Note: All information contained in this data sheet has been carefully checked and is believed to be accurate as of the date of publication; however, this data sheet cannot be a “controlled document”. Current revisions, if any, to these
specifications are maintained at the factory and are available upon your request. We recommend checking the revision level before finalization of your design documentation.
© 2002 Elantec Semiconductor, Inc.
EL2125C
Features
• Voltage noise of only 0.83nV/√Hz
• Current noise of only 2.4pA/√Hz
• 200µV offset voltage
• 175MHz -3dB BW for A
V
=10
• Low supply current - 10mA
• SOT23 package available
• ±2.5V to ±15V operation
Applications
• Ultrasound input amplifiers
• Wideband instrumentation
• Communication equipment
• AGC & PLL active filters
• Wideband sensors
Ordering Information
Part No Package Tape & Reel Outline #
EL2125CW-T7 5-Pin SOT23 7” MDP0038
EL2125CW-T13 5-Pin SOT23 13” MDP0038
EL2125CS 8-Pin SO - MDP0027
EL2125CS-T7 8-Pin SO 7” MDP0027
EL2125CS-T13 8-Pin SO 13” MDP0027
General Description
The EL2125C is an ultra-low noise, wideband amplifier that runs on
half the supply current of competitive parts. It is intended for use in
systems such as ultrasound imaging where a very small signal needs to
be amplified by a large amount without adding significant noise. Its
low power dissipation enables it to be packaged in the tiny SOT23
package, which further helps systems where many input channels cre-
ate both space and power dissipation problems.
The EL2125C is stable for gains of 10 and greater and uses traditional
voltage feedback. This allows the use of reactive elements in the feed-
back loop, a common requirement for many filter topologies. It
operates from ±2.5V to ±15V supplies and is available in the 5-pin
SOT23 and 8-pin SO packages.
The EL2125C is fabricated in Elantec’s proprietary complementary
bipolar process, and is specified for operation from -45°C to +85°C.
Connection Diagrams
1
2
3
4
8
7
6
5
EL2125CS
(8-Pin SO)
1
2
3
5
4
EL2125CW
(5-Pin SOT23)
-
+
-+
VS+
IN-IN+
VS-
OUT
NC
IN-
IN+
VS-
NC
VS+
OUT
NC
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
March 20, 2002
2
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Absolute Maximum Ratings
(T
A
= 25°C)
V
S
+ to V
S
- 33V
Continuous Output Current 40mA
Any Input V
S
- - 0.3V to V
S
+ + 0.3V
Power Dissipation See Curves
Operating Temperature -45°C to +85°C
Storage Temperature -60°C to +150°C
Maximum Die Junction Temperature +150°C
Important Note:
All parameters having Min/Max specifications are guaranteed. Typ values are for information purposes only. Unless otherwise noted, all tests are at the
specified temperature and are pulsed tests, therefore: T
J
= T
C
= T
A
Electrical Characteristics
V
S
= ±5V, T
A
= 25°C, R
F
= 180Ω, R
G
= 20Ω, R
L
= 500Ω unless otherwise specified.
