Datasheet

LTC2282
14
2282fb
APPLICATIONS INFORMATION
Figure 5 shows a single-ended input circuit. The impedance
seen by the analog inputs should be matched. This circuit
is not recommended if low distortion is required.
The 25Ω resistors and 12pF capacitor on the analog
inputs serve two purposes: isolating the drive circuitry
from the sample-and-hold charging glitches and limiting
the wideband noise at the converter input.
For input frequencies above 70MHz, the input circuits of
Figure 6, 7 and 8 are recommended. The balun transformer
gives better high frequency response than a fl ux coupled
center tapped transformer. The coupling capacitors allow
the analog inputs to be DC biased at 1.5V. In Figure 8, the
series inductors are impedance matching elements that
maximize the ADC bandwidth.
25Ω
25Ω
0.1μF
A
IN
+
A
IN
–
2.2μF
V
CM
ANALOG
INPUT
0.1μF
0.1μF
T1
T1 = MA/COM, ETC 1-1-13
RESISTORS, CAPACITORS, INDUCTORS
ARE 0402 PACKAGE SIZE
2282 F08
6.8nH
6.8nH
LTC2282
25Ω
25Ω
0.1μF
A
IN
+
A
IN
–
2.2μF
V
CM
ANALOG
INPUT
0.1μF
0.1μF
T1
T1 = MA/COM, ETC 1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
2282 F07
LTC2282
25Ω
25Ω
12Ω
12Ω
0.1μF
A
IN
+
A
IN
–
8pF
2.2μF
V
CM
ANALOG
INPUT
0.1μF
0.1μF
T1
T1 = MA/COM, ETC 1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
2282 F06
LTC2282
25Ω
0.1μF
ANALOG
INPUT
V
CM
A
IN
+
A
IN
–
1k
12pF
2282 F05
2.2μF
1k
25Ω
0.1μF
LTC2282
25Ω
25Ω
12pF
2.2μF
V
CM
2282 F04
–
–
+
+
CM
ANALOG
INPUT
HIGH SPEED
DIFFERENTIAL
AMPLIFIER
A
IN
+
A
IN
–
LTC2282
Figure 6. Recommended Front End Circuit for
Input Frequencies Between 70MHz and 170MHz
Figure 8. Recommended Front End Circuit for
Input Frequencies Above 300MHz
Figure 7. Recommended Front End Circuit for
Input Frequencies Between 170MHz and 300MHz
Figure 5. Single-Ended Drive
Figure 4. Differential Drive with an Amplifi er