kh205 Fairchild Semiconductor, kh205 Datasheet - Page 5

• Manufacturer Part Number: kh205
• Description: Overdrive-protected Wideband Op Amp
• Manufacturer: Fairchild Semiconductor

KH205
Controlling Bandwidth and Passband Response
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
how decreasing R
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.
REV. 1A February 2001
Figure 4: Active Current Limit Circuit (50mA)
kT = 4.00 x 10
V
i
i
n
i
n
is inverting spot noise current (A/√Hz)
is non-inverting spot noise current (A/√Hz)
is spot noise voltage (V/√Hz)
R
(MJE170)
(MJE180)
s
to pin 12
to pin 10
f
will increase bandwidth (and frequency
12Ω
12Ω
Q1
Q2
R
R
-21
R
c
c
+V
-V
n
f
cc
cc
Joules at 290°K
plot on the previous page shows
R
KH205
g
+
-
0.01ΩF
0.01ΩF
R
f
Q3
(2N3906)
R
14.3kΩ
Q4
(2N3904)
x
R
o
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
appropriate resistor at the input or output of the amplifier.
Figure 6 shows typical inverting and non-inverting circuit
configurations for matching transmission lines.
Non-inverting gain applications:
Inverting gain applications:
The input and output matching resistors attenuate the
signal by a factor of 2, therefore additional gain is needed.
Use C
greater frequency range. C
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
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
formula:
F
where R
V
V
1
2
(Noise Figure is for the Network Inside this Box.)
=
o
) of a transmission line or cable is to place the
+
+
Figure 5: Noise Figure Diagram and Equations
-
-
10
s
s
s
s
s
s
R
R
log
6
1
4
Connect R
Make R
Use R
loading caused by the transmission line,
or by parasitics.
Connect R
Make the resistors R
Make R
Figure 6: Transmission Line Matching
p
to match the output transmission line over a





=
1
+
R
distortion
3
HD3
R R
Z
Z
R
R
0
0
s
1
5
to isolate the amplifier from reactive
s
, R
s
n
II R
+
g
3
rd
+
R
2
n
directly to ground.
directly to ground.
, R
4
g
= 2
R
n
R
R
kT
= Z
2
5
R
R
s
;
6
3
g
, and R
•
⋅
o
A
(IP3




6
.
is
i
v
compensates for the increase
+
2
n
4
-
KH205
, R
=
o
+
R
f
7
– P
R
calculated
R
R
6
V
equal to Z
, and R
g
n
f
2
p
2
o
+
)
+
1
C
R
R
6
6
R
2
p
7
2
f
equal to Z
A
i
o
2
i
.
2
v
o
Z
DATA SHEET
with
0




= 10dBm.





o
R
.
the
7
V
5
o