APPLICATION NOTES

FEED FORWARD TOPOLOGY

Transition time optimization of the MSK 613 follows the same

basic rules as most any other amplifier. Best transition times

will be realized with minimum load capacitance, minimum ex-

ternal feedback resistance and lowest circuit gain. Transition

times will degrade if the output is driven too close to either

supply rail. Feedback and input resistor values will affect tran-

sition time as well. See Figure 1 and Table 1 for recommended

component values.

CURRENT LIMIT

Figure 2 is a possible active short circuit protection scheme

for the MSK 613. The following formula may be used for set-

ting current limit:

Current Limit ≈ 0.6V / Rsc

lows:

This formula guarantees that Q2 and Q4 will always have suf-

ficient base current to be in operation. This circuit can be made

tolerant of high frequency output current spikes with the addi-

limit is unnecessary, short pins20 & 21 to pins 22 & 23 and

pins 34 & 35 to pins 32 & 33 as shown in Figure 1.

1KΩ

Ω

Ω

Ω

Ω

249Ω

Ω

Ω

Ω

Ω

100Ω

Ω

Ω

Ω

Ω

-10V/V

-20V/V

-50V/V

0.5-5pF

N/A

N/A

10KΩ

Ω

Ω

Ω

Ω

5KΩ

Ω

Ω

Ω

Ω

5KΩ

Ω

Ω

Ω

Ω

VOLTAGE

GAIN

Table 1

Figure 2

INTERNAL COMPENSATION

Since the MSK 613 is a high voltage amplifier, it is com-

monly used in circuits employing large gains. Therefore, the

internal compensation was chosen for gains of -5V/V or greater.

In circuits running at gains of less than -5V/V, the user can

further compensate the device by adding compensation net-

works at the input or feedback node. Pin 2 (comp) should be

cations.

TRANSITION TIMES

HIGH VOLTAGE SUPPLIES

The positive and negative high voltage supplies on the MSK

613 can be adjusted to reduce power dissipation. The output

of the MSK 613 will typically swing to within 8V of either high

voltage power supply rail. Therefore, if the system in question

only needs the output of the amplifier to swing ±40V peak,

the power supply rails could be set to ±50V safely. For best

Unbalanced power supply rails are also allowed as long as one

or the other is not decreased to below 30V or above 80V. The

high voltage and low voltage power supplies should be decoupled

as shown in Figure 1.

The MSK 613 employs a circuit topology known as "feed

forward". This inverting configuration allows the user to real-

ize the excellent D.C. input characteristics of a differential am-

plifier without losing system bandwidth. The incoming signal

is split at the input into its A.C. and D.C. component. The D.C.

component is allowed to run through the differential amplifier

where any common mode noise is rejected. The A.C. compo-

nent is "fed forward" to the output section through a very high

speed linear amplifier where it is mixed back together with the

D.C. component. The result is an amplifier with most of the

benefits of a differential amplifier without the loss in system

bandwidth.

Rev. B 8/00

3

Figure 1