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Old 9th November 2012, 05:56 PM   #11
oshifis is offline oshifis  Hungary
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I mean something like this:
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Old 9th November 2012, 08:20 PM   #12
DF96 is offline DF96  England
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Quote:
Originally Posted by oshifis
The analog pulses coming from the DAC could be passed through a C-R differentiating circuit that converts them to short spikes. The negative spikes should be removed by a diode. The peak amplitude of the positive spikes is identical to the original pulses, and their waveform is an exponential decay (following the e^(-RC/t) function). If the waveform of each pulse is identical, it will be insensitive to jitter. Also the short pulses are different from the S/H in that there is no sin(x)/x rolloff.
The spikes will be equal in height to the difference between successive pulses, not the pulses themselves. If you could get spikes proportional to the actual pulse size then you would avoid the usual NOS HF roll-off. You would not avoid jitter - in fact I wonder if jitter might be worse. The output reconstruction filter would still need (in theory) to be a brickwall at 22kHz; in practice it might need to have an even better (i.e. higher attenuation) stopband as the spikes have more HF content than the usual sample-and-hold.

For a NOS DAC the rolloff is actually an advantage as it reduces the problems created by the poor filtering often used with NOS.
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