LTC2192 Datasheet, PDF (18/28 Pages) Linear Technology – 16-Bit, 65Msps/40Msps/25Msps Low Power Dual ADCs

LTC2192
LTC2191/LTC2190
APPLICATIONS INFORMATION
50Ω
ANALOG
INPUT
0.1µF T1
1:1
25Ω
25Ω 0.1µF
25Ω _25Ω
T1: MA/COM MABAES0060
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
V_CM
0.1µF
A_IN+
12pF
A_IN–
LTC2192
219210 F03
Figure 3. Analog Input Circuit Using a Transformer.
Recommended for Input Frequencies from 5MHz to 70MHz
50Ω
V_CM
0.1µF
ANALOG
INPUT
T1
0.1µF
T2
25Ω 0.1µF
25Ω
0.1µF
A_IN+
1.8pF
A_IN–
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1L
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
LTC2192
219210 F05
Figure 5. Recommended Front-End Circuit for Input Frequencies
from 150MHz to 250MHz
50Ω
V_CM
0.1µF
ANALOG
INPUT
T1
0.1µF
12Ω
T2
25Ω 0.1µF
25Ω _12Ω
0.1µF
A_IN+
8.2pF
A_IN–
T1: MA/COM MABA-007159-000000
T2: COILCRAFT WBC1-1L
RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE
LTC2192
219210 F04
Figure 4. Recommended Front-End Circuit for Input Frequencies
from 5MHz to 150MHz
0.1µF
ANALOG
INPUT
T1
50Ω
4.7nH
25Ω
0.1µF
V_CM
0.1µF
A_IN+
LTC2192
0.1µF
25Ω _4.7nH
A_IN–
T1: MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
219210 F06
Figure 6. Recommended Front-End Circuit for Input Frequencies
Above 250MHz
DC level. At higher input frequencies a transmission line
balun transformer (Figures 4 to 6) has better balance,
resulting in lower A/D distortion.
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 (Figures  4
to 6) should convert the signal to differential before driv-
ing the A/D.
ANALOG
INPUT
HIGH SPEED
DIFFERENTIAL
AMPLIFIER
0.1µF
+
200Ω 200Ω
25Ω
–
0.1µF
25Ω
V_CM
0.1µF
A_IN+
12pF
LTC2192
A_IN–
12pF
219210 F07
Figure 7. Front-End Circuit Using a High Speed
Differential Amplifier
18
219210p