RU5620A

The RU5620A has the following features including Universal: Implement any classical filter;Easy to use: No external components required;Look up table responses: No calculations required ;Q and fo independently programmed;Clock and control lines are TTL- and CMOS-compatible;Small size: 18-pin DIP;Low current consumption: Typically 4.5 mA.

The RU5620A is a digitally-programmable Universal Active Filter (UAF). It is implemented using Reticon's proven double poly NMOS switched-capacitor filter technology. It consists of a single second-order section with Q and fo programmable by separate 5-bit digital control words.   Basic filter types are selected by hard-wiring or switch-selecting the filter inputs Higher-order filters can be obtained by cascading RU5620A devices.  This cascadability, microprocessor control, and universality make the RU5620A an ideal, cost effective filter building block. The pinout configuration is shown in Figure 1, a block diagram is shown in Figure 2, and package dimensions are in Figure 13.The Q and center frequency response of the filter are controlled by seperate 5-bit digital inputs which may be microprocessor-controlled or hard-wired.  The clock-to-center frequency ratio (fc/fo) can be varied from 50 to 200 in 32 logarithmic increments.The Q values are selectable in 32 approximately logarithmic increments, ranging from 0.57 to 85. The typical filter responses can be chosen from Table 5, thus avoiding the cumbersome calculations and external components that other UAF devices require. The filter type is chosen by hard-wire programming the filter inputs as shown in Table 4. For optimum performance, all unused inputs should be grounded.

Double-poly NMOS capacitors are extremely stable over temperature. However, the impedances of parasitic capacitances(which affect clock feedthrough and power supply ripple rejeclion noise contributions) will vary in amplitude as a function of clock frequency or the frequency content of the power supply ripple.  Filtering of the power supply lines wilt minimize ripple noise and will help protect the device from random power line transients, including power-up spikes.