SPT1019AIN 查看數據表（PDF） - Signal Processing Technologies

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SPT1019AIN

8-BIT, HIGH SPEED D/A CONVERTER

Signal Processing Technologies 

nated 50 or 75 ohm load to standard video levels. In the

standard configuration of figure 5, the output voltage is the

product of the output current and load impedance and is

between 0 and -1.07 V. The Out- output (figure 9) will provide

a video output waveform with the Sync pulse bottom at the

-1.07 V level. The Out+ is inverted with Sync up.

Figure 4 - CONVert, CONVert Switching Levels

VIDF

0.0 V

VICM MIN

VICM MAX

Figure 5A - Standard Load

-1.3 V

CONV

CONV

OUT-

RS

75 Ω

SPT1019

Video Monitor

75 Ω COAX

RL

75 Ω

OUT +

RS

75 Ω

75 Ω COAX

Inverse

Video

RL

75 Ω

TYPICAL RGB GRAPHICS SYSTEM

In an RGB graphics system, the color displayed is determined

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 convert-

ers track each other over a wide range of operating condi-

tions. Since the D/A output is proportional to the product of the

reference and digital input code, a common 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 SPT1019 contains an internal precision bandgap refer-

ence 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 6 illustrate how a single SPT1019

may be used as a master reference in a system with multiple

DACs (such as RGB). The other DACs are simply slaved from

the SPT1019’s reference output. The SPT1018s shown are

especially well-suited to be slaved to a SPT1019 for a better

TC tracking from DAC-to-DAC, since they are essentially

SPT1019s without the reference. The SPT1018 is pin-com-

patible with the TDC1018, that does not have an internal

reference. Although either the TDC1018 or the SPT1018 may

be slaved from an SPT1019, the higher performance

SPT1018 and the above mentioned DAC-to-DAC TC track-

ing is the best choice for new designs.

Figure 5B - Test Load

OUT +

OUT -

CL

<5 pF

RL

37.5Ω

Video Out

0 to -1 Volt

No external reference is required for operation of the

SPT1019, as this function is provided internally. The internal

reference is a bandgap type and is suitable for operation over

extended temperature ranges. The SPT1018 must use an

external reference.

SPT

8

SPT1019

5/14/97

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