 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
AN540 Datasheet(PDF) 1 Page - Microchip Technology |
|
|
|||||||||||||||||||||||||||||
AN540 Datasheet(HTML) 1 Page - Microchip Technology |
|
|
1 / 17 page  © 1993 Microchip Technology Inc. DS00540B-page 1 Implementing IIR Digital Filters 4 Implementing IIR Digital Filters THEORY OF OPERATION Digital filters in most cases assume the following form of relationship between the output and input sequences. y(n) = - ∑ a iy(n - i) + ∑ bjx(n - j) The above equation basically states that the present output is a weighted sum of the past inputs and past outputs. In case of FIR filters, the weighted constants ai=0 and in case of IIR filters, at least one of the ai constant is non zero. In case of IIR, the above formula may be re written in terms of Z transform as: The above equation can further be rewritten in differ- ence equation format as follows: Realization of the above equation is called as the Direct Form II structure. For example, in case of a second order structure, M=N=2, gives the following difference equa- tions : d(n) = x(n) + a 1d(n-1) + a2d(n-2) (1) y(n) = b 0d(n) + b1d(n-1) + b2(d(n-2) (2) The above difference equations may be represented as shown in Figure 1. INTRODUCTION This application note describes the implementation of various digital filters using the PIC17C42, the first mem- ber of Microchip’s 2nd generation 8-bit microcontrollers. The PIC17C42 is a very high speed 8-bit microcontroller with an instruction cycle time of 250ns (@ 16 MHz input clock). Even though PIC17C42 is an 8-bit device, it’s high speed and efficient instruction set allows imple- mentation of digital filters for practical applications. Traditionally digital filters are implemented using expen- sive Digital Signal Processors (DSPs). In a system the DSP is normally a slave processor being controlled by either an 8- or 16-bit microcontroller. Where sampling rates are not high (esp. in mechanical control systems), a single chip solution is possible using the PIC17C42. This application note provides a few examples of imple- menting digital filters. Example code for 2nd order Infi- nite Impulse Response (IIR) filters is given. The follow- ing type of filters are implemented: • Low Pass • High Pass • Band Pass • Band Stop (notch) filter This application note does not explain how to design a filter. Filter design theory is well established and is beyond the scope of this application note. It is assumed that a filter is designed according to the desired specifi- cations. The desired digital filters may be designed using either standard techniques or using commonly available digital filter design software packages. Finite Impulse Response (FIR) filters have many advan- tages over IIR filters, but are much more resource intensive (both in terms of execution time and RAM). On the other hand, IIR filters are quite attractive for imple- menting with the PIC17C42 resources. Especially where phase information is not so important, IIR filters are a good choice (FIR filters have a linear phase response). Of the various forms used for realizing digital filters (like, Direct form, Direct II form, Cascade form, Parallel, Lattice structure, etc.) the Direct II form is used in this application note. It is easy to understand and simple macros can be built using these structures. ∑ b k Z -k M k=0 1 + ∑ a k Z -k H(z) = = Y(z) X(z) N k=1 N M y(n) = - ∑ a i y(n - i) + ∑ b j x(n - j) i=1 j=o M N i=o j=o X(n) b0 + Y(n) Z-1 b1 b2 -a1 -a2 Z-1 FIGURE 1 - 2ND ORDER DIRECT FORM II STRUCTURE (TRANSPOSED) AN540 4-129 |
Similar Part No. - AN540 |
|
Similar Description - AN540 |
|
|
|
Link URL |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link to Datasheet | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
