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#1
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SPDIF input and output levels
Hi,
Digital Audio receiver ICs like DIR9001 and CS8414 mention the diff voltage level at their input pins RXP and RXN as 200mv min while the Digital Audio Transsmitters like DIT4096 and CS8406 use 5V logic levels. How are they compatible with wide difference in levels? I am looking at using them for SPDIF transmission and reception. Thanks in advance -mjnk |
#2
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SPDIF input and output levels
Mahen K wrote:
Hi, Digital Audio receiver ICs like DIR9001 and CS8414 mention the diff voltage level at their input pins RXP and RXN as 200mv min while the Digital Audio Transsmitters like DIT4096 and CS8406 use 5V logic levels. How are they compatible with wide difference in levels? I am looking at using them for SPDIF transmission and reception. From IEC 958 5.3.3.3 "Minimum input signals", Minimum input voltage shall be 0.2V peak-to-peak That is, the MINIMUM input voltage. Now, if you actually read the specs for, oh, the DIT4096, you might discover that even though the "core voltage" is 5 volts, a figure more relevant to your issues is the "high-level output voltage Voh" which is listed at 0.8V Further inspection of the spec sheet reveals, in figure 11, a block referred to as the "output circuit," which is elucidated in figures 12, 13 and 14. FIgure 13 is, again, most relevant to your question. It shows the output circuit for a SP/DIF circuit, consisting, significantly of a 2:1 step-down pulse transformer, which would make it completely compatible with the IEC 958 standard. Aren't spec sheets wonderful? -- +--------------------------------+ + Dick Pierce | + Professional Audio Development | +--------------------------------+ |
#3
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SPDIF input and output levels
Mahen K wrote:
Digital Audio receiver ICs like DIR9001 and CS8414 mention the diff voltage level at their input pins RXP and RXN as 200mv min while the Digital Audio Transsmitters like DIT4096 and CS8406 use 5V logic levels. How are they compatible with wide difference in levels? I am looking at using them for SPDIF transmission and reception. For standard SPDIF you'd normally use a voltage divider and an isolation transformer on the output side. Look at 15.2, Isolating Transformer Requirements, in the CS8406 datasheet. Andrew. |
#4
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SPDIF input and output levels
On Aug 16, 10:42*pm, Dick Pierce wrote:
Mahen K wrote: Hi, Digital Audio receiver ICs like DIR9001 and CS8414 mention the diff voltage level at their input pins RXP and RXN as 200mv min while the Digital Audio Transsmitters like DIT4096 and CS8406 use *5V logic levels. How are they compatible with wide difference in levels? I am looking at using them for SPDIF transmission and reception. *From IEC 958 5.3.3.3 "Minimum input signals", * * Minimum input voltage shall be 0.2V peak-to-peak That is, the MINIMUM input voltage. Now, if you actually read the specs for, oh, the DIT4096, you might discover that even though the "core voltage" is 5 volts, a figure more relevant to your issues is the "high-level output voltage Voh" which is listed at 0.8V Further inspection of the spec sheet reveals, in figure 11, a block referred to as the "output circuit," which is elucidated in figures 12, 13 and 14. FIgure 13 is, again, most relevant to your question. It shows the output circuit for a SP/DIF circuit, consisting, significantly of a 2:1 step-down pulse transformer, which would make it completely compatible with the IEC 958 standard. Aren't spec sheets wonderful? -- +--------------------------------+ + * * * * Dick Pierce * * * * * *| + Professional Audio Development | +--------------------------------+ Thanks for quick response. I couldn't find Voh as 0.8V anywhere in the DIT4096 datasheet. The datasheet in page 3 says Voh for TX+ and TX- is "Vdd - 0.4v" typical which translates to 4.6v. With 4.6V and 2:1 step down transformer, is o/p compatible with consumer spdif inputs? I just chekced the levels for RX1+ and RX1- inputs of SRC4392 in the datasheet and it is max 200mv which is not compatible with the above scheme unless I am missing something. -mjnk |
#5
Posted to rec.audio.tech
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SPDIF input and output levels
On Aug 16, 10:42*pm, Dick Pierce wrote:
