KH205
+V
cc
R
c
12Ω
Q1
(MJE170)
0.01ΩF
DATA SHEET
Q3
(2N3906)
2
R
2
i
i2
R
s
R
s
2
V
n
f
F
=
10 log
1
+
+
⋅
i
n
+
+
2
2
R
n
4 kT
R
p
R
p
A
2
v
where R
p
=
R
s
R
n
;
R
s
+
R
n
A
v
=
R
f
R
g
+
1
to pin 12
to pin 10
0.01ΩF
R
x
14.3kΩ
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
(Z
o
) of a transmission line or cable is to place the
appropriate resistor at the input or output of the amplifier.
Figure 6 shows typical inverting and non-inverting circuit
configurations for matching transmission lines.
R
1
V
1
+
-
R
4
V
2
+
-
Z
0
Z
0
R
3
R
2
R
g
R
5
C
6
+
Q2
(MJE180)
R
c
12Ω
-V
cc
Q4
(2N3904)
Figure 4: Active Current Limit Circuit (50mA)
Controlling Bandwidth and Passband Response
K
In most applications, a feedback resistor value of 2kΩ
will provide optimum performance; nonetheless, some
applications may require a resistor of some other value.
The response versus R
f
plot on the previous page shows
how decreasing R
f
will increase bandwidth (and frequency
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.
kT = 4.00 x 10 Joules at 290°K
V
n
is spot noise voltage (V/√Hz)
i
n
is non-inverting spot noise current (A/√Hz)
i
i
is inverting spot noise current (A/√Hz)
-21
Z
0
R
6
KH205
-
V
o
R
7
R
f
Figure 6: Transmission Line Matching
Non-inverting gain applications:
s
s
s
Connect R
g
directly to ground.
Make R
1
, R
2
, R
6
, and R
7
equal to Z
o
.
Use R
3
to isolate the amplifier from reactive
loading caused by the transmission line,
or by parasitics.
Inverting gain applications:
s
s
s
Connect R
3
directly to ground.
Make the resistors R
4
, R
6
, and R
7
equal to Z
o
.
Make R
5
II R
g
= Z
o
.
The input and output matching resistors attenuate the
signal by a factor of 2, therefore additional gain is needed.
Use C
6
to match the output transmission line over a
greater frequency range. C
6
compensates for the increase
of the amplifier’s output impedance with frequency.
Dynamic Range (Intermods)
For RF applications, the KH205 specifies a third
order intercept of 30dBm at 60MHz and P
o
= 10dBm.
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:
HD3
rd
= 2
•
(IP3
o
– P
o
)
R
s
R
n
+
KH205
R
o
-
R
f
R
g
REV. 1A January 2004
5
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
