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.
EL2126C
Features
• Voltage noise of only 1.3nV/√Hz
• Current noise of only 1.2pA/√Hz
• 200µV offset voltage
• 100MHz -3dB BW for A
V
=10
• Very low supply current - 4.7mA
• SOT23 package
• ±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 #
EL2126CW-T7 5-Pin SOT23 7” MDP0038
EL2126CW-T13 5-Pin SOT23 13” MDP0038
EL2126CS 8-Pin SO - MDP0027
EL2126CS-T7 8-Pin SO 7” MDP0027
EL2126CS-T13 8-Pin SO 13” MDP0027
General Description
The EL2126C 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 EL2126C 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 5-pin SOT23
and 8-pin SO packages.
The EL2126C is fabricated in Elantec’s proprietary complementary
bipolar process, and is specified for operation over the full -40°C to
+85°C temperature range.
Connection Diagrams
1
2
3
4
8
7
6
5
EL2126C
(8-Pin SO)
1
2
3
5
4
EL2126C
(5-Pin SOT23)
-
+
-+
VS+
IN-IN+
VS-
OUT
NC
IN-
IN+
VS-
NC
VS+
OUT
NC
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
March 15, 2002
2
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
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 -40°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, 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 17 µV/°C
I
B
Input Bias Current -10 -7 µA
I
OS
Input Bias Current Offset 0.06 0.6 µA
T
CIB
Input Bias Current Temperature Coefficient 0.013 µA/°C
C
IN
Input Capacitance 2.2 pF
A
VOL
Open Loop Gain V
O
= -2.5V to +2.5V 80 87 dB
PSRR Power Supply Rejection Ratio
[1]
80 100 dB
CMRR Common Mode Rejection Ratio at CMIR 75 106 dB
CMIR Common Mode Input Range -4.6 3.8 V
V
OUTH
Positive Output Voltage Swing No load, R
F
= 1kΩ3.8 3.8 V
V
OUTL
Negative Output Voltage Swing No load, R
F
= 1kΩ-4 -3.9 V
V
OUTH2
Positive Output Voltage Swing R
L
= 100Ω3.2 3.45 V
V
OUTL2
Negative Output Voltage Swing R
L
= 100Ω-3.5 -3.2 V
I
OUT
Output Short Circuit Current
[2]
80 100 mA
I
SY
Supply Current 4.7 5.5 mA
AC Performance - R
G
= 20Ω, C
L
= 3pF
BW -3dB Bandwidth, R
L
= 500Ω100 MHz
BW ±0.1dB ±0.1dB Bandwidth, R
L
= 500Ω17 MHz
BW ±1dB ±1dB Bandwidth, R
L
= 500Ω80 MHz
Peaking Peaking, R
L
= 500Ω0.6 dB
SR Slew Rate V
OUT
= 2V
PP
, measured at 20% to 80% 80 110 V/µs
OS Overshoot, 4Vpk-pk Output Square Wave Positive 2.8 %
Negative -7 %
t
S
Settling Time to 0.1% of ±1V Pulse 51 ns
V
N
Voltage Noise Spectral Density 1.3 nV/√Hz
I
N
Current Noise Spectral Density 1.2 pA/√Hz
HD2 2nd Harmonic Distortion
[3]
-70 dBc
HD3 3rd Harmonic Distortion
[3]
-70 dBc
1. Measured by moving the supplies from ±4V to ±6V
2. Pulse test only and using a 10Ω load
3. Frequency = 1MHz, V
OUT
= 2Vpk-pk, into 500Ω and 5pF load
3
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Electrical Characteristics
V
S
+ = +15V, 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) 0.5 3 mV
Input Offset Voltage (SOT23-5) 3mV
T
CVOS
Offset Voltage Temperature Coefficient 4.5 µV/°C
I
B
Input Bias Current -10 -7 µA
I
OS
Input Bias Current Offset 0.12 0.7 µA
T
CIB
