MF8CCJ National Semiconductor, MF8CCJ Datasheet - Page 16

• Manufacturer Part Number: MF8CCJ
• Manufacturer: National Semiconductor

Specifications of MF8CCJ

• Architecture: Switched Capacitor
• Cutoff Frequency: 20KHz
• Dual Supply Voltage (typ): ±5V
• Power Supply Requirement: Single/Dual
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Package Type: MDIP
• Lead Free Status / RoHS Status: Not Compliant

1 0 Application Information
1 5 TRACKING AND CASCADED SECOND-ORDER
The individual second-order bandpass stages may be used
as ‘‘stand-alone’’ filters without adding external feedback
resistors The clock frequency and Q logic voltages set the
center frequency and bandwidth of both second-order
bandpass filters so the two filters will have equivalent re-
sponses Thus they may be used as separate ‘‘tracking’’
filters for two different signal sources as in Figure 2a or
cascaded as in Figure 2b For individual or cascaded sec-
ond-order bandpass filters the
amplitude response are given by the following two equa-
tions
where
BW(
various values of Q H
FIGURE 12 H(s) For second-order bandpass filters with
BANDPASS FILTERS
b
3)
e
the
H(s)
FIGURE 11 Eighth-Order multiple-feedback bandpass filter using two MF8s The circuit shown
b
BW(
e
3 dB bandwidth of the overall filter
accepts a TTL-level clock signal and has a clock-to-center-frequency ratio of 100 1
b
2
o
3)
c
normalized in each case to 0 dB
e
s
2
f
Q
0
a
2
w
b
Q
w
(1 N)
Q
0
3 dB bandwidth and the
0
s
s
a
b
w
1
0 2
N
(Continued)
TL H 8694–20
(1)
(2)
16
12 Curves are shown for several different values of Q Cen-
Q
f
w
N
H(s)
H(s) for a second order bandpass filter is plotted in Figure
ter frequency is normalized to 1 Hz and center-frequency
gain is normalized to 0 dB
To find the necessary order n for cascaded second-order
bandpass filters using the nomograph in Figure 13 first de-
termine the
SBW and minimum stopband attenuation A
tical line up from SBW BW(
across from A
just above the point of intersection of the two lines Remem-
ber that each second-order filter section will have a center
frequency gain of 2 so the overall gain of a cascaded filter
will be 2
Cascading filters in this way may provide acceptable per-
formance when minimum external parts count is very impor-
0
0
e
e
e
e
e
FIGURE 13 Design Nomograph for Cascaded
the Q of each second order bandpass stage
the center frequency of the filter in Hertz
2
per second
the overall filter transfer function
the number of cascaded second-order stages
Identical Second-Order Bandpass Filters
N
f
0
b
e
min
3 dB bandwidth BW(
the center frequency of the filter in radians
The required order is shown on the curve
b
3) and a horizontal line
b
3) stopband width
min
Draw a ver-
TL H 8694 – 19
TL H 8694 – 21
e
n
2