Datasheet

LTC2265-12/
LTC2264-12/LTC2263-12
21
22654312fb
Amplifier Circuits
Figure 7 shows the analog input being driven by a high speed
differential amplifier. The output of the amplifier is AC-
coupled to the A/D so the amplifier’s output common mode
voltage can be optimally set to minimize distortion.
25Ω
25Ω
50Ω
0.1µF
A
IN
+
A
IN
–
4.7pF
0.1µF
V
CM
ANALOG
INPUT
0.1µF
0.1µF
T1
T2
T1: MA/COM MABA-007159-000000
T2: MA/COM MABAES0060
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
226512 F04
LTC2265-12
25Ω
25Ω
50Ω
0.1µF
A
IN
+
A
IN
–
1.8pF
0.1µF
V
CM
ANALOG
INPUT
0.1µF
0.1µF
T1
T2
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1LB
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
226512 F05
LTC2265-12
25Ω
25Ω
50Ω
0.1µF
2.7nH
2.7nH
A
IN
+
A
IN
–
0.1µF
V
CM
ANALOG
INPUT
0.1µF
0.1µF
T1
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
226512 F06
LTC2265-12
25Ω
25Ω
200Ω
200Ω
0.1µF
A
IN
+
A
IN
–
12pF
0.1µF
V
CM
LTC2265-12
226512 F07
–
–
+
+
ANALOG
INPUT
HIGH SPEED
DIFFERENTIAL
AMPLIFIER
0.1µF
Figure 5. Recommended Front-End Circuit for Input
Frequencies from 170MHz to 300MHz
Figure 6. Recommended Front-End Circuit for Input
Frequencies Above 300MHz
Figure 4. Recommended Front-End Circuit for Input
Frequencies from 70MHz to 170MHz
Figure 7. Front-End Circuit Using a High Speed
Differential Amplifier
APPLICATIONS INFORMATION
At very high frequencies an RF gain block will often have
lower distortion than a differential amplifier. 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.