www.fairchildsemi.com
KH205
Overdrive-Protected Wideband Op Amp
Features
s
s
s
s
s
s
s
General Description
The KH205 is a wideband overdrive-protected opera-
tional amplifier designed for applications needing
both speed and low power operation. Utilizing a
well-established current feedback architecture, the
KH205 exhibits performance far beyond that of
conventional voltage feedback op amps. For example,
the KH205 has a bandwidth of 170MHz at a gain of
+20 and settles to 0.1% in 22ns. Plus, the KH205 has
a combination of important features not found in
other high-speed op amps.
For example, the KH205 has been designed to consume
little power – 570mW at ±15V supplies. The result is
lower power supply requirements and less system-
level heat dissipation. In addition, the device can be
operated on supply voltages as low as ±5V for even
lower power dissipation.
Complete overdrive protection has been designed
into the part. This is critical for applications, such as
ATE and instrumentation, which require protection
from signal levels high enough to cause saturation of
the amplifier. This feature allows the output of the
op amp to be protected against short circuits using
techniques developed for low-speed op amps. With
this capability, even the fastest signal sources can
feature effective short circuit protection.
The KH205 is constructed using thin film resistor/bipolar
transistor technology, and is available in the following
versions:
KH205AI
KH205AK
Supply
Voltage
-V
CC
10
-3dB bandwidth of 170MHz
0.1% settling in 22ns
Complete overdrive protection
Low power: 570mW (190mW at ±5V)
3MΩ input resistance
Output may be current limited
Direct replacement for CLC205
Applications
s
s
s
s
s
s
s
Fast, precision A/D conversion
Automatic test equipment
Input/output amplifiers
Photodiode, CCD preamps
IF processors
High-speed modems, radios
Line drivers
Large Signal Pulse Response
A
v
= +20
Output Voltage (2V/div)
A
v
= -20
Time (5ns/div)
Bottom View
Internal
Feedback
Case
ground
GND
7
R
f
8
-V
CC
9
Collector
Supply
Output
-25°C to +85°C
-55°C to +125°C
-55°C to +125°C
KH205AM
2000Ω
Non-Inverting
Input
Inverting
Input
Not
Connected
V+ 6
+
V- 5
NC 4
3
2
NC
6
6
-
11 V
o
12
+V
CC
KH205HXC
KH205HXA
-55°C to +125°C
-55°C to +125°C
12-pin TO-8 can
12-pin TO-8 can, features
burn-in & hermetic testing
12-pin TO-8 can,
environmentally
screened and electrically
tested to MIL-STD-883
SMD#: 5962-9083501HXC
SMD#: 5962-9083501HXA
Collector
Supply
1
+V
CC
Supply
Voltage
Typical Performance
Gain Setting
Parameter
+7 +20 +50
-1
-20 -50
Units
MHz
ns
V/ns
ns
-3dB bandwidth
220 170 80 220 130 80
rise time
1.7 2.2 4.7 1.7 2.9 4.7
slew rate
2.4 2.4 2.4 2.4 2.4 2.4
settling time (to 0.1%) 22 22 20 21 20 19
Case and
bias ground
GND
Not Connected
Pin 8 provides access to a 2000Ω feed-
back resistor which can be connected to
the output or left open if an external feed-
back resistor is desired.
