J
JESSD
- Jan 1, 1970
- 0
I'm designing a spdif/toslink (digital audio) switch and would like
some advice. The switch can convert from optical to coax, coax to
coax, optical to optical, or coax to optical automatically. I've got
a circuit that works for the output portion that can drive both the
optical and coax. The input portion is a little trickier.
This is what I have so far:
+--10K--+
10 nF | |
|| | |\ | |\
COAX/SPDIF|-----------+---||---100R--+--| O--+---+---| O---- (output
stage)
| || |/ | |/
75R 10K
| 74HCU04 |
--- ---
I want to add in the Optical audio receiver to the front end of this
circuit without affected the 75 ohm termination resistance needed for
the coax connection. The user would only connect either the coax or
optical to the input, never both.
The output of the optical TOSLINK receiver is TTL.
I thought of just connecting the optical output through a diode to the
coax input. My thinking is that the termination resistance would
remain the same since the diode should look like an open circuit one
way. See below:
Optical Output (TTL)
|
\/ Diode +--10K--+
-- 10 nF | |
| || | |\ | |\
COAX/SPDIF|-------+---+---||---100R--+--| O--+---+---| O---- (output
stage)
| || |/ | |/
75R 10K
| 74HCU04 |
--- ---
When the user plugs in the optical cable the diode would let the
signal through. When not connected the coax shouldn't notice the
extra circuitry hanging on since the diode would always be reverse
biased.
Any suggestions/comments or other options to consider are appreciated.
Thanks in advance.
some advice. The switch can convert from optical to coax, coax to
coax, optical to optical, or coax to optical automatically. I've got
a circuit that works for the output portion that can drive both the
optical and coax. The input portion is a little trickier.
This is what I have so far:
+--10K--+
10 nF | |
|| | |\ | |\
COAX/SPDIF|-----------+---||---100R--+--| O--+---+---| O---- (output
stage)
| || |/ | |/
75R 10K
| 74HCU04 |
--- ---
I want to add in the Optical audio receiver to the front end of this
circuit without affected the 75 ohm termination resistance needed for
the coax connection. The user would only connect either the coax or
optical to the input, never both.
The output of the optical TOSLINK receiver is TTL.
I thought of just connecting the optical output through a diode to the
coax input. My thinking is that the termination resistance would
remain the same since the diode should look like an open circuit one
way. See below:
Optical Output (TTL)
|
\/ Diode +--10K--+
-- 10 nF | |
| || | |\ | |\
COAX/SPDIF|-------+---+---||---100R--+--| O--+---+---| O---- (output
stage)
| || |/ | |/
75R 10K
| 74HCU04 |
--- ---
When the user plugs in the optical cable the diode would let the
signal through. When not connected the coax shouldn't notice the
extra circuitry hanging on since the diode would always be reverse
biased.
Any suggestions/comments or other options to consider are appreciated.
Thanks in advance.