AD9280 Analog Devices, AD9280 Datasheet - Page 11

• Manufacturer Part Number: AD9280
• Description: 8-Bit, Complete, 32 MSPS A/D Converter
• Manufacturer: Analog Devices

Specifications of AD9280

• Resolution (bits): 8bit
• # Chan: 1
• Sample Rate: 32MSPS
• Interface: Par
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: 1 V p-p,2 V p-p
• Adc Architecture: Pipelined
• Pkg Type: SOP

The actual reference voltages used by the internal circuitry of
the AD9280 appear on REFTF and REFBF. For proper opera-
tion, it is necessary to add a capacitor network to decouple these
pins. The REFTF and REFBF should be decoupled for all
internal and external configurations as shown in Figure 17.
Note: REFTF = reference top, force
INTERNAL REFERENCE OPERATION
Figures 18, 19 and 20 show sample connections of the AD9280
internal reference in its most common configurations. (Figures
18 and 19 illustrate top/bottom mode while Figure 20 illustrates
center span mode). Figure 29 shows how to connect the AD9280
for 1 V p-p differential operation. Shorting the VREF pin
directly to the REFSENSE pin places the internal reference
amplifier, A1, in unity-gain mode and the resultant reference
output is 1 V. In Figure 18 REFBS is grounded to give an input
range from 0 V to 1 V. These modes can be chosen when the
supply is either +3 V or +5 V. The VREF pin must be bypassed to
AVSS (analog ground) with a 1.0 F tantalum capacitor in
parallel with a low inductance, low ESR, 0.1 F ceramic capacitor.
1.0 F
REV. E
Figure 18. Internal Reference—1 V p-p Input Span
(Top/Bottom Mode)
REFBF = reference bottom, force
REFTS = reference top, sense
REFBS = reference bottom, sense
0.1 F
1V
0V
Figure 17. Reference Decoupling Network
0.1 F
SENSE
REFBS
REFTS
VREF
AIN
REF
0.1 F
10 F
10k
10k
0.1 F
A1
10k
10k
A2
1V
SHA
CORE
REFTF
REFBF
A/D
AD9280
AD9280
4.2k
TOTAL
REFTF
REFBF
MODE
0.1 F
AVDD
10 F
0.1 F
0.1 F
–11–
Figure 19 shows the single-ended configuration for 2 V p-p
operation. REFSENSE is connected to GND, resulting in a 2 V
reference output.
Figure 20 shows the single-ended configuration that gives the
good high frequency dynamic performance (SINAD, SFDR).
To optimize dynamic performance, center the common-mode
voltage of the analog input at approximately 1.5 V. Connect the
shorted REFTS and REFBS inputs to a low impedance 1.5 V
source. In this configuration, the MODE pin is driven to a volt-
age at midsupply (AVDD/2).
Maximum reference drive is 1 mA. An external buffer is re-
quired for heavier loads.
1.0 F
1.0 F
Figure 19. Internal Reference, 2 V p-p Input Span
(Top/Bottom Mode)
(Center Span Mode)
Figure 20. Internal Reference 1 V p-p Input Span
0.1 F
0.1 F
2V
1V
+1.5V
2V
0V
REFBS
REFTS
SENSE
REFBS
SENSE
REFTS
VREF
VREF
REF
AIN
AIN
REF
10k
10k
10k
10k
A1
A1
10k
10k
10k
10k
A2
A2
1V
1V
SHA
SHA
CORE
CORE
A/D
A/D
AD9280
AD9280
4.2k
TOTAL
4.2k
TOTAL
AD9280
0.1 F
REFTF
0.1 F
REFBF
REFTF
REFBF
MODE
MODE
AVDD
AVDD/2
10 F
0.1 F
10 F
0.1 F
0.1 F
0.1 F