Siemens ASIC SIM 1-2, Руководство по эксплуатации функций

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Application Examples
SIM 1-2
48
C79000-G8976-C215-01
4.2.2 Internal Pulse Duration Demodulator
Description of the Input Evaluation
In Galvanic Isolation Mode (GIM=H) the wanted signal for the PD demodulator is
obtained from the collector signal of the optocoupler transistor using a comparator.
The signal transitions (especially during operation with low currents) behave
differently over time depending on the characteristics of the optocoupler itself and
its circuitry.
Evaluation with a fixed discriminator threshold on the comparator leads to different
delays of the edges causing unacceptable signal distortions. It is possible to
minimize the distortion if the when the switching times of the comparator are close
to the beginning of the signal changes.
This, however, requires different switching thresholds dependent on the edge or
signal directions. A suitable adaptation of the switching threshold can be
implemented if this is derived from the wanted signal itself.
The principle behind this dynamic input signal evaluation is shown in the figure
below. At the same time, the reference signal of a comparator is obtained from the
wanted signal over a damping element a and a delay element.
Circuit Principle of Input Evaluation
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