
LTC2262-14
14
226214fc
For more information www.linear.com/LTC2262-14
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(Figure2).Theinputsshouldbedrivendifferentially
around a common mode voltage set by the VCM output
pin, which is nominally VDD/2. For the 2V input range, the
inputs should swing from VCM– 0.5V to VCM + 0.5V. There
should be 180° phase difference between the inputs.
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
alsolimitswidebandnoisefromthedrivecircuitry.Figure 3
shows an example of an input RC filter. 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 VCM, setting the A/D input at its optimal
CSAMPLE
3.5pF
RON
25
RON
25
VDD
LTC2262-14
AIN+
226214 F02
CSAMPLE
3.5pF
VDD
AIN–
ENC–
ENC+
1.2V
10k
1.2V
10k
CPARASITIC
1.8pF
CPARASITIC
1.8pF
10
25
50
0.1F
AIN+
AIN–
12pF
0.1F
VCM
LTC2262-14
ANALOG
INPUT
0.1F
T1
1:1
T1: MA/COM MABAES0060
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
226214 F03
Figure 2. Equivalent Input Circuit
Figure 3. Analog Input Circuit Using a Transformer.
Recommended for Input Frequencies from 5MHz to 70MHz
APPLICATIONS INFORMATION