PCM1690: Gain scaling whilst maintaining differential signals

Mark Thompson2

Part Number: PCM1690

Hi there,

I've done some searching around some support forum threads and data sheets etc. I am trying to get my head around gain scaling the differential outputs of the PCM1690 so that I can connect them to my amplifier that has a maximum Differential Input Voltage of 2 Vrms. I'm assuming I need to use op-amps of some kind to achieve this. Can you please help me in this design task?

Many thanks!

Mark

over 4 years ago

0 Akhilesh K over 4 years ago

TI__Mastermind 19086 points

Hi,

Since PCM1690 outputs differential signals with 8Vpp and you need to have some low pass filtering to remove the out of band noise plus attenuation of signal to get 2Vrms differential signals, both can be achieved by differential audio op amps like OPA6132. Below circuit is an example which show show this can be achieved.

Only one channel is shown. Cut off frequency is 55Khz. If you don't need AC coupled, you can safely remove capacitors C1 and C4 from below circuit.

PCM1690_Audio_Filter_1.TSC

0 Mark Thompson2 over 4 years ago in reply to Akhilesh K

Intellectual 630 points

Thank you!

And may I ask. Am I better off extending the signal cable from the PCM1690 to my amplifier board that would have the OpAmp mounted to it? Or should the filter and OpAmp be placed immediately at the PCM1690 output? Just concerned about long (>5m) balanced cable runs.

Kind regards,

Mark

0 Akhilesh K over 4 years ago in reply to Mark Thompson2

TI__Mastermind 19086 points

Hi Mark,

In that case I suggest drive the PCM1690 outputs directly with a buffer and place the above attenuation and filter circuit after the cable.

You may need to experiment with different configurations to better assess stability with long cable driving the buffer or PCM1690 directly.

Regards,

0 Mark Thompson2 over 4 years ago in reply to Akhilesh K

Intellectual 630 points

Sorry, now I have to ask. Why do I need a buffer? and, How do I choose an appropriate buffer?

Can I get away with no buffer if I'm only used short (10cm) lengths of analogue cabling between the PCM1690 and OPA6132?

Kind regards,

Mark

0 Akhilesh K over 4 years ago in reply to Mark Thompson2

TI__Mastermind 19086 points

Hi Mark,

If its 10cm, it will be ok to drive without buffer, for long cables ( >1m) you may require.

Regards,

Audio

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PCM1690: Gain scaling whilst maintaining differential signals