LTC2259-16 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2259-16' PDF : 28 Pages View PDF
LTC2259-16
APPLICATIONS INFORMATION
INPUT DRIVE CIRCUITS
Input Filtering
If possible, there should be an RC lowpass filter right at
the analog inputs. This lowpass filter 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 filter. The RC component
values should be chosen based on the application’s input
frequency.
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 VCM, setting the A/D input at its optimal
DC level. At higher input frequencies a transmission line
balun transformer (Figures 4 to 6) has better balance,
resulting in lower A/D distortion.
50Ω
ANALOG
INPUT
0.1μF T1
1:1
25Ω
25Ω 0.1μF
25Ω
25Ω
T1: MA/COM MABAES0060
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
VCM
0.1μF
AIN+
LTC2259-16
12pF
AIN–
225916 F03
Figure 3. Analog Input Circuit Using a Transformer.
Recommended for Input Frequencies from 5MHz to 70MHz
0.1μF
ANALOG
INPUT
T1
0.1μF
50Ω
VCM
0.1μF
T2
25Ω 0.1μF
AIN+
LTC2259-16
4.7pF
25Ω
AIN–
T1: MA/COM MABA-007159-000000
T2: MA/COM MABAES0060
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
Figure 4. Recommended Front-End Circuit for
Input Frequencies from 70MHz to 170MHz
225916 F04
0.1μF
ANALOG
INPUT
T1
0.1μF
50Ω
VCM
0.1μF
T2
25Ω 0.1μF
AIN+
LTC2259-16
1.8pF
25Ω
AIN–
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
225916 F05
50Ω
ANALOG
INPUT
0.1μF
T1
0.1μF
2.7nH
25Ω
0.1μF
25Ω 2.7nH
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
VCM
0.1μF
AIN+
LTC2259-16
AIN–
225916 F06
Figure 6. Recommended Front-End Circuit for
Input Frequencies Above 270MHz
225916f
14
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