DC1250A-BA Linear Technology, DC1250A-BA Datasheet - Page 20

• 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

LTM9001-Ax/LTM9001-Bx
APPLICATIONS INFORMATION
Alternatively, one could apply a narrowband impedance match
at the inputs for frequency selection and/or noise reduction.
Referring to Figure 4, amplifi er inputs can be easily
confi 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
impedance. In general, the single-ended input impedance
and termination resistor R
combination of R
Table 3. Single-Ended Amplifi er Input Termination Values
The LTM9001 amplifi er is stable with all source impedances.
The overall differential gain is affected by the source
impedance in Figure 5:
The noise performance of the amplifi er also depends upon
the source impedance and termination. For example, an
input 1:4 transformer in Figure 3 improves the input noise
fi gure by adding 6dB voltage gain at the inputs.
Reference and SENSE Pin Operation
Figure 6 shows the converter reference circuitry consisting
of a 2.5V bandgap reference, a programmable gain amplifi er
and control circuit. There are three modes of reference
operation: internal reference, 1.25V external reference
or 2.5V external reference. To use the internal reference,
20
A
V
= | V
400Ω
200Ω
50Ω
Z
IN
OUT
/V
IN
S
, Z
| = (1000/(R
IN
TIE TO V
EXTERNAL 1.25V
/2 and R
EXTERNAL 2.5V
INTERNAL 2.5V
OR INPUT FOR
OR INPUT FOR
REFERENCE
REFERENCE
REFERENCE
DD
TO USE
T
S
F
are determined by the
.
+ Z
SENSE
R
IN
68.5Ω
T
150Ω
59Ω
FIG 4
/2))
Figure 6. Reference Circuit
AND GAIN
CONTROL
SELECT
RANGE
tie the SENSE pin to V
simply apply either a 1.25V or 2.5V reference voltage to the
SENSE input pin. Both 1.25V and 2.5V applied to SENSE
will result in the maximum full-scale range.
+
–
+
–
0.1μF
R
V
50Ω
PGA
R
IN
S
Figure 4. Input Termination for Differential
50Ω Input Impedance Using Shunt Resistor
V
/R
R
R
S
R
IN
s
s
T
T
/2
/2
REFERENCE
Figure 5. Calculate Differential Gain
BANDGAP
0.1μF
0.1μF
REFERENCE
INTERNAL
2.5V
R
IN
IN
ADC
T
+
–
IN
IN
9001 F06
+
–
Z
Z
IN
IN
Z
Z
/2
/2
IN
IN
DD
/2
/2
. To use an external reference,
R
R
R
R
F
F
F
F
LTM9001
LTM9001
9001 F05
9001 F04
9001fc