LTC2172CUKG-14PBF LINER [Linear Technology], LTC2172CUKG-14PBF Datasheet - Page 19

• Manufacturer Part Number: LTC2172CUKG-14PBF
• Description: 14-Bit, 65Msps/40Msps/25Msps Low Power Quad ADCs
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
CONVERTER OPERATION
The LTC2172-14/LTC2171-14/LTC2170-14 are low power,
4-channel, 14-bit, 65Msps/40Msps/25Msps A/D convert-
ers that are powered by a single 1.8V supply. The analog
inputs should be driven differentially. The encode input
can be driven differentially for optimal jitter performance,
or single-ended for lower power consumption. The digital
outputs are serial LVDS to minimize the number of data
lines. Each channel outputs two bits at a time (2-lane
mode) or one bit at a time (1-lane mode). Many additional
features can be chosen by programming the mode control
registers through a serial SPI port.
ANALOG INPUT
The analog inputs are differential CMOS sample-and-hold
circuits (Figure 2). The inputs should be driven differen-
tially around a common mode voltage set by the V
ENC
ENC
A
A
IN
IN
+
–
+
–
LTC2172-14
10Ω
10Ω
Figure 2. Equivalent Input Circuit. Only One of
the Four Analog Channels Is Shown.
1.2V
1.2V
10k
V
V
10k
DD
DD
V
DD
C
1.8pF
C
1.8pF
PARASITIC
PARASITIC
25Ω
25Ω
R
R
ON
ON
C
C
SAMPLE
SAMPLE
3.5pF
3.5pF
217214 F02
CM12
or V
2V input range, the inputs should swing from V
to V
between the inputs.
The four channels are simultaneously sampled by a
shared encode circuit (Figure 2).
INPUT DRIVE CIRCUITS
Input Filtering
If possible, there should be an RC lowpass fi lter right
at the analog inputs. This lowpass fi lter isolates the
drive circuitry from the A/D sample-and-hold switch-
ing and limits wideband noise from the drive circuitry.
Figure 3 shows an example of an input RC fi lter. The
RC component values should be chosen based on the
application’s input frequency.
ANALOG
Figure 3. Analog Input Circuit Using a Transformer.
Recommended for Input Frequencies from 5MHz to 70MHz
CM34
CM
INPUT
LTC2171-14/LTC2170-14
+ 0.5V. There should be a 180° phase difference
output pins, which are nominally V
0.1μF
T1: MA/COM MABAES0060
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
1:1
T1
25Ω
25Ω
0.1μF
50Ω
25Ω
25Ω
LTC2172-14/
0.1μF
12pF
V
A
A
CM
IN
IN
+
–
LTC2172-14
DD
/2. For the
CM
217214 F03
19
– 0.5V
21721014f