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First-order hold (FOH) is a mathematical model of the practical reconstruction of sampled signals that could be done by a conventional digital-to-analog converter (DAC) and an analog circuit called an integrator. For FOH, the signal is reconstructed as a piecewise linear approximation to the original signal that was sampled.
The function is defined by the three poles in the left half of the complex frequency plane. Log density plot of the transfer function () in complex frequency space for the third-order Butterworth filter with =1. The three poles lie on a circle of unit radius in the left half-plane.
A forth order filter has a value for k of 1, which is odd, so the summation uses only odd values of i for and (), which includes only the i=1 term in the summation. The transfer function, T 4 ( j ω ) {\displaystyle T_{4}(j\omega )} , may be derived as follows:
The transfer function coefficients can also be used to construct another type of canonical form ˙ = [] + [] () = [] (). This state-space realization is called observable canonical form because the resulting model is guaranteed to be observable (i.e., because the output exits from a chain of integrators, every state has an effect on the output).
The Smith predictor (invented by O. J. M. Smith in 1957) is a type of predictive controller designed to control systems with a significant feedback time delay. The idea can be illustrated as follows.
Higher-order CIC structures are obtained by cascading identical simple moving average filters, then rearranging the sections to place all integrators first (decimator) or combs first (interpolator). Such rearrangement is possible because both the combs, the integrators, and the entire structure are linear time-invariant (LTI) systems .
A resistor and either a capacitor or an inductor can be configured as a first-order high-pass filter. The simple first-order capacitive high-pass filter shown in Figure 1 is implemented by placing an input voltage across the series combination of a capacitor and a resistor and using the voltage across the resistor as an output. The transfer ...
The transfer function for a first-order process with dead time is = + (), where k p is the process gain, τ p is the time constant, θ is the dead time, and u(s) is a step change input. Converting this transfer function to the time domain results in