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Filter building block ensures gain, phase repeatability

Posted: 02 May 2003 ?? ?Print Version ?Bookmark and Share

Keywords:linear technology? lt1568? active rc filter? high frequency filter?

Building a high-frequency filter for a cellular basestation or high-speed data acquisition system from discrete components is a costly and time-consuming process. Linear Technology Corp. hopes to reduce the cost and all but eliminate the time with its LT1568, an active RC filter building block that is precisely trimmed for predictable, repeatable performance.

"A great many factors are involved in filter design, each factor has an error associated with it and all of the factors interplay together," said product-marketing manager Erik Soule. "The BOM cost is high because of the need to buy higher-quality components than are actually needed. Engineering time adds to the cost, and if the group delay on the filter is off even by just a few nanoseconds, the production failure rate on large, multichannel boards can [be] a huge problem."

Designed for channel anti-aliasing or reconstruction applications within a 200kHz to 10MHz range, the LT1568 integrates a single four-pole low-pass filter or matched pair of two-pole Butterworth low-pass filters, and can also be connected as a bandpass filter. It offers the matched filter response (to 0.25dB) and channel-to-channel gain and phase repeatability that are critical for I/Q, Soule said.

Operating from a single 2.7V to 5V supply, the filter features a 92dB SNR and -84dB THD. Its internal capacitors are trimmed to 75 percent. Other features include rail-to-rail input and output voltages, single-ended or differential output, single-ended-to-differential conversion, and a power shutdown pin.

The device can be used as a dual matched second- or third-order low-pass filter, and fourth-order or higher response can be achieved by cascading the two second-order sections.

The LT1568 is packaged in a 16-pin narrow-body SSOP with the footprint of an SO-8, and specified for operation over commercial and industrial temperature ranges. It's priced from $4.25 in 1,000-piece quantities.

- John H. Day

EE Times

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