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.
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??
An externally hosted image should be here but it was not working when we last tested it.
Thanks in advance.
Hi,
Treat SPDIF as it where analog. I'd suggest a decent opamp like AD811, with 5 times gain or so.
regards
Treat SPDIF as it where analog. I'd suggest a decent opamp like AD811, with 5 times gain or so.
regards
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?
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?
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.
Isn't SPDIF 0-0.5V and CMOS 0-5V? So a gain of 10 would be required.
or 
?
Bricolo said:
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
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?
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?
banana said:
Hi
Yes, need bias at half of supply voltage
NEVER clip digital signal;s at such important places
regards
carlosfm said:Guido,
Is the LM6171 a good choice for that job?
Thanks
Hi Carlos
should work well - no clue on the sound (all you do there is audible, subtle but audible 🙂
regards
S/PDIF Input
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.
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.
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.
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.
An externally hosted image should be here but it was not working when we last tested it.
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