Datasheet

TVP5147M1
www.ti.com SLES140G –JULY 2005–REVISED FEBRUARY 2012
2.1.1 Video Input Switch Control
The TVP5147M1 decoder has two analog channels that accept up to ten video inputs. The user can
configure the internal analog video switches via the I
2
C interface. The ten analog video inputs can be used
for different input configurations, some of which are:
• Up to ten selectable individual composite video inputs
• Up to four selectable S-video inputs
• Up to three selectable analog YPbPr video inputs and one CVBS input
• Up to two selectable analog YPbPr video inputs, one S-video input, and two CVBS inputs
The input selection is performed by the input select register at I
2
C subaddress 00h (see Table 2-12).
2.1.2 Analog Input Clamping
An internal clamping circuit restores the ac-coupled video signal to a fixed dc level. The clamping circuit
provides line-by-line restoration of the video sync level to a fixed dc reference voltage. The selection
between bottom and mid clamp is performed automatically by the TVP5147M1 decoder.
2.1.3 Automatic Gain Control
The TVP5147M1 decoder uses two programmable gain amplifiers (PGAs), one per channel. The PGA can
scale a signal with a voltage-input compliance of 0.5-VPP to 2.0-VPP to a full-scale 10-bit A/D output code
range. A 4-bit code sets the coarse gain with individual adjustment per channel. Minimum gain
corresponds to a code 0x0 (2.0-VPP full-scale input, -6-dB gain) while maximum gain corresponds to code
0xF (0.5 VPP full scale, +6-dB gain). The TVP5147M1 decoder also has 12-bit fine gain controls for each
channel and applies independently to coarse gain controls. For composite video, the input video signal
amplitude can vary significantly from the nominal level of 1 VPP. The TVP5147M1 decoder can adjust its
PGA setting automatically: an automatic gain control (AGC) can be enabled and can adjust the signal
amplitude such that the maximum range of the ADC is reached without clipping. Some nonstandard video
signals contain peak white levels that saturate the ADC. In these cases, the AGC automatically cuts back
gain to avoid clipping. If the AGC is on, then the TVP5147M1 decoder can read the gain currently being
used.
The TVP5147M1 AGC comprises the front-end AGC before Y/C separation and the back-end AGC after
Y/C separation. The back-end AGC restores the optimum system gain whenever an amplitude reference
such as the composite peak (which is only relevant before Y/C separation) forces the front-end AGC to set
the gain too low. The front-end and back-end AGC algorithms can use up to four amplitude references:
sync height, color burst amplitude, composite peak, and luma peak.
The specific amplitude references being used by the front-end and back-end AGC algorithms can be
independently controlled using the AGC white peak processing register located at subaddress 74h. The
TVP5147M1 gain increment speed and gain increment delay can be controlled using the AGC increment
speed register located at subaddress 78h and the AGC increment delay register located at subaddress
79h.
2.1.4 Analog Video Output
One of the analog input signals is available at the analog video output terminal, which is shared with input
selected by I
2
C registers. The signal at this terminal must be buffered by a source follower. The nominal
output voltage is 2 V p-p, thus the signal can be used to drive a 75-Ω line. The magnitude is maintained
with an AGC in 16 steps controlled by the TVP5147M1 decoder. To use this function, terminal VI_1_A
must be set as an output terminal. The input mode selection register also selects an active analog output
signal.
Copyright © 2005–2012, Texas Instruments Incorporated Functional Description 17
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