Block Diagram

Functional Description

The LM1296 outputs a sawtooth and a variable DC voltage

for the vertical deflection amplifier. It also provides the hori-

zontal deflection output circuit with a waveform for Trap-

ezoid, Pincushion and Corner correction.

Referring to

Figure 3, pin 7 (V SYNC) goes to the Sync Po-

larity Correction Block that accepts either positive-going or

negative-going sync signals. The polarity-corrected sync is

sent to the Injection-Locked Oscillator so that the sawtooth

generated is synchronized with the vertical sync. With no

sync signal AC-coupled to pin 7, the oscillator free runs at

typically 40 Hz.

There are three capacitors and one control pin connected to

the Sawtooth Waveform Generation Block. C

ing capacitor for the Injection-Locked Oscillator. C

ter capacitor for an internal circuit that detects the existence

of vertical sync and prevents the Injection-Locked Oscillator

from locking at twice the vertical sync frequency. C

the automatic level control (ALC) circuit. The ALC circuit

maintains the sawtooth output amplitude, which is set by the

DC voltage at pin 2 (HEIGHT), regardless of the vertical sync

frequency. Since the output sawtooth goes to the geometry

correction circuit as well, the correction waveform generated

tracks the sawtooth amplitude, i.e., the height of the CRT

raster.

The S Correction block shapes the linear sawtooth into an

S-shape sawtooth. Pin 15 (SAWTOOTH OUT) outputs the

buffered S-shape sawtooth. The amount of S correction is

controlled by the DC voltage at pin 16 (S).

Referring to

Figure 4, the extent of S correction is defined by

the following equation.

k

The LM1296 is designed to drive an external vertical deflec-

tion amplifier that is operating with positive and negative

power supplies. The LM1296 outputs an S-corrected saw-

tooth with a DC level that is typical 3.85V. Pin 13 (DC OUT)

control voltage to pin 1 (POSITION), the output voltage at pin

13 can be varied. This sets the output DC current from the

vertical deflection amplifier, which in turn sets the raster ver-

tical position.

DS012894-9

FIGURE 3.

DS012894-10

FIGURE 4.

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