
PRODUCT SPECIFICATION
TMC22x5yA
53
Digital Burst Locked Loop
The digital burst locked loop provides sine and cosine signals 
which are phase locked to the incoming burst signal. These 
sine and cosine signals are used to demodulate the chromi-
nance data, producing the U and V color-difference signals. 
The U data are phase-referenced to sin(wt) and the V data to 
cos(wt). The demodulated signal is passed through a low pass 
filter to remove signals at twice the subcarrier frequency. 
The magnitude of the U and V data within the demodulated 
burst signal provides the error signal which, after filtering, is 
used to adjust the frequency and/or phase of the subcarrier 
DDS. The output of the subcarrier DDS is translated into sine 
and cosine signals in ROM-based lookup tables.
The PALODD signal is low on lines without the 180 degree 
phase advance in the modulated V signal, termed NTSC 
lines, and high for lines with the 180 degree phase advance, 
termed PAL lines. This signal is used in the burst locked loop 
to advance the phase of the cosine table on PAL lines. PAL-
ODD is always low for NTSC.
Color Kill Counter
The demodulated U and V components are compared to a 
programmable burst level threshold. If both the U and V data 
fall below this threshold, a color kill flag is set high. The 
color kill counter is incremented once per line if the color 
kill flag is high. If the count reaches 127 within one field, the 
color kill circuit becomes active during the next field group. 
When this occurs, the input video will be passed unaltered 
on the luminance channel and the color difference signals 
will be set to chroma black. 
The color kill signal remains active until a field with less 
than 127 lines without burst is encountered, at which time, 
during the next vertical blanking period, the decoder is reset. 
The operation of the color kill logic can be monitored exter-
nally by reading the MONO register bit in register 44h. The 
MONO bit is HIGH for composite and YC video signals and 
LOW for monochrome signals.
Field Flag, FLD
The FLD signal is the lsb of the field count FID
2-0
 and is 
LOW for fields where the first vertical sync occurs in the first 
half of the line and is HIGH for fields when it occurs in the 
second half of the line. This signal is synchronized with the 
frame and color frame flags in the FID generator.
Frame Bit
NTSC
The middle bit (frame bit) of the field count is determined, 
by the phase of the subcarrier on a given pixel and on a given 
line. The signal used to determine this is NFDET (New Field 
DETect), and occurs when the line count is zero and the pixel 
count is one of four programmable pixel positions, zero, one, 
two, or three.
PAL
The frame bit in PAL is detected through the Bruch blanking 
sequence. The error signal control circuit generates a color 
kill flag whenever a line is detected without a burst. It is 
therefore possible to compare this signal with specific line 
idents to determine the field sequence in both PAL-I and 
PAL-M. A set of specific patterns determine the correct 
phase of FID
1
; if any of these patterns is detected then FID
1
is forced to a known state and then flywheels until the next 
fixed pattern is detected.
Table 9. PAL-B,G,H,I Bruch Blanking Sequence
The frame bit is low for frames 0 and 2 and high for frames 1 
and 3.
Internal 
line #
5
309
6
309
5
309
6
309
Burst 
present
No
No
Yes
No
Yes
Yes
No
Yes
Internal 
frame #
0 or 2
0 or 2
0 or 2
0 or 2
1 or 3
1 or 3
1 or 3
1 or 3
Internal field #
0 or 4
0 or 4
1 or 5
1 or 5
2 or 6
2 or 6
3 or 7
3 or 7
.
Figure 21. Block Diagram of Digital Burst Locked Loop
Chrominance
Burst
Locked Loop
Gaussian
LPF
U Data
V Data
Gaussian
LPF
–
sin(wt)
65-22x5y-62
cos(wt+
f
)