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Digital Filter with Fast Response Time and Frequency Selective Coefficients

IP.com Disclosure Number: IPCOM000108639D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 4 page(s) / 121K

Publishing Venue

IBM

Related People

Chiang, S: AUTHOR [+2]

Abstract

Disclosed is a digital filter with a combined Finite Impulse Response and Infinite Impulse Response that provides a faster response time and a reliable signal. This system also provides the capability to adjust the cutoff frequency dynamically or statically as the application requires. The technique of this digital filter can be applied in many different applications and to meet specific needs (low pass, high pass, etc.).

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Digital Filter with Fast Response Time and Frequency Selective Coefficients

       Disclosed is a digital filter with a combined Finite
Impulse Response and Infinite Impulse Response that provides a faster
response time and a reliable signal.  This system also provides the
capability to adjust the cutoff frequency dynamically or statically
as the application requires.  The technique of this digital filter
can be applied in many different applications and to meet specific
needs (low pass, high pass, etc.).

      The filter algorithm has two phases, a fast-charge phase and a
normal filtering phase.  The magnitude of the signal is evaluated
during the fast-charge phase, when the Finite Impulse Response (FIR)-
moving average which can be described:

                            (Image Omitted)

      Based  on  the  evaluated  magnitude, the dynamic
state-variables of the normal filtering phase, Infinite Impulse
Response, can be calculated in one program cycle and then switched
into the normal filtering phase. Therefore, the algorithm provides
faster response times for the filter. In order to ensure the validity
of the technique, this technique is implemented with a Bessel 4-pole
low pass filter, and the transfer function is derived:

      The method is implemented in Direct Form II, shown in Fig. 1.
The dynamic state-variables S11, S12, S21, S22 function similarly to
the capacitors in an analog filter which need a fixed amount...