LTC2298 Linear Technology, LTC2298 Datasheet - Page 18

• Manufacturer Part Number: LTC2298
• Description: (LTC2296 - LTC2298) Low Power 3V ADCs
• Manufacturer: Linear Technology

LTC2298/LTC2297/LTC2296
APPLICATIO S I FOR ATIO
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.
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.
18
ANALOG
ANALOG
INPUT
INPUT
Figure 4. Differential Drive with an Amplifier
0.1µF
DIFFERENTIAL
+
CM
–
HIGH SPEED
Figure 5. Single-Ended Drive
AMPLIFIER
+
–
U
10k
25Ω
25Ω
U
10k
25Ω
25Ω
0.1µF
12pF
12pF
2.2µF
2.2µF
W
V
A
A
CM
IN
IN
V
A
A
CM
IN
IN
+
–
+
–
LTC2298
LTC2297
LTC2296
LTC2298
LTC2297
LTC2296
229876 F04
229876 F05
U
ANALOG
ANALOG
ANALOG
INPUT
INPUT
INPUT
Figure 6. Recommended Front End Circuit for
Input Frequencies Between 70MHz and 170MHz
Figure 7. Recommended Front End Circuit for
Input Frequencies Between 170MHz and 300MHz
Figure 8. Recommended Front End Circuit for
Input Frequencies Above 300MHz
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
T1 = MA/COM, ETC 1-1-13
RESISTORS, CAPACITORS, INDUCTORS
ARE 0402 PACKAGE SIZE
T1 = MA/COM, ETC 1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
T1
T1
T1
T1 = MA/COM, ETC 1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
25Ω
25Ω
25Ω
25Ω
25Ω
25Ω
6.8nH
12Ω
0.1µF
0.1µF
0.1µF
6.8nH
12Ω
2.2µF
2.2µF
2.2µF
8pF
V
A
A
V
V
A
A
A
A
CM
IN
IN
CM
CM
IN
IN
IN
IN
+
–
+
–
+
–
LTC2298
LTC2297
LTC2296
LTC2298
LTC2297
LTC2296
LTC2298
LTC2297
LTC2296
229876 F08
229876 F06
229876 F07
229876f