clc440 National Semiconductor Corporation, clc440 Datasheet - Page 6

• Manufacturer Part Number: clc440
• Description: High-speed, Low-power, Voltage Feedback Op Amp
• Manufacturer: National Semiconductor Corporation

The capacitances are defined as:
The transimpedance plot in the typical performance
section provides the recommended C
bandwidth for different gains and diode capacitances.
The feedback capacitances indicated on the plot
give optimum gain flatness and stability. If a smaller
capacitance is used, then peaking will occur.
frequency response shown in Figure 4 illustrates the
influence of the feedback capacitance on gain flatness.
The total input current noise density (i
transimpedance configuration is shown in Equation 3.
The plot of current noise density versus feedback
resistance is shown in Figure 5.
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Equation 3: Total Equivalent Input Referred Current
•
•
•
C
C
C
in
d
f
= Feedback Capacitance
40
35
25
20
15
10
30
= Equivalent Diode Capacitance
= Internal Input Capacitance of the CLC440
80
70
60
50
40
30
20
5
0
(typ 1.2pF)
0.1
Current Noise Density vs.
Feedback Resistance
10k
Transimpedance Amplifier
Frequency Response
I
in
i
e
R
i
i
f
n
ni
n
f
5
i
pF
ni
(Total)
Feedback Resistance (k )
100k
Noise Density
CLC440
-
+
i
Frequency (Hz)
1k
n
C
f
Figure 4
Figure 5
1M
1.0
e
R
C
n 2
100
f
f
= 2.5pF
10M
C
2
f
= 5pF
4kT
R
100M
f
C
C
C
ni
f
f
f
f
= 0
= 1pF
= 2pF
) for the basic
and expected
10
1G
The
6
Rectifier
The large bandwidth of the CLC440 allows for high speed
rectification. A common rectifier topology is shown in
Figure 6. R
a 5MHz, 2V
Tunable Low Pass Filter
The center frequency of the low pass filter (LPF) can be
adjusted by varying the CLC522 gain control voltage, V
V
in
o
R R C C
1 2 1 2
k
V
-0.4
-0.8
-1.2
-1.6
-2.0
2.0
1.6
1.2
0.4
0.8
in
0
R
R
Figure 8: Tunable Low Pass Filter
1
in
Rectifier Output
1
0
pp
Figure 6: Rectifier Topology
and R
Figure 7: Rectifier Output
sinusoidal input is shown in Figure 7.
Q
R
100
CLC440
+
k
-
1
C
20
R
2
1
f
R R C C
set the gain of the rectifier. V
1 2 1 2
RC
CLC522
200
2
Time (ns)
V
+
g
-
CLC440
R
+
-
2
R
R
300
g
2
R
R
g
T
V
1.8mA
in (max)
D
CLC440
+
-
1
V
400
C
out
R
R
D
2
a
2
A
v (max)
500
k 1.85
out
V
g
R
R
out
.
g
f
for