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Chapter 6: Filter Design

By Cotter W. Sayre
From Complete Wireless Design

Overview

A filter is used to selectively pass or attenuate a particular band of frequencies, and can be constructed of LC, RC, LCR, LR, or distributed components, and can be either active or passive in nature. Active filters will contain some sort of amplifier combined with any of the above lumped passive components, while passive filters will simply employ lumped or distributed components, with ceramic and crystal filters found in many passband and stopband applications. Any of these will dramatically improve a filter s shape factor (steepness of its skirts), as well as provide a variety of bandwidths all the way from ultranarrowband to wideband. Surface acoustic wave (SAW) passive filters are also becoming more common, and are available with superb shape factors from narrowband to ultrawideband.

The RF spectrum contains quite a broad range of frequencies. Obviously, a method had to be found that would allow us to segregate a small chunk of this spectrum for transmission and reception, without interfering with other communications channels. This can be done with the use of untuned and tuned filters. The basic passive untuned LC filter can function as a low-pass or high-pass filter because of the inductor s ability to increase its reactance, and a capacitor s ability to decrease its reactance, as the frequency is increased. This makes the untuned LC filter frequency-selective. To act as a low-pass filter and attenuate higher frequencies (Fig. 6.1), an inductor will be arranged in series (blocking the high frequencies), while a...

Copyright The McGraw-Hill Companies, Inc. 2001 under license agreement with Books24x7

Products & Services
Passive filters are implemented using only passive components such as resistors, capacitors and inductors. These filters do not produce any amplification of the input signal. Learn more about Passive Filters
Active filters are electronic filers that use active components such as voltage amplifiers or operational amplifiers. The amplifier shapes and stabilizes the behavior of the filter, and serves as a buffer interface to the driven component. Search by Specification | Learn more about Active Filters
Active band pass filters are used to attenuate frequencies below and above a range of frequencies (i.e., the bandwidth or passband of the filter). Learn more about Active Band Pass Filters
Signal filters block or decrease (attenuate) unwanted frequencies or signal wave characteristics. Search by Specification | Learn more about Signal Filters
Active low pass filters pass signals from low frequencies and reject signals from high frequencies. Search by Specification | Learn more about Active Low Pass Filters

Product Announcements
Anatech Electronics, Inc. - Lumped Elements (LC) Filters custom...
Anatech Electronics Lumped Elements filters covers the frequency range from 300 KHz to 15 GHz. The Lumped Elements filters are available in 2 to 15 sections, with power handling as high as 2Kwatts. (read more)
International Manufacturing Services, Inc. - IMF2293 Thick Film S-Band 2.5 GHz Low Pass Filter
A new thick film S-band 'drop-in' 2.5GHz low pass filter – planar, and completely integral – has been introduced by International Manufacturing Services, Inc. (IMS) as part of IMS' IMF... (read more)
International Manufacturing Services, Inc. - IMF2262 Thick Film L-band 1.6 GHz Low Pass Filter
Stable, compact, and high performance, the IMF2262 thick film L-band 1.6 GHz low pass filter is a new addition to IMS' IMF Series of filters. The IMF Series low pass filters (LPF) afford the customer... (read more)
Spectrum Advanced Specialty Products - D-Sub Connectors Now with Shorter Lead Times
Spectrum Control now offers its high performance series 700 D-subminiature filtered connectors in significantly shorter lead times. With their new State College, PA ceramics facility in full... (read more)
Spectrum Advanced Specialty Products - High Current/High Voltage Resin Sealed Filters
Spectrum Control, Inc. introduces a full line of high current/high voltage resin sealed EMI/RFI filters with current ratings to 100 Amps. (read more)
Spectrum Advanced Specialty Products - Power Filters Meet New Global EMI Standards
Spectrum Control, Inc. offers customized EMI power filters designed to meet updated requirements for filtering conducted emissions in the frequency range of 150 kHz to 30 MHz. NARTE-certified... (read more)
RESON - VP2000 Voltage Preamplifier with Band Pass Filters
The VP 2000 is a 1 MHz bandwidth voltage preamplifier designed for use in conjunction with piezoelectric hydrophones. VP 2000 offers excellent low-noise performance over the entire frequency range;... (read more)
 

Topics of Interest
Overview Mixers are 3-port active or passive devices. They are designed to yield both a sum and a difference frequency at a single output port when two distinct input frequencies are inserted into... (Read More)
Ron Mancini Thomas Kugelstadt 22.1 Introduction What is a filter? A filter is a device that passes electric signals at certain frequencies or frequency ranges while preventing the... (Read More)
11.7 Summary Analog filters are defined over a continuous range of frequencies. They are classified as low-pass, high-pass, band-pass and band-elimination (stop-band). An all-pass or phase... (Read More)
Why is modulation needed? Though there are many reasons, for our purposes here there’s only one: to translate (move) a given signal’s information to a different frequency. Why this is... (Read More)
4.5 The Gyrator: A Valuable Tool to Realize High-Value On-Chip Inductances A tuned amplifier can be interpreted as a band-pass filter that amplifies (passes) the frequencies in a certain band and... (Read More)
See more product announcements for Passive Filters
Video Isolation Transformers -

Video Isolation Transformers -
North Hills Signal Processing


V.C.O HDM7160

V.C.O HDM7160
Shoulder Electronics Ltd.


SAW FILTER HDAF389A4Dc

SAW FILTER HDAF389A4Dc
Shoulder Electronics Ltd.


11 See more product announcements for Passive Filters