Input Bias Current Temperature Coefficient 0.016 µA/°C
C
IN
Input Capacitance 2.2 pF
A
VOL
Open Loop Gain 80 90 dB
PSRR Power Supply Rejection Ratio
[1]
65 80 dB
CMRR Common Mode Rejection Ratio at CMIR 70 85 dB
CMIR Common Mode Input Range -14.6 13.8 V
V
OUTH
Positive Output Voltage Swing No load, R
F
= 1kΩ13.6 13.7 V
V
OUTL
Negative Output Voltage Swing No load, R
F
= 1kΩ-13.8 -13.7 V
V
OUTH2
Positive Output Voltage Swing R
L
= 100Ω, R
F
= 1kΩ10.2 11.2 V
V
OUTL2
Negative Output Voltage Swing R
L
= 100Ω, R
F
= 1kΩ-10.3 -9.5 V
I
OUT
Output Short Circuit Current
[2]
140 220 mA
I
SY
Supply Current 56mA
AC Performance - R
G
= 20Ω, C
L
= 3pF
BW -3dB Bandwidth, R
L
= 500Ω135 MHz
BW ±0.1dB ±0.1dB Bandwidth, R
L
= 500Ω26 MHz
BW ±1dB ±1dB Bandwidth, R
L
= 500Ω60 MHz
Peaking Peaking, R
L
= 500Ω2.1 dB
SR Slew Rate (±2.5V Square Wave, Measured
25%-75%)
130 150 V/µS
OS Overshoot, 4Vpk-pk Output Square Wave Positive 1.6 %
Negative -4.4 %
T
S
Settling Time to 0.1% of ±1V Pulse 48 ns
V
N
Voltage Noise Spectral Density 1.4 nV/√Hz
I
N
Current Noise Spectral Density 1.1 pA/√Hz
HD2 2nd Harmonic Distortion
[3]
-72 dBc
HD3 3rd Harmonic Distortion
[3]
-73 dBc
1. Measured by moving the supplies from ±13.5V to ±16.5V
2. Pulse test only and using a 10Ω load
3. Frequency = 1MHz, V
OUT
= 2Vpk-pk, into 500Ω and 5pF load
4
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Typical Performance Curves
Non-Inverting Frequency Response for Various R
F
10
6
2
-2
-6
-10
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
R
F
=1kΩ
R
F
=500Ω
R
F
=180Ω
R
F
=100Ω
V
S
=±5V
A
V
=10
C
L
=5pF
R
L
=500Ω
Non-Inverting Frequency Response for Various R
F
10
6
2
-2
-6
-10
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
R
F
=1kΩ
R
F
=500Ω
R
F
=180Ω
R
F
=100Ω
Inverting Frequency Response for Various R
F
8
4
0
-4
-8
-12
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
V
S
=±15V
A
V
=-10
C
L
=5pF
R
L
=500Ω
Inverting Frequency Response for Various R
F
8
4
0
-4
-8
-12
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
V
S
=±5V
A
V
=-10
C
L
=5pF
R
L
=500Ω
Non-Inverting Frequency Response for Various Gain
10
6
2
-2
-6
-10
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
A
V
=10
V
S
=±5V
R
G
=20Ω
R
L
=500Ω
C
L
=5pF
Non-Inverting Frequency Response for Various Gain
10
6
2
-2
-6
-10
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
R
F
=1kΩ
R
F
=350Ω
R
F
=100Ω
R
F
=200Ω
R
F
=500ΩR
F
=1kΩ
R
F
=500Ω
R
F
=200Ω
R
F
=100Ω
R
F
=350Ω
A
V
=20
A
V
=50
V
S
=±15V
R
G
=20Ω
R
L
=500Ω
C
L
=5pF
A
V
=10
A
V
=20
A
V
=50
V
S
=±15V
A
V
=10
C
L
=5pF
R
L
=500Ω
5
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Typical Performance Curves
Inverting Frequency Response for Various Gain
8
4
0
-4
-8
-12
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Inverting Frequency Response for Various R
F
8
4
0
-4
-8
-12
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Non-Inverting Frequency Response for Various Output
Signal Levels
10
6
2
-2
-6
-10
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Non-Inverting Frequency Response for Various Output
