| banana |
Hello all,
I'm working with DIR1701 as receiver. However, it's D_in only accept CMOS level, I need to convert SPIDF signal into CMOS level.
TI (on DEM-DIR1701 instruction manual) suggest using a two stage 74HCU04 buffer to do the level convert. Is there a better way to do it? Or are there any "low jitter" gates for building the buffer??
Thanks in advance. |
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| Guido Tent |
Hi,
Treat SPDIF as it where analog. I'd suggest a decent opamp like AD811, with 5 times gain or so.
regards |
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| till |
thread "CS8412 or AD1892?"
posting#41 |
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| banana |
Thanks Gudio and Till.
ADM1485 looks like a good fit. But I have no idea how it would compare to 74CU04, in terms of clock skew.
And about using Opamp..... How do I ensure the Opamp's output is 0~5V? Does it mean running the Opamp with +5V single supply? |
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| andrei |
| Use a specialized RS-485 receiver, like LTC1685 (or ADM1485). |
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| Guido Tent |
| quote: | Originally posted by andrei
Use a specialized RS-485 receiver, like LTC1685 (or ADM1485). |
be careful, they all sound different !
Guido |
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| Bricolo |
Guido, why a gain of 5 for the opamp?
Isn't SPDIF 0-0.5V and CMOS 0-5V? So a gain of 10 would be required. |
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| till |
"be careful, they all sound different !"
yea, and don´t forget the stone on your transport. |
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| carlosfm |
| quote: | Originally posted by Guido Tent
Hi,
Treat SPDIF as it where analog. I'd suggest a decent opamp like AD811, with 5 times gain or so.
regards |
What about the LM6171? :up: or :down: ?
5 times gain?
Shouldn't it be 10x?:scratch: |
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| Guido Tent |
| quote: | Originally posted by Bricolo
Guido, why a gain of 5 for the opamp?
Isn't SPDIF 0-0.5V and CMOS 0-5V? So a gain of 10 would be required. |
Yes, in theory, but I like to reduce the amplitude in order to reducce the RF current entering the receiving. A tradeof between slope and amplitude
You can play around with it, ofcourse
regards |
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| Bricolo |
ok I'll try this
I have some AD8065, are they OK for this use?a |
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| banana |
Guido,
About the Opamp approah. Do I need to add bias to the SPDIF signal before feeding it to the Opamp? I mean offsetting the "bipolar" +0.25/-0.25V input signal into "single-ended" +2.75/+2.25V, before amplification.
Or should I run the Opamp with +5V single supply and simply clip the output to +5/0V? |
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| Guido Tent |
| quote: | Originally posted by banana
Guido,
About the Opamp approah. Do I need to add bias to the SPDIF signal before feeding it to the Opamp? I mean offsetting the "bipolar" +0.25/-0.25V input signal into "single-ended" +2.75/+2.25V, before amplification.
Or should I run the Opamp with +5V single supply and simply clip the output to +5/0V? |
Hi
Yes, need bias at half of supply voltage
NEVER clip digital signal;s at such important places
regards |
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| carlosfm |
Guido,
Is the LM6171 a good choice for that job?
Thanks:angel: |
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| Guido Tent |
| quote: | Originally posted by carlosfm
Guido,
Is the LM6171 a good choice for that job?
Thanks:angel: |
Hi Carlos
should work well - no clue on the sound (all you do there is audible, subtle but audible :-)
regards |
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| dmfraser |
You can't use most op-amps because the signal is in the 6 MHz range. If the lvel is too high coming from your source, you can attenuate it with a resistor. However, I use a 74AC04 operating on a 3.3V supply to buffer the input on my unit. You don't need anything fancier. On the electrical input, I couple the S/PDIF signal through a DC blocking capacitor to the input of the 74AC04 through a 220 ohm resistor. The input is biased with two resistors to 40% of the supply voltage.
On my opto input, the output of the TORX141 is buffered through another section of the 74AC04. |
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| banana |
A little sharing, though most of you might already know. TTL gate does not work in the case of U3 on DEM-DIR1701 instruction manual. The first gate is actually a linear amplifier and only CMOS gates are suitable for doing this.
Before I learned this, I tried 74F04 and 74LS04. No matter how I bias the input DC, these TTL gates won't have symmetric output duty cycle. And they don't amplify, instead they simply switch on or off.
Finally, I settle on ADM1485. It's plug and play, trouble free. Thanks Andrei.
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