3.0 PC Board Considerations
CX25870/871
3.6 Applications Information
Flicker-Free Video Encoder with Ultrascale Technology
3.6.2.7 Standard and
Adaptive Flicker Filter
Flicker occurs when the refresh rate of the video is too low. In digital encoders,
flicker can also occur when processing an image that contains many fine vertical
divisions such as lines that are only 1 or 2 lines wide. When the encoder stores,
combines (by vertically interpolating data), and converts two consecutive
incoming frames into 1 output field, portions of the image containing just a few
lines can be placed on different analog output lines. Since the position of the
output line is not equivalent from field to field, it appears to flicker at the vertical
refresh rate.
This annoying artifact can be eliminated by selecting an appropriate flicker
filter setting, one that trades off vertical resolution and text clarity against flicker
reduction. The flicker filter slider shown in Figure 3-6 modifies the F_SELY[2:0]
and F_SELC[2:0] bit fields together anytime the end-user changes the particular
level. Internal testing has shown that certain application programs such as
spreadsheets look best with more flicker filtering while others, such as games and
DVD movies, look best with less. In addition, the active resolution also affects the
amount of flicker filtering required. 640x480 and lower resolutions rarely require
a maximum flicker filter setting, whereas the 1024x768 resolution often does.
With five standard flicker filter levels available, Conexant recommends
programming the following bit values according to the slider level.
Flicker Filter Slider Level
F_SELY[2:0]
F_SELC[2:0]
Level 5 = Maximum
Level 4
000 = 5 line. DIS_FFILT = 0.
011 = 4 line. DIS_FFILT = 0.
010 = 3 line. DIS_FFILT = 0.
001 = 2 line. DIS_FFILT = 0.
Do not care. DIS_FFILT = 1.
011 = 4 line. DIS_FFILT = 0.
010 = 3 line. DIS_FFILT = 0.
001 = 2 line. DIS_FFILT = 0.
001 = 2 line. DIS_FFILT = 0.
Do not care. DIS_FFILT = 1.
Level 3
Level 2
Level 1 = Minimum
NOTE: The optimal performance for the Standard Flicker Filter is usually
achieved by configuring F_SELC to 1 line less than F_SELY.
The CX25870/871 also has an adaptive flicker filter (i.e., Adaptive FF). This
feature is explained in section 1 of the data sheet. The recommended TV Out
Graphical User Interface allows the usage of the adaptive flicker filter only if the
box to enable it is checked. Once this is done, the ADPT_FF bit should get
set (=1).
3-18
Conexant
100381B
CONEXANT [ CONEXANT SYSTEMS, INC ]
