EL2125 ® Data Sheet April 21, 2005 Ultra-Low Noise, Low Power, Wideband Amplifier The EL2125 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 SOT-23 package, which further helps systems where many input channels create both space and power dissipation problems. The EL2125 is stable for gains of 10 and greater and uses traditional voltage feedback. This allows the use of reactive elements in the feedback loop, a common requirement for many filter topologies. It operates from ±2.5V to ±15V supplies and is available in the 5-pin SOT-23 and 8-pin SO packages. The EL2125 is fabricated using Elantec’s proprietary complementary bipolar process, and is specified for operation from -45°C to +85°C. FN7045.2 Features • Voltage noise of only 0.83nV/√Hz • Current noise of only 2.4pA/√Hz • 200µV offset voltage • 175MHz -3dB BW for AV = 10 • Low supply current - 10mA • SOT-23 package available • ±2.5V to ±15V operation • Pb-Free available (RoHS compliant) Applications • Ultrasound input amplifiers • Wideband instrumentation • Communication equipment • AGC & PLL active filters • Wideband sensors Ordering Information Pinouts EL2125 (5-PIN SOT-23) TOP VIEW PACKAGE TAPE & REEL PKG. DWG. # EL2125CW-T7 5-Pin SOT-23 7” (3K pcs) MDP0038 EL2125CW-T7A 5-Pin SOT-23 7” (250 pcs) MDP0038 EL2125CS 8-Pin SO - MDP0027 VS- 2 EL2125CS-T7 8-Pin SO 7” MDP0027 IN+ 3 EL2125CS-T13 8-Pin SO 13” MDP0027 EL2125CSZ (See Note) 8-Pin SO (Pb-free) - MDP0027 EL2125CSZ-T7 (See Note) 8-Pin SO (Pb-free) 7” MDP0027 EL2125CSZ-T13 (See Note) 8-Pin SO (Pb-free) 13” MDP0027 PART NUMBER OUT 1 1 + 4 IN- EL2125 (8-PIN SO) TOP VIEW NC 1 IN- 2 NOTE: Intersil Pb-free products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020. 5 VS+ IN+ 3 VS- 4 8 NC + 7 VS+ 6 OUT 5 NC CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-352-6832 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2003, 2005. All Rights Reserved All other trademarks mentioned are the property of their respective owners. EL2125 Absolute Maximum Ratings (TA = 25°C) VS+ to VS- . . . . . . . . . . . . . . . . . . . . . . . . . . 33V Continuous Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . 40mA Any Input . . . . . . . . . . . . . . . . . . . . . . . . . . VS- - 0.3V to VS+ + 0.3V Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Curves Ambient Operating Temperature . . . . . . . . . . . . . . . .