AD9683-170EBZ Analog Devices, AD9683-170EBZ Datasheet - Page 20

• Manufacturer Part Number: AD9683-170EBZ
• Description: Data Conversion IC Development Tools
• Manufacturer: Analog Devices
• Type: ADCr
• Series: AD9683r

Specifications of AD9683-170EBZ

• Rohs: yes
• Product: Evaluation Boards
• Tool Is For Evaluation Of: AD9683-170
• Interface Type: SPI
• Operating Supply Voltage: 1.8 V
• Description/function: Evaluation board with AD9683-170
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Operating Supply Current: 135 mA
• For Use With: AD9683-170

AD9683
The output common-mode voltage of the
set with the VCM pin of the
driver can be configured in a Sallen-Key filter topology to
provide band limiting of the input signal.
For baseband applications where SNR is a key parameter,
differential transformer coupling is the recommended input
configuration. An example is shown in Figure 45. To bias the
analog input, the VCM voltage can be connected to the center
tap of the secondary winding of the transformer.
Consider the signal characteristics when selecting a transformer.
Most RF transformers saturate at frequencies below a few
megahertz. Excessive signal power can also cause core saturation,
which leads to distortion.
At input frequencies in the second Nyquist zone and above, the
noise performance of most amplifiers is not adequate to achieve
the true SNR performance of the AD9683. For applications where
SNR is a key parameter, differential double balun coupling is
the recommended input configuration (see Figure 46). In this
configuration, the input is ac-coupled and the VCM voltage is
provided to each input through a 33 Ω resistor. These resistors
compensate for losses in the input baluns to provide a 50 Ω
impedance to the driver.
2V p-p
VIN
2V p-p
0.1µF
Figure 44. Differential Input Configuration Using the
0.1µF
76.8Ω
Figure 45. Differential Transformer-Coupled Configuration
P
Figure 46. Differential Double Balun Input Configuration
A
49.9Ω
S
120Ω
90Ω
S
0.1µF
ADA4930-1
P
200Ω
200Ω
0.1µF
0.1µF
AD9683
33Ω
33Ω
R1
R1
33Ω
33Ω
33Ω
C1
C2
C2
R3
15pF
5pF
0.1µF
R3
(see Figure 44), and the
15pF
R2
R2
R1
R1
15Ω
15Ω
C2
C2
C1
R3
ADA4930-1
R3
33Ω
R2
R2
VIN+
VIN–
VIN–
VIN+
33Ω
VIN+
VIN–
ADA4930-1
ADC
ADC
ADC
VCM
AVDD
VCM
is easily
VCM
0.1µF
0.1µF
0.1µF
Rev. 0 | Page 20 of 44
In the double balun and transformer configurations, the value
of the input capacitors and resistors is dependent on the input
frequency and source impedance. Based on these parameters,
the value of the input resistors and capacitors may need to be
adjusted or some components may need to be removed. Table 9
displays recommended values to set the RC network for different
input frequency ranges. However, these values are dependent on
the input signal and bandwidth. Use these values only as a starting
guide. Note that the values given in Table 9 are for the R1, R2, C1,
C2, and R3 components shown in Figure 45 and Figure 46.
Table 9. Example RC Network
Frequency
Range
(MHz)
0 to 100
100 to 400
>400
An alternative to using a transformer-coupled input at frequencies
in the second Nyquist zone is to use an amplifier with variable
gain. The
provides good performance for driving the AD9683. Figure 47
shows an example of the
a band-pass antialiasing filter.
VOLTAGE REFERENCE
A stable and accurate voltage reference is built into the AD9683.
The full-scale input range can be adjusted by varying the reference
voltage via the SPI. The input span of the ADC tracks the reference
voltage changes linearly.
NOTES
1. ALL INDUCTORS ARE COILCRAFT
2. FILTER VALUES SHOWN ARE FOR A 20MHz BANDWIDTH FILTER
EXCEPTION OF THE 1µH CHOKE INDUCTORS (COILCRAFT 0603LS).
CENTERED AT 140MHz.
AD8375
Figure 47. Differential Input Configuration Using the
1µH
1µH
AD8375
R1
Series
(Ω)
33
15
15
1000pF
1000pF
VPOS
1nF
digital variable gain amplifier (DVGA)
180nH
180nH
301Ω
5.1pF
C1
Differential
(pF)
8.2
8.2
≤3.9
AD8375
220nH
220nH
3.9pF
®
0603CS COMPONENTS WITH THE
165Ω
165Ω
driving the
R2
Series
(Ω)
0
0
0
15pF
VCM
1nF
68nH
AD9683
Data Sheet
C2
Shunt
(pF)
15
8.2
≤3.9
20kΩ║2.5pF
AD8375
ADC
through
R3
Shunt
(Ω)
24.9
24.9
24.9