RU5621A

The RU5621A  has the following features including Easy to use;Small size: 14- or 20-pin DIP;Low power consumption:as low as 25 mW per package;Low sensitivity to external component variation;Wide Q range: 0.5 up to 500;Wide clock-to-center/corner frequency range: 25:1 to over 100:1.

The RU5621A is double-poly NMlJS resistorprogrammable switched-capacitor universal active filters. With only an external clock and up to seven external resistors, any classical filter type can be configured. Center frequencies of all filter types including all pass and notch can be adjusted by changing the external resistor ratios or varying the clock frequency.  Therefore, filter accuracy and stability are relatively insensitive to component variations. Filter Qs are also adjustable using resistor ratios. The filter sections are cascadable and up to an eighth-order filter may be achieved with only one package. The pinout configurations for these devices are shown in Figure 1,and package dimensions are shown in Figure 5.Selection of resistor values is also important. In all cases, unused inputs should be grounded to prevent crosstalk from these pins (see Table 4).The gain from Vout to BP- can be used to control the Q of the second-order section. If Vout is tied directly to BP- then the Q is nominally 0.5 (this will vary as a function of feedback to LP). If a resistor divider is tied between Vout and BP-then the Q can be adjusted to a value greater than 0.5. If the input signal is resistor summed into this input, then an inverting bandpass filter can be implemented.  The BP+ and HP inputs are used primarily as inputs for the high pass and non-inverting bandpass modes.

As with all sampled data devices RU5621A , care should be taken to prevent aliasing of signals into the passband. If signals exist near the sample rate or its harmonics that might be aliased into the passband, then prefiltering is required.  Since clock-to-center frequency ratios on switched-capacitor filters are quite large, this can usually be accomplished with a simple RC filter.The output of the devices will contain about 30 mVrms clock feedthrough.  If this noise can affect system performance, it should be removed.  Once again, a simple RC is usually adequate.  When cascading second-order sections that have the same sample rate, it is only necessary to provide antialias filtering to the first filter section.