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FIR kit flies right.

Quickfilter QF1D512 Development Kit, Quickfilter Technologies. $199.

I admit a fascination with filter circuits and have designed my share, from op-amp-based active filters to switched-capacitor filters. But I drew the line at digital filters because they require a lot of math and hardware. Then I learned about Quickfilter's QF1D512 FIR-filter engine that provides a 512-tap filter in a tiny chip. Quickfilter sent me a QF1D512 Development Kit to try, and I enjoyed working with it. If you need a filter in a design, this device and the development kit deserve your close attention.

The kit includes a development board, software, cables, and a startup guide. The guide provides plenty of screen shots and clear, easy-to-follow instructions, so I installed the software without any problems. The CD-ROM contains a lot of documentation, including a 35-page manual for the kit. After you start the QF1D512 software, click Help and look under Open Documents Folder. That folder also holds product specifications and a schematic diagram for the development board.

As I connected the board to my PC's USB port, several additional steps configured drivers. After that, I connected the board to my lab PC's sound card and the fun got underway. The software installed a white-noise WAV file, which provided a test signal for my filter designs. (Quickfilter's Audio-Mojo add-on board, due out about now, provides codecs so developers can test filter designs on their own audio signals.)


The design software lets you choose one of four filter types; low-pass, high-pass, band-pass or band-stop, and you can choose from four filter-coefficient algorithms. A multi-band Parks-McClellan type of filter allows you to combine several filter types to meet complicated signal-processing requirements. A graphical editor lets developers plot frequency-response curves that the program converts into filter coefficients. I "designed" several filter types and downloaded filter coefficients to the QF1D512. An FFT display let me observe the effect of my FIR filter on the white-noise signal. Additional windows displayed the chip's status and other filter and chip details.

As you design a filter, a graphic display shows specifications that relate to filter performance. Numeric data you enter provides design criteria. After I designed a simple filter, the filter's calculated performance and impulse response appeared--a nice way to check expectations.

The software let me quickly edit filter values without first downloading them to the chip. After I completed a filter design, downloading coefficients occurred quickly and the FFT display showed how my filter processed the white-noise signal. If you try to do something a filter cannot, such as design a low-pass filter with the same pass-band upper frequency and stop-band lower frequency, an error "balloon" alerts you to the problem.

The QF1D512 filter chip has more capabilities than a short review can cover. A data-format editor, for example, lets you program the chip to accept data from almost any serial-output ADC. You can load and save configuration files, which simplifies programming during prototyping and production. And, you can cascade filters.

by Jon Titus, Senior Technical Editor

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Title Annotation:Books & Kits
Author:Titus, Jon
Publication:ECN-Electronic Component News
Date:Jun 1, 2007
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