Signal Levels
8
4
0
-4
-8
-12
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Inverting Frequency Response for Various Output Signal
Levels
8
4
0
-4
-8
-12
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Inverting Frequency Response for Various Output Signal
Levels
8
4
0
-4
-8
-12
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
V
S
=±5V
C
L
=5pF
R
G
=35Ω
A
V
=-10
A
V
=-20
A
V
=-50
V
S
=±15V
C
L
=5pF
R
G
=20Ω
A
V
=-10
A
V
=-20
A
V
=-50
V
S
=±5V
C
L
=5pF
R
L
=500Ω
R
F
=180Ω
A
V
=10
V
O
=2.5V
PP
V
O
=5V
PP
V
O
=1V
PP
V
O
=30mV
PP
V
O
=500mV
PP
V
S
=±15V
C
L
=5pF
R
L
=500Ω
R
F
=180Ω
A
V
=10
V
O
=5V
PP
V
O
=1V
PP
V
O
=2.5V
PP
V
O
=30mV
PP
V
O
=500mV
PP
V
O
=10V
PP
V
S
=±5V
C
L
=5pF
R
L
=500Ω
R
F
=350Ω
A
V
=10
V
O
=3.4V
PP
V
O
=1V
PP
V
O
=2.5V
PP
V
O
=30mV
PP
V
O
=500mV
PP
V
S
=±15V
C
L
=5pF
R
L
=500Ω
R
F
=200Ω
A
V
=10
V
O
=3.4V
PP
V
O
=1V
PP
V
O
=2.5V
PP
V
O
=30mV
PP
V
O
=500mV
PP
6
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Typical Performance Curves
Non-Inverting Frequency Response for Various C
L
10
6
2
-2
-6
-10
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Non-Inverting Frequency Response for Various C
L
10
6
2
-2
-6
-10
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Inverting Frequency Response for Various C
L
8
4
0
-4
-8
-12
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Inverting Frequency Response for Various C
L
8
4
0
-4
-8
-12
1M 10M 100M
Frequency (Hz)
Normalized Gain (dB)
Open Loop Gain/Phase
100
80
60
40
20
0
10k 10M 1G
Frequency (Hz)
Open Loop Gain (dB)
Supply Current vs Supply Voltage
0.6/div
1.5/div
Supply Voltage (V)
Supply Current (mA)
C
L
=28pF
C
L
=16pFC
L
=11pF
C
L
=5pF
C
L
=1pF
V
S
=±15V
R
F
=180Ω
A
V
=10
R
L
=500Ω
C
L
=28pF
C
L
=16pF
C
L
=11pF
C
L
=5pF
C
L
=1.2pF
V
S
=±5V
R
F
=350Ω
R
L
=500Ω
A
V
=-10
C
L
=28pF
C
L
=16pF
C
L
=11pF
C
L
=5pF
C
L
=1.2pF
C
L
=28pF
C
L
=16pF
C
L
=11pF
C
L
=5pF
C
L
=1.2pF
V
S
=±15V
R
F
=200Ω
R
L
=500Ω
A
V
=-10
100k 100M1M
250
150
50
-50
-150
-250
Open Loop Phase (°)
0
0
V
S
=±5V
R
F
=150Ω
A
V
=10
R
L
=500Ω
Gain
Phase
V
S
=±5V
7
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Typical Performance Curves
Peaking vs V
s
3.0
2.5
2.0
1.0
0.5
0
0246810 1416
±Supply Voltage (V)
Peaking (dB)
12
1.5
Bandwidth vs V
s
160
140
100
80
40
20
0
0246810 1416
±V
S
(V)
-3dB Bandwidth
12
60
120
1MHz Harmonic Distortion vs Output Swing
-40
-50
-60
-80
-90
-100
012345 78
V
OUT
(V
P-P
)
Harmonic Distortion (dBc)
6
-70
1MHz Harmonic Distortion vs Output Swing
-30
-40
-60
-80
-90
-100
0 5 10 15 20 25
V
OUT
(V
P-P
)
Harmonic Distortion (dBc)
-70
-50
V
S
=±5V
R
G
=20Ω
R
L
=500Ω
C
L
=5pF
A
V
=10
A
V
=-10
2nd HD
3rd HD
2nd HD
V
S
=±5V
R
G
=20Ω
R
L
=500Ω
C
L
=5pF
V
S
=±5V
V
O
=2V
P-P
R
F
=180Ω
A
V
=10
R
L
=500Ω
A
V
=-10
A
V
=10
A
V
=-20
A
V
=-20
A
V
=50
A
V
=-50
V
S
=±5V
V
O
=2V
P-P
R
F
=180Ω
A
V
=10
R
L
=500Ω
3rd HD
Large Signal Step Response
0.5V/div
10ns/div
Small Signal Step Response
20mV/div
10ns/div
V
S
=±5V
V
O
=100mV
PP
R
F
=180Ω
R
