ltc2226iuh-trpbf Linear Technology Corporation, ltc2226iuh-trpbf Datasheet - Page 18

• Manufacturer Part Number: ltc2226iuh-trpbf
• Description: Ltc2227 - 12-bit, 40msps Low Power 3v Adcs
• Manufacturer: Linear Technology Corporation

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.
LTC2228/LTC2227/LTC2226
APPLICATIO S I FOR ATIO
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
INPUT
ANALOG
INPUT
Figure 4. Differential Drive with an Amplifier
0.1µF
DIFFERENTIAL
+
CM
–
Figure 5. Single-Ended Drive
HIGH SPEED
AMPLIFIER
U
+
–
1k
1k
U
25Ω
25Ω
0.1µF
25Ω
25Ω
12pF
2.2µF
2.2µF
12pF
W
V
A
A
V
A
A
CM
IN
IN
CM
IN
IN
+
–
+
–
LTC2228/27/26
LTC2228/27/26
222876 F04
222876 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
ARE 0402 PACKAGE SIZE
T1 = MA/COM, ETC 1-1-13
RESISTORS, CAPACITORS, INDUCTORS
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
12Ω
6.8nH
2.2µF
2.2µF
8pF
2.2µF
V
V
V
A
A
A
A
A
A
CM
IN
IN
CM
CM
IN
IN
IN
IN
+
–
+
–
+
–
LTC2228/27/26
LTC2228/27/26
LTC2228/27/26
222876 F08
222876 F06
222876 F07
222876fa