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  • TI Thinks Resolved

PCM9211: typical connection when coaxial and optical input

Intellectual 890 points

Replies: 1

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Part Number: PCM9211

Hi Team,

I am wondering what's the typical connection for audio transceiver when coaxial or optical input.

1. coaxial input

In PCM9211 datasheet, we can see that pull down resistor and series capacitor(R4 and C11 in Page 117) is required when coaxial input, is it followed by any standard? How to select the resistor and capacitor value?

2. Optical input

PCM9211 don't show a schematic of optical input, the PCM9211EVM add a buffer for signal conditioning. But if we don't add the buffer(for lower cost), does the series capacitor still needed?

Look for other solution such as AK4117, they add a 470 ohm resistor here, what's the function of resistor here? Does PCM9211 need the resistor?

Thanks.

Wiky

  • Hi Wiky,

    Recommendations for these component values are provided in the typical circuit components table below the connection diagram. We recommend a 75 Ohm resistor to terminate the coax line because 75 ohms is the typical characteristic impedance of coax cables and this helps to reduce reflections on the line. The capacitor is just a dc blocking capacitor and the value is not critical as long as it's large enough not to filter out any of your signal. This capacitor is used for analog inputs, not for optical. You typically don't need a buffer for the optical module and the circuit design for the optical inputs on the EVM is a bit convoluted because an IO expander was included to control which inputs receive optical data. If you look at the optical input on the DIR9001 EVM for example, you can see no buffer is used.

    I'd rather not comment on the AK4117 part since this is not a TI device and I have no familiarity with it, but there is no need to include this resistor on the PCM9211 input.

    Best,

    Zak

    Regards,

    Zak Kaye
    Precision Data Converter Applications

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