-45°C to +85°C Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . -65°C to +150°C Maximum Die Junction Temperature . . . . . . . . . . . . . . . . . . . +150°C CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless otherwise noted, all tests are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA VS = ±5V, TA = 25°C, RF = 180Ω, RG = 20Ω, RL = 500Ω unless otherwise specified. Electrical Specifications PARAMETER DESCRIPTION CONDITIONS MIN TYP MAX UNIT 0.2 2 mV 3 mV DC PERFORMANCE VOS Input Offset Voltage (SO8) Input Offset Voltage (SOT23-5) TCVOS Offset Voltage Temperature Coefficient IB Input Bias Current IOS Input Bias Current Offset 0.4 TCIB Input Bias Current Temperature Coefficient 0.09 µA/°C CIN Input Capacitance 2.2 pF AVOL Open Loop Gain 80 87 dB PSRR Power Supply Rejection Ratio (Note 1) 80 97 dB CMRR Common Mode Rejection Ratio 80 106 dB CMIR Common Mode Input Range VOUTH Output Voltage Swing High No load, RF = 1kΩ VOUTL Output Voltage Swing Low No load, RF = 1kΩ VOUTH2 Output Voltage Swing High RL = 100Ω VOUTL2 Output Voltage Swing Low RL = 100Ω IOUT Output Short Circuit Current (Note 2) IS Supply Current -30 at CMIR 1.8 µV/°C -22 µA -4.6 3.5 3.8 3.65 -3.87 3 -3.7 V V V -3 100 10.1 µA V 3.3 -3.5 80 2 V mA 11 mA AC PERFORMANCE - RG = 20Ω, CL = 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 VOUT = 2VP-P, measured at 20% to 80% 185 V/µs OS Overshoot, 4VP-P Output Square Wave Positive 0.6 % Negative 2.7 % 42 ns 0.83 nV/√Hz tS Settling Time to 0.1% of ±1V Pulse VN Voltage Noise Spectral Density 2 10kHz 150 FN7045.2 April 21, 2005 EL2125 VS = ±5V, TA = 25°C, RF = 180Ω, RG = 20Ω, RL = 500Ω unless otherwise specified. (Continued) Electrical Specifications PARAMETER DESCRIPTION IN Current Noise Spectral Density HD2 HD3 CONDITIONS MIN 10kHz TYP MAX UNIT 2.4 pA/√Hz 2nd Harmonic Distortion (Note 3) -74 dBc 3rd Harmonic Distortion -91 dBc NOTES: 1. Measured by moving the supplies from ±4V to ±6V 2. Pulse test only 3. Frequency = 1MHz, VOUT = 2VP-P, into 500Ω and 5pF load Electrical Specifications PARAMETER VS = ±15V, TA = 25°C, RF = 180Ω, RG = 20Ω, RL = 500Ω unless otherwise specified. DESCRIPTION CONDITIONS MIN TYP MAX UNIT 0.6 3 mV 3 mV DC PERFORMANCE VOS Input Offset Voltage (SO8) Input Offset Voltage (SOT23-5) TCVOS Offset Voltage Temperature Coefficient IB Input Bias Current IOS Input Bias Current Offset 0.4 TCIB Input Bias Current Temperature Coefficient 0.08 µA/°C CIN Input Capacitance 2.2 pF AVOL Open Loop Gain 80 87 dB PSRR Power Supply Rejection Ratio (Note 1) 80 97 dB CMRR Common Mode Rejection Ratio 75 105 dB CMIR Common Mode Input Range VOUTH Output Voltage Swing High No load, RF = 1kΩ VOUTL Output Voltage Swing Low No load, RF = 1kΩ VOUTH2 Output Voltage Swing High RL = 100Ω VOUTL2 Output Voltage Swing Low RL = 100Ω IOUT Output Short Circuit Current (Note 2) IS Supply Current -30 at CMIR 4.9 µV/°C -24 µA -14.6 13.35 13.8 