MF10CCWM National Semiconductor, MF10CCWM Datasheet - Page 15

• 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

18a) or a low-impedance half-supply voltage can be made
3 0 Applications Information
3 2 SINGLE SUPPLY OPERATION
The MF10 can also operate with a single-ended power sup-
ply Figure 17 shows the example filter with a single-ended
power supply V
positive power supply (8V to 14V) and V
connected to ground The A
for single supply operation This half-supply point should be
very ‘‘clean’’ as any noise appearing on it will be treated as
an input to the filter It can be derived from the supply volt-
age with a pair of resistors and a bypass capacitor (Figure
using a three-terminal voltage regulator or an operational
amplifier (Figures 18b and 18c) The passive resistor divider
with a bypass capacitor is sufficient for many applications
provided that the time constant is long enough to reject any
power supply noise It is also important that the half-supply
reference present a low impedance to the clock frequency
so at very low clock frequencies the regulator or op-amp
approaches may be preferable because they will require
smaller capacitors to filter the clock frequency The main
power supply voltage should be clean (preferably regulated)
and bypassed with 0 1 F
3 3 DYNAMIC CONSIDERATIONS
The maximum signal handling capability of the MF10 like
that of any active filter is limited by the power supply volt-
ages used The amplifiers in the MF10 are able to swing to
within about 1V of the supplies so the input signals must be
kept small enough that none of the outputs will exceed
these limits If the MF10 is operating on
the outputs will clip at about 8 V
voltage multiplied by the filter gain should therefore be less
than 8 V
Note that if the filter Q is high the gain at the lowpass or
highpass outputs will be much greater than the nominal filter
gain (Figure 6) As an example a lowpass filter with a Q of
(a) Resistive Divider with
Decoupling Capacitor
p – p
A
a
and V
FIGURE 18 Three Ways of Generating
TL H 10399–27
D
a
GND
are again connected to the
pin must be tied to V
p– p
The maximum input
g
A
5V for example
b
and V
(Continued)
(b) Voltage Regulator
D
b
a
are
2
15
V
10 will have a 20 dB peak in its amplitude response at f
the nominal gain of the filter H
f
be less than 800 mV
Also note that one output can have a reasonable small volt-
age on it while another is saturated This is most likely for a
circuit such as the notch in Mode 1 (Figure 7) The notch
output will be very small at f
apply a large signal to the input However the bandpass will
have its maximum gain at f
one output clips the performance at the other outputs will
be degraded so avoid overdriving any filter section even
ones whose outputs are not being directly used Accompa-
nying Figures 7 through 15 are equations labeled ‘‘circuit
dynamics’’ which relate the Q and the gains at the various
outputs These should be consulted to determine peak cir-
cuit gains and maximum allowable signals for a given appli-
cation
3 4 OFFSET VOLTAGE
The MF10’s switched capacitor integrators have a higher
equivalent input offset voltage than would be found in a
typical continuous-time active filter integrator Figure 19
shows an equivalent circuit of the MF10 from which the out-
put DC offsets can be calculated Typical values for these
offsets with S
V
V
V
When S
DC offset at the BP output is equal to the input offset of the
lowpass integrator (V
depend on the mode of operation and the resistor ratios as
described in the following expressions
g
O
2
a
os1
os2
os3
5V supplies
will be 10 The maximum input signal at f
TL H 10399 – 28
for Single-Supply Operation
e b
e b
e
A B
opamp offset
150 mV
70 mV
is tied to V
A B
tied to V
50 1
50 1
os3
p–p
e
b
) The offsets at the other outputs
g
V
when the circuit is operated on
a
os2
(c) Operational Amplifier
5 mV
O
are
O
OLP
and can clip if overdriven If
will approximately halve The
so it might appear safe to
with Divider
is equal to 1 the gain at
b
b
O
300 mV
140 mV
must therefore
TL H 10399– 29
100 1
100 1
O
If