LTC2173-14 Linear Technology Corporation, LTC2173-14 Datasheet - Page 20

• Manufacturer Part Number: LTC2173-14
• Description: (LTC217x-14) 125Msps Low Power Quad ADCs
• Manufacturer: Linear Technology Corporation

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tap is biased with V
mal DC level. At higher input frequencies a transmission
line balun transformer (Figures 4 to 6) has better balance,
resulting in lower A/D distortion.
Amplifi er Circuits
Figure 7 shows the analog input being driven by a high
speed differential amplifi er. The output of the amplifi er is
AC-coupled to the A/D so the amplifi er’s output common
mode voltage can be optimally set to minimize distor-
tion.
ANALOG
LTC2175-14/
LTC2174-14/LTC2173-14
ANALOG
20
APPLICATIONS INFORMATION
INPUT
INPUT
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1LB
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
T1: MA/COM MABA-007159-000000
T2: MA/COM MABAES0060
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
Figure 4. Recommended Front End Circuit for Input
Frequencies from 70MHz to 170MHz
Figure 5. Recommended Front End Circuit for Input
Frequencies from 170MHz to 300MHz
0.1μF
0.1μF
0.1μF
0.1μF
T1
T1
CM
, setting the A/D input at its opti-
T2
T2
25Ω
25Ω
25Ω
25Ω
0.1μF
0.1μF
50Ω
50Ω
0.1μF
1.8pF
0.1μF
4.7pF
V
A
A
V
A
A
CM
CM
IN
IN
IN
IN
+
–
+
–
LTC2175-14
LTC2175-14
217514 F05
217514 F04
At very high frequencies an RF gain block will often have
lower distortion than a differential amplifi er. If the gain
block is single-ended, then a transformer circuit (Figures
4 to 6) should convert the signal to differential before
driving the A/D.
Reference
The LTC2175-14/LTC2174-14/LTC2173-14 has an internal
1.25V voltage reference. For a 2V input range using the
internal reference, connect SENSE to V
range using the internal reference, connect SENSE to
ANALOG
ANALOG
Figure 6. Recommended Front End Circuit for Input
Frequencies Above 300MHz
INPUT
INPUT
Figure 7. Front End Circuit Using a High Speed
Differential Amplifi er
DIFFERENTIAL
HIGH SPEED
0.1μF
0.1μF
+
–
AMPLIFIER
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
+
–
T1
0.1μF
0.1μF
25Ω
25Ω
200Ω
50Ω
2.7nH
2.7nH
0.1μF
200Ω
25Ω
25Ω
0.1μF
12pF
0.1μF
V
A
A
CM
IN
IN
DD
A
A
V
+
–
CM
IN
IN
+
–
. For a 1V input
LTC2175-14
LTC2175-14
217514 F06
217514 F07
21754314p