HMP8117 Datasheet, PDF (5/45 Pages) Intersil Corporation – NTSC/PAL Video Decoder

HMP8117
Introduction
The HMP8117 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, these devices include
hardware to decode different types of VBI data and to
generate full-screen blue, black and color bar patterns.
Digital PLLs are used to synchronize to all NTSC and PAL
standards. A chroma PLL is used to maintain color lock for
chroma demodulation while a line-locked PLL is used to
maintain vertical spatial alignment. The PLLs are designed
to maintain lock in the presence of VCR head switches, VCR
trick-mode and multi-path noise.
The HMP8117 provides the Videolyzer feature for
Macrovision (MV) copy-protection bypass and detection.
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 HMP8117.
Analog Video Inputs
The HMP8117 supports either three composite or two
composite 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 CVBS3(Y) 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-alias Filters
Although a 23 tap digital halfband anti-alias filter is provided
for each A/D channel, an external passive filter is
recommended for optimum performance. The digital filter
has a flat response out to 5.4MHz with an approximate -3dB
bandwidth of 6.3MHz using a 27MHz input CLK2 sample
rate. For the CVBSx inputs, the filter is connected between
the YOUT and YIN pins. For the C (chroma) input, the anti-
alias filter should be connected before the C input.
Recommended filter configurations are shown on the
reference schematic in Figure 20. These filters have flat
response out to 4.2MHz with an approximate -3dB
bandwidth of 8MHz. If upgrading from the HMP8115 or
HMP8112A, the previous filter configurations may be used
but with slightly degraded bandwidth. Alternative higher or
lower performance filters configurations may substituted.
Digitization of Video
Prior to A/D conversion, the input signal is offset and scaled to
known video levels. After digitization, sample rate converters
and a comb filter are used to perform color separation and
demodulation.
A/D Conversion
Each CVBSX video input channel has a video clamp circuit
that is independent of PLL timing. The input clamp provides
a coarse signal offset to position the sync tip within the A/D
converter sampling range so that the AGC and DC-
RESTORE logic can operate.
A/D Conversion
Video data is sampled at the CLK2 frequency then processed
by the input sample rate converter. The output levels of the
ADC after AGC and DC restoration processing are:
white
black
blank
sync
(M) NTSC
(M, N) PAL
196
66
56
0
(B, D, G, H, I, N_C)
PAL
196
59
59
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. To obtain a
stable DC reference for the AGC, a digital low-pass filter
removes the chroma burst from the input signal’s backporch.
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. The appropriate
windows are automatically determined by the decoder when
the input signal is auto-detected or manually selected.
VIDEO INPUT
AGC
DC RESTORE
FIGURE 1. AGC AND DC RESTORE INTERNAL TIMING
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