Electronic Design

Chip Set Simplifies Low-Frequency Design

The collapse of the I-35 bridge in Minneapolis on August 1 was a catastrophe. But it should provoke a greater effort to monitor the movement and stresses of buildings, bridges, and rail tracks using strain gauges, piezo sensors, and other inputs receiving vibration sensor data. For designers, that means a need for low-frequency and ultra-low-frequency filters.

The eponymously named AnadigmFilter1 chip set is available as a circuit-board module as well. It combines Anadigm's dynamically programmable Analog Signal Processor (dpASP) technology and a state machine to enable designers to quickly create a dynamically programmable filter for frequencies from dc to 600 kHz.

Filter types comprise sixth-order, low-pass, band-pass, high-pass, or band-stop circuits with Butterworth, Bessel, Chebyshev, or inverse Chebyshev characteristics. The band-pass and band-stop filters provide two pass/stop bandwidths and the ability to configure the circuit to bypass mode.

Designers can choose either of two fixed input stages and set them up for gain or attenuation, level shifting, single-ended to differential conversion, or first-order low-pass or high-pass filtering by means of external resistors and capacitors. Inside the dpASP chip, a sixth-order filter is programmed either by using the DIP switches, by hardwiring, or, if one wants to sweep the frequency response, dynamically from a controller.

Adjusting the internal clock dividers or changing the external reference clock permits larger, discrete changes in filter frequency. The accuracy of filter gain and corner frequency is typically better than 1%.Typical operating power is 200 mW, with a low-current standby mode.

Structural monitoring is a hot topic. But using the AnadigmFilter1 as a board or in a custom configuration also could benefit applications with ultrasonic, acoustic, or other low-frequency signals that require filtering.

In quantities of 1000 units, the AN231E04 dpASP and AN236C04 state machine are priced at $11.28 each. The AN236K04-EVAL2 evaluation board costs $199. All three products are available directly from Anadigm or from NuHorizons.


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