LTC2259-16 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2259-16' PDF : 28 Pages View PDF
LTC2259-16
APPLICATIONS INFORMATION
Amplifier Circuits
Figure 7 shows the analog input being driven by a high
speed differential amplifier. The output of the amplifier is
AC-coupled to the A/D so the amplifier’s output common
mode voltage can be optimally set to minimize distortion.
At very high frequencies an RF gain block will often have
lower distortion than a differential amplifier. If the gain
block is single-ended, then a transformer circuit (Figures 4
to 6) should convert the signal to differential before driv-
ing the A/D.
Reference
The LTC2259-16 has an internal 1.25V voltage reference.
For a 2V input range using the internal reference, connect
SENSE to VDD. For a 1V input range using the internal
reference, connect SENSE to ground. For a 2V input range
with an external reference, apply a 1.25V reference voltage
to SENSE (Figure 9.)
The input range can be adjusted by applying a voltage to
SENSE that is between 0.625V and 1.30V. The input range
will then be 1.6 • VSENSE.
The VREF, REFH and REFL pins should be bypassed as
shown in Figure 8. The 0.1μF capacitor between REFH
and REFL should be as close to the pins as possible (not
on the back side of the circuit board).
ANALOG
INPUT
HIGH SPEED
DIFFERENTIAL
AMPLIFIER
0.1μF
++
200Ω 200Ω
25Ω
– – 0.1μF
25Ω
VCM
0.1μF
AIN+
LTC2259-16
12pF
AIN–
Figure 7. Front-End Circuit Using a High
Speed Differential Amplifier
225916 F07
1.25V
LTC2259-16
VREF
1μF
5Ω
1.25V BANDGAP
REFERENCE
0.625V
TIE TO VDD FOR 2V RANGE;
TIE TO GND FOR 1V RANGE;
RANGE = 1.6 • VSENSE FOR
0.65V < VSENSE < 1.300V
SENSE
0.1μF
REFH
RANGE
DETECT
AND
CONTROL
BUFFER
INTERNAL ADC
HIGH REFERENCE
2.2μF
0.1μF
0.1μF
0.8x
DIFF AMP
REFL
INTERNAL ADC
LOW REFERENCE
Figure 8. Reference Circuit
225916 F08
1.25V
EXTERNAL
REFERENCE
VREF
1μF
SENSE
LTC2259-16
1μF
225916 F09
Figure 9. Using an External 1.25V Reference
225916f
15
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