Parameter Description Conditions Min Typ Max Unit
DC Performance
V
OS
Input Offset Voltage (SO8) 0.2 2 mV
Input Offset Voltage (SOT23-5) 3mV
T
CVOS
Offset Voltage Temperature Coefficient 1.8 µV/°C
I
B
Input Bias Current -30 -22 µA
I
OS
Input Bias Current Offset 0.42µA
T
CIB
Input Bias Current Temperature Coefficient 0.09 µA/°C
C
IN
Input Capacitance 2.2 pF
A
VOL
Open Loop Gain 80 87 dB
PSRR Power Supply Rejection Ratio
[1]
80 97 dB
CMRR Common Mode Rejection Ratio at CMIR 80 106 dB
CMIR Common Mode Input Range -4.6 3.8 V
V
OUTH
Output Voltage Swing High No load, R
F
= 1kΩ3.5 3.65 V
V
OUTL
Output Voltage Swing Low No load, R
F
= 1kΩ-3.87 -3.7 V
V
OUTH2
Output Voltage Swing High R
L
= 100Ω33.3 V
V
OUTL2
Output Voltage Swing Low R
L
= 100Ω-3.5 -3 V
I
OUT
Output Short Circuit Current
[2]
80 100 mA
I
S
Supply Current 10.1 11 mA
AC Performance - R
G
= 20Ω, C
L
= 5pF
BW -3dB Bandwidth 175 MHz
BW ±0.1dB ±0.1dB Bandwidth 34 MHz
BW ±1dB ±1dB Bandwidth 150 MHz
Peaking Peaking 0.4 dB
SR Slew Rate V
OUT
= 2V
PP
, measured at 20% to 80% 150 185 V/µ s
OS Overshoot, 4Vpk-pk Output Square Wave Positive 0.6 %
Negative 2.7 %
t
S
Settling Time to 0.1% of ±1V Pulse 42 ns
V
N
Voltage Noise Spectral Density 0.83 nV/√Hz
I
N
Current Noise Spectral Density 2.4 pA/√Hz
HD2 2nd Harmonic Distortion
[3]
-74 dBc
HD3 3rd Harmonic Distortion
[4]
-91 dBc
1. Measured by moving the supplies from ±4V to ±6V
2. Pulse test only
3. Frequency = 1MHz, V
OUT
= 2Vpk-pk, into 500Ω and 5pF load
3
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Electrical Characteristics
V
S
= ±15V, T
A
= 25°C, R
F
= 180Ω, R
G
= 20Ω, R
L
= 500Ω unless otherwise specified.
Parameter Description Conditions Min Typ Max Unit
DC Performance
V
OS
Input Offset Voltage (SO8) 0.6 3 mV
Input Offset Voltage (SOT23-5) 3mV
T
CVOS
Offset Voltage Temperature Coefficient 4.9 µV/°C
I
B
Input Bias Current -30 -24 µA
I
OS
Input Bias Current Offset 0.4 2 µA
T
CIB
Input Bias Current Temperature Coefficient 0.08 µA/°C
C
IN
Input Capacitance 2.2 pF
A
VOL
Open Loop Gain 80 87 dB
PSRR Power Supply Rejection Ratio
[1]
80 97 dB
CMRR Common Mode Rejection Ratio at CMIR 75 105 dB
CMIR Common Mode Input Range -14.6 13.8 V
V
OUTH
Output Voltage Swing High No load, R
F
= 1kΩ13.35 13.5 V
V
OUTL
Output Voltage Swing Low No load, R
F
= 1kΩ-13.6 -13 V
V
OUTH2
Output Voltage Swing High R
L
= 100Ω11 11.6 V
V
OUTL2
Output Voltage Swing Low R
L
= 100Ω-10.4 -9.8 V
I
OUT
Output Short Circuit Current
[2]
120 250 mA
I
S
Supply Current 10.8 12 mA
AC Performance - R
G
= 20Ω, C
L
= 5pF
BW -3dB Bandwidth 220 MHz
BW ±0.1dB ±0.1dB Bandwidth 23 MHz
BW ±1dB ±1dB Bandwidth 63 MHz
Peaking Peaking 2.5 dB
SR Slew Rate V
OUT
= 2V
PP
, measured at 20% to 80% 180 225 V/µs
OS Overshoot, 4Vpk-pk Output Square Wave 0.6 %
t
S
Settling Time to 0.1% of ±1V Pulse 38 ns
V
N
Voltage Noise Spectral Density 0.95 nV/√Hz
I
N
Current Noise Spectral Density 2.1 pA/√Hz
HD2 2nd Harmonic Distortion
[3]
-73 dBc
HD3 3rd Harmonic Distortion
[4]
-96 dBc
1. Measured by moving the supplies from ±13.5V to ±16.5V
2. Pulse test only
