1.1 Zero Order Hold

Higher the order of the derivatives to be estimated is, larger will be the number of delayed pulses required. Since time delay degrades the stability of a closed loop control system, using higher order derivatives of f(t) for more accurate reconstruction often causes serious stability problem. Moreover a high order extrapolation requires complex circuitry and results in high cost.

For the above reasons, use of only the first term in the power series to approximate f(t) during the time interval is very popular and the device for this type of extrapolation is known as zero-order extrapolator or zero order hold. It holds the value of f(kT) for until the next sample arrives. Figure 1 illustrates the operation of a ZOH where the green line represents the original continuous signal and brown line represents the reconstructed signal from ZOH.

 

Figure 1: Zero order hold operation