Datasheet

LTC2298/LTC2297/LTC2296
18
229876fa
25Ω
0.1µF
ANALOG
INPUT
V
CM
A
IN
+
A
IN
–
1k
12pF
229876 F05
2.2µF
1k
25Ω
0.1µF
LTC2298
LTC2297
LTC2296
Figure 5 shows a single-ended input circuit. The imped-
ance seen by the analog inputs should be matched. This
circuit is not recommended if low distortion is required.
APPLICATIO S I FOR ATIO
WUUU
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
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
229876 F06
LTC2298
LTC2297
LTC2296
Figure 5. Single-Ended Drive
Figure 4. Differential Drive with an Amplifier
25Ω
25Ω
12pF
2.2µF
V
CM
229876 F04
–
–
+
+
CM
ANALOG
INPUT
HIGH SPEED
DIFFERENTIAL
AMPLIFIER
A
IN
+
A
IN
–
LTC2298
LTC2297
LTC2296
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 trans-
former gives better high frequency response than a flux
coupled center tapped transformer. The coupling capaci-
tors 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
ARE 0402 PACKAGE SIZE
229876 F07
LTC2298
LTC2297
LTC2296
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
229876 F08
6.8nH
6.8nH
LTC2298
LTC2297
LTC2296