HMP8115 Intersil Corporation, HMP8115 Datasheet - Page 5

• Manufacturer Part Number: HMP8115
• Description: Ntsc/pal Video Decoder
• Manufacturer: Intersil Corporation

Introduction
The HMP8115 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 HMP8115 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 HMP8115 contains two 8-bit A/D converters and an I
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 HMP8115.
ANALOG VIDEO INPUTS
The HMP8115 supports either three composite or two com-
posite and one S-video input.
Three analog video inputs (NTSC/PAL 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 NTSC/PAL 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.
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 NTSC/PAL 1-3 inputs, a single filter is connected
between the YOUT and YIN pins. For the C input, the anti-
aliasing filter should be connected before the C input. A rec-
ommended filter is shown in Figure 1.
S-VIDEO CHROMA GAIN CONTROL
The Chroma portion of S-video is AC coupled through an
anti-aliasing filter as shown in the applications section.
Unlike the composite/luma inputs, the Automatic Gain Con-
trol (AGC) for the chroma portion of S-video is done digitally
FIGURE 1. RECOMMENDED ANTI-ALIASING FILTER
YOUT
332
R
33pF
1
C
1
8.2 H
L
1
82pF
C
2
R
4.02K
2
YIN
HMP8115
2
C
5
inside the decoder as determined by bits 7 and 6 of the
COLOR PROCESSING register 06
nal AGC, the designer can also apply some gain to the
chroma before it reaches the internal AGC logic. This gain is
controlled by pin 28. The voltage at this pin determines the
gain of the chroma before it gets digitized by the chroma A/D
with a typical gain performance as shown in Figure 2.
Digitization of Video
Prior to A/D conversion, the video signal is DC restored and
gained to generate known video levels into the digital pro-
cessing logic. This process is addressed in the “AGC and
DC Restoration” section. After digitization, sample rate con-
verters and a comb filter are used to perform color separa-
tion and demodulation.
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 processing are:
AGC AND DC RESTORATION
The AGC amplifier attenuates or amplifies the analog video
signal to ensure that the sync tip level generates code 0. The
difference from the ideal sync tip level of 0 is used to control
the amount of attenuation or gain of the analog video signal.
The capacitor on the LAGC_CAP pin is used to store the
voltage which sets the gain level of the input video amplifier.
DC restoration positions the video signal such that the DC
level of the back porch generates an average code 64. The
back porch is sampled to determine the average value. The
capacitor on the L_CAP pin is used to store the voltage
7
6
5
4
3
2
1
0
1.6
white
black
blank
sync
TEMPERATURE = 25
V
CC
FIGURE 2. CHROMINANCE AMPLIFIER GAIN
1.8
= 5V
CONTROL VOLTAGE ON THE GAIN_CTRL PIN
2.0
(M) NTSC
(M, N) PAL
224
76
64
0
2.2
o
C
2.4
2.6
(B, D, G, H, I, N
H
. In addition to the inter-
2.8
PAL
213
64
64
0
3.0
C
3.2
)
3.4