Design Criteria for Reconstruction Filter-Optimized Sample and Hold Circuits
The digital to analog conversion process in the digital audio world has three major modules: Digital to Analog Converter (DAC), Sample & Hold (S&H)) or Deglitcher and Reconstruction Low Pass Filter (LPF). The over-all requirements on these modules depend on the word length (normally 14 to 16 bit), the sampling rate (44 to 48 kHz) and the used signal processing procedures. The output signal spectrum of a S&H circuit depends on the type of the S&H. This, combined with word length, sampling factor and sampling rate defines the requirements on the reconstruction filter. For the judgement upon the applicability of a S&H in a given combination of DAC/ S&H/ LPF the natural audio signal is simulated by using three different test signals (sinus and hard band limited square and triangle). The type of the S&H circuit, the choice of its parameters and its influence on the input spectrum of the reconstruction filter is graphically demonstrated. The paper describes the different types of sample and hold circuits usable primarely in reconstruction circuits (zero and first order hold, rise adapted hold, polygon hold, exponential hold, higher order hold), their output spectra, limitations for the practical circuit design, and the design principles of sample & hold circuits.
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