REV. 1A February 2001
DATA SHEET
KH205
KH205 Electrical Characteristics
PARAMETERS
Ambient Temperature
Ambient Temperature
FREQUENCY DOMAIN RESPONSE
✝
-3dB bandwidth
large-signal bandwidth
gain flatness
✝
peaking
✝
peaking
✝
rolloff
group delay
linear phase deviation
TIME DOMAIN RESPONSE
rise and fall time
settling time to 0.1%
to 0.05%
overshoot
slew rate
NOISE AND DISTORTION RESPONSE
✝
2nd harmonic distortion
✝
3rd harmonic distortion
equivalent input noise
voltage
inverting current
non-inverting current
noise floor
integrated noise
noise floor
integrated noise
STATIC, DC PERFORMANCE
* input offset voltage
average temperature coefficient
* input bias current
average temperature coefficient
* input bias current
average temperature coefficient
* power supply rejection ratio
common mode rejection ratio
* supply current
MISCELLANEOUS PERFORMANCE
non-inverting input resistance
non-inverting input capacitance
output impedance
output voltage range
internal feedback resistor
absolute tolerance
temperature coefficient
inverting input current self limit
KH205AI
(A
v
= +20V, V
CC
= ±15V, R
L
= 200Ω, R
f
= 2kΩ; unless specified)
TYP
+25°C
+25°C
170
100
0
0
–
3.0 ± .2
0.8
2.2
4.8
22
24
7
2.4
-57
-68
2.1
22
4.8
-157
39
-157
39
3.5
11
3.0
15
2.0
20
69
60
19
3.0
5.0
–
±12
–
–
2.2
MIN & MAX RATINGS
-55°C
-55°C
>140
>72
<0.3
<0.5
<0.8
–
<3.0
<2.6
<5.5
<27
<30
<14
>1.8
<-50
<-55
<3.0
<30
<6.5
<-154
<55
<-154
<55
<8.0
<25
<25
<100
<22
<150
>55
>50
<20
>1.0
<7.0
<0.1
>±11
–
–
<3.0
+25°C
+25°C
>140
>80
<0.3
<0.5
<0.8
–
<2.0
<2.6
<5.5
<27
<30
<14
>2.0
<-50
<-55
<3.0
<30
<6.5
<-154
<55
<-154
<55
<8.0
<25
<15
<100
<10
<150
>55
>50
<20
>1.0
<7.0
<0.1
>±11
<0.2
-100 ±40
<3.0
+125°C
+125°C
>125
>80
<0.5
<0.8
<0.8
–
<3.0
<3.0
<5.5
<27
<30
<14
>2.0
<-50
<-55
<3.5
<35
<7.5
<-153
<61
<-153
<61
<11.0
<25
<15
<100
<25
<150
>55
>50
<22
>1.0
<7.0
<0.1
>±11
–
–
<3.2
MHz
MHz
dB
dB
dB
ns
°
ns
ns
ns
ns
%
V/ns
dBc
dBc
nV/√Hz
pA/√Hz
pA/√Hz
dBm(1Hz)
µV
dBm(1Hz)
µV
mV
µV/°C
µΑ
nA/°C
µA
nA/°C
dB
dB
mA
MΩ
pF
Ω
V
%
ppm/°C
mA
SSBW
FPBW
GFPL
GFPH
GFR
GD
LPD
TRS
TRL
TS
TSP
OS
SR
HD2
HD3
VN
ICN
NCN
SNF
INV
SNF
INV
VIO
DVIO
IBN
DIBN
IBI
DIBI
PSRR
CMRR
ICC
RIN
CIN
RO
VO
RFA
RFTC
ICL
UNITS
SYM
CONDITIONS
KH205AK/AM/HXC/HXA
V
o
= <2V
pp
V
o
= <10V
pp
V
o
= <2V
pp
0.1 to 35MHz
>35MHz
at 70MHz
to 70MHz
to 70MHz
2V step
10V step
10V step, note 2
10V step, note 2
5V step
20V
pp
at 50MHz
2V
pp
, 20MHz
2V
pp
, 20MHz
>100kHz
>100kHz
>100kHz
>100kHz
1kHz to 150MHz
>5MHz
5MHz to 150MHz
non-inverting
inverting
no load
DC
70MHz
DC
no load
Min/max ratings are based on product characterization and simulation. Individual parameters are tested as noted. Outgoing quality levels are
determined from tested parameters.
