Datasheet
Table Of Contents
- Features
- Description
- Applications
- Typical Application
- Absolute Maximum Ratings
- Pin Configuration
- Order Information
- Converter Characteristics
- Analog Input
- Digital Accuracy
- Internal Reference Characteristics
- Digital Inputs and Outputs
- Power Requirements
- Timing Characteristics
- Electrical Characteristics
- Timing Diagrams
- Typical perForMance Characteristics
- Pin Functions
- Block Diagram
- Applications Information
- Typical Applications
- Package Description
- Revision History
- Related Parts
LTC2268-14/
LTC2267-14/LTC2266-14
19
22687614fa
CONVERTER OPERATION
The LTC2268-14/LTC2267-14/LTC2266-14 are low power,
2-channel, 14-bit, 125Msps/105Msps/80Msps A/D con-
verters 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 perfor-
mance, or single-ended for lower power consumption.
To minimize the number of data lines the digital outputs
are serial LVDS. Each channel outputs two bits at a time
(2-lane mode). At lower sampling rates there is a one bit
per channel option (1-lane mode). Many additional features
can be chosen by programming the mode control registers
through a serial SPI port.
applicaTions inForMaTion
ANALOG INPUT
The analog inputs are differential CMOS sample-and-hold
circuits (Figure 2). The inputs should be driven differentially
around a common mode voltage set by the V
CM1
or V
CM2
output pins, which are nominally V
DD
/2. For the 2V input
range, the inputs should swing from V
CM
– 0.5V to V
CM
+ 0.5V. There should be 180° phase difference between
the inputs.
The two channels are simultaneously sampled by a shared
encode circuit (Figure 2).
INPUT DRIVE CIRCUITS
Input filtering
If possible, there should be an RC lowpass filter right at
the analog inputs. This lowpass filter 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 filter. The RC component
values should be chosen based on the application’s input
frequency.
Figure 2. Equivalent Input Circuit. Only One
of the Two Analog Channels is Shown
Figure 3. Analog Input Circuit Using a Transformer.
Recommended for Input Frequencies from 5MHz to 70MHz
C
SAMPLE
3.5pF
R
ON
25Ω
R
ON
25Ω
V
DD
V
DD
LTC2268-14
A
IN
+
226814 F02
C
SAMPLE
3.5pF
V
DD
A
IN
–
ENC
–
ENC
+
1.2V
10k
1.2V
10k
C
PARASITIC
1.8pF
C
PARASITIC
1.8pF
10Ω
10Ω
25Ω
25Ω
25Ω
25Ω
50Ω
0.1µF
A
IN
+
A
IN
–
12pF
0.1µF
V
CM
LTC2268-14
ANALOG
INPUT
0.1µF
T1
1:1
T1: MA/COM MABAES0060
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
226814 F03