LTC2259-16 LINER [Linear Technology], LTC2259-16 Datasheet - Page 15

• Manufacturer Part Number: LTC2259-16
• Description: 16-Bit, 80Msps Ultralow Power 1.8V ADC
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Amplifi er Circuits
Figure 7 shows the analog input being driven by a high
speed differential amplifi er. The output of the amplifi er is
AC-coupled to the A/D so the amplifi er’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 amplifi er. 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 V
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 • V
The V
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
REF
DIFFERENTIAL
, REFH and REFL pins should be bypassed as
HIGH SPEED
+
–
AMPLIFIER
Figure 7. Front-End Circuit Using a High
Speed Differential Amplifi er
DD
+
–
. For a 1V input range using the internal
SENSE
0.1μF
0.1μF
.
200Ω
200Ω
25Ω
25Ω
12pF
0.1μF
V
A
A
IN
IN
CM
+
–
LTC2259-16
225916 F07
TIE TO GND FOR 1V RANGE;
TIE TO V
RANGE = 1.6 • V
0.65V < V
DD
2.2μF
FOR 2V RANGE;
SENSE
0.1μF
0.1μF
Figure 9. Using an External 1.25V Reference
1.25V
SENSE
< 1.300V
REFERENCE
EXTERNAL
FOR
Figure 8. Reference Circuit
1.25V
0.1μF
1μF
SENSE
REFH
V
REFL
REF
LTC2259-16
SENSE
1μF
1μF
CONTROL
V
5Ω
DETECT
RANGE
REF
AND
LTC2259-16
LTC2259-16
1.25V BANDGAP
DIFF AMP
REFERENCE
INTERNAL ADC
HIGH REFERENCE
0.8x
INTERNAL ADC
LOW REFERENCE
225916 F09
0.625V
BUFFER
15
225916f
225916 F08