3. Frequency = 1MHz, V
OUT
= 2Vpk-pk, into 500Ω and 5pF load
4
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Typical Performance Curves
Non-Inverting Frequency Response for Various R
F
5
-5
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Inverting Frequency Response for Various R
F
6
2
-2
-6
-10
-14
1M 10M 100M 300M
Frequency (Hz)
Normalized Gain (dB)
Inverting Frequency Response for Various R
F
6
2
-2
-6
-10
-14
1M 10M 100M 300M
Frequency (Hz)
Normalized Gain (dB)
Non-Inverting Frequency Response for Various R
F
5
0
-5
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
0
R
F
=1kΩR
F
=499Ω
R
F
=180Ω
R
F
=100Ω
R
F
=1kΩ
R
F
=180Ω
R
F
=700Ω
R
F
=100Ω
R
F
=499Ω
V
S
=±5V
A
V
=-10
R
L
=560Ω
C
L
=5pF
R
F
=1kΩ
R
F
=350Ω
R
F
=200Ω
R
F
=97.6Ω
R
F
=499ΩR
F
=1kΩ
R
F
=350Ω
R
F
=200Ω
R
F
=499Ω
R
F
=97.6Ω
V
S
=±5V
A
V
=10
R
L
=500Ω
C
L
=5pF
V
S
=±15V
A
V
=10
R
L
=500Ω
C
L
=5pF
-5
0
5
1M 10M 100M 200M
Frequency (Hz)
Normalized Gain (dB)
Non-Inverting Frequency Response vs Gain
V
S
=±5V
R
L
=500Ω
C
L
=5pF
R
G
=20Ω
-5
0
5
Normalized Gain (dB)
Non-Inverting Frequency Response for Various Gain
V
S
=±15V
R
L
=500Ω
C
L
=5pF
R
F
=700Ω
1M 10M 100M 200M
Frequency (Hz)
200M 300M
A
V
=50 A
V
=20
A
V
=10
A
V
=50
A
V
=20
A
V
=10
V
S
=±15V
A
V
=-10
R
L
=500Ω
C
L
=5pF
5
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Typical Performance Curves
6
Normalized Gain (dB)
Inverting Frequency Response vs Gain
2
-2
-6
-10
-14
0
6
Normalized Gain (dB)
Inverting Frequency Response vs Gain
1M 10M 100M 300M
Frequency (Hz)
-14
A
V
=-10
A
V
=-50
A
V
=-20
1M 10M 100M 300M
Frequency (Hz)
A
V
=-50 A
V
=-20
A
V
=-10
V
S
=±15V
R
L
=500Ω
C
L
=5pF
R
G
=50Ω
-5
5
Normalized Gain (dB)
Non-Inverting Frequency Response for Various Output
Signal Levels
0
-14
6
Normalized Gain (dB)
Inverting Frequency Response for Various Output Signal
Levels
0
1M 10M 100M 200M
Frequency (Hz)
V
S
=±5V
A
V
=10
R
F
=180Ω
R
L
= 500Ω
C
L
=5pF
2V
PP
4V
PP
30mV
PP
500mV
PP
1V
PP
1M 10M 100M 300M
Frequency (Hz)
V
S
=±5V
A
V
=-10
R
F
=350Ω
R
L
= 500Ω
C
L
=5pF
2.5V
PP
500mV
PP
3.3V
PP
250mV
PP
3mV
PP
5
Normalized Gain (dB)
Non-Inverting Frequency Response for Various C
L
3
1
-1
-3
0
5
Normalized Gain (dB)
Non-Inverting Frequency Response for Various C
L
-5
1M 10M 100M 200M
Frequency (Hz)
V
S
=±5V
A
V
=10
R
F
=180Ω
R
L
=500Ω
-5
1M 10M 100M 200M
Frequency (Hz)
V
S
=±5V
A
V
=10
R
F
=700Ω
R
L
=500Ω
1V
PP
C
L
=28.5pF
C
L
=16pF
C
L
=5pF
C
L
=1pF
C
L
=17pF
C
L
=11pF
C
L
=1.2pF
C
L
=5pF
V
S
=±5V
R
L
=500Ω
C
L
=5pF
R
G
=35Ω
6
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Typical Performance Curves
6
Normalized Gain (dB)
Inverting Frequency Response for Various C
L
0
6
Normalized Gain (dB)
Inverting Frequency Response for Various C
L
2
-2
-6
-10
1M 10M 100M 300M
Frequency (Hz)
-14
C
L
=29.4pF
C
L
=16.4pF
C
L
=11.4pF
C
L
=5.1pF
C
L
=1.2pF
V
S
=±5V
A
V
=10
R
F
=350Ω
R
L
=500Ω
-14
1M 10M 100M 300M
Frequency (Hz)
C
L
=29.4pF
C
L
=16.4pF
C
L
=11.4pF
C
L
=5.1pF
C
L
=1.2pF
V
S
=±15V
A
V
=10
R
F
=500Ω
R
L
=500Ω
Open Loop Gain (dB)
0
40
20
10k
