Tektronix TG8000 Service Manual

GPS7 module theory of operation
Genlock c ontrol loop
When in Genlock
mode, the Black 1 output is turned o ff and the BNC is u sed as
an input. The input reference video is buffered then drives a sync separator and an
Analog to Digital Converter (ADC). The sync signals allow the Genlock logic
to roughly align the internal sync to the incoming video. The sync signal also
allows the genlock logic to window on the ADC samples from the sync edge
or the burst. The samples are read by the SW which then "closes t he loop" by
writing to t
he DAC that controls the OCXO. This sets the phase and frequency of
all the internal clocks.
The Genloc
k Control Loop is only available on GPS7 modules with the REF IN
connector on the rear panel.
MTOD clock
The Master Time of Day (MTOD) clock contains the precise current time, which
is phase
locked to the selected time source. The MTOD is used for all time code
generation and positioning of the frame reset pulses.
Outputs
The three Black Generation Engines and the four LTC engines each receive one
of thre
e frame reset pulses from the TG8000 mainframe, which lock the video
frames in all engines to exact ref erences based on MTOD.
In ord
er for many units to have the same phase when locked to GPS, the instrument
times the frame pulses to an “Epoch.” This means they are timed as though they
all started on the time indicated by TAI and the proposed SMPTE time o f GMT
midnight (00:00:00) on January 1st 1958. The video sequences generated by the
GPS7 are set to the correct time by calculating the total time from the SMPTE
epoch to the present, and adjusting the frame reset pulses accordingly. The frame
res
et pulses are used to reset the video generation outputs start position in time.
The GPS7 has 1 GPI (General Purpose Interface) input and 2 GPI outputs that can
be
set up for event triggering or detection as configured by the user. These are
under SW control via FPGA registers.
Time code reader
The time code reader operates on the same ADC data as the genlock. This data is
processed to extract the VITC bits and check for valid CRC and continuity. When
valid time code is detected, the SW reads the time values from the reader circuits.
The Time Code Reader is only available on GPS7 modules w ith the REF IN
connector on the rear panel.
10–6 TG8000 Multiformat Test Signal Generator Service Manual

Tektronix TG8000 Specifications

General

Brand	Tektronix
Model	TG8000
Category	Portable Generator
Language	English