MSK1901 データシートの表示（PDF） - M.S. Kennedy Corporation
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MSK1901 Datasheet PDF : 6 Pages
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APPLICATION NOTES
INITIAL SETUP
It is important to set the VOFF and VGAIN inputs to ob-
tain balanced rise/fall times during initial setup of the
MSK 1901. If the quiescent current level of VOFF is set
too low, it will slow the rise time and limit the bandwidth
of the MSK 1901.
VIDEO INPUTS
The analog inputs (±VIN) are designed to accept RS343
signals, ±0.714VPP, and will operate properly with a com-
mon mode range of ±0.5V with respect to ground. There-
fore, it is recommended that the input signal be limited
to ±1.3V with respect to ground, (signal+common
mode). Although large offsets of ±2V (with respect to
ground, signal included) can be tolerated without dam-
age to the hybrid, output linearity suffers and therefore it
is not recommended.
VGAIN
VGAIN is the DC gain (contrast) control which varies the
gain from 0 to 80V/V. The internal reference (VREF) is
available to drive this input. Normally a 5K potentiometer
is connected between VREF and GND is used to vary the
gain, but any 0-5V external DC source may be used with
some additional degredation of gain stability over tem-
perature. A 0.1µF capacitor should be connected from
the VGAIN pin to ground to improve stability.
The gain equation for the MSK 1901 is:
VLRS-VO=VIN x GM x RL
=VIN (VGAIN x 0.08) RL
The overall gain of the MSK 1901 may vary by ±20%
due to process variations of the internal components.
Temperature variations also effect gain, <150ppm/°C.
If more than one MSK 1901 is used in a system, steps
should be taken to make them track thermally (i.e. a
common heat sink). This will reduce any mismatches due
to varying temperatures.
VOFF
VOFF is the output offset (brightness) control used to
set the output quiescent current and consequently the
DC output voltage (black level). Output quiescent cur-
rent adjustment range is from several µA to 100mA nomi-
nal (80 to 130mA actual). Normally a 5K potentiometer
is connected between VREF and GND to this input, but
any 0-5V external DC source may be used. A 0.1µF ca-
pacitor should be connected from this pin to signal ground
to improve the amplifier's stability.
BLACK LEVEL
The voltage developed across the external load resis-
tor with a 0V video input to the MSK 1901 is the black
level. This voltage may be changed by adjusting the load
resistor or by varying the output quiescent current of the
MSK 1901as described in VOFF above. The black level
could also be affected by the VGAIN control voltage if the
video input has a DC component. AC coupling of the
video input will prevent this phenomenon from occuring.
BLANKING
The blank input is a TTL active high input. When active
it will disable the video input of the MSK 1901 and allow
the output to rise to approximately VLRS. If the blank in-
put rises above 3V some interaction between VOFF and
BLANK level may occur. The BLANK input is indepen-
dent of the input signal and must be tied "low" to acti-
vate the amplifier if the blanking function is not used.
VREF OUTPUT
VREF is a buffered zener reference with a nominal out-
put voltage of 5.5V ±5% which can source up to 4mA.
It is available for use in adjusting the offset and gain. If
multiple amplifiers are used for RGB amplification, they
should all share the same VREF pin from one of the hy-
brids. The VREF pin should be buffered with a unity gain
precise amplifier when driving three amplifiers for RGB
applications.
VCB
The VCB input is the base connection to the output
stage consisting of a common base, high voltage stage
and a high speed, low voltage current amplifier in a
cascode arrangement. This input requires a very stable
10V DC nominal voltage. Any AC signals at this point
will be amplified and reflected in the output. The PSRR
of the output stage is directly related to the stability of
this VCB voltage.
VIDEO OUTPUT
The video output voltage is obtained from the open
collector of a cascode circuit designed to operate with a
nominal output supply (VLRS) of +70V. VLRS must be
greater than the applied VCB voltage, but less than VCB
+65V. The output of MSK 1901 will drive loads up to
250mA when proper heat sinking is used.
3
Rev. A 5/02
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