CLC446A8B NSC [National Semiconductor], CLC446A8B Datasheet - Page 9

• Manufacturer Part Number: CLC446A8B
• Description: 400MHz, 50mW Current-Feedback Op Amp
• Manufacturer: NSC [National Semiconductor]

high frequency performance, maintain low parasitic
capacitance from the diodes D
from the input of the CLC522 to ground.
Elliptic Low-pass, Anti-aliasing Filter
Elliptic filters are often used in anti-aliasing applications.
If there is noise or undesired signals at frequencies
above 1/2 the sampling rate of an A/D converter, then
these signals are aliased down into the operating
frequency range, degrading the signal of interest. To
filter out these undesired signal components, place a low
pass filter in front of the A/D converter.
The Typical Application depicted on the front page is a
10MHz, third-order elliptic filter. It has a voltage-
controlled, voltage source (VCVS) topology using a
CLC446. To calculate the component values for this
filter, do the following:
V
in
50
R
250
in
1. Select the filter approximation function for your
2. Find the pole and zero locations. Reference [1]
application (see References [1-2]). For this design
we chose:
These choices produce the following results:
gave the following for our filter:
3
2
250
250
Filter type = Elliptic
Filter order (n) = 3
Passband ripple = 0.18dB
Mininimum stopband attenuation (A
Cuttoff frequency = 10MHz (at 0.18dB
-3dB frequency = 12.7MHz
Stopband corner frequency = 29.3MHz
Pole 1:
Pole 2:
Zero 1:
Zero 2:
+
CLC446
-
Figure 11: Full-Wave Rectifier
37.44dB
attenuation)
D
D
6
1
2
o
= 1.13897
= 0.38621
= 0.88668
= 3.3505
500
50
50
R
R
2
1
162
R
1
g
and D
3
4
5
6
V
CLC522
+
-
20
g
2
2
12
9
to ground, and
800
R
10
f
min
50
R
) =
o
V
o
9
3. Denormalize the frequency by multiplying by
4. Calculate these intermediate coefficients used
5. Set the following resistance and capacitance
6. Calculate the capacitor, resistor and gain (K)
7. Select the feedback resistor (R
the cutoff frequency (
For our filter we have:
in Reference [2].
For this design, a = 0.64226, b = 7.7612 and
c = 75.556 x 10
scaling factors:
We chose C = 47pF and R = 1.00k .
values using these equations:
R
R
R
R
For this design, the calculated values are:
C
C
R
setting resistor (R
inverting voltage gain of A
Gain (non-inverting) sub-section for details
on selecting these values.
C
C
C
C
K
c
1
1
1
5
4
3
2
3
4
5
5
Cutoff frequency:
Pole 1: ' =
Pole 2:
Zero 1: ' =
Zero 2: ' =
R = an arbitrary value
C = an arbitrary value
= 47pF, C
= 17.95pF, R
= 3190 , R
2
R
C
R
C
C b 1
cC b
cC 1 b
R '
62.832 x 10
2
4
1
2C
'
1
4
C
o
2
R
2
C
2
2
4 b
3
' =
o
2
2 b
'
= 91pF, C
5
6
2
a
1
4cC
= 1000
.
o
o
o o
= R
g
6
o
) values to obtain a non-
rad/s
= 21.052 x 10
= 24.266 x 10
2
= 55.712 x 10
2
C b
a
= 71.564 x 10
o
o
= 202.1 , R
2
) in radians/second.
= 2 (10MHz) =
3
2 '
= C
and K = 4.928.
v
c
= K. See the DC
cR
4
1
f
= 23.5pF,
) and gain-
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4
b
6
6
rad/s
rad/s
3
6
aC
rad/s
6
= 101.1 ,
rad/s
2
c
'
2