DATA SHEET

KH231

4

REV. 1A January 2004

Operation

The KH231 Buffer/Amplifier is based on the current feed-

back op amp topology, a design that uses current feed-

back instead of the usual voltage feedback.

The use of the KH231 is basically the same as that of the

conventional op amp (see Figures 1 and 2). Since the

device is designed specifically for low gain applications,

the best performance is obtained when the circuit is used

at gains between ±1 and ±5. Additionally, performance is

optimum when a 250

Ω feedback resistor is used.

Figure 1: Recommended non-inverting gain circuit

Figure 2: Recommended inverting gain circuit

Layout Considerations

To assure optimum performance the user should follow

good layout practices which minimize the unwanted

coupling of signals between nodes. During initial bread-

boarding of the circuit use direct point to point wiring,

keeping the lead lengths to less than 0.25”. The use of

solid, unbroken ground plane is helpful. Avoid wire-wrap

type pc boards and methods. Sockets with small, short

pin receptacles may be used with minimal performance

degradation although their use is not recommended.

During pc board layout keep all traces short and direct

to pin 5 to minimize capacitance at that point. For the

same reason, remove ground plane from the vicinity of

pins 5 and 6. In other areas, use as much ground plane

as possible on one side of the board. It is especially

important to provide a ground return path for current from

the load resistor to the power supply bypass capacitors.

Ceramic capacitors of 0.01 to 0.1

µf (with short leads)

should be less than 0.15 inches from pins 1 and 9.

Larger tantalum capacitors should be placed within one

can be made directly from pins 9 and 1, but better supply

rejection and settling time are obtained if they are

separately bypassed as in figures 1 and 2. To prevent

signal distortion caused by reflections from impedance

mismatches, use terminated microstrip or coaxial cable

when the signal must traverse more than a few inches.

Since the pc board forms such an important part of the

circuit, much time can be saved if prototype boards of

any high frequency sections are built and tested early in

the design phase. Evaluation boards designed for either

inverting or non-inverting gains are available.

Distortion and Noise

frequency on the preceding page make it easy to predict

the distortion at any frequency given the output voltage of

power output in dBm. At the frequency of interest, its 2nd

two-tone third order intermodulation products. These

approximations are useful for P < -1dB compression levels.

Approximate noise figure can be determined for the

KH231 using the equivalent input noise graph on the

preceding page. The following equation can be used to

determine noise figure (F) in dB.

current. Beyond the breakpoint of the curves (i.e., where

they are flat), broadband noise figure equals spot noise fig-

ure, so

∆f should equal one (1) and V

read directly off the graph. Below the breakpoint, the noise

must be integrated and

∆f set to the appropriate bandwidth.

33

Ω

+15V

0.1

3.9

.01

Capactance in

µF

1

12

5

3,7

100

Ω

10

11

33

Ω

.01

0.1

3.9

-15V

9

+

-

KH231

6

49.9

Ω

A

R

R

v

f

g

= 1+

250

Ω

33

Ω

+15V

0.1

3.9

.01

Capactance in

µF

1

12

5

3,7

100

Ω

10

11

33

Ω

.01

0.1

3.9

-15V

9

+

-

KH231

6

100

Ω

250

Ω

A

R

R

v

f

g

= −













F

10log 1

V

iR

A

4kTR

f

n

2

n

2

f

2

v

2

s

=+

+

































∆