SPT5140

TYPICAL RGB GRAPHICS SYSTEM

In an RGB graphics system, the color displayed is deter-

mined by the combined intensities of the red, green and

blue (RGB) D/A converter outputs. A change in gain or

offset in any of the RGB outputs will affect the apparent

hue displayed on the CRT screen.

Thus, it is very important that the outputs of the D/A con-

verters track each other over a wide range of operating

conditions. Since the D/A output is proportional to the

product of the reference and digital input code, a com-

mon reference should be used to drive all three D/As in

an RGB system to minimize RGB DAC-to-DAC mismatch

and improve TC tracking.

The SPT5140 contains an internal precision bandgap

reference which completely eliminates the need for an

external reference. The reference can supply up to 50

µA

to an external load, such as two other DAC reference

inputs.

The circuits shown in figure 8 illustrate how a single

SPT5140 may be used as a master reference in a system

with multiple DACs (such as RGB). The other DACs are

simply slaved from the SPT5140’s reference output.

750

Ω

500

Ω

750

Ω

500

Ω

SPT5140

(Master)

R

SPT5140

(Slave)

G

1k

Ω

Ref In

SPT5140

(Slave)

B

1 k

Ω

Ref In

Ref Out

750

Ω

500

Ω

Ref In

Figure 8 – Typical RGB Graphics System

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