AD7266 Analog Devices, AD7266 Datasheet - Page 14

• Manufacturer Part Number: AD7266
• Description: Differential/Single-Ended Input, Dual, Simultaneous Sampling, 2 MSPS, 12-Bit, 3-Channel SAR A/D Converter
• Manufacturer: Analog Devices

Specifications of AD7266

• Resolution (bits): 12bit
• # Chan: 12
• Sample Rate: 2MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (2Vref) p-p,(Vref) p-p,2.5V p-p,5V p-p,Uni (Vref),Uni (Vref) x 2,Uni 2.5V,Uni 5.0V
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

AD7266
When no amplifier is used to drive the analog input, the source
impedance should be limited to low values. The maximum source
impedance depends on the amount of THD that can be toler-
ated. The THD increases as the source impedance increases and
performance degrades. Figure 19 shows a graph of the THD vs.
the analog input signal frequency for different source impedances
in single-ended mode, while Figure 20 shows the THD vs. the
analog input signal frequency for different source impedances
in differential mode.
Conversion Phase—Switches Open, Track Phase—Switches Closed
–50
–55
–60
–65
–70
–75
–80
–85
–90
–60
–65
–70
–75
–80
–85
–90
0
0
F
V
RANGE = 0V TO V
F
V
RANGE = 0V TO V
SAMPLE
DD
Figure 19. THD vs. Analog Input Frequency for Various
SAMPLE
DD
100
= 3V
= 3V
Various Source Impedances, Differential Mode
Figure 20. THD vs. Analog Input Frequency for
100
Figure 18. Equivalent Analog Input Circuit,
V
V
R
R
Source Impedances, Single-Ended Mode
= 1.5MSPS
IN+
IN–
SOURCE
SOURCE
= 1.5MSPS
R
200
SOURCE
C1
C1
300
200
= 0Ω
= 10Ω
REF
R
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
REF
SOURCE
= 10Ω
R
SOURCE
V
V
400
DD
DD
D
D
D
D
300
= 47Ω
500
= 100Ω
R
SOURCE
R
SOURCE
600
R
400
R
SOURCE
R
SOURCE
SOURCE
R1 C2
R1 C2
= 300Ω
700
= 47Ω
= 300Ω
500
= 100Ω
= 0Ω
800
900
600
1000
Rev. B | Page 14 of 28
Figure 21 shows a graph of the THD vs. the analog input
frequency for various supplies while sampling at 2 MSPS. In this
case, the source impedance is 47 Ω.
ANALOG INPUTS
The AD7266 has a total of 12 analog inputs. Each on-board
ADC has six analog inputs that can be configured as six single-
ended channels, three pseudo differential channels, or three
fully differential channels. These may be selected as described
in the Analog Input Selection section.
Single-Ended Mode
The AD7266 can have a total of 12 single-ended analog input
channels. In applications where the signal source has high
impedance, it is recommended to buffer the analog input
before applying it to the ADC. The analog input range can be
programmed to be either 0 to V
If the analog input signal to be sampled is bipolar, the internal
reference of the ADC can be used to externally bias up this
signal to make it correctly formatted for the ADC. Figure 22
shows a typical connection diagram when operating the ADC
in single-ended mode.
+1.25V
–1.25V
Figure 21. THD vs. Analog Input Frequency for Various Supply Voltages
0V
–50
–55
–60
–65
–70
–75
–80
–85
–90
0
F
V
RANGE = 0 TO V
SAMPLE
Figure 22. Single-Ended Mode Connection Diagram
DD
100
= 3V/5V
V
SINGLE-ENDED MODE
= 1.5MSPS/2MSPS
DD
200
V
IN
= 5V
300
1
REF
ADDITIONAL PINS OMITTED FOR CLARITY.
INPUT FREQUENCY (kHz)
3R
R
V
DIFFERENTIAL MODE
R
DD
400
= 3V
500
REF
R
or 0 to 2 × V
+2.5V
600
V
DIFFERENTIAL MODE
0V
V
SINGLE-ENDED MODE
DD
DD
700
= 5V
= 3V
V
V
A1
B6
800
REF
D
CAP
AD7266
.
900
A/D
CAP
0.47µF
1000
1
B