LTM9008-14 Datasheet, PDF (22/36 Pages) Linear Technology – 14-Bit, 65Msps/40Msps/25Msps Low Power Octal ADCs

LTM9008-14/
LTM9007-14/LTM9006-14
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.
See back page for a DC-coupled example.
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 driv-
ing the A/D.
0.1µF
ANALOG
INPUT
T1
0.1µF
50Ω
V_CM
0.1µF
T2
25Ω 0.1µF
A_IN+
LTM9008-14
0.1µF
ANALOG
INPUT
T1
4.7pF
25Ω
A_IN–
0.1µF
50Ω
V_CM
0.1µF
T2
25Ω 0.1µF
A_IN+
LTM9008-14
1.8pF
25Ω
A_IN–
T1: MA/COM MABA-007159-000000
T2: MA/COM MABAES0060
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
90067814 F04
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1LB
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
90067814 F05
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
ANALOG
INPUT
0.1µF
T1
0.1µF
50Ω
2.7nH
25Ω
0.1µF
V_CM
0.1µF
A_IN+
LTM9008-14
25Ω _2.7nH
A_IN–
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
90067814 F06
Figure 6. Recommended Front End Circuit for Input
Frequencies Above 300MHz
ANALOG
INPUT
HIGH SPEED
DIFFERENTIAL
AMPLIFIER
0.1µF
++
200Ω 200Ω
25Ω
– ^{– 0.1µF}
25Ω
V_CM
0.1µF
A_IN+
LTM9008-14
12pF
A_IN–
90067814 F07
Figure 7. Front End Circuit Using a High Speed
Differential Amplifier
22
90067814f