AD9244 datasheet(22/36 Pages) AD

22 / 36 page

REV. A

–22–

AD9244

from single-ended signals to differential. Optimal AD9244 perfor-

mance is achieved above 500 kHz by using the input transformer. To

drive the AD9244 via the transformer, connect solderable Jumpers

JP45 and JP46. DC bias is provided by the Resistors R8 and R28.

The evaluation board has positions for through-hole and surface-

mount transformers. For applications requiring lower frequencies

or dc applications, the AD8138 can be used. The AD8138 will

provide good distortion and noise performance, as well as input

buffering, up to 30 MHz. For more information, refer to the

AD8138 data sheet. To use the AD8138 to drive the AD9244,

remove the transformer (T1 or T4) and connect solderable

Jumpers JP42 and JP43. The AD9244 can be driven single-ended

directly via S3 and can be ac-coupled or dc-coupled by removing

or inserting JP5. To run the evaluation board in this way, remove

the transformer (T1 or T4) and connect solderable Jumpers

JP40 and JP41. The Resistors R40, R41, R8, and R28 are used

to bias the AD9244 inputs to the correct common-mode levels

in this application.

Reference Configuration

As described in the Analog Input and Reference Overview section

earlier in this data sheet, the AD9244 can be configured to use its

own internal or an external reference. An external reference, D3,

and reference buffer, U5, are included on the AD9244 evaluation

board. Jumpers JP8 and JP22–JP24 can be used to select the

desired reference configuration (Table VI).

Clock Configuration

The AD9244 evaluation board was designed to achieve optimal

performance as well as to be easily configurable by the user. To

configure the clock input, begin by connecting the correct com-

bination of solderable Jumpers JP11–JP15 (Table VII). The

specific jumper configuration is dependent on the application and

can be determined by referring to the clock input modes section.

If the differential clock input mode is selected, an external sine

wave generator applied to S5 can be used as the clock source.

The clock buffer/drive MC10EL16 from ON Semiconductor is

used on the evaluation board to buffer and square the clock input.

If the single-ended clock configuration is used, an external clock

source can be applied to S1.

The AD9244 evaluation board generates a buffered clock at

TTL/CMOS levels for use with a data capture system, such as the

HSC-ADC-EVAL-SC system. The clock buffering is provided

by U4 and U7 and is configured by Jumpers JP3, JP4, JP9, and

JP18 (Table VII).

For the digital decoupling shown in Figure 18, 0.1

µF ceramic

chip and 10

µF tantalum capacitors are appropriate. The decou-

pling capacitors (especially 0.1

µF) should be located as close to

the pins as possible. Reasonable capacitive loads on the data

pins are less than 20 pF per bit. Applications involving greater

digital loads should consider increasing the digital decoupling

and/or using external buffers/latches.

A complete decoupling scheme will also include large tantalum

or electrolytic capacitors on the power supply connector to reduce

low frequency ripple to insignificant levels.

AD9244

DRVDD

DGND

10 F

0.1 F*

*LOCATE AS CLOSE AS POSSIBLE TO SUPPLY PINS

Figure 18. Digital Supply Decoupling

CML

The AD9244 has a midsupply reference point. This is used within

the internal architecture of the AD9244 and must be decoupled

with a 0.1

µF capacitor. It will source or sink a load of up to

300

µA. If more current is required, the CML pin should be

buffered with an amplifier.

VR is an internal bias point on the AD9244. It must be decoupled

to AGND with a 0.1

µF capacitor.

AD9244

CML

0.1 F

Figure 19. CML/VR Decoupling

EVALUATION BOARD

Analog Input Configuration

Table V provides a summary of the analog input configuration.

The analog inputs of the AD9244 on the evaluation board can be

driven differentially through a transformer via Connector S4, or

the AD8138 amplifier via Connector S2, or driven single-ended

directly via Connector S3. When using the transformer or AD8138

amplifier, a single-ended source may be used as both of these

devices are configured on the AD9244 evaluation board to convert

AD9244 Datasheet(PDF) 22 Page - Analog Devices

AD9244 Datasheet(HTML) 22 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Datasheet Download

Link URL