AD9226 Analog Devices, AD9226 Datasheet - Page 15

• Manufacturer Part Number: AD9226
• Description: 12-Bit, 65 MSPS Analog-to-Digital Converter
• Manufacturer: Analog Devices

Specifications of AD9226

• Resolution (bits): 12bit
• # Chan: 1
• Sample Rate: 65MSPS
• Interface: Par
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (Vref) p-p,1 V p-p,2 V p-p,Uni (Vref),Uni 1.0V,Uni 2.0V
• Adc Architecture: Pipelined
• Pkg Type: QFP,SOP

2.5V
1.25V
0.75V
1.5V
1.25V
0.75V
2.5V
1.5V
1.5V
0.5V
3.0V
1.0V
10 F
10 F
49.9
49.9
33
10 F
33
10 F
33
33
33
33
0.1 F
0.1 F
15pF
1V
15pF
33
2V
15pF
15pF
0.1 F
0.1 F
33
1V
2V
VINA
VINB
REFCOM
REFCOM
VREF
SENSE
VINA
VINB
VREF
SENSE
AD9226
VINA
VINB
VREF
SENSE
AD9226
VINA
VINB
VREF
SENSE
AD9226
AD9226
CAPB
CAPB
CAPT
CAPT
CAPB
CAPT
CAPB
CAPT
0.1 F
0.1 F
0.1 F
0.1 F
0.1 F
0.1 F
0.1 F
0.1 F
10 F
0.1 F
10 F
0.1 F
10 F
0.1 F
10 F
0.1 F
The differential input characterization for this data sheet was
performed using the configuration shown in Figure 7.
Since not all applications have a signal preconditioned for
differential operation, there is often a need to perform a single-
ended-to-differential conversion. In systems that do not need to
be dc-coupled, an RF transformer with a center tap is the best
method to generate differential inputs for the AD9226. It pro-
vides all the benefits of operating the ADC in the differential
mode without contributing additional noise or distortion. An RF
transformer also has the added benefit of providing electrical
isolation between the signal source and the ADC. An improvement
in THD and SFDR performance can be realized by operating
the AD9226 in the differential mode. The performance enhance-
ment between the differential and single-ended mode is most
noteworthy as the input frequency approaches and goes beyond
the Nyquist frequency (i.e., f
The circuit shown in Figure 6a is an ideal method of applying
a differential dc drive to the AD9226. It uses an AD8138 to
derive a differential signal from a single-ended one. Figure 6b
illustrates its performance.
Figure 7 presents the schematic of the suggested transformer
circuit. The circuit uses a Minicircuits RF transformer, model
T1-1T, which has an impedance ratio of four (turns ratio of 2).
The schematic assumes that the signal source has a 50 Ω source
impedance. The center tap of the transformer provides a con-
venient means of level-shifting the input signal to a desired
common-mode voltage. In Figure 7 the transformer centertap
is connected to a resistor divider at the midsupply voltage.
2.75V
2.25V
3.0V
2.5V
2.0V
2.5V
2.75V
3.0V
2.5V
2.0V
2.5V
2.0V
49.9
49.9
33
33
10 F
33
33
10 F
10k
2.5V
0.1 F
10k
0.1 F
15pF
0.1 F
15pF
0.1 F
2V
1V
2.5V
IN
AVDD
> F
CMLEVEL
VINA
VINB
VREF
SENSE
VINA
VINB
VREF
SENSE
S
AD9226
/2).
(LQFP)
AD9226
CAPB
CAPT
CAPB
CAPT
AD9226
0.1 F
0.1 F
0.1 F
0.1 F
10 F
0.1 F
10 F
0.1 F