I2S Specifications

[Aschrum]

Hi dear forum,
at my institute we use an I²S-radiosystem to transmit vibration data.
Therefor I'd like to know the voltage level of I²S.
The old datasheet from Philips tells input from 0.8 to 2.0 Volt and output from 0.4 to 2.4 Volt. Is that still correct or was there something changed about I²S? At least I couldn't find any new specifications. If so, does that mean, that the signal is being falsified while the transmission?
Please note that I am not a technician. I only am the one who was elected to attend to this topic.
Thanks for your replies.
Greets,
André

 

[(*steve*)]

It sounds very much like TTL voltage levels. I'm not familiar with I2S but it looks to be similar to I2C in that signals are actively pulled low, and passively pulled high (which allows for multiple devices to be connected together on the same bus).

If you can't find a newer specification, then it is unlikely that the voltage levels have changed. It may be worth bearing in mind that those quoted vltage levels may be minimum specifications, not the actual voltages you might see.

For example, the specs for inputs may require that a low signal is detected from 0.8 volts and lower, and that a high from 2.0 volts and above. The corresponding output specs may be that a low pulls the bus down to at least 0.4V and high allows it to float up to at least 2.4V. The difference in specs between input and output allow for noise margin, so that some amount of noise or degradation of the signal is allowed.

Typical inputs may be more sensitive (say 0.9 to 1.8) and outputs more capable (0.3 to 2.6) and this may vary slightly by device (note that there may be other specs more deeply buried that limit the maximum as well as the minimums).

One normally thinks of digital signals as one voltage level or another, with fast rise times and nothing remotely analogue about them. However in reality this is never truly the case. This is a spec for sending signals over a bus, a situation that has a habit of being most troublesome for fast rise and fall times, clean signals, and specific voltage levels (oops!).

In reality, the stray capacitance, inductance, and resistance all combine to create weird filter effects that reduce rise and fall times, cause ringing and reflections of signals, and all manner of other stuff. The signal at one end of a bus may bear very little resemblance to the signal at the other.