MF4CN-50 National Semiconductor, MF4CN-50 Datasheet - Page 9

• Manufacturer Part Number: MF4CN-50
• Description: IC LOWPASS FILTER 4TH ORD SW CAP
• Manufacturer: National Semiconductor

Specifications of MF4CN-50

• Filter Type: Butterworth, Lowpass Switched Capacitor
• Frequency - Cutoff Or Center: 20kHz
• Number Of Filters: 1
• Max-order: 4th
• Voltage - Supply: 5 V ~ 14 V
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *MF4CN-50; MF4NC-50

2.0 Designing With The MF4
2.3 CHANGING CLOCK FREQUENCY
INSTANTANEOUSLY
The MF4 will respond favorably to an instantaneous change
in clock frequency. If the control signal in Figure 12 is low the
MF4-50 has a 100 kHz clock making f
signal goes high the clock frequency changes to 50 kHz
yielding f
changes quickly and smoothly in response to a sudden
change in clock frequency.
The step response of the MF4 in Figure 13 is dependent on
f
low-pass filter.
V
V
V
c
IH
IL
cc
(Continued)
. The MF4 responds as a classical fourth-order Butterworth
= V
0.2 V
0.8 V
+
− V
c
cc
cc
= 1 kHz. As the Figure illustrates, the output signal
−
FIGURE 2. Split Supply Operation with CMOS Level Clock
c
= 2 kHz; when this
FIGURE 1. Schmitt Trigger R/C Oscillator
9
2.4 ALIASING CONSIDERATIONS
Aliasing effects have to be considered when input signal fre-
quencies exceed half the sampling rate. For the MF4 this
equals half the clock frequency (f
contains a component at a frequency higher than half the
clock frequency f
be “reflected” about f
f
band of the filter and of large enough amplitude it can cause
problems. Therefore, if frequency components in the input
signal exceed f
applied to the MF4 input. The necessary amount of attenua-
tion will vary depending on system requirements. In critical
applications the signal components above f
be attenuated at least to the filter’s residual noise level.
CLK
/2, as in Figure 14b . If this component is within the pass-
CLK
CLK
2 they must be attenuated before being
DS005064-12
/2, as in Figure 14a , that component will
CLK
DS005064-11
/2 into the frequency range below
CLK
). When the input signal
CLK
/2 will have to
www.national.com