DC1250A-BA Linear Technology, DC1250A-BA Datasheet - Page 25

• Manufacturer Part Number: DC1250A-BA
• Description: BOARD EVAL LTM9001-BA
• Manufacturer: Linear Technology
• Type: Baseband Receiverr

Specifications of DC1250A-BA

• Design Resources: Demo Circuit 1250A Schematic
• Frequency: 0Hz ~ 300MHz
• Features: LTM9001 16bit Receiver Subsystem, DC-300MHz LPF
• Tool / Board Applications: Wireless Connectivity-ZigBee, RF, Infrared, USB
• Mcu Supported Families: LTM9001
• For Use With/related Products: LTM9001
• Lead Free Status / RoHS Status: Not applicable / Not applicable

APPLICATIONS INFORMATION
example, if the converter is driving a DSP powered by a
1.8V supply, then OV
supply. OV
to the 3.6V. OGND can be powered with any voltage from
ground up to 1V and must be less than OV
outputs will swing between OGND and OV
Internal Dither
The LTM9001 is a 16-bit receiver subsystem with a very
linear transfer function; however, at low input levels even
slight imperfections in the transfer function will result in
unwanted tones. Small errors in the transfer function are
usually a result of ADC element mismatches. An optional
internal dither mode can be enabled to randomize the input
location on the ADC transfer curve, resulting in improved
SFDR for low signal levels.
As shown in Figure 14, the output of the sample-and-hold
amplifi er is summed with the output of a dither DAC. The
dither DAC is driven by a long sequence pseudo-random
number generator; the random number fed to the dither
DAC is also subtracted from the ADC result. If the dither
DAC is precisely calibrated to the ADC, very little of the
dither signal will be seen at the output. The dither signal
that does leak through will appear as white noise. The dither
IN
IN
+
–
DD
can be powered with any logic voltage up
LTM9001
DD
should be tied to that same 1.8V
Figure 14. Functional Equivalent Block Diagram of Internal Dither Circuit
ENC
CLOCK/DUTY
CONTROL
AMP
+
S/H
CYCLE
DD
DD
ENC
.
. The logic
–
PRECISION
PIPELINED
ADC CORE
DAC will cause a small elevation in the noise fl oor of the
ADC, as compared to the noise fl oor with dither off.
For best noise performance with the dither signal on, the
driving impedance connected across pins IN
closely match that of the module (see Table 1). A source
impedance that is resistive and matches that of the module
within 10% will give the best results.
Supply Sequencing
The V
pin provides the supply to the ADC. The amplifi er and the
ADC are separate integrated circuits within the LTM9001;
however, there are no supply sequencing considerations
beyond standard practice. It is recommended that the
amplifi er and ADC both use the same low noise, 3.3V
supply, but the amplifi er may be operated from a lower
voltage level if desired. Both devices can operate from the
same 3.3V linear regulator but place a ferrite bead between
the V
used without additional supply sequencing circuitry if they
have common input supplies.
16-BIT
DAC
CC
CC
LTM9001-Ax/LTM9001-Bx
pin provides the supply to the amplifi er and the V
and V
SUMMATION
DD
DIGITAL
pins. Separate linear regulators can be
LOW = DITHER OFF
PSEUDO-RANDOM
HIGH = DITHER ON
MULTIBIT DEEP
DITHER ENABLE
GENERATOR
NUMBER
DRIVERS
OUTPUT
DITH
9001 F14
CLKOUT
D15
OF
D0
+
•
•
•
/IN
–
25
should
9001fc
DD