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| LTC2261-12 Datasheet, PDF (18/32 Pages) Linear Technology – 12-Bit, 125/105/80Msps Ultralow Power 1.8V ADCs | |||
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LTC2261-12
LTC2260-12/LTC2259-12
APPLICATIONS INFORMATION
balun transformer (Figures 4 to 6) has better balance,
resulting in lower A/D distortion.
Ampliï¬er Circuits
Figure 7 shows the analog input being driven by a high
speed differential ampliï¬er. The output of the ampliï¬er is AC
coupled to the A/D so the ampliï¬erâs output common mode
voltage can be optimally set to minimize distortion.
0.1μF
ANALOG
INPUT
T1
0.1μF
50Ω
VCM
0.1μF
T2
25Ω 0.1μF
AIN+
LTC2261-12
4.7pF
25Ω
AINâ
T1: MA/COM MABA-007159-000000
T2: MA/COM MABAES0060
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
226112 F04
Figure 4. Recommended Front-End Circuit for Input
Frequencies from 70MHz to 170MHz
At very high frequencies an RF gain block will often have
lower distortion than a differential ampliï¬er. 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
T2
25Ω 0.1μF
25Ω
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1LB
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
VCM
0.1μF
AIN+
LTC2261-12
1.8pF
AINâ
226112 F05
Figure 5. Recommended Front-End Circuit for Input
Frequencies from 170MHz to 270MHz
ANALOG
INPUT
0.1μF
T1
0.1μF
50Ω
2.7nH
25Ω
0.1μF
VCM
0.1μF
AIN+
LTC2261-12
25Ω 2.7nH
AINâ
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
226112 F06
Figure 6. Recommended Front-End Circuit for Input
Frequencies Above 270MHz
226112f
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