G
=20Ω
V
S
=±5V
V
O
=2V
PP
R
F
=180Ω
R
G
=20Ω
8
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Typical Performance Curves
Group Delay vs Frequency
16
8
0
-4
1M 10M 100M 400M
Frequency (Hz)
Group Delay (ns)
4
12
V
S
=±5V
R
L
=500Ω
A
V
=10
A
V
=-10
Noise vs Frequency
10
1
10 100 10k 100k
Frequency (Hz)
I
N
(pA/√Hz), V
N
(nV/√Hz)
1k
CMRR vs Frequency
-10
-50
-90
-110
10 1M 10M 100M
Frequency (Hz)
CMRR (dB)
-70
-30
1k 100k100 10k
Settling Time vs Accuracy
70
40
20
0
0.1 1.0 10.0
Accuracy (%)
Settling Time (ns)
30
50
V
S
=±5V, V
O
=5V
P-P
V
S
=±15V, V
O
=5V
P-P
V
S
=±15V, V
O
=2V
P-P
V
S
=±5V, V
O
=2V
P-P
60
10
Total Harmonic Distortion vs Frequency
-20
-50
-80
-90
1k 10k 100M
Frequency (Hz)
THD (dBc)
V
S
=±5V
V
O
=2V
P-P
100k 1M 10M
-30
-40
-70
-60
PSRR vs Frequency
110
70
30
10
10k 100k 1M 10M 200M
Frequency (Hz)
PSRR (dB)
50
90
V
S
=±5V
PSRR+
PSRR-
I
N
, V
S
=±5V
V
N
, V
S
=±15V
I
N
, V
S
=±15V
V
N
, V
S
=±5V
9
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Typical Performance Curves
Closed Loop Output Impedance vs Frequency
100
10
1
0.1
0.01
10k 1M 100M
Frequency (Hz)
Closed Loop Output Impedance (Ω)
Bandwidth and Peaking vs Temperature
120
100
60
40
20
0
-40 40 160
Temperature
Bandwidth (MHz)
100k 10M
V
S
=±5V V
S
=±5V
80
800120
3.5
3
2.5
2
1.5
1
0.5
0
-0.5
Peaking (dB)
Slew Rate vs Swing
220
180
140
100
60
-1
V
OUT
Swing (V
PP
)
Slew Rate (V/µs)
3 7 11 15
5V
SR
+
5V
SR
-
15V
SR
+
15V
SR
-
15913
200
160
120
80
Bandwidth
Peaking
1
-2
0
-1
4.8
5.2
5.1
5
4.9
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)
CMRR vs Temperature
-50 0 100 15050
Die Temperature (°C)
CMRR (dB)
120
110
100
90
80
V
S
=±5V
10
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Typical Performance Curves
110
86
90
94
98
102
106
82
PSRR vs Temperature
-50 0 100 15050
Die Temperature (°C)
PSRR (dB)
V
S
=±5V
V
S
=±15V
Positive Output Swing vs Temperature
-50 0 100 15050
Die Temperature (°C)
V
OUTH
(V)
V
S
=±5V
Positive Output Swing vs Temperature
-50 0 100 15050
Die Temperature (°C)
V
OUTH
(V)
V
S
=±15V
4.05
4
3.95
3.9
3.85
3.8
13.85
13.8
13.75
13.7
13.65
13.6
-3.9
-3.95
-4.05
-4.25
-4.15
-13.76
-13.78
-13.8
-13.82
Negative Output Swing vs Temperature
-50 0 100 15050
Die Temperature (°C)
V
OUTL
(V)
V
S
=±5V
Negative Output Swing vs Temperature
-50 0 100 15050
Die Temperature (°C)
V
S
=±15V
V
OUTL
(V)
-4
-4.1
-4.2
Slew Rate vs Temperature
-50 0 100 15050
Die Temperature (°C)
Slew Rate (V/µs)
102
100
96
92
88
98
94
90
V
S
=±5V
11
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Typical Performance Curves
155
150
140
135
3.52
3.5
3.46
3.44
Slew Rate vs Temperature
-50 0 100 15050
Die Temperature (°C)
SR (V/µs)
V
O
=2V
PP
V
S
=±15V
Positive Loaded Output Swing vs Temperature
-50 0 100 15050
Die Temperature (°C)
V
OUTH2
(V)
V
S
=±5V
11.8
11.6
11.2
10.8
10.6
Positive Loaded Output Swing vs Temperature
-50 0 100 15050
Die Temperature (°C)
SR (V/µs)
V
S
=±15V
145 3.48
11.4
11
-3.35
-3.4
-3.45
-3.6
-3.5
3.55
-9.4
-9.8
-10.2
-10.6
Negative Loaded Output Swing vs Temperature
