ISL26310 Datasheet, PDF (13/23 Pages) Intersil Corporation – 12-bit, 125kSPS Low-power ADCs with Single-ended and Differential Inputs and Multiple Input Channels

ISL26310, ISL26311, ISL26312, ISL26313, ISL26314, ISL26315, ISL26319
011...111
011...110
1LSB = 2•VREF/4096
111...111
111...110
1LSB = 2•VREF/4096
000...001
000...000
111...111
100...001
100...000
011...111
100...010
100...001
100...000
–VREF
+ ½LSB
0V
+VREF
– 1½LSB
ANALOG INPUT
AIN+ – (AIN–)
+VREF
– 1LSB
FIGURE 21. IDEAL TRANSFER CHARACTERISTICS, DIFFERENTIAL INPUT
Analog Inputs
Some members of the ISL26310/11/12/13/14/15/19 family
feature a fully differential input with a nominal full-scale range
equal to twice the applied VREF voltage. Those devices with
differential inputs have a nominal full scale range equal to twice
the applied VREF voltage. Each input swings VREF volts (peak-to-
peak), 180° out of phase from one another for a total differential
input of 2*VREF (refer to Figures 23 and 24).
V_CM
V_{REF PP}
V_{REF PP}
AIN+
ISL2631X/32X
AIN-
FIGURE 23. DIFFERENTIAL INPUT SIGNALING
Differential signaling offers several benefits over a single-ended
input, such as:
• Doubling of the full-scale input range (and therefore the
dynamic range)
• Improved even order harmonic distortion
• Better noise immunity due to common mode rejection
Figure 24 shows the relationship between the reference voltage
and the full-scale differential input range for two different values
of VREF. Note that the common-mode input voltage must be
maintained within ±200mV of VREF/2 for differential inputs.
Those devices with singled-ended inputs have a ground-
referenced peak-to-peak input voltage span equal to the
reference voltage.
000...010
000...001
000...000
–VREF
+ ½LSB
+VREF +VREF
– 1½LSB – 1LSB
ANALOG INPUT
FIGURE 22. IDEAL TRANSFER CHARACTERISTICS, SINGLE-ENDED INPUT
V
5.0
4.0
3.0
2.5Vpp
AIN+
2.0
1.0
AIN–
Allowable VCM Range
V
5.0
5Vpp
VREF = 2.5V
AIN+
t
AIN–
4.0
VCM
3.0
Allowable VCM Range
2.0
1.0
t
VREF = 5V
FIGURE 24. RELATIONSHIP BETWEEN VREF AND FULL-SCALE
RANGE FOR DIFFERENTIAL INPUTS
13
FN7549.1
July 3, 2012