13.5 -13.6 11 -13 V V V -9.8 250 10.8 µA V 11.6 -10.4 120 2 V mA 12 mA AC PERFORMANCE - RG = 20Ω, CL = 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 225 V/µs OS Overshoot, 4VP-P Output Square Wave 0.6 % tS Settling Time to 0.1% of ±1V Pulse 38 ns VN Voltage Noise Spectral Density 0.95 nV/√Hz VOUT = 2VP-P, measured at 20% to 80% 3 10kHz 180 FN7045.2 April 21, 2005 EL2125 Electrical Specifications PARAMETER VS = ±15V, TA = 25°C, RF = 180Ω, RG = 20Ω, RL = 500Ω unless otherwise specified. (Continued) DESCRIPTION CONDITIONS IN Current Noise Spectral Density HD2 HD3 MIN TYP 10kHz MAX UNIT 2.1 pA/√Hz 2nd Harmonic Distortion (Note 3) -73 dBc 3rd Harmonic Distortion -96 dBc NOTES: 1. Measured by moving the supplies from ±13.5V to ±16.5V 2. Pulse test only 3. Frequency = 1MHz, VOUT = 2VP-P, into 500Ω and 5pF load Typical Performance Curves VS=±5V AV=10 RL=500Ω CL=5pF 5 RF=499Ω RF=1kΩ 0 RF=180Ω RF=100Ω -5 1M NORMALIZED GAIN (dB) NORMALIZED GAIN (dB) 5 RF=499Ω RF=180Ω RF=100Ω 10M FREQUENCY (Hz) RF=499Ω 2 -2 RF=350Ω RF=200Ω -6 RF=97.6Ω VS=±5V AV=-10 RL=560Ω CL=5pF 10M 100M 300M FREQUENCY (Hz) FIGURE 3. INVERTING FREQUENCY RESPONSE FOR VARIOUS RF 4 NORMALIZED GAIN (dB) 6 RF=1kΩ NORMALIZED GAIN (dB) 300M FIGURE 2. NON-INVERTING FREQUENCY RESPONSE FOR VARIOUS RF 6 -14 1M 100M FREQUENCY (Hz) FIGURE 1. NON-INVERTING FREQUENCY RESPONSE FOR VARIOUS RF -10 RF=700Ω RF=1kΩ 0 -5 1M 100M 200M 10M VS=±15V AV=10 RL=500Ω CL=5pF -2 RF=350Ω RF=200Ω -6 -10 -14 1M RF=499Ω RF=1kΩ 2 VS=±15V AV=-10 RL=500Ω CL=5pF RF=97.6Ω 10M 100M 300M FREQUENCY (Hz) FIGURE 4. INVERTING FREQUENCY RESPONSE FOR VARIOUS RF FN7045.2 April 21, 2005 EL2125 Typical Performance Curves (Continued) 5 5 NORMALIZED GAIN (dB) NORMALIZED GAIN (dB) VS=±5V RL=500Ω CL=5pF RG=20Ω AV=10 0 AV=20 AV=50 -5 1M 10M VS=±15V RL=500Ω CL=5pF RF=700Ω 0 AV=20 AV=50 -5 1M 100M 200M 10M FREQUENCY (Hz) FIGURE 6. NON-INVERTING FREQUENCY RESPONSE FOR VARIOUS GAIN 6 2 NORMALIZED GAIN (dB) NORMALIZED GAIN (dB) 6 AV=-10 -2 AV=-50 -6 VS=±5V -10 RL=500Ω CL=5pF RG=35Ω -14 1M AV=-20 10M 100M 0 AV=-20 AV=-50 VS=±15V RL=500Ω CL=5pF RG=50Ω 10M 100M 300M FREQUENCY (Hz) FIGURE 7. INVERTING FREQUENCY RESPONSE vs GAIN FIGURE 8. INVERTING FREQUENCY RESPONSE vs GAIN 6 VS=±5V AV=10 RF=180Ω RL= 500Ω CL=5pF 3mVPP 30mVPP 500mVPP 0 4VPP 2VPP 1VPP 10M 100M 200M FREQUENCY (Hz) FIGURE 9. NON-INVERTING FREQUENCY RESPONSE FOR VARIOUS OUTPUT SIGNAL LEVELS 5 NORMALIZED GAIN (dB) NORMALIZED GAIN (dB) AV=-10 -14 1M 300M FREQUENCY (Hz) -5 1M 100M 200M FREQUENCY (Hz) FIGURE 5. NON-INVERTING FREQUENCY RESPONSE vs GAIN 5 AV=10 500mVPP 250mVPP 0 3.3VPP VS=±5V AV=-10 RF=350Ω RL= 500Ω CL=5pF -14 