Absolute Maximum Ratings
V
CC
±20V
±75mA
I
o
common mode input voltage
±(|V
CC
| -1)V
differential input voltage
±3V
thermal resistance
(see thermal model)
operating temperature
AI: -25°C to +85°C
AK/AM/HXC/HXA: -55°C to +125°C
sample tested storage temperature
-65°C to +150°C
lead temperature (soldering 10s)
+300°C
Recommended Operating Conditions
V
CC
I
o
common mode input voltage
gain range
note 1:
* AI/AK/AM/HXC/HXA
✝
AK/AM/HXC/HXA
±5V to ±15V
±50mA
±(|V
CC
| -5)V
+7 to +50, -1 to -50
note 2:
100% tested at +25°C
100% tested at +25°C and
at -55°C and +125°C
✝
AI
sample tested at +25°C
Settling time specifications require the use of an
external feedback resistor (2Ω)
REV. 1A February 2001
2
KH205
DATA SHEET
KH205 Typical Performance Characteristics
(T
A
= +25°C, A
v
= +20, V
CC
= ±15V, R
L
= 200Ω; unless specified)
Non-Inverting Frequency Response
Normalized Magnitude (1dB/div)
Normalized Magnitude (1dB/div)
Inverting Frequency Response
Frequency Response vs. External R
f
A
v
= +50
R
f
= 1.5kΩ
R
f
= 2kΩ
R
f
= 3kΩ
R
f
= 1.5kΩ
A
v
= +20
R
f
= 3kΩ
R
f
= 2kΩ
Gain
A
v
= +20
A
v
= +50
Phase
A
v
= +50
A
v
= +20
A
v
= +7
A
v
= -7
Phase
A
v
= -50
A
v
= -20
A
v
= -7
A
v
= -50
A
v
= -20
A
v
= -1
Relative Gain (5dB/div)
A
v
= +7
Gain
A
v
= -1
Phase (45°/div)
Phase (45°/div)
R
f
= 1.5kΩ
R
f
= 2kΩ
A
v
= +7
R
f
= 3kΩ
0
20
40
60
80 100 120 140 160 180 200
0
20
40
60
80 100 120 140 160 180 200
0
20
40
60
80 100 120 140 160 180 200
Frequency (MHz)
Large Signal Gain and Phase
V
o
= 10V
pp
Frequency (MHz)
Relative Bandwidth vs. V
CC
1.0
0.9
Gain
Frequency (MHz)
Gain and Phase for Various Loads
R
L
= 50Ω
R
L
= 100Ω
R
L
= 200Ω
R
L
= 1kΩ
Magnitude (1dB/div)
Gain
0.8
0.7
0.6
0.5
0.4
0.3
0.2
Magnitude (1dB/div)
Relative Bandwidth
Phase (45°/div)
Phase (45°/div)
Phase
Phase
R
L
= 1kΩ
R
L
= 200Ω
R
L
= 100Ω
R
L
= 50Ω
0
15
30
45
60
75
90 105 120 135 150
4
6
8
10
12
14
16
0
20
40
60
80 100 120 140 160 180 200
Frequency (MHz)
Small Signal Pulse Response
Output Voltage (0.4V/div)
±V
CC
(V)
Large Signal Pulse Response
0.20
A
v
= +20
Frequency (MHz)
Settling Time
0.15
10V step
R
f
= 2kΩ (external)
Output Voltage (2V/div)
A
v
= +20
Settling Error (%)
A
v
= -20
0.10
0.05
0
-0.05
-0.10
-0.15
-0.20
A
v
= -20
Time (5ns/div)
Time (5ns/div)
Time (5ns/div)
2nd and 3rd Harmonic Distortion
-30
-35
-40
V
o
= 2V
pp
2-Tone 3rd Order Intermodulation Intercept
45
40
100
CMRR and PSRR
PSRR and CMRR (dB)
80
PSRR
Distortion (dBc)
-45
-50
-55
-60
-65
-70
-75
-80
1
10
100
3rd
2nd
Intercept (dBm)
35
30
25
20
0
20
40
60
80
100
60
40
20
0
CMRR
100
1k
10k
100k
1M
10M
100M
Frequency (MHz)
Equivalent Input Noise
100
100
200°C/W
T
j(pnp)
P
pnp
Frequency (MHz)
Frequency (Hz)
T
case
Thermal Model
200°C/W
T
j(npn)
P
npn
17.5
°
C/W
T
j(circuit)
P
circuit
+
-
T
ambient
θ
ca
Noise Voltage (nV/√Hz)
Noise Current (pA/√Hz)
Inverting Current 18.3 pA/√Hz
10
10
P
circuit
= [(+V
CC
) – (-V
CC
)]
2
/ 1.77kΩ
P
xxx
= [(±V
CC
) – V
out
(% duty cycle)
–
Non-Inverting Current 2.5 pA/√Hz
(I
col
) (R
col
+ 6)]
(I
col
)
I
col
= V
out
/R
load
or 3mA, whichever is greater.