Open Loop Gain and Phase
10M
60
80
100
100k 100M
Frequency (Hz)
1M
Phase (°)
-250
-50
-150
50
150
250
0
0
Supply Voltage (±V)
Supply Current (mA)
Supply Current vs Supply Voltage
4.8
12
2.4
31215
9.6
7.2
69
Peaking vs Supply Voltage
3
2.5
2
1.5
1
0.5
0
2 4 6 8 10 12 14 16
V
S
(±V)
Peaking (dB)
A
V
=10
A
V
=-10
A
V
=50A
V
=-50 A
V
=20A
V
=-20
3dB Bandwidth vs Supply Voltage
250
200
150
100
50
0
246810121416
V
S
(±V)
Bandwidth (MHz)
A
V
=10
A
V
=-10
A
V
=50 A
V
=-50A
V
=20A
V
=-20
400M
Gain
Phase
V
S
=±5V
7
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Typical Performance Curves
10ns/div
20mV/div
Small Signal Step Response Small Signal Step Response
V
IN
x2
V
O
V
S
=±5V
R
L
=500Ω
R
F
=180Ω
A
V
=10
C
L
=5pF
10ns/div
20mV/div
V
IN
x2
V
O
V
S
=±15V
R
L
=500Ω
R
F
=180Ω
A
V
=10
C
L
=5pF
Time (20ns/div)
Output Voltage (0.5V/div)
Large-Signal Step Response
V
S
=±5V
R
L
=500Ω
R
F
=180Ω
A
V
=10
C
L
=5pF
Time (20ns/div)
Output Voltage (0.5V/div)
Large-Signal Step Response
V
S
=±15V
R
L
=500Ω
R
F
=180Ω
A
V
=10
C
L
=5pF
1MHz Harmonic Distortion vs Output Swing
-40
-50
-60
-70
-90
-100
-110
067
V
OUT
(V
PP
)
Distortion (dBc)
1MHz Harmonic Distortion vs Output Swing
-30
-40
-60
-80
-90
-100
-110
05 25
V
OUT
(V
PP
)
Distortion (dBc)
45231
-80
V
S
=±5V
R
F
=180Ω
A
V
=10
R
L
=500Ω
2nd HD
3rd HD
V
S
=±15V
R
F
=180Ω
A
V
=10
R
L
=500Ω
10 15 20
-50
-70
2nd HD
3rd HD
8
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Typical Performance Curves
Voltage and Current Noise vs Frequency
100
10
1
0.1
10 100 1k 10k 100k
Frequency (Hz)
Voltage Noise (nV/√Hz), Current Noise (pA/√Hz)
V
N
, V
S
=±15V
I
N
, V
S
=±5V
I
N
, V
S
=±15V
V
N
, V
S
=±5V
Settling Time vs Accuracy
60
50
40
30
20
10
0
0.1 1 10
Accuracy (%)
Settling Time (ns)
V
S
=±15V
V
O
=5V
PP
V
S
=±5V
V
O
=5V
PP
V
S
=±15V
V
O
=2V
PP
V
S
=±5V
V
O
=2V
PP
Total Harmonic Distortion vs Frequency
-30
-60
-80
-90
1k 10k 100M
Frequency (Hz)
THD (dBc)
V
S
=±5V
V
O
=2V
PP
A
V
=10
R
F
=180Ω
R
L
=500Ω
100k 1M 10M
-40
-50
-70
-6
14
1400
Frequency (MHz)
Group Delay (ns)
Group Delay
2
10
6
-2
10 100
A
V
=20
A
V
=10
V
S
=±15V
-110
-10
10 100M
Frequency (Hz)
CMRR (dB)
CMRR
-70
-30
-50
-99
100 10M1k 10k 100k 1M
PSRR (dB)
10
50
30
10K
PSRR
10M
70
90
110
100K 100M
Frequency (Hz)
1M
PSRR-
PSRR+
600M
9
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Typical Performance Curves
Bandwidth vs Temperature
200
160
40
0
-40 160
Temperature (°C)
-3dB Bandwidth (MHz)
120
80
80040 120
3.5
3
2.5
1.5
2
1
0.5
0
Peaking (dB)
Bandwidth
Peaking
R
OUT
(Ω)
0.001
0.1
0.01
10k
Closed Loop Output Impedance vs Frequency
1
10
100
Frequency (Hz)
100M100k 1M 10M
Slew Rate (V/µs)
100
200
150
0
Slew Rate vs Swing
250
300
350
V
OUT
Swing (V
PP
)
2051015
5V
SR
-
15V
SR
+
15V
SR
-
5V
SR
+
13
12
11
9
10
0
-1
-2
-3
Supply Current vs Temperature
-50 0 100 15050
Die Temperature (°C)
I
S
(mA)
V
S
=±5V
V
S
=±15V
Offset Voltage vs Temperature
-50 0 100 15050
Die Temperature (°C)
V
S
=±5V
V
S
=±15V
V
OS
(mV)
Input Bias Current vs Temperature
-50 0 100 15050
Die Temperature (°C)
I
B
+ (µA)
-10
-15
-20
-25
