Implementation of High-Performance Integrated Analog Filters and Filter Banks

M.Sc. E. Hjalmarson, Dr. H. Johansson, and Prof. L. Wanhammar

---

Background

This project involves the design and implementation of high-performance integrated analog filters and filter banks for use in analog/digital interfaces, anti-aliasing and reconstruction filters in A/D and D/A converters, etc.

There is a clear trend towards using analog signal processing instead of digital signal processing for wide band signals, particularly in applications with relatively low requirements on SNR. In such cases an analog data path can often be implemented using lower power consumption. Hence we can expect an increasing use of analog filtering. Further there are applications where analog filters are inherently necessary, for example in data converters. A wideband input signal to an A/D converter needs to be bandlimited in order to reduce the aliasing, occuring in the sampling process. The analog output of a D/A converter needs to be filtered by an analog reconstruction filter, to smooth the output spectrum.

Major problems in current design and implementation approaches are how to achieve sufficiently accurate and stable components,  large dynamic signal range, and alleviate non-linear effects. These problems are particularly severe in integrated analog filters. We believe that to improve the performance of integrated active filters all the filter design steps need to be cooptimized. A well designed high-performance itegrated filter includes approximation and synthesis problems solved combined with properly chosen implementation techniques.

A large number of active filter realizations need to be investigated and compared with respect to their suitability for integration. Efficient and reliable design tools need to be developed. This will enable fast, reliable and fair comparisons of different designs and techniques.

Research

We identify the following topics of research in this project

• Evaluation of filter structures
  A number of filter structures and techniques have to be evaluated with respect to their suitability to implement high-performance active filters.
• Design tool
  An efficient and reliable tool for design will be developed in order to support comparison of filter structures. This enables huge time savings as well as design reliability.
• New circuit configurations and modifications
  New circuit configurations or modifications to existing techniques will be investigated in corporation with Robert Hägglund, which is works in the INTELECT project  High-Performance Integrated Active Filters.

Research status

This project has recently started. A M.Sc final year project on the implementation of a place and route program for analog integrated circuits has been done. The program supports some special features like component matching, variable wire sizing and shielded paths.

Analog diplexers and trees of diplexer structures based on LC networks, i.e., analog LC filter banks are investigated with respect to element sensitivity. Dramatic improvement in sensitivity have been demonstrated compart to the "optimal" doubly terminated LC ladder structures. These low-sensitivity filter banks will serve as reference filters, i.e., will be simulated by using active filter techniques. The active filter structure will inherit the sensitivity of the reference filter. Note the low element sensitivity is strongly related to high dynamic signal range, which is one of the main targets in this project.

Members

Currently the following persons are involved in this project.

• Emil Hjalmarson, M.Sc., e-mail emilh@isy.liu.se, phone +46 13 281721.
• Håkan Johansson, Dr., e-mail hakanj@isy.liu.se, phone +46 13 137892.
• Lars Wanhammar, Prof., Dr., e-mail larsw@isy.liu.se, phone +46 13 281344.

Project funding

This project is funded by the INTELECT programme, which is financed by the Foundation for Strategic Research, SSF.

Publications

• E. Hjalmarson, "Implementering av verktyg för automatisk konstruktion av analoga kretsar"

M.Sc Thesis, Dept. of Electrical Engineering, Linköping University, Jun. 2000.

---

For information and questions regarding this web site, please contact Emil Hjalmarson, emilh@isy.liu.se