HMP8116 Datasheet, PDF (5/43 Pages) Intersil Corporation – NTSC/PAL Video Decoder

HMP8116
Introduction
The HMP8116 is designed to decode baseband composite
or S-video NTSC and PAL signals, and convert them to
either digital YCbCr or RGB data. In addition to performing
the basic decoding operations, the HMP8116 includes hard-
ware to decode different types of VBI data and to generate
digital video patterns for a blue screen, black screen and full
screen color bars.
The digital PLLs are designed to synchronize to all NTSC
and PAL standards. A chroma PLL is used to maintain
chroma lock for demodulation of the color information; a line-
locked PLL is used to maintain vertical spatial alignment.
The PLLs are designed to maintain lock even in the event of
VCR headswitches and multipath noise.
The HMP8116 contains two 8-bit A/D converters and an I²C
interface for programming internal registers
External Video Processing
Before a video signal can be digitized the decoder has some
external processing considerations that need to be
addressed. This section discusses those external aspects of
the HMP8116.
ANALOG VIDEO INPUTS
The HMP8116 supports either three composite or two com-
posite and one S-video input.
Three analog video inputs (CVBS 1-3) are used to select
which one of three composite video sources are to be
decoded. To support S-video applications, the Y channel
drives the CVBS 3 analog input, and the C channel drives
the C analog input.
The analog inputs must be AC-coupled to the video signals,
as shown in the Applications section.
toration” section. After digitization, sample rate converters and
a comb filter are used to perform color separation and demod-
ulation.
A/D CONVERSION
Video data is sampled at the CLK2 frequency then pro-
cessed by the input sample rate converter. The output levels
of the ADC after AGC and DC restoration processing are:
(M) NTSC
(M, N) PAL
(B, D, G, H, I, N_C)
PAL
white
196
196
black
66
59
blank
56
59
sync
0
0
AGC AND DC RESTORATION
The AGC amplifier attenuates or amplifies the analog video
signal to ensure that the blank level generates code 56 or 59
depending on the video standard. The difference from the
ideal blank level of 56 or 59 is used to control the amount of
attenuation or gain of the analog video signal.
DC restoration positions the video signal so that the sync tip
generates a code 0. The internal timing windows for AGC
and DC Restoration are show in Figure 3.
VIDEO INPUT
AGC
ANTI-ALIASING FILTERS
An external anti-alias filter is required to achieve optimum
performance and prevent high frequency components from
being aliased back into the video image.
For the CVBS 1-3 inputs, a single filter is connected between
the YOUT and YIN pins. For the C input, the antialiasing filter
should be connected before the C input. A recommended fil-
ter is shown in Figure 1.
YOUT
R₁
332
C₁
33pF
L₁
8.2uH
C₂
82pF
YIN
R₂
4.02K
FIGURE 1. RECOMMENDED ANTI-ALIASING FILTER
Digitization of Video
Prior to A/D conversion, the video signal is DC restored and
gained to generate known video levels into the digital process-
ing logic. This process is addessed in the “AGC and DC Res-
DC RESTORE
FIGURE 2. AGC AND DC RESTORE INTERNAL TIMING
INPUT SIGNAL DETECTION
It is assumed there is no video input if a horizontal sync is
not detected for 16 consecutive lines. When no video has
been detected, nominal video timing is generated for the
previously detected or programmed video standard. A
maskable interrupt is included to flag when no video has
been detected (bit 6 of the INTERRUPT MASK register 0F_H)
allowing for blue/black/color bar output modes to be enabled
if desired. The vertical sync interrupt can be used in deter-
mining when a video signal is present on the currently
selected video mux input. Bit 0 of register 0F_H is used to
enable vertical sync interrupts.
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