A filter is a device that modifies an electronic signal. This is often done to improve the quality of a signal and reduce the amount of noise in the signal. There are a wide variety of filter types, designs, functions, and construction that can be used, depending on the application. There are several filter functions:
- High pass – attenuate (or suppress the amplitude of) frequencies beneath a certain level
- Low pass – attenuate frequencies above a certain level
- Band pass – attenuate frequencies above and below a specified frequency range
- Band reject – attenuate frequencies within a specified frequency range
- All pass – passed all frequencies but changes the phase relationship between frequencies
Filters are used by , in many processes and equipment, from audio tuners to laboratory data acquisition of signals from sensors.
Types of Filters
There are three types of filters:
- Analog – Analog filters are used to filter analog signals. Passive analog filters can filter analog signals without any additional power input, and are constructed from a combination of resistors, inductors, and capacitors.
- Mechanical - Mechanical filters are a special type of analog filters that are physical components. Mechanical filters work in purely mechanical systems, or convert an electrical signal into a mechanical vibration, which is then mechanically filtered, and then converted back into an electronic signal.
- Digital - A digital filter uses mathematical algorithms to filter a discrete time digital signal. If an analog signal is to be filtered with a digital filter, the signal must first be fed through an analog-to-digital converter (ADC). Digital filters can perform more complex filtering options than analog filters can. A digital filter can also be designed directly into an integrated circuit, allowing for a smaller electronic package.
Some hybrid filters do exist, particularly analog amplifiers combined with mechanical resonators.
Filter Applications
Filters are used in a variety of products and processes:
- Radio – A radio can be tuned to a specific frequency through a variable filter. The filter attenuates all frequencies above and below the specified frequency.
- Audio – Filters are used to direct specific frequencies to different speakers. For example, a low-pass filter is used on a signal being directed to a woofer speaker for low-freqency signals, and a high-pass filter is used for the signal being directed to a tweeter speaker.
- Image Processing – Filters can be used to modify digital images
- Data Analysis – A high-pass filter is often used to remove high frequency noise from a data signal. Bandstop filters can also be used to remove specific frequencies that are introduced by outside sources, such as 60 Hz electrical noise
Filters are an important part of many consumer products, industrial processes, and research activities. A variety of filter designs and functions are available and new options continue to become available.
Susan Kristoff - Susan Kristoff is mechanical engineer by trade, but has a diverse set of professional and personal interests. The glue that binds all of ...
Join the Conversation