ltc2258cuj-12 Linear Technology Corporation, ltc2258cuj-12 Datasheet - Page 18

• Manufacturer Part Number: ltc2258cuj-12
• Description: 12-bit, 65/40/2 5msps Ultralow Power 1.8v Adcs
• Manufacturer: Linear Technology Corporation

LTC2258-12
LTC2257-12/LTC2256-12
18
APPLICATIONS INFORMATION
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 distortion.
ANALOG
INPUT
Figure 4. Recommended Front-End Circuit for Input
Frequencies from 70MHz to 170MHz
T1: MA/COM MABA-007159-000000
T2: MA/COM MABAES0060
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
0.1μF
0.1μF
T1
T2
25Ω
25Ω
0.1μF
50Ω
0.1μF
4.7pF
V
A
A
CM
IN
IN
+
–
LTC2258-12
225812 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 driv-
ing the A/D.
ANALOG
INPUT
ANALOG
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1LB
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
Figure 5. Recommended Front-End Circuit for Input
Frequencies from 170MHz to 270MHz
Figure 6. Recommended Front-End Circuit for Input
Frequencies Above 270MHz
INPUT
0.1μF
0.1μF
0.1μF
0.1μF
T1
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
T1
T2
25Ω
25Ω
50Ω
2.7nH
2.7nH
25Ω
25Ω
0.1μF
0.1μF
50Ω
0.1μF
V
A
A
CM
IN
IN
+
–
LTC2258-12
0.1μF
1.8pF
V
A
A
CM
IN
IN
+
–
225812 F06
LTC2258-12
225812p
225812 F05