DC1298A-AA Linear Technology, DC1298A-AA Datasheet - Page 20

• Manufacturer Part Number: DC1298A-AA
• Description: BOARD EVAL LTM9002-AA
• Manufacturer: Linear Technology
• Type: Baseband Receiverr

Specifications of DC1298A-AA

• Design Resources: Demo Circuit 1298A Schematic
• Frequency: 0Hz ~ 300MHz
• Features: LTM9002 14bit Dual Receiver Subsystem, DC-170MHz LPF
• Tool / Board Applications: Wireless Connectivity-ZigBee, RF, Infrared, USB
• Mcu Supported Families: LTM9002
• Development Tool Type: Hardware - Eval/Demo Board
• For Use With/related Products: LTM9002
• Lead Free Status / RoHS Status: Not applicable / Not applicable

LTM9002
APPLICATIONS INFORMATION
INPUT SPAN
The LTM9002 is confi gured with a given input span and
input impedance. With the amplifi er gain and the ADC
input network described above for LTM9002-AA, the
full-scale input range of the driver circuit is 0.1V
recommended ADC input span is achieved by tying the
SENSE pin to V
changed if required for the application. The resulting input
span at the IN
the gain.
The LTM9002 is intended to be driven through the IN
IN
not intended to be used in the application. These are test
points within the ADC input fi lter network. However, care
should be taken with these pins as they connect directly
to the internal signal path. They should be soldered to an
unconnected pad and should be well isolated.
Input Impedance and Matching
The input impedance of the amplifi er is 50Ω, 200Ω or
400Ω depending on the gain of the amplifi er. In some
applications the differential inputs may need to be ter-
minated to a lower value impedance, e.g. 50Ω, in order
to provide an impedance match for the source. Several
choices are available.
One approach is to use a differential shunt resistor
(Figure 4). Another approach is to employ a wide band
transformer and shunt resistor (Figure 5). Both methods
provide a wide band match. The termination resistor or
the transformer must be placed close to the input pins in
order to minimize the refl ection due to input mismatch.
Alternatively, one could apply a narrowband impedance
match at the inputs for frequency selection and/or noise
reduction.
Table 4. Differential Amplifi er Input Termination Values
20
–
GAIN (dB)
pins. The DNC pins are used for test purposes and are
14
20
26
8
+
/IN
DD
–
. However, the ADC input span can be
200Ω
100Ω
100Ω
Z
pins is the ADC input span divided by
25Ω
IN
/2
R
T
FIGURE 4
66.5Ω
66.5Ω
None
57Ω
R
T
FIGURE 5
400Ω
None
None
None
P-P
+
. The
and
Referring to Figure 6, amplifi er inputs can be easily con-
fi gured for single-ended input without a balun. The signal
is fed to one of the inputs through a matching network
while the other input is connected to the same matching
network and a source resistor. Because the return ratios
of the two feedback paths are equal, the two outputs have
the same gain and thus symmetrical swing. In general,
the single-ended input impedance and termination resis-
tor R
R
Table 5. Single-Ended Amplifi er Input Termination Values
F
, see Table 5.
T
GAIN (dB)
are determined by the combination of R
Figure 4. Input Termination for Differential 50Ω
Input Impedance Using Shunt Resistor
Figure 5. Input Termination for Differential 50Ω
Input Impedance Using a Balun
+
–
14
20
26
8
V
25Ω
25Ω
+
–
IN
V
25Ω
25Ω
IN
•
1:4
•
R
IN
IN
T
+
–
R
IN
IN
T
+
–
Z
Z
IN
IN
/2
/2
200Ω
100Ω
100Ω
Z
Z
Z
25Ω
IN
IN
IN
/2
/2
/2
500Ω
500Ω
500Ω
500Ω
LTM9002
LTM9002
R
9002 F04
T
FIGURE 6
68.5Ω
66.5Ω
150Ω
9002 F05
59Ω
S
, R
G
and
9002f