AD9216 Analog Devices, AD9216 Datasheet - Page 21

• Manufacturer Part Number: AD9216
• Description: 10-Bit, 65/80/105 MSPS Dual A/D Converter
• Manufacturer: Analog Devices

Specifications of AD9216

• Resolution (bits): 10bit
• # Chan: 2
• Sample Rate: 105MSPS
• Interface: Par
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p,(Vref) p-p,1 V p-p,2 V p-p
• Adc Architecture: Pipelined
• Pkg Type: CSP

For example, a 2 V p-p signal may be applied to VIN+, while a
1 V reference is applied to VIN−. The AD9216 then accepts an
input signal varying between 2 V and 0 V. In the single-ended
configuration, distortion performance may degrade signifi-
cantly as compared to the differential case. However, the effect
is less noticeable at lower input frequencies.
Differential Input Configurations
As previously detailed, optimum performance is achieved while
driving the AD9216 in a differential input configuration. For
baseband applications, the AD8138 differential driver provides
excellent performance and a flexible interface to the ADC. The
output common-mode voltage of the AD8138 is easily set to
AVDD/2, and the driver can be configured in a Sallen-Key filter
topology to provide band limiting of the input signal.
At input frequencies in the second Nyquist zone and above, the
performance of most amplifiers is not adequate to achieve the
true performance of the AD9216. This is especially true in IF
under-sampling applications where frequencies in the 70 MHz
to 200 MHz range are being sampled. For these applications,
differential transformer coupling is the recommended input
configuration, as shown in Figure 43.
The signal characteristics must be considered when selecting a
transformer. Most RF transformers saturate at frequencies
below a few MHz, and excessive signal power can also cause
core saturation, which leads to distortion.
2V p-p
85
80
75
70
65
60
55
50
45
40
0.25
Figure 42. Input Common-Mode Voltage Sensitivity
Figure 43. Differential Transformer Coupling
ANALOG INPUT COMMON-MODE VOLTAGE (V)
49.9Ω
0.75
0.1µF
1.25
2V p-p SFDR
2V p-p SNR
1kΩ
1kΩ
50Ω
10pF
50Ω
10pF
1.75
VIN_A
VIN_B
2.25
AD9216
AVDD
AGND
2.75
Rev. A | Page 21 of 40
For dc-coupled applications, the AD8138, AD8139, or
AD8351 can serve as a convenient ADC driver, depending on
requirements. Figure 44 shows an example with the AD8138.
The AD9216 PCB has an optional AD8139 on board, as shown
in Figure 53. Note the AD8351 typically yields better perform-
ance for frequencies greater than 30 MHz to 40 MHz.
Single-Ended Input Configuration
A single-ended input may provide adequate performance in
cost-sensitive applications. In this configuration, there is a
degradation in SFDR and distortion performance due to the
large input common-mode swing. However, if the source
impedances on each input are matched, there should be little
effect on SNR performance.
SCALE/2
FULL
0.1µF
Figure 45. Analog Input Full Scale (Full Scale = 2 V)
DIGITAL OUT = ALL ONES
VIN+
SENSE = GROUND
AVDD/2
VIN–
Figure 44. Driving the ADC with the AD8138
1kΩ
1kΩ
49.9Ω
499Ω
523Ω
499Ω
499Ω
AD8138
33Ω
33Ω
DIGITAL OUT = ALL ZEROES
20pF
VIN+
VIN–
AD9216
AGND
AVDD
AVDD/2
AD9216