DATA SHEET

KH205

4

REV. 1A January 2004

Current Feedback Amplifiers

Some of the key features of current feedback technology

are:

Current feedback operation can be described using a simple

equation. The voltage gain for a non-inverting or inverting

current feedback amplifier is approximated by Equation 1.

Equation 1

where:

gain

s

is the loop gain

The denominator of Equation 1 is approximately equal to

1 at low frequencies. Near the -3dB corner frequency,

performance. The value of the feedback resistor has a

has the following affects:

Overdrive Protection

Unlike most other high-speed op amps, the KH205 is not

damaged by saturation caused by overdriving input

limits the current at the inverting input when the output is

saturated (see the inverting input current self limit

specification); this ensures that the amplifier will not be

damaged due to excessive internal currents during overdrive.

For protection against input signals which would exceed

either the maximum differential or common mode input

voltage, the diode clamp circuits below may be used.

Figure 1: Diode Clamp Circuits for Common Mode

and Differential Mode Protection

Short Circuit Protection

Damage caused by short circuits at the output may be

prevented by limiting the output current to safe levels.

The most simple current limit circuit calls for placing

resistors between the output stage collector supplies and

the output stage collectors (pins 12 and 10). The value

of this resistor is determined by:

expected load resistance (0

Ω for a short to ground).

Bypass capacitors of 0.01

µF on should be used on the

collectors as in Figures 2 and 3.

Figure 2: Recommended Non-Inverting Gain Circuit

Figure 3: Recommended Inverting Gain Circuit

A more sophisticated current limit circuit which provides a

page 5.

With the component values indicated, current limiting

occurs at 50mA.

temperature

dependent,

the

limit

current

is

likewise temperature dependent.

differential protection

KH205

+

-

common mode

protection

K

R

V

I

R

C

C

I

I

=−

33

Ω

+15V

.1

3.9

.01

Capactance in

µF

1

12

8

3,7

200

Ω

10

11

33

Ω

.01

.1

3.9

-15V

9

+

-

KH205

6

5

50

Ω

A1

R

R

v

f

g

=+

33

Ω

+15V

.1

3.9

.01

Capactance in

µF

1

12

8

5

3,7

200

Ω

10

11

33

Ω

.01

.1

3.9

-15V

9

+

-

KH205

6

50

Ω

A

-R

R

v

f

g

=

V

V

A

1

R

Zj

o

in

v

f

=

ω

Zj

ω

()