MF8 Datasheet, PDF (1/24 Pages) National Semiconductor (TI) – 4th-Order Switched Capacitor Bandpass Filter

January 1995
MF8 4th-Order Switched Capacitor Bandpass Filter
General Description
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 sec-
ond-order bandpass filters or cascaded to form a single
fourth-order bandpass filter The center frequency is con-
trolled 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 refer-
enced 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 self-
oscillate using an external resistor and capacitor
By using the uncommitted amplifier and resistors for nega-
tive 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 V^b
Filters with order higher than four can be built by cascading
MF8s
Features
Y _{Center frequency set by external clock}
Y _{Q set by five-bit digital word}
Y _{Uncommitted inverting op amp}
Y _{4th-order all-pole filters using only three external}
resistors
Y _{Cascadable for higher-order filters}
Y _{Bandwidth response characteristic and center}
frequency independently programmable
Y _{Separate TTL and CMOS clock inputs}
Y _{18 pin 0 3 wide package}
Key Specifications
Y _{Center frequency range 0 1 Hz to 20 kHz}
Y _{Q range 0 5 to 90}
Y _{Supply voltage range 9V to 14V (}g_{4 5V to} g_7V)
Y _{Center frequency accuracy 1% over full temperature}
range
Typical Application Connection Diagrams
Dual-In-Line Package
Fourth-Order Butterworth Bandpass Filter
TL H 8694 – 1
Top View
TL H 8694 – 2
Order Number MF8CCJ
or MF8CCN
See NS Package Number
J18A or N18A
C1995 National Semiconductor Corporation TL H 8694
RRD-B30M115 Printed in U S A