AD768 查看數據表（PDF） - Analog Devices

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AD768

16-Bit, 30 MSPS D/A Converter

Analog Devices 

AD768

Clock Input

An external sample clock must be provided to either the BNC

connector labeled “CLOCK” or on Pin 33 of the IDC connec-

tor. This clock must comply with the logic levels outlined in the

AD768 data sheet. The “CLOCK” input is terminated with a

removable 51 Ω resistor. The IDC connector clock connection

is unterminated.

SW1. Clock source select switch. When SW1 is in position 1, Pin

33 of the IDC connected is applied to the CLOCK input of the

AD768. When SW2 is in position 2, the “CLOCK” BNC connec-

tor is applied to the CLOCK input of the AD768.

Digital Inputs

The digital inputs of the AD768, DB0–DB15, are available via

J1, a 40-pin IDC connector. These inputs should comply with

the specifications given in the AD768 data sheet.

Layout Considerations

Figures 28 and 29 show the AD768-EB ground and power

plane layouts. Figures 35–38 show the schematic diagram, trace

routing, silk screening, and component layout for the AD768 4

layer evaluation board.

Separate ground and power planes have several advantages for

high speed layouts. (For further information outlining these

advantages, see the application note “Design and Layout of a

Video Graphics System for Reduced EMI” [E1309] available

from Analog Devices [(617) 461-3392].) A solid ground plane

can be used if the digital return current can be routed such that

it does not modulate the analog ground plane. If this is not pos-

sible, it may be necessary to split the ground plane in order to

force currents to flow in a controlled direction. This type of

grounding scheme is shown in the Figure 28. The ground plane

is separated into analog and digital planes that are joined

together under the AD768. In any case, the AD768 should be

treated as an analog component and a common ground connec-

tion should be made underneath the AD768 despite some pins

being labeled “digital” ground and some as “analog” ground.

A complete parts list for the AD768 evaluation board is given in

Table IV.

Table III. Summary of Jumper Functionality

Installed

Jumper Function

Jumper

JP1

JP2

JP3 (STBY)

JP4

JP5

Buffered Output A

50 Ω Transformer Output

Unbuffered Output A

Unbuffered Output B

Buffered Output B

Table IV. AD768-EB Parts List

Reference Value / Part Type Package

Qty/Bd

U1

AD768

28-Pin SOIC

1

U2

AD811

8-Pin DIP

1

T1

Mini-Circuits

Not Installed

1

T4–6T

A, B, CLOCK BNC JACKs,

Small, Vertical

3

Small

JP1–5

Header

2-Pin

5

SW1, 2

SPDT, Secme 0.1" × 0.3"

2

J1

40-Pin IDC

R.A., Male,

1

Connector

w/ Latches

R1

500 Ω

1/4 W, 0.01%,

1

Vishay

R2

25 Ω

1/4 W, 0.01%,

1

Vishay

R3, R13–21, &

R23–29

Wire Jumpers

17

R5

500 Ω

1/4 W, 0.01%,

1

Vishay

R7

100 Ω

1/4 W, 0.01%,

1

Vishay

R11

51 Ω

1/8 W, 5%, Carbon 1

R12

10 kΩ Pot.

3266 W

1

C1–4

1 µF Ceram. Cap. Leaded

4

C5–8, C10, 12,

14, & C16–19

0.1 µF Chip Cap,

1206

11

C9, 11, 13, 15 22 µF Tant. Cap., Teardrop,

4

25 V

0.1" Spacing

–16–

REV. B

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