LTC2265-14_15 Datasheet, PDF (19/32 Pages) Linear Technology – 14-Bit, 65Msps/40Msps/ 25Msps Low Power Dual ADCs

LTC2265-14/
LTC2264-14/LTC2263-14
APPLICATIONS INFORMATION
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.
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.
0.1µF
ANALOG
INPUT
T1
0.1µF
50Ω
V_CM
0.1µF
T2
25Ω 0.1µF
A_IN+
LTC2265-14
4.7pF
25Ω
A_IN–
ANALOG
INPUT
0.1µF
T1
0.1µF
50Ω
2.7nH
25Ω
0.1µF
25Ω
2.7nH
V_CM
0.1µF
A_IN+
LTC2265-14
A_IN–
T1: MA/COM MABA-007159-000000
T2: MA/COM MABAES0060
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
226514 F04
Figure 4. Recommended Front-End Circuit for Input
Frequencies from 70MHz to 170MHz
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
226514 F06
Figure 6. Recommended Front-End Circuit for Input
Frequencies Above 300MHz
0.1µF
ANALOG
INPUT
T1
0.1µF
50Ω
V_CM
0.1µF
T2
25Ω 0.1µF
A_IN+
LTC2265-14
1.8pF
25Ω
A_IN–
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1LB
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
226514 F05
Figure 5. Recommended Front-End Circuit for Input
Frequencies from 170MHz to 300MHz
ANALOG
INPUT
HIGH SPEED
DIFFERENTIAL
AMPLIFIER
0.1µF
++
200Ω 200Ω
25Ω
– ^{– 0.1µF}
25Ω
V_CM
0.1µF
A_IN+
LTC2265-14
12pF
A_IN–
226514 F07
Figure 7. Front-End Circuit Using a High Speed
Differential Amplifier
22654314fb
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