AD9639 Analog Devices, Inc., AD9639 Datasheet - Page 18

• Manufacturer Part Number: AD9639
• Description: Quad, 12-bit, 170 Msps/210 Msps Serial Output 1.8 V Adc
• Manufacturer: Analog Devices, Inc.

AD9639
For applications where SNR is a key parameter, differential
transformer coupling is the recommended input configuration
to achieve the true performance of the AD9639 (see Figure 38
to Figure 40).
Regardless of the configuration, the value of the shunt capacitor, C,
is dependent on the input frequency and may need to be reduced
or removed.
1.25V p-p
1.25V p-p
*C
DIFF IS OPTIONAL
1.25V p-p
Figure 38. Differential Transformer-Coupled Configuration
Figure 39. Differential Transformer-Coupled Configuration
Figure 40. Differential Transformer-Coupled Configuration
65Ω
L
50Ω
0.1μF
0.1μF
0.1µF
for Narrow-Band IF Applications
for Wideband IF Applications
1:1 Z RATIO
1:1 Z RATIO
ADT1-1WT
1:1 Z RATIO
ADT1-1WT
for Baseband Applications
ADT1-1WT
0.1μF
0.1μF
0.1μF
250Ω
250Ω
33Ω
33Ω
*C
L
L
33Ω
33Ω
DIFF
C
C
2.2pF
33Ω
33Ω
L
VIN + x
VIN – x
VIN + x
VIN – x
AD9639
AD9639
ADC
ADC
VIN + x
VIN – x
AD9639
ADC
AGND
Rev. 0 | Page 18 of 36
1.25V p-p
Single-Ended Input Configuration
A single-ended input may provide adequate performance in
cost-sensitive applications. In this configuration, SFDR and
distortion performance can degrade due to input common-mode
swing mismatch. If the application requires a single-ended input
configuration, ensure that the source impedances on each input
are well matched to achieve the best possible performance. A
full-scale input of 1.25 V p-p can be applied to the VIN + x pin
of the AD9639 while the VIN − x pin is terminated. Figure 42
shows a typical single-ended input configuration.
1.25V p-p
0.1µF
Figure 41. Differential Balun-Coupled Configuration
BALUN
1:1 Z
0.1µF
49.9Ω
Figure 42. Single-Ended Input Configuration
for Wideband IF Applications
BALUN
1:1 Z
0.1µF
25Ω
0.1µF
0.1µF
66Ω
33Ω
33Ω
*C
*C
DIFF
DIFF IS OPTIONAL
33Ω
4.7pF
33Ω
C
C
VIN + x
VIN – x
VIN + x
VIN – x
AD9639
ADC
AD9639
ADC