LTC2226 LINER [Linear Technology], LTC2226 Datasheet - Page 18

• Manufacturer Part Number: LTC2226
• Description: 12-Bit, 65/40/25Msps Low Power 3V ADCs
• Manufacturer: LINER [Linear Technology]

LTC2228/LTC2227/LTC2226
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.
18
ANALOG
ANALOG
INPUT
INPUT
Figure 4. Differential Drive with an Amplifi er
0.1μF
DIFFERENTIAL
+
CM
–
HIGH SPEED
Figure 5. Single-Ended Drive
AMPLIFIER
+
–
1k
1k
25Ω
25Ω
25Ω
25Ω
0.1μF
12pF
2.2μF
12pF
2.2μF
V
A
A
V
A
A
CM
IN
IN
CM
IN
IN
+
–
+
–
LTC2228/27/26
LTC2228/27/26
222876 F04
222876 F05
ANALOG
ANALOG
ANALOG
INPUT
INPUT
INPUT
Figure 7. Recommended Front-End Circuit for
Input Frequencies Between 170MHz and 300MHz
Figure 8. Recommended Front-End Circuit for
Input Frequencies Above 300MHz
Figure 6. Recommended Front-End Circuit for
Input Frequencies Between 70MHz and 170MHz
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 = MA/COM, ETC 1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
T1
25Ω
25Ω
25Ω
25Ω
25Ω
25Ω
6.8nH
12Ω
0.1μF
0.1μF
0.1μF
12Ω
6.8nH
2.2μF
2.2μF
2.2μF
8pF
V
V
A
A
A
A
V
A
A
CM
CM
IN
IN
IN
IN
CM
IN
IN
+
–
+
–
+
–
LTC2228/27/26
LTC2228/27/26
LTC2228/27/26
222876 F07
222876 F08
222876 F06
222876fb