clc449 National Semiconductor Corporation, clc449 Datasheet - Page 11

• Manufacturer Part Number: clc449
• Description: 1.1ghz Ultra-wideband Monolithic Op Amp
• Manufacturer: National Semiconductor Corporation

Application Division
Realized third-order output distortion is highly dependent
upon the external circuit. Some of the common external
circuit choices that improve 3
Dynamic Range (Noise)
In RF applications, noise is frequently specified as Noise
Figure (NF). Figure 7 plots NF for the CLC449 at a gain of
10, with a feedback resistor R
matching resistor. The minimum Noise Figure (2.5dB) for
these conditions occurs when the source resistance equals
700 .
The CLC449 noise model in Figure 8 is used to develop the
equation below.
The equation for Noise Figure (NF) is:
Where:
• dBm is the power in mW, at the load, expressed in dB.
• short and equal return paths from the load to the
• de-coupling capacitors of the correct value.
• higher load resistance
• a lower ratio of the output swing to the power supply
V
• R
NF 10LOG
s
supplies.
voltage.
s
+
-
10
20
15
is the source resistance at the non-inverting input.
5
0
10
R
e
FIGURE 8. CLC449 Noise Model
ni
s
FIGURE 7. Noise Figure Plot
2
i R
bn s
*
*
Source Resistance ( )
i
i
bn
bi
2
100
e
*
4 TR
n
k
rd
s
f
4 TR
order distortion are:
of 100 , and with no input
R
k
i
g
bi
CLC449
+
(Continued)
-
s
R ||R
1000
f
R
f
g
2
4 T R ||R
k
DS012715-38
10000
DS012715-39
f
g
V
o
11
Printed Circuit Board Layout
High Frequency op amp performance is strongly dependent
on proper layout, proper resistive termination and adequate
power supply decoupling. The most important layout points
to follow are:
Evaluation boards are available for proto-typing and
measurements. Additional layout information is available in
the evaluation board literature.
Low Noise Composite Amp With Input Matching
The composite circuit shown in Figure 9 eliminates the need
for a matching resistor to ground at the input. By connecting
two amplifiers in series, the first non-inverting and second
inverting, an overall inverting gain is realized. The feedback
resistor (R
amplifier to the non-inverting input of the first amplifier closes
the loop, and generates a set input resistance (R
be matched to R
matching resistor to ground at the input.
The input resistance and DC voltage gain of the amplifier
are:
Match the source resistance by setting: R
Noise voltage produced by R
• There is no matching resistor from the input to ground.
• e
• 4kT = 16 x 10
•
• Use a ground plane
• Bypass power supply pins with monolithic:
• ceramic capacitors of about 0.1µF placed less than 0.1”
• tantalum capacitors of about 6.8µF for large signal
• Minimize trace and lead lengths for components between
• Remove ground plane underneath the amplifier package
• If parts must be socketed, always use flush-mounted
V
R
V
V
s
in
o
s
(see in the Distortion and Noise Response sub-section
of the Electrical Characteristics section).
resistor.
(3mm) from the pin
current swings or improved power supply noise rejection;
we recommend a minimum of 2.2 µF for any circuit
the inverting and output pins
and 0.1” (3mm) from all input/output pads
socket pins instead of high profile sockets.
+
-
ni
R
, i
R
1 G
f
bn
s
G
is the feedback resistor and R
R
, i
f
bi
f
) connected from the output of the second
R
R
FIGURE 9. Composite Amplifier
, where G
R
are the voltage and current noise density terms
in
g1
in
R
s
. This resistor generates less noise than a
in
−21
R
CLC449
+
-
J, T= 290˚K.
s
R
f1
1
f
, referred to the source V
R
R
f 1
g1
R
20
g2
R
f
R
R
g
g2
f2
is the gain setting
CLC449
+
in
-
= R
R
f2
s
www.national.com
in
) that can
DS012715-41
s
is:
V
o