-30
10
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Typical Performance Curves
120
100
80
60
110
100
90
80
CMRR vs Temperature
-50 0 100 15050
Die Temperature (°C)
CMRR (dB)
V
S
=±5V
V
S
=±15V
PSRR vs Temperature
-50 0 100 15050
Die Temperature (°C)
PSRR (dB)
V
S
=±5V
V
S
=±15V
240
220
200
180
160
Slew Rate vs Temperature
-50 0 100 15050
Die Temperature (°C)
SR (V/µs)
V
S
=±5V
V
S
=±15V
V
O
=2V
PP
3.9
3.7
3.6
3.5
3.8
Positive Output Swing vs Temperature
-50
Die Temperature (°C)
V
OUTH
(V)
010015050
V
S
=±5V
13.6
13.5
13.4
-9.75
-9.8
-9.85
-9.9
-9.95
Positive Output Swing vs Temperature
-50
Die Temperature (°C)
010015050
V
OUTH
(V)
V
S
=±15V
Negative Output Swing vs Temperature
-50
Die Temperature (°C)
V
OUTL
(V)
010050
V
S
=±5V
11
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Typical Performance Curves
-13.4
-13.5
-13.6
-13.7
-3.42
-3.44
-3.46
-3.48
-3.5
-3.52
-9.6
-9.8
-10
-10.2
-10.4
-10.6
-10.8
Negative Output Swing vs Temperature
-50
Die Temperature (°C)
V
OUTL
(V)
010015050
V
S
=±15V
Loaded Negative Output Swing vs Temperature
-50
Die Temperature (°C)
V
OUTL2
(V)
010015050
V
S
=±5V
Negative Output Swing vs Temperature
-50
Die Temperature (°C)
V
OUTL2
(V)
010015050
V
S
=±15V
3.35
3.3
3.25
12
11.8
11.6
11.4
11.2
11
Loaded Positive Output Swing vs Temperature
-50
Die Temperature (°C)
V
OUTH2
(V)
010015050
V
S
=±5V
Loaded Positive Output Swing vs Temperature
-50
Die Temperature (°C)
V
OUTH2
(V)
010015050
V
S
=±15V
1.2
0.6
0
Package Power Dissipation vs Ambient Temperature
JEDEC JESD51-3 Low Effective Thermal Conductivity Test Board
0
Ambient Temperature (°C)
Power Dissipation (W)
25 125 15075
1
0.4
0.8
0.2
10050 85
488mW
781mW
θ
JA
=160°C/W
SO8
θ
JA
=256°C/W
SOT23-5
12
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Typical Performance Curves
1.8
0.8
0
1.6
0.4
1.2
0.2
0.6
1.4
1
Package Power Dissipation vs Ambient Temperature
JEDEC JESD51-7 High Effective Thermal Conductivity Test Board
0
Ambient Temperature (°C)
Power Dissipation (W)
25 125 15075 10050 85
543mW
θ
JA
=110°C/W
SO8
1.136W
θ
JA
=230°C/W
SOT23-5
13
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Pin Descriptions
EL2125CW
(5-Pin SOT23)
EL2125CS
(8-Pin SO) Pin Name Pin Function Equivalent Circuit
1 6 VOUT Output
Circuit 1
2 4 VS- Supply
3 3 VINA+ Input
Circuit 2
4 2 VINA- Input Reference Circuit 2
5 7 VS+ Supply
V
OUT
V
S
+
V
IN
-V
IN
+
V
S
+
V
S
-
14
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
Applications Information
Product Description
The EL2125C is an ultra-low noise, wideband mono-
lithic operational amplifier built on Elantec's proprietary
high speed complementary bipolar process. It features
0.83nV/√Hz input voltage noise, 200µV offset voltage,
and 73dB THD. It is intended for use in systems such as
ultrasound imaging where very small signals are needed
to be amplified. The EL2125C also has excellent DC
specifications: 200µV V
OS
, 22µ A IB, 0.4µA I
OS
, and
106dB CMRR. These specifications allow the EL2125C
to be used in DC-sensitive applications such as differ-
ence amplifiers.
