DATA SHEET

ML6426

REV. 3A August 2004

7

Typical Applications

Reconstruction filter selection for HDTV and

VGA signal filtering

The filtering requirements for HDTV and VGA standards

vary depending on the resolution of the image to be dis-

played, and its refresh rate. The actual refresh rate of the dis-

play is not necessarily the same as the transmission rate of

the frames of images. Some formats use a frame rate of

30Hz, but the display of those formats cannot be scanned

onto the CRT at 30Hz. Excessive large area flicker would

result. Such kinds of flicker can be seen on a PAL display

with its brightness set high. To avoid this, the video will need

to be stored in a frame buffer. This buffer already exists in

the MPEG decoder of HDTV systems, so there is no cost

penalty. The buffer is read out at twice the rate as the frame

rate for 30Hz systems, thus getting us a refresh rate of 60Hz.

Similar things are done for the 24Hz frame rate formats to

boost them to a 60Hz refresh rate.

Table 1. HDTV / Advanced TV Applications: (From Table 10.3 from ATSC document A54)

P=progressive scan, I=interlaced scan

Table 2. Choosing the Correct Reconstruction Filter and Video Amplifier for TV Applications, ML6426 options

P=progressive scan, I=interlaced scan, na = not available

Notes

1. NTSC display rates, can be fed directly into NTSC encoder (set top box)

2. 60 Hz also includes 59.94Hz

3. Custom frequencies ranging ± 3 to 6MHz can be special cut to order

Pixels

Vertical Lines

Aspect Ratio

Picture Transmission Rate

1920

1080

16:9

60I, 30P, 24P

1280

720

16:9

60P, 30P, 24P

704

480

16:9 and 4:3

60P, 60I, 30P, 24P

640

480

4:3

60P, 60I, 30P, 24P

1920

1080

30P, 24P

60Hz

70.6KHz

162MHz

81MHz

N/A

SMPTE

1280

720

60P, 30P,

24P

60Hz

47.1KHz

60MHz

30MHz

ML6426-5

ML6426-4

704

60I

60Hz

15.7KHz

13.5MHz

6.75MHz

ML6426-1

704

480

60P, 30P,

24P

60Hz

31KHz

27MHz

13.5MHz

ML6426-2

ML6426-4

640

60I

60Hz

15.7KHz

24.5MHz

12MHz

ML6426-2

640

480

60P, 30P,

24P

60Hz

31KHz

12.27MHz

6MHz

ML6426-1