SPDIF input and output levels

[Mahen K]

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

[Dick Pierce[_2_]]

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 |
+--------------------------------+

[Andrew Haley]

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.

[Mahen K]

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

[Mahen K]

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

[Arny Krueger[_4_]]

"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?

[Dave Platt]

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
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