(Include feedback R in R
load
.)
R
col
is a resistor (33Ω recommended) between the
xxx collector and ±V
CC
.
T
j (pnp)
= P
pnp
(200 +
θ
ca
) + (P
cir
+ P
npn
)θ
ca
+ T
a
,
similar for T
j (npn)
.
T
j (cir)
= P
cir
(17.5 +
θ
ca
) + (P
pnp
+ P
npn
)θ
ca
+ T
a
.
Voltage 1.8 nV/√Hz
0
100
1k
10k
100k
1M
100
0
100M
(For positive V
o
and V
CC
, this is the power in the
npn output stage.)
(For negative V
o
and V
CC
, this is the power in the
pnp output stage.)
Frequency (Hz)
REV. 1A February 2001
3
DATA SHEET
KH205
Current Feedback Amplifiers
Some of the key features of current feedback technology
are:
s
Independence of AC bandwidth and voltage gain
s
Adjustable frequency response with feedback resistor
s
High slew rate
s
Fast settling
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.
V
o
A
v
=
V
in
1
+
R
f
Z
(
j
ω
)
where:
s
s
s
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:
R
C
=
V
C
−
R
I
I
I
Equation 1
where I
I
is the desired limit current and R
I
is the minimum
expected load resistance (0Ω for a short to ground).
Bypass capacitors of 0.01µF on should be used on the
collectors as in Figures 2 and 3.
+15V
3.9
33Ω
.1
6
1
12
8
10
3,7
9
11
A
v
is the closed loop DC voltage gain
R
f
is the feedback resistor
Z(jω) is the CLC205’s open loop transimpedance
gain
Z
(
j
ω
)
is the loop gain
R
f
Capactance in
µF
.01
V
in
R
i
50Ω
R
g
+
-
s
KH205
5
V
o
200Ω
The denominator of Equation 1 is approximately equal to
1 at low frequencies. Near the -3dB corner frequency, the
interaction between R
f
and Z(jω) dominates the circuit
performance. The value of the feedback resistor has a
large affect on the circuits performance. Increasing R
f
has the following affects:
s
s
s
s
s
-15V
3.9
.1
33Ω
.01
R
f
R
g
R
f
= 2000Ω (internal)
A
v
=
1
+
Decreases loop gain
Decreases bandwidth
Reduces gain peaking
Lowers pulse response overshoot
Affects frequency response phase linearity
Figure 2: Recommended Non-Inverting Gain Circuit
33Ω
.1
50Ω
6
1
12
8
10
3,7
9
11
+15V
3.9
Capactance in
µF
.01
Overdrive Protection
Unlike most other high-speed op amps, the KH205 is not
damaged by saturation caused by overdriving input
signals (where V
in
x gain > max. V
o
). The KH205 self
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.
differential protection
V
in
+
-
V
in
R
i
-15V
R
g
5
KH205
V
o
200Ω
33Ω
3.9
.1
.01
A
v
=
-R
f
R
g
R
f
= 2000Ω (internal)
For Z
in
= 50Ω, select R
g
||R
i
= 50Ω
Figure 3: Recommended Inverting Gain Circuit
A more sophisticated current limit circuit which provides
a limit current independent of R
I
is shown in Figure 4 on
page 5.
With the component values indicated, current limiting
occurs at 50mA. For other values of current limit (I
I
),
select R
C
to equal V
be
/l
I
. Where V
be
is the base to
emitter voltage drop of Q3 (or Q4) at a current of [2V
CC
–
1.4] / R
x
, where R
x
≤
[(2V
CC
– 1.4) / I
I
] B
min
.
Also, B
min
is the minimum beta of Q1 (or Q2) at a current
of I
I
. Since the limit current depends on V
be
, which is
temperature dependent, the limit current is
likewise temperature dependent.
REV. 1A February 2001
+
KH205
V
o
-V
cc
R
g
+V
cc
-
common mode
protection
Figure 1: Diode Clamp Circuits for Common Mode
and Differential Mode Protection
4
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
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 February 2001
5
