DC1398A-GA Linear Technology, DC1398A-GA Datasheet - Page 20

• Manufacturer Part Number: DC1398A-GA
• Description: BOARD EVAL LTM9001-GA
• Manufacturer: Linear Technology
• Type: Baseband Receiverr

Specifications of DC1398A-GA

• Design Resources: Demo Circuit 1398A Schematic
• Frequency: 0Hz ~ 300MHz
• Kit Contents: Board, Manual
• Features: LTM9001 16bit Receiver Subsystem, DC-10MHz LPF
• Tool / Board Applications: Wireless Connectivity-ZigBee, RF, Infrared, USB
• Development Tool Type: Hardware - Eval/Demo Board
• Mcu Supported Families: LTM9001
• For Use With/related Products: LTM9001
• Lead Free Status / RoHS Status: Not applicable / Not applicable

APPLICATIONS INFORMATION
LTM9001-GA
As shown in Figure 12, 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
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
20
CC
pin provides the supply to the amplifi er and the V
IN
IN
+
–
LTM9001-GA
Figure 12. Functional Equivalent Block Diagram of Internal Dither Circuit
CLOCK/DUTY
CONTROL
AMP
S/H
CYCLE
CLK
+
/IN
–
should
DD
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.
Grounding and Bypassing
The LTM9001 requires a printed circuit board with a
clean unbroken ground plane; a multilayer board with an
internal ground plane is recommended. The pinout of the
LTM9001 has been optimized for a fl ow-through layout
so that the interaction between inputs and digital outputs
is minimized. A continuous row of ground pads facilitate
a layout that ensures that digital and analog signal lines
are separated as much as possible.
The LTM9001 is internally bypassed with the amplifi er (V
and ADC (V
(GND). The digital output supply (0V
OGND. Additional bypass capacitance is optional and may
be required if power supply noise is signifi cant.
The differential inputs should run parallel and close to each
other. The input traces should be as short as possible to
minimize capacitance and to minimize noise pickup.
PRECISION
PIPELINED
ADC CORE
16-BIT
DAC
CC
and V
DD
DD
) supplies returning to a common ground
SUMMATION
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-GA F14
DD
) is returned to
CLKOUT
D15
OF
D0
•
•
•
9001gaf
CC
)