KH205

DATA SHEET

REV. 1A January 2004

5

Figure 4: Active Current Limit Circuit (50mA)

Controlling Bandwidth and Passband Response

In most applications, a feedback resistor value of 2k

Ω

will provide optimum performance; nonetheless, some

applications may require a resistor of some other value.

response peaking, which may lead to instability).

Conversely, large values of feedback resistance tend to

roll off the response.

The best settling time performance requires the use of an

external feedback resistor (use of the internal resistor

results in a 0.1% to 0.2% settling tail). The settling

performance may be improved slightly by adding a

capacitance of 0.4pF in parallel with the feedback

resistor (settling time specifications reflect performance

with an external feedback resistor but with no external

capacitance).

Noise Analysis

Approximate noise figure can be determined for the

KH205 using the Equivalent Input Noise plot on page 3

and the equations shown below.

Figure 5: Noise Figure Diagram and Equations

(Noise Figure is for the Network Inside this Box.)

Driving Cables and Capacitive Loads

When driving cables, double termination is used to

prevent reflections. For capacitive load applications, a

small series resistor at the output of the KH205 will

improve stability and settling performance.

Transmission Line Matching

One method for matching the characteristic impedance

appropriate resistor at the input or output of the amplifier.

Figure 6 shows typical inverting and non-inverting circuit

configurations for matching transmission lines.

Figure 6: Transmission Line Matching

Non-inverting gain applications:

loading caused by the transmission line,

or by parasitics.

Inverting gain applications:

The input and output matching resistors attenuate the

signal by a factor of 2, therefore additional gain is needed.

of the amplifier’s output impedance with frequency.

Dynamic Range (Intermods)

For RF applications, the KH205 specifies a third

A 2-Tone, 3rd Order IMD Intercept plot is found in

the Typical Performance Characteristics section.

The output power level is taken at the load. Third-order

harmonic

distortion

is

calculated

with

the

formula:

KH205

+

-

F

R

R

R

kT

i

V

R

Ri

RA

where R

RR

RR

A

R

R

s

n

s

n

n

p

f

i

pv

p

sn

sn

v

f

g

=+

+

⋅

+

+





































=

+

=+

10

1

4

1

2

2

2

22

22

log

;

Q3

(2N3906)

14.3k

Ω

Q4

(2N3904)

0.01

ΩF

0.01

ΩF

12

Ω

Q1

(MJE170)

Q2

(MJE180)

12

Ω

to pin 10

to pin 12

K

KH205

+

-

+

-