2C noise is getting coupled into the audio signals and I can hear the rhythmic noise from the speakers proportionate to the display refreshing. If the display is paused the noise also pauses. >> >> > >> >> >What could be the issue? Appreciate any help. >> >> > >> >> >Both MCU and TDA7719 are powered by separate regulators. Input to the TDA is from MCU which has built in DAC. Problem in the audio source from MCU+DAC is already ruled out as direct connection to the amplifier bypassing TDA is outputting clean audio output. >> >> > >> >> >Thanks >> >> >markj >> >> >> >> Do you have any opamps after the TDA? >> >> >> >> >> >> -- >> >> >> >> John Larkin Highland Technology Inc >> >> www.highlandtechnology.com jlarkin at highlandtechnology dot com >> >> >> >> Precision electronic instrumentation >> >> Picosecond-resolution Digital Delay and Pulse generators >> >> Custom timing and laser controllers >> >> Photonics and fiberoptic TTL data links >> >> VME analog, thermocouple, LVDT, synchro, tachometer >> >> Multichannel arbitrary waveform generators > >No John. Output of TDA is fed to TPA3110D2 amplifier.
OK, similar situation. You might try lowpass filtering the inputs of the TPA, maybe just some small caps to ground to test the idea. The front end of the TPA could be rectifying fast spikes from the I2C. You could also try slowing down the I2C edges. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Mon, 09 Dec 2013 10:21:57 -0700, <markjsunil@gmail.com> wrote:

>> ...snip... > > You can send the zip to markjsunil at live dot com > > The power supply should be OK as LM317L SOT89 pack can supply 100ma and > TDA7719 max current is 35ma.
sent, look forward to your comments not to be too ascerbic, but what does that PS chip have to do with anything? From memory that chip's not so good either. the ratings you quoted are DC, check the spec sheet and you'll see a fairly high impedance even as low as 10KHz. That's why caps are usually added. BUT! a lot of these 3 terminal regulators go through a huge output impedance spike for your whole PS system depending on the value of cap you use. TI makes a great series of 3T's that let you include the cap in the feedback loop minimizing that effect. John mentioned slowing the I2C edges. That can solve a lot of problems even with the source coming from different reasons. ie, capacitive feed, gnd spikes, ps spikes, magnetic feed, etc etc. Be careful shorting energy to ground WITHOUT providing a way to starve the energy supply, else the problem can simply exacerbate itself. From years of working in EMC mitigation learned the hard way that bypassing doesn't always do what you think it does. *IF* you don't include some series resistance. Just have to change your thinking from voltage in time, to ENERGY in time, then you can find where to stomp on unwanted signals. After all, at those higher frequencies, nature doesn't care if it's voltage OR current flying around.
On 12/9/2013 10:05 AM, markjsunil@gmail.com wrote:
> We have TDA7719 audio processor and OLED display connected to the > same I2C bus as I2C slaves. Both the devices are driven by MCU which > is I2C master. > I can hear the rhythmic noise from the speakers proportionate to the > display refreshing. If the display is paused the noise also pauses. > > What could be the issue? Appreciate any help.
Typical design mistake. Don't run active communication at, to, or near analog processing ICs. Run control I2C from separate I2C port or at least isolate I2C by 3-state buffer or multiplexer. Slowing I2C edges, splitting power/ground may help to some extent; however the right solution is changing design to isolate I2C. Vladimir Vassilevsky DSP and Mixed Signal Designs www.abvolt.com
markjsunil@gmail.com wrote:
> We have TDA7719 audio processor and OLED display connected to the same I2C bus as I2C slaves. Both the devices are driven by MCU which is I2C master. After TDA7719 is initialized with I2C for input selection and volume, it starts working. The MCU keeps refreshing the display by continuously writing data to the display through the same I2C bus. This I2C noise is getting coupled into the audio signals and I can hear the rhythmic noise from the speakers proportionate to the display refreshing. If the display is paused the noise also pauses. > > What could be the issue? Appreciate any help. > > Both MCU and TDA7719 are powered by separate regulators. Input to the TDA is from MCU which has built in DAC. Problem in the audio source from MCU+DAC is already ruled out as direct connection to the amplifier bypassing TDA is outputting clean audio output. > > Thanks > markj
Short circuit on i2c lines? MCU driving it active hi?