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Ardee 25th August 2007 09:48 AM

Can anyone advise as to the best way to convert low voltage TTL to SPDIF, please? Quality is more important to me than cost/complexity.


bocka 25th August 2007 10:50 AM

Use a 74LV86 (or similar XOR-Gate) to obtain a SOUT and /SOUT signal. Use this differential signal to feed an AD8132 high-speed differential op-amp and use a balun SPDIF output transformer.

novec 12th September 2007 05:29 AM

Does this compete with regular DITs like the Burr-Brown DIT4192 from TI? I do like the simplicity of it, and all I need is TTL-S/PDIF buffering, no sample rate conversion or anything.

Ardee 12th September 2007 07:45 AM

I think the DIT4192 converts I2S plus user bits to SPDIF. My question was how to convert LVTTL SPDIF to something which will drive a 75ohm interface.

Thanks for the suggestion bocka , btw.

novec 12th September 2007 11:39 AM

Of course, my bad.

rfbrw 12th September 2007 12:37 PM


Originally posted by Ardee
My question was how to convert LVTTL SPDIF to something which will drive a 75ohm interface.

nonoise 12th September 2007 10:48 PM

Just keep in mind that the output level should be 500mv P-P into 75 Ohm +/- 20% This is if you prefer to keep to the standard (IEC60958-3)

gmarsh 13th September 2007 01:44 PM

Use a 5V powered HCT gate (74HCT04, Tinylogic chip, etc) to convert LVTTL to +5V CMOS. You can use a faster logic family (VHCT, ACT) but be careful with decoupling.

On the output of the gate, put a 0.1uF series ceramic capacitor for DC blocking, then a resistor divider of a 330 ohm series and 100 ohm shunt.

(Actually, re-arrange that - put the 330 ohm resistor directly at the output pin of the logic gate, followed by the series capacitor and 100 ohm shunt.)

This gives you a 1.5Vpp unloaded, 0.75Vpp loaded SPDIF output with a near-75-ohm source impedance.

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