PRODUCT SPECIFICATION

FMS3110/3115

REV. 1.05 12/21/00

9

Applications Discussion

Figure 5 illustrates a typical FMS3110/3115 interface cir-

cuit. In this example, an optional 1.2 Volt bandgap reference

is

age reference source.

Grounding

It is important that the FMS3110/3115 power supply is well-

regulated and free of high-frequency noise. Careful power

supply decoupling will ensure the highest quality video sig-

nals at the output of the circuit. The FMS3110/3115 has sep-

arate analog and digital circuits. To keep digital system noise

from the D/A converter, it is recommended that power supply

and all ground connections (GND) be made to the analog

ground plane. Power supply pins should be individually

decoupled at the pin.

Printed Circuit Board Layout

Designing with high-performance mixed-signal circuits

demands printed circuits with ground planes. Overall system

performance is strongly influenced by the board layout.

Capacitive coupling from digital to analog circuits may

result in poor D/A conversion. Consider the following sug-

gestions when doing the layout:

1.

ble from all digital signals. The FMS3110/3115 should

be located near the board edge, close to the analog out-

put connectors.

2.

Power plane for the FMS3110/3115 should be separate

from that which supplies the digital circuitry. A single

the power supply for the FMS3110/3115 is the same as

that of the system's

digital circuitry, power to the FMS3110/3115 should be

decoupled with 0.1µF and 0.01µF capacitors and iso-

lated with a ferrite bead.

3.

The ground plane should be solid, not cross-hatched.

Connections to the ground plane should have very short

leads.

4.

If the digital power supply has a dedicated power plane

layer, it should not be placed under the FMS3110/3115,

the voltage reference, or the analog outputs. Capacitive

coupling of digital power supply noise from this layer to

the FMS3110/3115 and its related analog circuitry can

have an adverse effect on performance.

5.

CLK should be handled carefully. Jitter and noise on

this clock will degrade performance. Terminate the

clock line carefully to eliminate overshoot and ringing.

Related Products

• FMS38XX Triple 8-bit 150 Msps D/A Converters

• FMS9884A 3 x 8-bit 140 Ms/s A/D Converter

Figure 5. Typical Interface Circuit

+5V

0.1

µF

10

µF

VDD

GND

FMS31XX

Triple 10-bit

D/A Converter

CLK

SYNC

BLANK

RED PIXEL

INPUT

GREEN PIXEL

INPUT

BLUE PIXEL

INPUT

CLOCK

SYNC

BLANK

COMP

+5V

0.1

µF

0.1

µF

560

Ω

3.3k

Ω (not required without

external reference)

LM185-1.2

(Optional)

75

Ω

75

Ω

75

Ω

75

Ω

75

Ω

75

Ω

Z

Red

Green w/Sync

Blue

Z

Z