MF8

w w e e MF8 4th-Order Switched Capacitor Bandpass Filter h S Description General Features a t a D . w The MF8 consists of two second-order bandpass filter stages and an inverting operational amplifier The two filter stages are identical and may be used as two tracking second-order bandpass filters or cascaded to form a single fourth-order bandpass filter The center frequency is controlled by an external clock for optimal accuracy and may be set anywhere between 0 1 Hz and 20 kHz The ratio of clock frequency to center frequency is programmable to 100 1 or 50 1 Two inputs are available for TTL or CMOS clock signals The TTL input will accept logic levels referenced to either the negative power supply pin or the ground pin allowing operation on single or split power supplies The CMOS input is a Schmitt inverter which can be made to selfoscillate using an external resistor and capacitor By using the uncommitted amplifier and resistors for negative feedback any all-pole (Butterworth Chebyshev etc ) filter can be formed This requires only three resistors for a fourth-order bandpass filter Q of the second-order stages may be programmed to any of 31 different values by the five ‘‘Q logic’’ pins The available Q values span a range from 0 5 through 90 Overall filter bandwidth is programmed by connecting the appropriate Q logic pins to either V a or Vb Filters with order higher than four can be built by cascading MF8s Y Y Y Y Y Y Y Y U 4 t m o .c January 1995 MF8 4th-Order Switched ...