ltc2182 Linear Technology Corporation, ltc2182 Datasheet - Page 20

• Manufacturer Part Number: ltc2182
• Description: 16-bit, 65msps/ 40msps/25msps Low Power Dual Adcs
• Manufacturer: Linear Technology Corporation

Amplifier Circuits
Figure 7 shows the analog input being driven by a high
speed differential amplifier. The output of the amplifier is AC-
coupled to the A/D so the amplifier’s output common mode
voltage can be optimally set to minimize distortion.
At very high frequencies an RF gain block will often have
lower distortion than a differential amplifier. If the gain
block is single-ended, then a transformer circuit (Figure 4
to Figure 6) should convert the signal to differential before
driving the A/D.
ANALOG
ANALOG
LTC2182/LTC2181/LTC2180
20
APPLICATIONS INFORMATION
INPUT
INPUT
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1TL
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1TL
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
Figure 4. Recommended Front-End Circuit for Input
Frequencies from 5MHz to 150MHz
Figure 5. Recommended Front-End Circuit for Input
Frequencies from 150MHz to 250MHz
0.1µF
0.1µF
0.1µF
0.1µF
T1
T1
T2
T2
25
25
25
25
0.1µF
0.1µF
12
12
50
50
0.1µF
0.1µF
8.2pF
1.8pF
V
V
A
A
A
A
CM
CM
IN
IN
IN
IN
+
–
+
–
LTC2182
LTC2182
218210 F04
218210 F05
Reference
The LTC2182/LTC2181/LTC2180 has an internal 1.25V
voltage reference. For a 2V input range using the internal
reference, connect SENSE to V
using the internal reference, connect SENSE to ground.
For a 2V input range with an external reference, apply a
1.25V reference voltage to SENSE (Figure 9).
The input range can be adjusted by applying a voltage to
SENSE that is between 0.625V and 1.30V. The input range
will then be 1.6 • V
The V
shown in Figure 8. A low inductance 2.2µF interdigitated
capacitor is recommended for the bypass between REFH
and REFL. This type of capacitor is available at a low cost
from multiple suppliers.
ANALOG
ANALOG
INPUT
INPUT
REF
Figure 6. Recommended Front-End Circuit for Input
Frequencies Above 250MHz
Figure 7. Front-End Circuit Using a High Speed
Differential Amplifier
, REFH and REFL pins should be bypassed as
0.1µF
0.1µF
DIFFERENTIAL
HIGH SPEED
+
–
AMPLIFIER
+
–
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
T1
SENSE
0.1µF
0.1µF
.
25
25
200
50
200
4.7nH
4.7nH
0.1µF
DD
25
25
. For a 1V input range
0.1µF
12pF
12pF
0.1µF
V
A
A
V
A
A
CM
IN
IN
IN
IN
CM
+
–
+
–
LTC2182
LTC2182
218210
218210
F07
F06
218210f