High Pass Filter Design

- high pass filter design techniques, equations and concepts and how to transform the design from a low pass starting point.

The design of low pass and high pass filters is relatively straightforward.

Normally, a low pass filter is used as the starting point and then this is transformed to provide the high pass filter design.

The concepts for the basic low pass filter design are provided on the previous page. Once the basic design has been achieved, the high pass filter design can then be effected by easily transforming the values to give the required high pass filter functionality.


High pass filter design basics

Although there are programmes that will enable the design of a high pass filter circuit, often a more manual method may be required. The typical approach that is used is to design a low pass filter, and then transform this to a high pass filter design.

When choosing the basic requirements for the high pass filter design, elements such as in-band ripple will remain the same.

It is possible to utilise the same response curves by inverting the f/fc axis. This is because the response of the high pass filter is the inverse of the low pass filter in frequency terms. In other words in a high pass filter design, it is necessary to measure the attenuation at frequencies at a proportion below the cut-off frequency rather than above the cut-off frequency. For example an attenuation level at 1/2 the cut-off frequency may be required for a high pass filter design rather than 2 times the frequency.

RF high pass filter design

Using this information and any other it is possible to find a response that satisfies the requirements. The next stage is to determine the values of the circuit elements for the normalised low pass filter version.


Circuit element transformation

After the circuit elements have been determined, the next stage in the high pass filter design is to transform the circuit elements from the low pass version into one for the high pass filter design.

To complete the high pass filter design, the element values are easily determined by replacing each filter element with an element of the opposite type, i.e. replace a capacitor by an inductor and an inductor by a capacitor. The value of the capacitor is equal to the reciprocal of the inductor and vice versa, i.e. Ln = 1/Cn and Cm = 1/Lm.

RF high pass filter design

The values in the above example and purely fictional and only to be sued for the purposes of the explanation. These would then transform to:

RF high pass filter design

By Ian Poole


<< Previous   |   Next >>



Read more popular RF filter tutorials . . . . .

Filter basics Filter design HPF design  
Simple LPF Simple HPF Simple BPF  
Butterworth Chebyshev Bessel Elliptic / Cauer

Share this page


Want more like this? Register for our newsletter





What makes e-paper the best display technology for Makers? Scott Soong | Pervasive Displays
What makes e-paper the best display technology for Makers?
Scott Sonng or Pervasive Displays discusses how e-paper technology is contributing to the world of makers rather than just major companies enabling makers to utilise its advantages in projects based around Raspberry Pi and other single board computers.
Training
Online - Transmission Lines, S-Parameters & Smith Chart
Understand these essential concepts without complex mathematics

More training courses

Whitepapers
High Voltage DC Distribution
Vicor explains how high-voltage DC distribution is key to increased system efficiency and renewable-energy opportunities.

More whitepapers










Radio-Electronics.com is operated and owned by Adrio Communications Ltd and edited by Ian Poole. All information is © Adrio Communications Ltd and may not be copied except for individual personal use. This includes copying material in whatever form into website pages. While every effort is made to ensure the accuracy of the information on Radio-Electronics.com, no liability is accepted for any consequences of using it. This site uses cookies. By using this site, these terms including the use of cookies are accepted. More explanation can be found in our Privacy Policy