Gain-Bandwidth Product
The EL2125C has a gain-bandwidth product of 800MHz
at ±5V. For gains greater than 20, its closed-loop -3dB
bandwidth is approximately equal to the gain-bandwidth
product divided by the small signal gain of the circuit.
For gains less than 20, higher-order poles in the ampli-
fier's transfer function contribute to even higher closed-
loop bandwidths. For example, the EL2125C has a -3dB
bandwidth of 175MHz at a gain of 10 and decreases to
40MHz at gain of 20. It is important to note that the extra
bandwidth at lower gain does not come at the expenses
of stability. Even though the EL2125C is designed for
gain > 10 with external compensation, the device can
also operate at lower gain settings. The RC network
shown in Figure 1 reduces the feedback gain at high fre-
quency and thus maintains the amplifier stability. R
values must be less than RF divided by 9 and 1 divided
by 2
π
RC must be less than 400MHz.
Choice of Feedback Resistor, RF
The feedback resistor forms a pole with the input capac-
itance. As this pole becomes larger, phase margin is
reduced. This increases ringing in the time domain and
peaking in the frequency domain. Therefore, RF has
some maximum value which should not be exceeded for
optimum performance. If a large value of RF must be
used, a small capacitor in the few pF range in parallel
with RF can help to reduce this ringing and peaking at
the expense of reducing the bandwidth. Frequency
response curves for various RF values are shown the in
typical performance curves section of this data sheet.
Noise Calculations
The primary application for the EL2125C is to amplify
very small signals. To maintain the proper signal-to-
noise ratio, it is essential to minimize noise contribution
from the amplifier. Figure 2 below shows all the noise
sources for all the components around the amplifier.
V
N
is the amplifier input voltag e noise
I
N
+ is the amplifier positive input cu r r ent noise
I
N
- is the ampli fie r ne gative input curre nt noise
V
RX
is the thermal noise associated with each resistor:
where:
- k is Boltzmann's constant = 1.380658 x 10
-23
- T is temperature in degrees Kelvin (273+ °C)
-
+
R
F
R
C
V
IN
V
OUT
Figure 1.
-
+V
ON
V
IN
I
N
+
I
N
-
R
2
R
3
R
1
V
N
V
R3
V
R2
V
R1
Figure 2.
V
RX
4kTRx=
15
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
The total noise due to the amplifier seen at the output of
the amplifier can be calculated by using the following
equation:
As the above equation shows, to keep noise at a mini-
mum, small resistor values should be used. At higher
amplifier gain configuration where R
2
is reduced, the
noise due to IN-, R
2
, and R
1
decreases and the noise
caused by IN+, VN, and R
3
starts to dominate. Because
noise is summed in a root-mean-squares method, noise
sources smaller than 25% of the largest noise source can
be ignored. This can greatly simplify the formula and
make noise calculation much easier to calculate.
Output Drive Capability
The EL2125C is designed to drive low impedance load.
It can easily drive 6V
P-P
signal into a 100Ω load. This
high output drive capability makes the EL2125C an
ideal choice for RF, IF, and video applications. Further-
more, the EL2125C is current-limited at the output,
allowing it to withstand momentary short to ground.
