LTC2262-14 Linear Dimensions Semiconductor, LTC2262-14 Datasheet - Page 14

• Manufacturer Part Number: LTC2262-14
• Description: 150Msps Ultralow Power 1.8V ADC
• Manufacturer: Linear Dimensions Semiconductor

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LTC2262-14
APPLICATIONS INFORMATION
CONVERTER OPERATION
The LTC2262-14 is a low power 14-bit 150Msps A/D
converter that is powered by a single 1.8V supply. The
analog inputs should be driven differentially. The encode
input can be driven differentially, or single ended for lower
power consumption. The digital outputs can be CMOS,
double data rate CMOS (to halve the number of output
lines), or double data rate LVDS (to reduce digital noise in
the system.) Many additional features can be chosen by
programming the mode control registers through a serial
SPI port. See the Serial Programming Mode section.
ANALOG INPUT
The analog input is a differential CMOS sample-and-hold
circuit (Figure 2). The inputs should be driven differentially
around a common mode voltage set by the V
pin, which is nominally V
14
ENC
ENC
A
A
IN
IN
+
–
+
–
LTC2262-14
10Ω
10Ω
1.2V
1.2V
Figure 2. Equivalent Input Circuit
10k
10k
V
V
DD
DD
V
DD
DD
C
1.8pF
C
1.8pF
/2. For the 2V input range, the
PARASITIC
PARASITIC
25Ω
25Ω
R
R
ON
ON
C
C
CM
SAMPLE
SAMPLE
3.5pF
3.5pF
226214 F02
output
inputs should swing from V
should be 180° phase difference between the inputs.
INPUT DRIVE CIRCUITS
Input fi ltering
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 switching, and
also 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.
Transformer Coupled Circuits
Figure 3 shows the analog input being driven by an RF
transformer with a center-tapped secondary. The center
tap is biased with V
Figure 3. Analog Input Circuit Using a Transformer.
Recommended for Input Frequencies from 5MHz to 70MHz
ANALOG
INPUT
0.1μF
T1: MA/COM MABAES0060
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
1:1
T1
CM
, setting the A/D input at its optimal
25Ω
25Ω
CM
0.1μF
50Ω
25Ω
25Ω
– 0.5V to V
0.1μF
12pF
V
A
A
CM
IN
IN
+
–
CM
LTC2262-14
+ 0.5V. There
226214 F03
226214p