AD9246-105EB Analog Devices Inc, AD9246-105EB Datasheet - Page 16

• Manufacturer Part Number: AD9246-105EB
• Description: BOARD EVAL FOR 105MSPS AD9246
• Manufacturer: Analog Devices Inc

Specifications of AD9246-105EB

• Number Of Adc's: 1
• Number Of Bits: 14
• Sampling Rate (per Second): 105M
• Data Interface: Serial
• Inputs Per Adc: 1 Differential
• Input Range: 2 Vpp
• Power (typ) @ Conditions: 373mW @ 105MSPS
• Voltage Supply Source: Single
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9246-105
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD9246
DIFFERENTIAL INPUT CONFIGURATIONS
Optimum performance is achieved by driving the AD9246 in
a differential input configuration. For baseband applications,
the
and a flexible interface to the ADC. The output common-mode
voltage of the AD8138 is easily set with the CML pin of the
AD9246 (see Figure 37), and the driver can be configured in
a Sallen-Key filter topology to provide band limiting of the
input signal.
1V p-p
For baseband applications where SNR is a key parameter,
differential transformer coupling is the recommended input
configuration (see Figure 38). The CML voltage can be
connected to the center tap of the secondary winding of the
transformer to bias the analog input.
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 cause core
saturation, which leads to distortion.
2V p-p
AD8138
0.1µF
Figure 37. Differential Input Configuration Using the AD8138
Figure 38. Differential Transformer-Coupled Configuration
49.9Ω
49.9Ω
differential driver provides excellent performance
499Ω
523Ω
0.1µF
AD8138
499Ω
499Ω
R
R
R
R
C
C
1V p-p
VIN+
VIN–
10µF
VIN+
VIN–
AD9246
49.9Ω
AD9246
Figure 39. Single-Ended Input Configuration
CML
AVDD
CML
0.1µF
10µF
0.1µF
Rev. A | Page 16 of 44
AVDD
1kΩ
1kΩ
1kΩ
1kΩ
AVDD
R
R
C
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 AD9246. For applications where
SNR is a key parameter, transformer coupling is the recom-
mended input.
For applications where SFDR is a key parameter, differential
double balun coupling is the recommended input configuration
(see Figure 40).
As an alternative to using a transformer-coupled input at
frequencies in the second Nyquist zone, the
driver can be used (see Figure 41).
In any configuration, the value of the shunt capacitor, C, is
dependent on the input frequency and source impedance and
may need to be reduced or removed. Table 8 displays recom-
mended values to set the RC network. However, these values are
dependent on the input signal and should only be used as a
starting guide.
Table 8. RC Network Recommended Values
Frequency Range (MHz)
0 to 70
70 to 200
200 to 300
>300
Single-Ended Input Configuration
Although not recommended, it is possible to operate the
AD9246 in a single-ended input configuration, as long as the
input voltage swing is within the AVDD supply. Single-ended
operation 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 39 details a typical
single-ended input configuration.
VIN+
VIN–
AD9246
R Series (Ω) C Differential (pF)
33
33
15
15
15
5
5
Open
AD8352
differential