However, the power dissipation with output-shorted
cannot exceed the power dissipation capability of the
package.
Driving Cables and Capacitive Loads
Although the EL2125C is designed to drive low imped-
ance load, capacitive loads will decreases the amplifier's
phase margin. As shown the in the performance curves,
capacitive load can result in peaking, overshoot and pos-
sible oscillation. For optimum AC performance,
capacitive loads should be reduced as much as possible
or isolated with a series resistor between 5Ω to 20Ω.
When driving coaxial cables, double termination is
always recommended for reflection-free performance.
When properly terminated, the capacitance of the coax-
ial cable will not add to the capacitive load seen by the
amplifier.
Power Supply Bypassing And Printed Circuit
Board Layout
As with any high frequency devices, good printed circuit
board layout is essential for optimum performance.
Ground plane construction is highly recommended.
Lead lengths should be kept as short as possible. The
power supply pins must be closely bypassed to reduce
the risk of oscillation. The combination of a 4.7µF tanta-
lum capacitor in parallel with 0.1µF ceramic capacitor
has been proven to work well when placed at each sup-
ply pin. For single supply operation, where pin 4 (V
S
-) is
connected to the ground plane, a single 4.7µF tantalum
capacitor in parallel with a 0.1µF ceramic capacitor
across pins 7 (V
S
+) and pin 4 (V
S
-) will suffice.
For good AC performance, parasitic capacitance should
be kept to a minimum. Ground plane construction again
should be used. Small chip resistors are recommended to
minimize series inductance. Use of sockets should be
avoided since they add parasitic inductance and capaci-
tance which will result in additional peaking and
overshoot.
Supply Voltage Range and Single Supply
Operation
The EL2125C has been designed to operate with supply
voltage range of ±2.5V to ±15V. With a single supply,
the EL2125C will operate from +5V to +30V. Pins 4 and
7 are the power supply pins. The positive power supply
is connected to pin 7. When used in single supply mode,
pin 4 is connected to ground. When used in dual supply
mode, the negative power supply is connected to pin 4.
As the power supply voltage decreases from +30V to
+5V, it becomes necessary to pay special attention to the
input voltage range. The EL2125C has an input voltage
range of 0.4V from the negative supply to 1.2V from the
positive supply. So, for example, on a single +5V sup-
ply, the EL2125C has an input voltage range which
spans from 0.4V to 3.8V. The output range of the
EL2125C is also quite large, on a +5V supply, it swings
from 0.4V to 3.6V.
V
ON
BW=VN
2
1
R
1
R
2
------
+
2
×IN-
2
R
1
2
IN+
2
R
3
2
1
R
1
R
2
------
+
2
××+×4KTR
1
4KTR
2
R
1
R
2
------
2
××××+××× 4KTR
3
1
R
1
R
2
------
+
2
××××++ +
×
16
EL2125C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2125C
General Disclaimer
Specifications contained in this data sheet are in effect as of the publication date shown. Elantec, Inc. reserves the right to make changes in the cir-
cuitry or specifications contained herein at any time without notice. Elantec, Inc. assumes no responsibility for the use of any circuits described
herein and makes no representations that they are free from patent infringement.
WARNING - Life Support Policy
Elantec, Inc. products are not authorized for and should not be used
within Life Support Systems without the specific written consent of
Elantec, Inc. Life Support systems are equipment intended to sup-
port or sustain life and whose failure to perform when properly used
in accordance with instructions provided can be reasonably
expected to result in significant personal injury or death. Users con-
templating application of Elantec, Inc. Products in Life Support
Systems are requested to contact Elantec, Inc. factory headquarters
to establish suitable terms & conditions for these applications. Elan-
tec, Inc.’s warranty is limited to replacement of defective
components and does not cover injury to persons or property or
other consequential damages.
March 20, 2002
Printed in U.S.A.
Elantec Semiconductor, Inc.
675 Trade Zone Blvd.
Milpitas, CA 95035
Telephone: (408) 945-1323
(888) ELANTEC
Fax: (408) 945-9305
European Office: +44-118-977-6020
Japan Technical Center: +81-45-682-5820
