Digital filters are devices that modify the spectrum and phase of an input signal. They perform a mathematical operation on a set of digital data. They are one of the biggest parts of digital signal processing. They are used for separating unwanted information from signals or restoring signals. There are two main types of digital filters, Finite Impulse response filters (FIR) and Infinite Impulse Response Filters (IIR). The main difference between these two filter types is that FIR filters have a feed-forward signal path, while IIR filters have a feed-back signal path.
Filters typically have a single input and a single output. Filters are designed to have a specific frequency response. There are 2 main types of digital filters that are characterized by the length of their impulse response. These responses could remove high-frequency noise, normalize offsets and many other operations. The maximum frequency of a digital filter is determined by the Nyquist frequency limit. Digital filters are implemented using fixed-point arithmetic. Circular buffers are used to prevent the need to move data values around in memory. The newest data point simply replaces the oldest one.
FIR Filters
[[S-Domain Low-Pass Filter]]
[[Digital Filter Input]]
[[Digital Filter Output]]
[[Nyquist Frequency Limit]]
[[Decimation Filter]]
[[Digital Filter Design]]
IIR Filters
[[Transfer Function of a Digital Filter]]
[[Transition Band]]
[[Circular Buffer]]
[[Fixed-Point Arithmetic]]
[[Design considerations for creating a satellite constellation]] – Big use of filters.
Space Shuttle PIO– was prevented with a gain-reduction filter
[[Panavia Tornado SPILS]] – used pre-filters to tune handling qualities without affecting the feedback system.
[[Broadband Direction Finding]] – uses a digital filter bank
[[F-8 DFBW Flight Control System]] – used modifiable digital filter coefficients
[[JAS-39 Processors]] – abstract data types are useful for implementing filters
[[Delay Lines]] – can be used to implement digital filters
[[Filters for Sensor Conditioning]] – you should use the simplest digital filter design as possible
Sources
- D. Marinov, “Part 1: Digital filters in FPGAs,” VHDLwhiz. Accessed: Nov. 30, 2022. [Online]. Available: https://vhdlwhiz.com/part-1-digital-filters-in-fpgas/
- FIR Filter Design and Software Implementation – Phil’s Lab #17, (Dec. 20, 2020). Accessed: Jan. 02, 2023. [Online Video]. Available: https://www.youtube.com/watch?v=uNNNj9AZisM
- ADMIN, “Difference between IIR and FIR filters: a practical design guide,” ASN Home. Accessed: Jan. 08, 2023. [Online]. Available: https://www.advsolned.com/difference-between-iir-and-fir-filters-a-practical-design-guide/
Backlinks
[[Digital Signal Processing]]
[[Fixed Point Arithmetic]]
Impulse Response
[[Transfer Function]]