LTC2259-16 LINER [Linear Technology], LTC2259-16 Datasheet - Page 14

• Manufacturer Part Number: LTC2259-16
• Description: 16-Bit, 80Msps Ultralow Power 1.8V ADC
• Manufacturer: LINER [Linear Technology]

LTC2259-16
INPUT DRIVE CIRCUITS
Input Filtering
If possible, there should be an RC lowpass fi lter right at
the analog inputs. This lowpass fi lter isolates the drive
circuitry from the A/D sample-and-hold switching, and
also limits wideband noise from the drive circuitry. Figure 3
shows an example of an input RC fi lter. The RC component
values should be chosen based on the application’s input
frequency.
ANALOG
14
APPLICATIONS INFORMATION
INPUT
Figure 3. Analog Input Circuit Using a Transformer.
Recommended for Input Frequencies from 5MHz to 70MHz
ANALOG
INPUT
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1LB
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
0.1μF
0.1μF
Figure 5. Recommended Front-End Circuit for
Input Frequencies from 170MHz to 270MHz
0.1μF
T1: MA/COM MABAES0060
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
T1
1:1
T1
25Ω
25Ω
T2
0.1μF
50Ω
25Ω
25Ω
25Ω
25Ω
0.1μF
50Ω
0.1μF
12pF
V
A
A
CM
IN
IN
+
–
0.1μF
1.8pF
LTC2259-16
V
A
A
CM
IN
IN
+
–
225916 F03
LTC2259-16
225916 F05
Transformer-Coupled Circuits
Figure 3 shows the analog input being driven by an RF
transformer with a center-tapped secondary. The center
tap is biased with V
DC level. At higher input frequencies a transmission line
balun transformer (Figures 4 to 6) has better balance,
resulting in lower A/D distortion.
ANALOG
INPUT
ANALOG
T1: MA/COM MABA-007159-000000
T2: MA/COM MABAES0060
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
INPUT
0.1μF
0.1μF
Figure 4. Recommended Front-End Circuit for
Input Frequencies from 70MHz to 170MHz
Figure 6. Recommended Front-End Circuit for
Input Frequencies Above 270MHz
0.1μF
0.1μF
T1
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
T1
CM
, setting the A/D input at its optimal
T2
25Ω
25Ω
50Ω
2.7nH
2.7nH
25Ω
25Ω
0.1μF
0.1μF
50Ω
0.1μF
V
A
A
CM
IN
IN
+
–
LTC2259-16
0.1μF
4.7pF
V
A
A
CM
IN
IN
+
–
225916 F06
LTC2259-16
225916f
225916 F04