Dynamically programmable 600 kHz 6th-order filter

EDN Europe, 17 Aug 2007

17th August 2007 - Anadigm has introduced AnadigmFilter1, the first in a family of chipsets using its dynamically programmable dpASP and a state machine. The chip provides a universal analogue filter architecture that DC to 600 kHz, using a 6th order filter. Low pass, band pass, high pass or band stop circuits can be quickly implemented, without digital-to-analogue conversions or writing DSP or microprocessor programming code. The designer selects from a library of pre-sets: on-board filters can be selected to emulate Butterworth, Bessel, Chebyshev and inverse-Chebyshev filter approximations. Applications include low and ultra-low frequency filters for tasks such as monitoring the movement and stresses of buildings, bridges and rail tracks; strain gauges; and piezo sensors or other inputs receiving vibration sensor data. You can also use the device with ultrasonic, acoustic or other low-frequency signals.
As well as the four types of filters, you set frequency and gain control using a 16-bit control interface, DIP switches or hard wired pull-up and pull-down resistors. The chipset input consists of a choice of one or two fixed input stages (which can be summed), each of which can be configured using external resistors and capacitors to provide gain or attenuation, level shifting, single-ended-to-differential conversion and 1st-order low-pass and high-pass filtering. Gain and stop-band frequency can be dynamically controlled in real time without interruption to the signal, allowing filter gain and frequency to be swept across one full octave of the frequency spectrum. Large changes in filter frequency are realised by adjusting the internal clock dividers, or external reference clock frequency changes to the clock. Summing stage input connections and filter circuit architecture or approximation can also be realised in real time when these parameters are changed, although there will be a momentary break in the circuit connections and step response settling time. Filter gain and corner frequency settings are typically better than 1% accurate; these settings are stable over the entire industrial temperature range - with almost no temperature drift. Chipset power consumption is typically 200 mW. Low-current standby mode/sleep mode is also available.
The AN236K04 chipset consists of the AN231E04 dpASP and AN236C04 State Machine and costs US$11.28 (1000). The AN236K04-EVAL2 AnadigmFilter1 evaluation board, which includes the AN236K04 chipset, costs US$199.00.