NTE7137 データシートの表示（PDF） - NTE Electronics
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NTE7137 Datasheet PDF : 5 Pages
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Functional Description:
RGB input signals (0.7VP–P) are capacitively coupled into the NTE7137 (Pin2, Pin5, and Pin8) from
a low ohmic source and are clamped to an internal DC voltage (artificial balck level). Composite sig-
nals will not disturb normal operations because an internal clipping circuit cuts all signal parts below
black level. Channes 1 and 3 have a maximum total voltage gain of 6dB (maximum contrast and maxi-
mum individual channel gain), Channel 2 of 4dB (maximum contrast and nominal channel gain). With
the nominal channel gain of 1dB and nominal contrast setting the nominal black–to–white output am-
plitude is 0.8VP–P.
DC voltages are used for brightness, contrast and gain control. Brightness control yeilds a simulta-
neous signal black level shift of the three channels relative to a reference black level. For nominal
brightness (Pin1 open–circuit) the signal black level is equal to the reference black level.
Contrast control is achieved by a voltage at Pin6 and affects the three channels simultaneously.
To provide the correct white point, an individual gain control (Pin3 and Pin11) adjusts the signals of
Channels 1 and 3 compared to the reference Channel 2. Gain setting affects contrast and brightness
to achieve correct grey scale tracking.
Each output stage provides a current output (Pin20, Pin17 and Pin14) and a voltage output (Pin19,
Pin16 and Pin13). External cascode transistors reduce power consumption of the IC and prevent
breakdown of the output transistors. Signal output currents and peaking characteristics are deter-
mined by external components at the voltage outputs and the video supply.
The three channels have separate internal feedback loops which ensure large signal linearity and
marginal signal distortion in spite of output transistor thermal VBE variation.
The clamping pulse (Pin10) is used for input clamping only. The input signals have to be at black level
during the clamping pulse and are clamped to an internal artificial black level. The coupling capacitors
are used in this way for black level storage. Because the threshold for the clamping pulse is higher
than that for vertical blanking (Pin10) the rise and fall times of the clamping pulse have to be faqster
than 75ns/V (1V to 3.5V).
The vertical blanking pulse will be detected if the input voltage (Pin10) is higher than the threshold
voltage for approximately 300ns but does not exceed the threshold for the clamping pulse in the time
between. During the vertical blanking pulse the input clamping is disabled to avoid misclamping in
the event of composite input signals. The input signal is blanked and the artificial black level is inserted
instead. Additionally the brightness is internally set to its nominal value, thus the output signal is at
reference black levels. The DC value of the reference black level will be adjusted by cut–off stabiliza-
tion.
During horizontal blanking (Pin9) the output signal is set to reference black level as previously de-
scribed and output clamping is activated. If the voltage at Pin9 exceeds the switch off threshold the
signal is blanked and switched to ultra black level for screen protection and spot suppression during
V–flyback. Ultra black level is the lowest possible output voltage (at voltage outputs) and does not
depend on cut–off stabilization.
For cut–off stabilization (DC coupling to the CRT) respectively black level stabilization (AC couplking)
the video signal at the cathode or the coupling capacitor is divided by an adjustable voltage divider
and fed to the feedback inputs (Pin18, Pin15 and Pin12). During horizontal blanking time this signal
is compared with an internal DC voltage of approzimately 5.8V. Any difference will lead to a reference
black level correction by charging or discharging the integrated capacitor which stores the reference
black level information between the horizontal blanking pulses.
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