WT8045

Synchronous

Signal

Discriminator

and

Power Saving Detector for Green Monitor





Weltrend

Semiconductor,

Inc.

2F., No. 24, Industry E. 9th Rd.

Science-Based Industrial Park

Hsin-Chu, Taiwan, R.O.C.

Tel:

886-35-780241

Fax: 886-35-770419

16

In case of using output pulse of V_MONO_STABLE as voltage source, in order to prevent the

problem of slow response time, causing from the low frequency on vertical synchronous signal,

WT8045 internally increases the vertical signal frequency to 128 times the original frequency,

that is from 50Hz - 120 Hz to 6.4KHz - 15.36KHz. Then WT8045 uses this increased frequency

as the input signal of MONO_STABLE, so the leading edge of the signal of the increased

frequency will trigger the MONO_STABLE circuit.

An external resistor (Rx) and an external capacitor (Cx) control the timing and accuracy of the

circuit. Adjustment of Rx and Cx provides a wide range of output pulse widths from the Q and

Q-bar terminals. The delay time from trigger input to output transition is independent of Rx and

Cx.

The minimum value of external resistor Rx is 10k ohms. The typical value of external capacitor

Cx is 100 pF. The time period (T) for this multi-vibrator can be calculated with the formula: T

≈

1.1 Rx

• Cx.

H/V Frequency Divisions and Video Modes

Figure 1 illustrates the typical frequency ranges of H and V sync signals for display monitors.

The operating video modes are determined by the H and V frequencies, and occasionally, by

their polarities. The typical video modes of display monitors include the IBM VGA, VESA VGA,

European VGA/super VGA, VESA super VGA, IBM 8514/A, XGA, and 1280x 1024.

WT8045 can determine 13 standard video modes for 32 pin package (refer to Table 3) according

to H and V frequencies and polarities. These standard video modes include the IBM VGA,

VESA VGA, VESA super VGA and IBM 8514/A. This provides the users with the capability to

adjust the screen size for different modes.

WT8045 pre-sets the discriminating points both on H and V frequencies. The discriminating

points for H sync are 33KHz, 36.2KHz, 43.5KHz, 52KHz and 60KHz (for 32 pin). These

discriminating points will be able to identify various video modes as shown in Fig. 1. WT8045

also provides the flexibility for users to define these discriminating points through mask option.