MF10CCWM National Semiconductor, MF10CCWM Datasheet - Page 13

• Manufacturer Part Number: MF10CCWM
• Description: IC,FILTER,AP/BP/HP/LP/NOTCH,CMOS,SOP,20PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of MF10CCWM

• Rohs Compliant: NO

Mode
2 0 Modes of Operation
1a
3a
6a
6b
3 0 Applications Information
The MF10 is a general-purpose dual second-order state
variable filter whose center frequency is proportional to the
frequency of the square wave applied to the clock input
(f
the filter center frequency f
f
varied over a wide frequency range by adjusting the clock
frequency If desired the f
external resistors as in Figures 9 10 11 13 14 and 15 The
filter Q and gain are determined by external resistors
All of the five second-order filter types can be built using
either section of the MF10 These are illustrated in Figures 1
through 5 along with their transfer functions and some relat-
ed equations Figure 6 shows the effect of Q on the shapes
of these curves When filter orders greater than two are
desired two or more MF10 sections can be cascaded
3 1 DESIGN EXAMPLE
In order to design a second-order filter section using the
MF10 we must define the necessary values of three param-
eters f
band gain and the filter’s Q These are determined by the
characteristics required of the filter being designed
As an example let’s assume that a system requires a
fourth-order Chebyshev low-pass filter with 1 dB ripple unity
gain at DC and 1000 Hz cutoff frequency As the system
order is four it is realizable using both second-order sec-
tions of an MF10 Many filter design texts include tables that
list the characteristics (f
der filter sections needed to synthesize a given higher-order
g
1
2
3
4
5
CLK
CLK
6%) by using a crystal clock oscillator or can be easily
) By connecting pin 12 to the appropriate DC voltage
100 or f
H
0
H
OBP1
OBP2
the filter section’s center frequency H
Unless otherwise noted gains of various filter outputs are inverting and adjustable by resistor ratios
BP
(2)
CLK
e b
e a
TABLE I Summary of Modes Realizable filter types (e g low-pass) denoted by asterisks
50 f
Q
1
O
H
O
H
can be very accurately set (within
OLP2
OLP1
H
and Q) of each of the second-or-
CLK
OLP
O
LP
(2)
can be made equal to either
e
e a
a
f
O
b
R2
1
ratio can be altered by
R3
1
(Continued)
HP
N
0
the pass-
AP
Number of
Resistors
13
3
2
3
4
7
3
4
3
2
filter For the Chebyshev filter defined above such a table
yields the following characteristics
f
f
For unity gain at DC we also specify
H
H
The desired clock-to-cutoff-frequency ratio for the overall
filter of this example is 100 and a 100 kHz clock signal is
available Note that the required center frequencies for the
two second-order sections will not be obtainable with clock-
to-center-frequency ratios of 50 or 100 It will be necessary
to adjust
can be used to produce a low-pass filter with resistor-adjust-
able center frequency
In most filter designs involving multiple second-order
stages it is best to place the stages with lower Q values
ahead of stages with higher Q especially when the higher Q
is greater than 0 707 This is due to the higher relative gain
at the center frequency of a higher-Q stage Placing a stage
with lower Q ahead of a higher-Q stage will provide some
attenuation at the center frequency and thus help avoid clip-
ping of signals near this frequency For this example stage
A has the lower Q (0 785) so it will be placed ahead of the
other stage
For the first section we begin the design by choosing a
convenient value for the input resistance R
absolute value of the passband gain H
0A
0B
0A
0B
e
e
Yes (above f
e
e
529 Hz
993 Hz
1
1
or f
Adjustable
f
CLK
f
f
CLK
CLK
0
Yes
Yes
No
No
No
externally From Table I we see that Mode 3
f
100)
O
CLK
Q
Q
50
A
B
e
e
May need input buffer
Poor dynamics for
high Q
Universal State-Variable
Filter Best general-purpose mode
As above but also includes
resistor-tuneable notch
Gives Allpass response with
H
Gives flatter allpass response
than above if R
Single pole
Single Pole
0 785
3 559
OAP
e b
1 and H
OLPA
Notes
1
e
1A
is made equal
OLP
R
e
2
e
e b
20k The
0 02R
2
4