AD9219-65EB Analog Devices Inc, AD9219-65EB Datasheet - Page 29

• Manufacturer Part Number: AD9219-65EB
• Description: Quad 10-bit 65 MSPS Serial LVDS ADC EB
• Manufacturer: Analog Devices Inc

Specifications of AD9219-65EB

• Number Of Adc's: 4
• Number Of Bits: 10
• Sampling Rate (per Second): 40M
• Data Interface: Serial
• Inputs Per Adc: 2 Single
• Input Range: 2 Vpp
• Power (typ) @ Conditions: 378mW @ 1.8 V
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9219
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Internal Reference Operation
A comparator within the AD9219 detects the potential at the
SENSE pin and configures the reference. If SENSE is grounded,
the reference amplifier switch is connected to the internal
resistor divider (see Figure 64), setting VREF to 1 V.
The REFT and REFB pins establish the input span of the ADC
core from the reference configuration. The analog input full-
scale range of the ADC equals twice the voltage of the reference
pin for either an internal or an external reference configuration.
If the reference of the AD9219 is used to drive multiple
converters to improve gain matching, the loading of the refer-
ence by the other converters must be considered. Figure 66
depicts how the internal reference voltage is affected by loading.
1µF
1µF
+
SENSE
0.1µF
VIN + x
VIN – x
0.1µF
SENSE
VIN + x
VIN – x
VREF
R2
R1
VREF
Figure 64. Internal Reference Configuration
Figure 65. External Reference Operation
SELECT
LOGIC
SELECT
LOGIC
CORE
ADC
CORE
ADC
0.5V
0.5V
REFT
REFB
REFT
REFB
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
+
+
2.2µF
2.2µF
Rev. D | Page 29 of 52
External Reference Operation
The use of an external reference may be necessary to enhance
the gain accuracy of the ADC or to improve thermal drift charac-
teristics. Figure 67 shows the typical drift characteristics of the
internal reference in 1 V mode.
When the SENSE pin is tied to AVDD, the internal reference is
disabled, allowing the use of an external reference. The external
reference is loaded with an equivalent 6 kΩ load. An internal
reference buffer generates the positive and negative full-scale
references, REFT and REFB, for the ADC core. Therefore, the
external reference must be limited to a nominal 1.0 V.
–0.02
–0.04
–0.06
–0.08
–0.10
–0.12
–0.14
–0.16
–0.18
–30
–10
–15
–20
–25
0.02
–5
5
0
0
–40
0
0.5
–20
Figure 66. V
Figure 67. Typical V
1.0
CURRENT LOAD (mA)
0
TEMPERATURE (°C)
REF
1.5
Accuracy vs. Load
20
2.0
REF
Drift
40
2.5
60
3.0
AD9219
80
3.5