AD9280ARSZ Просмотр технического описания (PDF) - Analog Devices

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AD9280ARSZ

Complete 8-Bit, 32 MSPS, 95 mW CMOS A/D Converter

Analog Devices 

AD9280

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.

10␮F 0.1␮F

0.1␮F 0.1␮F

REFTF

AD9280

REFBF

Figure 17. Reference Decoupling Network

Note: REFTF = reference top, force

REFBF = reference bottom, force

REFTS = reference top, sense

REFBS = reference bottom, sense

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 µF tantalum capacitor in

parallel with a low inductance, low ESR, 0.1 µF ceramic capacitor.

1V

AIN

0V

REFTS

REFBS

1.0␮F 0.1␮F

VREF

REF

SENSE

SHA

AD9280

MODE

AVDD

10k⍀

10k⍀

A2

10k⍀

REFTF 0.1␮F

A/D

CORE

4.2k⍀ 0.1␮F

TOTAL

10␮F

10k⍀

A1

1V

REFBF

0.1␮F

Figure 18. Internal Reference—1 V p-p Input Span

(Top/Bottom Mode)

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.

2V

0V

1.0␮F 0.1␮F

AIN

REFTS

REFBS

VREF

REF

SENSE

AD9280 MODE

SHA

AVDD

10k⍀

REFTF 0.1␮F

10k⍀

A2

10k⍀

A/D

CORE

4.2k⍀ 0.1␮F

TOTAL

10␮F

10k⍀

A1

1V

0.1␮F

REFBF

Figure 19. Internal Reference, 2 V p-p Input Span

(Top/Bottom Mode)

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.

2V

AIN

1V

+1.5V

REFTS

REFBS

1.0␮F 0.1␮F

VREF

REF

SENSE

AD9280 MODE

SHA

AVDD/2

10k⍀

10k⍀

A2

A/D

CORE

REFTF 0.1␮F

4.2k⍀ 0.1␮F

TOTAL

10␮F

10k⍀ 10k⍀

A1

1V

REFBF

0.1␮F

Figure 20. Internal Reference 1 V p-p Input Span

(Center Span Mode)

REV. E

–11–

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