Data Sheet S13944EJ2V0DS00

9

8. RELATIONSHIP BETWEEN OUTPUT DATA AND D/A CONVERTER

The

µPD16715A is a dot inversion and inverts dots by alternately using a charging output buffer and a discharging

output buffer. Therefore, the output voltage of the first line may not be correctly written because the last line’s output

polarity of frame n (n + 1) and the first line’s output polarity are the same (refer to Figure 8-1).

Consequently, polarity inversion and write operation must be performed between frames (vertical blanking period)

in order to invert (clear) the polarity of the wiring level of the liquid crystal panel by using the last line output of the

previous frame (refer to Figure 8-2).

Figure 8-1. Incase of the output voltage may not be correctly written

,,,

,,,

,,,

,,,

,,,

,,,

STB

Last line of frame n

Vertical blanking period

Second line of frame

(n

+ 1)

First line of frame

(n

+ 1)

Charging output

buffer

Discharging output

buffer

POL

Hi-Z

Hi-Z

Hi-Z

If the write voltage of the first line of the last (n + 1) frame is greater than the

write voltage of

the last line of frame n, the targeted voltage cannot be correctly written with the

Figure 8-2. Polarity inversion and write operation

,,,

,,,

,,,

,,,

,,,

,,,

,,,

Last line of frame n

Vertical blanking period

First line of frame

(n

+ 1)

Second line of frame

(n

+ 1)

Hi-Z

Hi-Z

Hi-Z

Hi-Z

STB

POL

Because data of negative polarity is to be written on the first line of

frame (n + 1),