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SPT5220

10-BIT, 80 MWPS VIDEO DAC

Signal Processing Technologies 

PC BOARD CONSIDERATIONS

DIGITAL SIGNAL INTERCONNECT

LAYOUT CONSIDERATIONS

To minimize noise on the power lines and ground lines, shield

and decouple the digital inputs. Keep the trace length be-

tween groups of VDD (AVDD, DVDD) and VSS (AVSS, DVSS)

as short as possible to minimize inductive ringing.

SUPPLY AND GROUND CONSIDERATIONS

Use a 0.1 µF ceramic capacitor in parallel with a 10 µF

tantalum capacitor for decoupling between the power line

and the ground line. The digital power plane (DVDD) and the

analog power plane (AVDD) are connected through a ferrite

bead. The digital ground plane (DVSS) and the analog

ground plane (AVSS) are also connected through a ferrite

bead. (See figures 3 and 4). Locate these ferrite beads within

three inches of the SPT5220.

The PCB line between the TTL driver (that drives the SPT5220)

and the input to the SPT5220 will have a low impedance

source and be terminated with a high impedance. It behaves

like a low impedance transmission line so signal transitions

will be reflected from the high impedance input of the SPT5220.

To reduce ringing caused by transmission line mismatch,

shorten the line length or terminate the line. Both serial and

parallel termination methods will work, but serial is preferred.

Serial termination is achieved by installing a resistor of

approximately 50 Ω between the TTL driver output and the

SPT5220 digital input.

ANALOG SIGNAL INTERCONNECT

To minimize noise pickup and reflections due to impedance

mismatch, locate the SPT5220 as closely as possible to the

output connector. The line between the DAC output and the

monitor input should be regarded as a transmission line since

it can cause problems in transmission line mismatch. Use the

double-termination method to avoid these problems. By

using the double terminated method, the transmission lines

are matched, providing an ideal, nonreflective system.

28

1

A

B

C

SPT

28-LEAD PLASTIC DIP (PDIP) PACKAGE OUTLINE

J

D

INCHES

MILLIMETERS

K

SYMBOL MIN

MAX

MIN

MAX

A

0.198 typ

5.08 typ

B

0.117

0.140

3.00

3.60

C

0.014

0.022

0.36

0.56

D

0.099 typ

2.54 typ

E

0.055

0.063

1.42

1.62

F

0.008

0.014

0.20

0.35

I

G

0.142

0.158

3.65

4.05

H

0.000

0.594

15.24

I

0.523

0.538

13.40

13.80

J

1.439

1.455

36.90

37.30

K

0 .080 typ

2.04 typ

L

0°

15°

H

F

G

L

E

SPT5220

7

12/30/98

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