Toshiba TW40F80 User Manual download pdf (Page 86)

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1. OUTLINE

The digital convergence circuit develops outputs to correct

screen distortion and perform color matching. The digital

convergence circuit used is of an all digital type and allows

good adjustments in comprise with a conventional analog type

circuit.

Followings are features of the digital convergence circuit.

1) No adjustment controls (volumes)

2) Registration accuracy increased.

3) Space saved

4) Adjustment by a remote control

The data adjusted are classed into 4 screens for each screen

mode. These data are stored on E

PROMs inside the unit.

The memory size used in this case is 4 Kbits per one screen.

Each screen adjustment is carried out by calling the adjust-

ment screen with the remote control unit supplied and the

adjustment is carried out according to the dimensions speci-

fied for each screen. The control of the unit is carried out in

the I

C format.

2. CIRCUIT DESCRIPTION

2-1. Configuration

Fig. 11-1 shows a block diagram. The digital convergence

unit consists of Q701 T7K64 which plays a major role, Q707

PLL circuit which locks a sync entered, Q713 E

PROM to

store the data, and Q703-5 D/A converter which develops a

correction wave form.

The output signal from the Q703 – 705 D/A converter is

amplified and wave form shaped by Q715, Q717 and Q719,

and comes out from the unit.

The clock signal for the PLL is adjusted by L719 to a refer-

ence frequency of 32 ± 0.1MHz under no input status.

A test pattern generator is also built inside Q701 and devel-

ops R, G, B signals and a Ys switching signal.

2-2. Circuit Description

(1) With the power turned on, the unit is reset and enters

an operation standby status. And a sync signal of the

unit enters external Q707 and Q701. The signal en-

tered Q707 is counted down by a counter inside the

Q701 and this is used as the reference clock. Q701

works in synchronization with the reference clock sig-

nal and the sync signal.

(2) A command is sent from the microcomputer in the unit

and Q701 is set up to load the data in Q713 to the in-

ternal RAM. (8 (horizontal) x 7 (vertical) x 3 (color))

(3) Q701 transfers a serial data specified to Q703 – 705

according to the RAM data. In this case, interpolation

for the RAM data is automatically carried out by a built

-in digital filter inside Q701.

(4) The serial data sent from Q701 are digital-analog con-

verted by Q703 – 705, thus developing the analog type

wave form.

(5) The signals sent from Q703 – 705 are amplified Q715,

Q717, Q719, respectively, and then filtered in the next

stage to smooth and shape the wave form. Thus pro-

cessed signals are used as H and V correction wave

forms for R, G, and B signals.

SECTION XI: DIGITAL CONVERGENCE CIRCUIT

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Toshiba TW40F80 User Manual Page 86

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