[sdiy] Suitable DACs for Demultiplexing

[Ingo Debus]

Am 21.10.2009 um 22:17 schrieb Tom Wiltshire:

> However, I ran into a problem. The DAC is a Sigma-Delta type and  
> uses an upsampling digital filter to produce a pulse train at 256  
> times the sample frequency. What this seems to mean is that the  
> output is filtered. Instead of stepping abruptly from one sample to  
> another, it glides smoothly between them. Obviously for audio (the  
> DAC's intended purpose) this is ideal behaviour, but for  
> demultiplexing it's a nightmare. The output sample has only just  
> reached the level you wanted it to have when it is time for the  
> next one to be sent. The effect on the demultiplexed outputs is for  
> an 'echo' of the previous channel's signal to break through on each  
> output channel.

Could still work if you add a delay after outputting tha DAC value  
and before enabling the multiplexer. This delay has to be long enough  
for the DAC output to settle.
This requires a multiplexer that can be disabled of course, like the  
4051 for instance.

Ingo