-50 0 100 15050
Die Temperature (°C)
V
OUTL2
(V)
V
S
=±5V
Negative Loaded Output Swing vs Temperature
-50 0 100 15050
Die Temperature (°C)
V
S
=±15V
V
OUTL2
(V)
18
-9.6
-10
-10.4
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
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
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
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Pin Descriptions
EL2126CW
(5-Pin SOT23)
EL2126CS
(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
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
Applications Information
Product Description
The EL2126C is an ultra-low noise, wideband mono-
lithic operational amplifier built on Elantec's proprietary
high speed complementary bipolar process. It features
1.3nV/√Hz input voltage noise, 200µV typical 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 EL2126C also has excellent
DC specifications: 200µV V
OS
, 22µA IB, 0.4µA I
OS
,
and 106dB CMRR. These specifications allow the
EL2126C to be used in DC-sensitive applications such
as difference amplifiers.
Gain-Bandwidth Product
The EL2126C has a gain-bandwidth product of 650MHz
at ±5V. For gains less than 20, higher-order poles in the
amplifier's transfer function contribute to even higher
closed-loop bandwidths. For example, the EL2126C has
a -3dB bandwidth of 100MHz at a gain of 10 and
decreases to 33MHz 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 EL2126C 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 frequency and thus maintains the amplifier stabil-
ity. R values must be less than RF divided by 9 and 1
divided by 2
π
RC must be less than 200MHz.
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 in the
typical performance curves section of this data sheet.
Noise Calculations
The primary application for the EL2126C 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
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
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 EL2126C 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 EL2126C an
ideal choice for RF, IF, and video applications. Further-
more, the EL2126C 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 EL2126C is designed to drive low imped-
ance load, capacitive loads will decreases the amplifier's
phase margin. As shown 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 EL2126C has been designed to operate with supply
voltage range of ±2.5V to ±15V. With a single supply,
the EL2126C 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 EL2126C 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 EL2126C has an input voltage range which
spans from 0.4V to 3.8V. The output range of the
EL2126C is also quite large, on a +5V supply, it swings
from 0.4V to 3.8V.
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
EL2126C
Ultra-Low Noise, Low Power, Wideband Amplifier
EL2126C
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 15, 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