Datasheet

AD9216
Rev. A | Page 24 of 40
VOLTAGE REFERENCE
A stable and accurate 0.5 V voltage reference is built into
the AD9216. The input range can be adjusted by varying the
reference voltage applied to the AD9216, using either the inter-
nal reference with different external resistor configurations or
an externally applied reference voltage. The input span of the
ADC tracks reference voltage changes linearly.
Internal Reference Connection
A comparator within the AD9216 detects the potential at the
SENSE pin and configures the reference into three possible
states, which are summarized in Table 9. If SENSE is grounded,
the reference amplifier switch is connected to the internal resistor
divider (see Figure 47), setting VREF to 1 V. If a resistor divider
is connected, as shown in Figure 48, the switch is again set to the
SENSE pin. This puts the reference amplifier in a noninverting
mode with the VREF output defined as
VREF = 0.5 × (1 + R2/R1)
Note: The optimum performance is obtained with VREF =
1.0 V; performance degrades as VREF (and full scale) reduces
(see Figure 25). In all reference configurations, REFT and REFB
drive the ADC core and establish its input span. The input
range of the ADC always equals twice the voltage at the refer-
ence pin for either an internal or an external reference.
VIN+
VIN–
10µF
10µF
0.1µF
0.1µF
REFT
ADC
CORE
SELECT
LOGIC
SENSE
0.1µF
0.5V
AD9216
REFB
0.1µF
VREF
04775-014
Figure 47. Internal Reference Configuration (One Channel Shown)
Table 9. Reference Configuration Summary
Selected Mode SENSE Voltage Resulting VREF (V) Resulting Differential Span (V p-p)
External Reference AVDD N/A 2 × External Reference
Programmable Reference 0.2 V to VREF 0.5 × (1 + R2/R1) 2 × VREF (see Figure 48)
Internal Fixed Reference AGND to 0.2 V 1.0 2.0