參數(shù)資料
型號(hào)： TDA4887PS
廠商： NXP SEMICONDUCTORS
元件分類： 音頻／視頻放大
英文描述： 160 MHz bus-controlled monitor video preamplifier
中文描述： 3 CHANNEL, VIDEO PREAMPLIFIER, PDIP24
封裝： 0.400 INCH, PLASTIC, SDIP-24
文件頁(yè)數(shù)： 44/68頁(yè)
文件大?。?/td> 425K
代理商： TDA4887PS
2001 Oct 19
44
Philips Semiconductors
Product specification
160 MHz bus-controlled monitor video
preamplifier
TDA4887PS
12.3
Building the application board
12.3.1
G
ENERAL
Double-sided board
Short HF loops by large ground plane on the rear
SMD components with minimum parasitics.
12.3.2
V
OLTAGE OUTPUTS
Capacitive loads as small as possible
Be aware of internal output resistance (typically 75
).
12.3.3
S
UPPLY VOLTAGES
Capacitors as near as possible to the pins
Use electrolytic capacitors with small serial resistance
and inductance.
12.3.4
F
LASHOVER
High electric field strength is present between the gun
electrodes of picture tubes. In case of a flashover large
transient currents and voltages may damage electronic
components. It is therefore important to provide protective
circuits with spark gaps, series resistors and protection
diodes. Be aware that not only electronic components that
are directly connected to the tube socket are endangered
if interconnection lines on the application board are
unfavourably routed.
12.4
Application hints
12.4.1
A
LIGNMENT RECOMMENDATIONS USING BRIGHTNESS
CONTROL WITH GREY SCALE TRACKING
12.4.1.1
Introduction (philosophy of TDA4887PS)
With the TDA4887PS the user may change contrast,
brightness and even colour temperature (R, G, B gains) or
any combination at will. The ‘x,y’ colour point will remain
stable for the full grey scale. This feature is achieved in the
following way:
A change of brightness will cause a change of black
level which is proportional to the actual gain setting
Conversely, a change of gain setting will cause a
change of black level that is proportional to the deviation
of brightness from its nominal setting.
To benefit fully from this colour tracking feature, the
reference black levels of the video amplifiers must match
exactly to the cut-off points of the cathodes.
Re-adjustments of black level settings by the end user
should be avoided, because this will upset the tracking
feature.
12.4.1.2
Difficulty during monitor production
The factory cut-off alignment is done at a quite high level
(e.g. 2.4 cd/m
2
). As a consequence it is not certain that the
reference black level will match the cut-off exactly after a
first black level adjustment. If then the R, G, B gains are
adjusted for the (x, y) white point at e.g. 102.8 cd/m
2
, the
white balance at 2.4 cd/m
2
will have changed. So two or
more alignment cycles may be needed to achieve good
results.
12.4.1.3
Considerations for a single-pass factory
alignment
The nominal brightness setting is 40H. In this condition the
black level equals reference black level and must match to
the CRT cut-off.
For a better understanding, discrete values for luminance,
video and feedback gain have been taken (these values
should beregarded as examples). For special applications
actual values have to be taken instead.
White point must be aligned at maximum luminance
(e.g. at 102.8 cd/m
2
) with maximum contrast and nominal
brightness. It is recommended to use only a small white
square for white point alignment, to prevent variations of
the voltage at grid G1 (V
g1
) and grid G2 (V
g2
) and to
prevent unwanted activation of the automatic beam limiter
(ABL).
For practical reasons, alignment of the R, G, B reference
black levels must be done with a small amount of drive for
obtaining a luminance level of approximately 2.4 cd/m
2
.
This drive can be simulated by setting the brightness to a
certain value. Assuming 102.8 cd/m
2
luminance with full
white video (100% drive) and a cathode characteristic with
gamma = 2.25, the drive for black level adjustment can be
shown as:
which corresponds to a brightness setting of B8H.
After black level adjustment for L = 2.4 cd/m
2
, the cathode
voltages are fixed and the cut-off voltages are set with
equal gain condition in all channels. During white point
adjustment the gains will be changed. In the factory
procedure for single pass adjustment, the luminance level
for black level alignment (2.4 cd/m
2
) is kept constant while
adjusting the gain settings. To achieve this, the black level
references are compensated by software and an
alignment computer (this compensation is for factory
alignment only and is not needed for any user change of
R, G, B gain).
102.8
1/2.25
--------2.4
100 = 18.8% drive
×
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