AD9269 Analog Devices, AD9269 Datasheet - Page 21

• Manufacturer Part Number: AD9269
• Description: 16-Bit, 20 MSPS/40 MSPS/65 MSPS/80 MSPS, 1.8 V Dual Analog-to-Digital Converter
• Manufacturer: Analog Devices

Specifications of AD9269

• Resolution (bits): 16bit
• # Chan: 2
• Sample Rate: 80MSPS
• Interface: Par
• Analog Input Type: Diff-Uni
• Ain Range: 2 V p-p
• Adc Architecture: Pipelined
• Pkg Type: CSP

In any configuration, the value of Shunt Capacitor C is dependent
on the input frequency and source impedance and may need to
be reduced or removed. Table 9 displays the suggested values to set
the RC network. However, these values are dependent on the
input signal and should be used only as a starting guide.
Table 9. Example RC Network
Frequency Range (MHz)
0 to 70
70 to 200
Single-Ended Input Configuration
A single-ended input can provide adequate performance in
cost-sensitive applications. In this configuration, SFDR and
distortion performance degrade due to the large input common-
mode swing. If the source impedances on each input are matched,
there should be little effect on SNR performance. Figure 44
shows a typical single-ended input configuration.
VOLTAGE REFERENCE
A stable and accurate 1.0 V voltage reference is built into the
AD9269. V
reference or an externally applied 1.0 V reference voltage. The
various reference modes are summarized in the sections that
follow. The Reference Decoupling section describes the best-
practices PCB layout of the reference.
Table 10. Reference Configuration Summary
Selected Mode
Fixed Internal Reference
Fixed External Reference
1V p-p
10µF
REF
49.9Ω
Figure 44. Single-Ended Input Configuration
can be configured using either the internal 1.0 V
0.1µF
10µF
0.1µF
AVDD
1kΩ
1kΩ
1kΩ
1kΩ
AVDD
R Series
(Ω Each)
33
125
R
R
SENSE Voltage (V)
AGND to 0.2
AVDD
C
C Differential (pF)
22
Open
VIN+x
VIN–x
ADC
Resulting V
1.0 internal
1.0 applied to external VREF pin
Rev. 0 | Page 21 of 40
REF
(V)
Internal Reference Connection
A comparator within the AD9269 detects the potential at the
SENSE pin and configures the reference into two possible modes,
which are summarized in Table 10. If SENSE is grounded, the
reference amplifier switch is connected to the internal resistor
divider (see Figure 45), setting V
If the internal reference of the AD9269 is used to drive multiple
converters to improve gain matching, the loading of the reference
by the other converters must be considered. Figure 46 shows
how the internal reference voltage is affected by loading.
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
0
0
1.0µF
0.2
Figure 45. Internal Reference Configuration
Figure 46. V
VIN+A/VIN+B
VIN–A/VIN–B
0.4
0.1µF
SENSE
Resulting Differential Span (V p-p)
2.0
2.0
VREF
0.6
REF
LOAD CURRENT (mA)
INTERNAL V
Accuracy vs. Load Current
0.8
REF
1.0
SELECT
LOGIC
to 1.0 V.
REF
1.2
= 0.993V
ADC
0.5V
1.4
CORE
ADC
1.6
1.8
AD9269
2
.0