1M 2.5VPP 1VPP 10M 100M 300M FREQUENCY (Hz) FIGURE 10. INVERTING FREQUENCY RESPONSE FOR VARIOUS OUTPUT SIGNAL LEVELS FN7045.2 April 21, 2005 EL2125 Typical Performance Curves NORMALIZED GAIN (dB) 3 5 VS=±5V AV=10 RF=180Ω RL=500Ω CL=28.5pF NORMALIZED GAIN (dB) 5 (Continued) CL=16pF 1 -1 CL=5pF -3 CL=1pF -5 1M 10M VS=±5V AV=10 RF=700Ω RL=500Ω CL=5pF CL=1.2pF 10M FREQUENCY (Hz) 6 NORMALIZED GAIN (dB) CL=16.4pF NORMALIZED GAIN (dB) FIGURE 12. NON-INVERTING FREQUENCY RESPONSE FOR VARIOUS CL CL=29.4pF 0 CL=11.4pF CL=5.1pF VS=±5V AV=10 RF=350Ω RL=500Ω CL=1.2pF -14 1M 10M 100M 200M FREQUENCY (Hz) FIGURE 11. NON-INVERTING FREQUENCY RESPONSE FOR VARIOUS CL 6 CL=11pF 0 -5 1M 100M 200M CL=17pF 100M CL=29.4pF 2 CL=16.4pF -2 CL=11.4pF -6 CL=5.1pF VS=±15V AV=10 RF=500Ω RL=500Ω -10 -14 1M 300M CL=1.2pF 10M 100M 300M FREQUENCY (Hz) FREQUENCY (Hz) FIGURE 13. INVERTING FREQUENCY RESPONSE FOR VARIOUS CL 100 FIGURE 14. INVERTING FREQUENCY RESPONSE FOR VARIOUS CL 250 PHASE 60 50 40 -50 20 -150 VS=±5V 0 10K 100K 1M 10M 100M -250 400M FREQUENCY (Hz) FIGURE 15. OPEN LOOP GAIN AND PHASE 6 SUPPLY CURRENT (mA) 150 PHASE (°) OPEN LOOP GAIN (dB) 12 GAIN 80 9.6 7.2 4.8 2.4 0 0 3 6 9 12 15 SUPPLY VOLTAGE (±V) FIGURE 16. SUPPLY CURRENT vs SUPPLY VOLTAGE FN7045.2 April 21, 2005 EL2125 Typical Performance Curves (Continued) 250 3 AV=-10 150 100 AV=-20 AV=20 AV=50 2 PEAKING (dB) BANDWIDTH (MHz) 2.5 AV=10 200 AV=-50 AV=-10 1.5 1 50 0 AV=10 0.5 2 4 6 8 10 12 14 0 16 AV=-20 2 6 8 10 AV=50 12 14 16 VS (±V) VS (±V) VS=±5V RL=500Ω RF=180Ω AV=10 CL=5pF VINx2 FIGURE 18. PEAKING vs SUPPLY VOLTAGE 20mV/DIV FIGURE 17. 3dB BANDWIDTH vs SUPPLY VOLTAGE 20mV/DIV 4 AV=20 AV=-50 VS=±15V RL=500Ω RF=180Ω AV=10 CL=5pF VINx2 VO VO 10ns/DIV 10ns/DIV OUTPUT VOLTAGE (0.5V/DIV) VS=±5V RL=500Ω RF=180Ω AV=10 CL=5pF TIME (20ns/DIV) FIGURE 21. LARGE SIGNAL STEP RESPONSE 7 FIGURE 20. SMALL SIGNAL STEP RESPONSE VS=±15V RL=500Ω RF=180Ω AV=10 CL=5pF OUTPUT VOLTAGE (0.5V/DIV) FIGURE 19. SMALL SIGNAL STEP RESPONSE TIME (20ns/DIV) FIGURE 22. LARGE SIGNAL STEP RESPONSE FN7045.2 April 21, 2005 EL2125 Typical Performance Curves -40 -30 VS=±5V RF=180Ω AV=10 RL=500Ω -60 2ND HD -70 -80 3RD HD -90 -100 -110 VS=±15V RF=180Ω AV=10 RL=500Ω -40 -50 DISTORTION (dBc) -50 DISTORTION (dBc) (Continued) 2ND HD -60 -70 -80 3RD HD -90 -100 0 1 2 3 4 5 6 -110 7 0 5 10 FIGURE 23. 1MHz HARMONIC DISTORTION vs OUTPUT SWING THD (dBc) -40 -50 100 VS=±5V VO=2VPP AV=10 RF=180Ω RL=500Ω -60 -70 -80 -90 1K 10K 100K 1M 10M 10 IN, VS=±5V VN, VS=±15V 1 VN, VS=±5V 0.1 10 100M 100 FREQUENCY (Hz) 14 SETTLING TIME (ns) GROUP DELAY (ns) VS=±15V VO=5VPP VS=±5V VO=5VPP 30 20 10 VS=±5V VO=2VPP VS=±15V VO=2VPP 0 0.1 1 10 ACCURACY (%) FIGURE 27. SETTLING TIME vs ACCURACY 8 10K 100K FIGURE 26. VOLTAGE AND CURRENT NOISE vs FREQUENCY 60 40 1K IN, VS=±15V FREQUENCY (Hz) FIGURE 25. TOTAL HARMONIC DISTORTION vs FREQUENCY 50 25 20 FIGURE 24. 