Grass Valley 8980TLS - Manual (Page 8)

2 8980TLS Instruction Manual
8980TLS NTSC to HDTV Tri-level Sync Converter
Functional Description
Refer to Figure 1 while reading this functional description. The 525-line
NTSC reference input signal feeds a sync separator and a color burst phase-
locked loop. The color burst phase-locked loop generates an output at six
times subcarrier frequency that is locked to the incoming color burst. This
six-times subcarrier frequency signal drives a counter which produces an
output at 33.7 kHz which is a subharmonic of the 74.17 MHz high defini-
tion clock frequency. Another output from the color burst locked loop at
two-times subcarrier frequency feeds SC/H phase tracking circuitry. This
circuit resolves any timing variation between the separated horizontal sync
and incoming burst phase which may be caused by reference signal SC/H
phase variations. The phase corrected horizontal timing is gated with ref-
erence field timing to create an output at frame rate (29.97 Hz). This output
is used to set the phase of the 33.7 kHz generator to a known value once per
frame.
The high definition timing generator uses the 33.7 kHz signal as a reference
to generate a clock signal for the pulse generation logic. The frame rate
pulse is used by the high definition timing generator to set its phase once
per frame. Timing control switches at the front of the module feed into the
sync generator logic. Output pulses are produced by the sync generator
logic and are shifted in time with respect to the 33.7 kHz and frame rate
pulses by an amount determined by the timing controls. The logic pulses
from the sync generator logic are shaped and feed an output line-driver
amplifier which provides the module’s four isolated outputs.
Figure 1. 8980TLS Functional Block Diagram
NTSC
Reference
Input
Sync Separator
and
SC/H
Tracker
SC/H
Centering
Adjustment
Output
Level
Tri-level
Sync
Outputs
Output
DC
Output
Timing
Controls
HDTV
Video
Standard
Selection
Burst
Phase
Locked
Loop
33.7 KHz
Generator
Reference Frame Pulse
High
Definition
Sync
Generator
Output
Amplifier
0515_01