Mahen K wrote: Hi, Digital Audio receiver ICs like DIR9001 and CS8414 mention the diff voltage level at their input pins RXP and RXN as 200mv min while the Digital Audio Transsmitters like DIT4096 and CS8406 use *5V logic levels. How are they compatible with wide difference in levels? I am looking at using them for SPDIF transmission and reception. *From IEC 958 5.3.3.3 "Minimum input signals", * * Minimum input voltage shall be 0.2V peak-to-peak That is, the MINIMUM input voltage. Now, if you actually read the specs for, oh, the DIT4096, you might discover that even though the "core voltage" is 5 volts, a figure more relevant to your issues is the "high-level output voltage Voh" which is listed at 0.8V Further inspection of the spec sheet reveals, in figure 11, a block referred to as the "output circuit," which is elucidated in figures 12, 13 and 14. FIgure 13 is, again, most relevant to your question. It shows the output circuit for a SP/DIF circuit, consisting, significantly of a 2:1 step-down pulse transformer, which would make it completely compatible with the IEC 958 standard. Aren't spec sheets wonderful? -- +--------------------------------+ + * * * * Dick Pierce * * * * * *| + Professional Audio Development | +--------------------------------+ Thanks for quick response. I couldn't find Voh as 0.8v anywhere in the DIT4096 datasheet?? Page 3 of the datasheet says Voh for TX+ and TX- as Vdd - 0.4v which translates to 4.6v. With 4.6V and 2:1 transfo o/p is around 2.3v which is not compatible with consumer spdif inputs unless I am missing something. Also, I just looked at the datasheet of SRC4392 which says RX1+ and RX1- input levels are 200mv max. This clearly will not work with the aboev scheme. -mjnk |
#6
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SPDIF input and output levels
"Mahen K" wrote in message ... Hi, Digital Audio receiver ICs like DIR9001 and CS8414 mention the diff voltage level at their input pins RXP and RXN as 200mv min while the Digital Audio Transsmitters like DIT4096 and CS8406 use 5V logic levels. How are they compatible with wide difference in levels? I am looking at using them for SPDIF transmission and reception. Sounds about right. Why would there necessarily be a problem if the transmitter puts out more than the minimum voltage required by the receiver? Wouldn't that always have to be true, especially when line losses are considered? |
#7
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SPDIF input and output levels
In article ,
Andrew Haley wrote: Digital Audio receiver ICs like DIR9001 and CS8414 mention the diff voltage level at their input pins RXP and RXN as 200mv min while the Digital Audio Transsmitters like DIT4096 and CS8406 use 5V logic levels. How are they compatible with wide difference in levels? I am looking at using them for SPDIF transmission and reception. For standard SPDIF you'd normally use a voltage divider and an isolation transformer on the output side. Look at 15.2, Isolating Transformer Requirements, in the CS8406 datasheet. Or, more simply, just use a moderate-value coupling capacitor between the transmitting IC and your SPDIF-out jack. The presence of the receiver's termination resistance will pull the average value of at the jack down to 0 volts, and so you'll end up with a voltage at the receiver which swings both positive and negative. This lets you simply ground one of the two differential-input pins, and feed the other from the signal. The receiver will probably be able to handle a +/- 2.5 volt swing without difficulty. If you want to drop it down to +/- 1 volt or so, you don't need a full voltage divider at the transmitter... you can use the 75-ohm coax characteristic impedance / termination load as half of it, and so all you need is a series resistor. So... quick-and-dirty approach would be to go from the transmitting IC, through a 75-ohm-or-so buildout / padding resistor, through a .1 uF cap, and out to the jack. At the receiving end, go through another ..1 uF cap, into one differential-input pin (with a 75-ohm resistor to ground) and ground the other differential input pin. There are, I agree, good reasons to use a proper SPDIF isolation transformer at each end... a very good idea if your sending and receiving devices are any great distance apart, might be on different power circuits with different ground potentials, or are in high-RF areas. Many less-expensive devices don't bother (just use capacitive isolation) and work well under less-demanding conditions. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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