AD9627-125EBZ Analog Devices Inc, AD9627-125EBZ Datasheet - Page 27

• Manufacturer Part Number: AD9627-125EBZ
• Description: 12Bit 125 Msps Dual 1.8V PB Free ADC
• Manufacturer: Analog Devices Inc

Specifications of AD9627-125EBZ

• Number Of Adc's: 2
• Number Of Bits: 12
• Sampling Rate (per Second): 125M
• Data Interface: Serial
• Inputs Per Adc: 1 Differential
• Input Range: 2 Vpp
• Power (typ) @ Conditions: 900mW @ 125MSPS
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9627
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The output common-mode voltage of the AD8138 is easily set
with the CML pin of the AD9627 (see Figure 46), 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. An example is shown in Figure 47. To bias the
analog input, the CML voltage can be connected to the center
tap of the secondary winding of the transformer.
The signal characteristics must be considered when selecting
a transformer. Most RF transformers saturate at frequencies
below a few megahertz (MHz). 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 AD9627. For applications where
SNR is a key parameter, differential double balun coupling is the
recommended input configuration (see Figure 49).
2V p-p
0.1µF
Figure 46. Differential Input Configuration Using the AD8138
Figure 47. Differential Transformer-Coupled Configuration
49.9Ω
49.9Ω
499Ω
523Ω
0.1µF
AD8138
499Ω
499Ω
ANALOG INPUT
ANALOG INPUT
2V p-p
R
R
R
R
C
C
0.1µF
C
P
D
A
0.1µF
0.1µF
R
Figure 50. Differential Input Configuration Using the AD8352
D
Figure 49. Differential Double Balun Input Configuration
0Ω
0Ω
S
VIN+
VIN–
AD9627
VIN+
VIN–
AD9627
R
S
G
16
1
2
3
4
5
CML
AVDD
CML
AD8352
P
V
Rev. B | Page 27 of 76
0.1µF
0.1µF
CC
14
0.1µF
8, 13
10
11
25Ω
25Ω
0.1µF
0.1µF
An alternative to using a transformer-coupled input at frequencies
in the second Nyquist zone is to use the AD8352 differential driver.
An example is shown in Figure 50. See the
for more information.
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 13 displays recommended 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 13. Example RC Network
Frequency Range (MHz)
0 to 70
70 to 200
200 to 300
>300
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 48 shows a typical
single-ended input configuration.
0.1µF
1V p-p
200Ω
200Ω
0.1µF
R
R
C
10µF
0.1µF
49.9Ω
R
R
C
Figure 48. Single-Ended Input Configuration
VIN+
VIN–
0.1µF
10µF
0.1µF
AD9627
AVDD
VIN+
VIN–
AD9627
1kΩ
1kΩ
1kΩ
1kΩ
AVDD
CML
R Series
(Ω Each)
33
33
15
15
CML
R
R
C
AD8352
C Differential (pF)
15
5
5
Open
VIN+
VIN–
AD9627
data sheet
AD9627