MF5CWM National Semiconductor, MF5CWM Datasheet - Page 11

• Manufacturer Part Number: MF5CWM
• Description: IC FILTER MONO SW CAP SO14
• Manufacturer: National Semiconductor

Specifications of MF5CWM

• Filter Type: Universal Switched Capacitor
• Frequency - Cutoff Or Center: 30kHz
• Number Of Filters: 1
• Max-order: 2nd
• Voltage - Supply: 8 V ~ 14 V
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *MF5CWM

Mode
6 shows the effect of Q on the shapes of these curves
2 0 Modes of Operation
3 0 Applications Information
The MF5 is a general-purpose second-order state variable
filter whose center frequency is proportional to the frequen-
cy of the square wave applied to the clock input (f
connecting pin 9 to the appropriate DC voltage the filter
center frequency f
or f
using a crystal clock oscillator or can be easily varied over
a wide frequency range by adjusting the clock frequency If
desired the f
tors 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 the
MF5 These are illustrated in Figures 1 through 5 along with
their transfer functions and some related equations Figure
When filter orders greater than two are desired two or more
MF5s can be cascaded The MF5 also includes an uncom-
mitted CMOS operational amplifier for additional signal pro-
cessing applications
3 1 DESIGN EXAMPLE
An example will help illustrate the MF5 design procedure
For the example we will design a 2nd order Butterworth
low-pass filter with a cutoff frequency of 200 Hz and a pass-
band gain of
supply and the clock amplitude will be
1a
3a
6a
6b
1
2
3
4
5
TABLE I Summary of Modes Realizable filter types (e g low-pass) denoted by asterisks Unless otherwise noted
CLK
50 f
H
H
OBP1
OBP2
o
b
CLK
can be very accurately set (within
2 The circuit will operate from a
BP
(2)
e b
e a
f
o
o
can be made equal to either f
ratio can be altered by external resis-
Q
1
gains of various filter outputs are inverting and adjustable by resistor ratios
H
H
H
OLP2
OLP
OLP
LP
(2)
e
e a
e a
b
R2
g
R3
1
1
(Continued)
5v (CMOS) levels)
HP
g
g
5V power
0 6%) by
CLK
CLK
) By
N
100
11
AP
From
f
Q
In section 2 0 are several modes of operation for the MF5
each having different characteristics Some allow adjust-
ment of f
filter types some are inverting while others are non-invert-
ing etc These characteristics are summarized in Table I To
keep the example simple we will use mode 1 which has
notch bandpass and lowpass outputs and inverts the sig-
nal polarity Three external resistors determine the filter’s Q
and gain From the equations accompanying Figure 7
Q
the input signal is driving a summing junction through R
the input impedance will be equal to R
value for R
impedance For H
R
For Q
R
For operation on
V
should be ‘‘clean’’ (regulated supplies are preferred) and
0 1 F bypass capacitors are recommended
o
b
2
3
e
e
e
e b
e
Number of
200 Hz H
0 707
R
resistors
to
3
R
e
the
b
R
2
3
2
3
4
7
3
4
3
2
R
Q
2
CLK
0 707 we have
5V and AGND to ground The power supplies
1
1
and the passband gain H
H
e
10k is convenient and gives a reasonable input
OLP
specifications
f
20k
o
OLP
others produce different combinations of
e
g
OLP
c
eb
5V supplies V
Adjustable
Yes (above
f
10k
f
CLK
CLK
f
0 707
e b
CLK
2 and for Butterworth response
Yes
Yes
No
No
No
c
50 or
100)
f
2 we have
2
e
o
the
e
14 14k Use 15k
20k
a
filter
OLP
May need input buf-
fer Poor dynamics
for high Q
Universal State-
Variable Filter Best
general-purpose mode
As above but also
includes resistor-
tuneable notch
Gives Allpass res-
ponse with H
and H
Gives flatter allpass
response than above
if R
Single pole
Single pole
is connected to
1
1
Start by choosing a
e b
e
parameters
OLP
R
2
Notes
R
e
eb
2
0 02R
OAP
R
2
1
eb
Since
a
4
are
5V
1
1