user to vary the video gain. By simply applying a DC voltage

pin through a 5kΩ pot to ground. For convenient stable gain

adjustment, a 0.1µF bypass capacitor should be connected near

sources. Digital gain control can be accomplished by connect-

ture tracking performance may be lost when using an external

The overall video output of the MSK 1900 can be charac-

terized using the following expression:

Here is a sample calculation for the MSK1900:

Given information

Rp=200Ω (external)

The expected video output would swing from approximately

should be used as a nominal result because the overall gain may

vary as much as ±10% due to internal high speed device varia-

tions. Changing ambient conditions can also effect the video

gain of the amplifier slightly. It is wise to connect all video

amplifiers to a common heat sink to maximize thermal tracking

when multiple amplifiers are used in applications such as RGB

shared by all three amplifiers. This voltage should be buffered

with a suitable low-drift op-amp for best tracking performance.

APPLICATION NOTES

POWER SUPPLIES

The input stage of the MSK 1900 requires power supplies of

+10V and -10.5V for optimum operation. The negative power

supply can be increased to -12V if -10.5V is not available, but

additional power dissipation will cause the internal temperature

to rise. Both low voltage power supplies sould be effectively

decoupled with tantalum capacitors (at least 1µF) connected as

close to the amplifiers pins as possible. The MSK 1900 has

internal 0.01µF capacitors that also improve high frequency per-

formance. Additionally, it is also recommended to put 0.1µF

decoupling capacitors on the +10V and -10.5V supplies as

well.

amplifiers output stage and must be kept as stable as possible.

ers DC output is directly related to the high voltage value. The

large a capacitor as possible to improve output stability.

VIDEO INPUTS

range of ±0.5V with respect to ground. Therefore, it is recom-

mended 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 damage to the hybrid, output linearity suffers and there-

fore it is not recommended.

The output pin of the MSK 1900 can be protected from tran-

sients by connecting reversed biased ultra-low capacitance di-

can also be protected from arc voltages by inserting a small value

(50-100Ω) resistor in series with the amplifier. This resistor will

reduce system bandwidth along with the load capacitance, but a

series inductor can reduce the problem substantially.

OUTPUT PROTECTION

VIDEO OUTPUT

Rp=200Ω, the device is capable of approximately 62Vpp total

output swing.

The MSK 1900 is conservatively specified with low values

for external Lp which yield about 5% overshoot. Additional

peaking can be obtained by using a high self-resonant frequency

can be very dependent on circuit layout, it is best to determine

its value by experimentation. A good starting point is typically

0.47µH for the MSK 1900.

SUPPLY SEQUENCING

the other DC control inputs. If power supply sequencing is not

possible, the time difference between each supply should be

less than five milliseconds. If the DC control signals are being

output, reverse biased diodes should be connected from each

3

Rev. B 9/99

sisting 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