Datasheet

LTC6430-15
19
643015f
50MHz to 1000MHz CATV Push-Pull Amplifier:
75Ω Input and 75Ω Output
Wide bandwidth, excellent linearity and low output noise
makes the LTC6430-15 an exceptional candidate for CATV
amplifier applications.
As expected, the LTC6430-15 works well in a push-pull
circuit to cover the entire 40MHz to 1000MHz CATV band.
Using readily available SMT baluns, the LTC6430-15 of-
fers high linearity and low noise across the whole CATV
band. Remarkably, this performance is achieved with
only 800mW of power at 5V. Its low power dissipation
greatly reduces the heat sinking requirements relative to
traditional “block” CATV amplifiers.
The native LTC6430-15 device is well matched to 100Ω
differential impedance at both the input and the output.
Therefore, we can employ 1:1.33 surface mount (SMT)
baluns to transform its native 100Ω impedance to the
standard 75Ω CATV impedance, while retaining all the
exceptional characteristics of the LTC6430-15. In addition,
the balun’s excellent phase balance and the 2nd order
linearity of the LTC6430-15 combine to further suppress
2nd order products across the entire CATV band. As with
any wide bandwidth application, care must be taken when
Figure 10. CATV Amplifier: 75Ω Input and 75Ω Output
selecting a choke. An SMT wire wound ferrite core inductor
was chosen for its low series resistance, high self reso-
nant frequency (
SRF) and compact size. An input stability
network is not required for this application as the balun
presents a low impedance to the LTC6430-15’s input at
low frequencies. Our resulting push-pull CATV amplifier
circuit is simple, compact, completely SMT and extremely
power efficient.
The LTC6430-15 push-pull circuit has 14.1dB of gain with
±0.4dB of flatness across the entire 50MHz to 1000MHz
band. It sports an OIP3 of 46dBm and a noise figure of
only 4.5dB. The CTB and CSO measurements have not
been taken as of this writing.
These characteristics make the LTC6430-15 an ideal
amplifier for head-end cable modem applications or CATV
distribution amplifiers. The circuit is shown in Figure 10,
with 75Ω “F” connectors at both input and output. The
evaluation board may be loaded with either 75Ω “F” con-
nectors, or 75Ω BNC connectors, depending on the users
preference. Please note that the use of substandard con-
nectors can limit usable bandwidth of the circuit.
643015 F10
V
CC
= 5V
T1
1:1.33
PORT
INPUT
RF
OUT
75Ω,
CONNECTOR
RF
IN
75Ω,
CONNECTOR
PORT
OUTPUT
BALUN_A
BALUN_A
BALUN_A = TC1.33-282+ FOR 50MHz TO 1000MHz
MINI-CIRCUITS 1:1.33 BALUN
C1
0.047µF
L1
560nH
LTC6430-15
DNC
DNC
DNC
DNC
DNC
DNC
+OUT
GND
T_DIODE
DNC
GND
–OUT
+IN
GND
V
CC
DNC DNC DNC
–IN GND V
CC
DNC DNC DNC
••
C2
0.047µF
C4
0.047µF
C3
0.047µF
C5
1000pF
C6
0.1µF
100Ω
DIFFERENTIAL
100Ω
DIFFERENTIAL
L2
560nH
T2
1.33:1
applicaTions inForMaTion