1MHz HARMONIC DISTORTION vs OUTPUT SWING VOLTAGE NOISE (nV/√Hz), CURRENT NOISE (pA/√Hz) -30 15 VOUT (VPP) VOUT (VPP) VS=±15V 10 AV=20 6 2 AV=10 -2 -6 1 10 100 400 FREQUENCY (MHz) FIGURE 28. GROUP DELAY FN7045.2 April 21, 2005 EL2125 Typical Performance Curves (Continued) -10 110 -30 90 PSRR (dB) -50 -70 -99 70 PSRR+ 50 30 -110 10 100 1K 10K 100K 1M 10 10K 10M 100M 100K FIGURE 29. CMRR -3dB BANDWIDTH (MHz) ROUT (Ω) 1 0.1 0.01 0.001 10K 100K 1M 600M 3.5 200 10 10M BANDWIDTH 160 3 2.5 120 2 PEAKING 1.5 80 1 40 0.5 0 -40 100M FREQUENCY (Hz) 0 40 80 120 0 160 TEMPERATURE (°C) FIGURE 31. CLOSED LOOP OUTPUT IMPEDANCE vs FREQUENCY FIGURE 32. BANDWIDTH vs TEMPERATURE 350 13 300 12 15VSR- 250 IS (mA) SLEW RATE (V/µs) 100M 10M FIGURE 30. PSRR 100 5VSR- 200 150 100 1M FREQUENCY (Hz) FREQUENCY (Hz) PEAKING (dB) CMRR (dB) PSRR- 10 5VSR+ 0 VS=±15V 11 VS=±5V 15VSR+ 5 10 15 VOUT SWING (VPP) FIGURE 33. SLEW RATE vs SWING 9 20 9 -50 0 50 100 150 DIE TEMPERATURE (°C) FIGURE 34. SUPPLY CURRENT vs TEMPERATURE FN7045.2 April 21, 2005 EL2125 Typical Performance Curves (Continued) 0 -10 VS=±5V -15 -1 IB+ (µA) VOS (mV) VS=±15V -20 -2 -25 -3 -50 0 50 100 -30 -50 150 DIE TEMPERATURE (°C) 0 50 100 150 DIE TEMPERATURE (°C) FIGURE 35. OFFSET VOLTAGE vs TEMPERATURE FIGURE 36. INPUT BIAS CURRENT vs TEMPERATURE 120 110 VS=±15V 80 PSRR (dB) CMRR (dB) VS=±5V 100 VS=±5V 60 -50 0 50 100 100 VS=±15V 90 80 -50 150 DIE TEMPERATURE (°C) 150 FIGURE 38. PSRR vs TEMPERATURE VS=±15V 3.8 VOUTH (V) 220 SR (V/µs) 100 3.9 VO=2VPP 200 VS=±5V 180 160 -50 50 DIE TEMPERATURE (°C) FIGURE 37. CMRR vs TEMPERATURE 240 0 3.7 VS=±5V 3.6 0 50 100 150 DIE TEMPERATURE (°C) FIGURE 39. SLEW RATE vs TEMPERATURE 10 3.5 -50 0 50 100 150 DIE TEMPERATURE (°C) FIGURE 40. POSITIVE OUTPUT SWING vs TEMPERATURE FN7045.2 April 21, 2005 EL2125 Typical Performance Curves (Continued) 13.6 -9.75 -9.8 VOUTL (V) VOUTH (V) VS=±15V 13.5 VS=±5V -9.85 -9.9 13.4 -50 0 50 100 -9.95 -50 150 0 50 150 100 DIE TEMPERATURE (°C) DIE TEMPERATURE (°C) FIGURE 41. POSITIVE OUTPUT SWING vs TEMPERATURE FIGURE 42. NEGATIVE OUTPUT SWING vs TEMPERATURE -13.4 -3.42 -13.5 VOUTL2 (V) VOUTL (V) -3.44 VS=±15V -13.6 -3.46 VS=±5V -3.48 -3.5 -13.7 -50 0 50 100 -3.52 -50 150 0 50 100 150 DIE TEMPERATURE (°C) DIE TEMPERATURE (°C) FIGURE 43. NEGATIVE OUTPUT SWING vs TEMPERATURE FIGURE 44. LOADED NEGATIVE OUTPUT SWING vs TEMPERATURE -9.6 3.35 -10 VOUTH2 (V) VOUTL2 (V) -9.8 VS=±15V -10.2 -10.4 VS=±5V 3.3 -10.6 -10.8 -50 0 50 100 150 DIE TEMPERATURE (°C) FIGURE 45. NEGATIVE OUTPUT SWING vs TEMPERATURE 11 3.25 -50 0 50 100 150 DIE TEMPERATURE (°C) FIGURE 46. LOADED POSITIVE OUTPUT SWING vs TEMPEARTURE FN7045.2 April 21, 2005 EL2125 Typical Performance Curves (Continued) 12 1.2 POWER DISSIPATION (W) 11.8 VOUTH2 (V) VS=±15V 11.6 11.4 11.2 11 -50 0 50 100 150 DIE TEMPERATURE (°C) JEDEC JESD51-3 LOW EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 1 781mW 0.8 SO8 θJA=160°C/W 0.6 0.4 488mW SOT23-5 θJA=256°C/W 0.2 0 0 25 50 75 85 100 125 150 AMBIENT TEMPERATURE (°C) FIGURE 47. LOADED POSITIVE OUTPUT SWING vs TEMPERATURE POWER DISSIPATION (W) 1.8 FIGURE 48. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE JEDEC JESD51-7 HIGH EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 1.6 1.4 1.2 1.136W SO8 θJA=110°C/W 1 0.8 0.6 543mW 0.4 SOT23-5 θJA=230°C/W 0.2 0 0 25 50 75 85 100 125 150 AMBIENT TEMPERATURE (°C) FIGURE 49. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE 12 FN7045.2 April 21, 2005 EL2125 Pin Descriptions 5-PIN SOT-23 8-PIN SO PIN NAME PIN FUNCTION 1 6 VOUT Output EQUIVALENT CIRCUIT VS+ VOUT CIRCUIT 1 2 4 VS- Supply 3 3 VINA+ Input VS+ VIN+ VIN- VSCIRCUIT 2 4 2 VINA- Input 5 7 VS+ Supply Applications Information Product Description The EL2125 is an ultra-low noise, wideband monolithic 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 EL2125 also has excellent DC specifications: 200µV VOS, 22µA IB, 0.4µA IOS, and 106dB CMRR. These specifications allow the EL2125 to be used in DC-sensitive applications such as difference amplifiers. Gain-Bandwidth Product The EL2125 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 amplifier's transfer function contribute to even higher closed-loop bandwidths. For example, the EL2125 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 EL2125 is designed for gain > 10 with external 13 Reference Circuit 2 compensation, the device can also operate at lower gain settings. The RC network shown in Figure 50 reduces the feedback gain at high frequency and thus maintains the amplifier stability. R values must be less than RF divided by 9 and 1 divided by 2πRC must be less than 400MHz. RF R C + VOUT VIN FIGURE 50. Choice of Feedback Resistor, RF The feedback resistor forms a pole with the input capacitance. 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. FN7045.2 April 21, 2005 EL2125 Noise Calculations The primary application for the EL2125 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 51 below shows all the noise sources for all the components around the amplifier. VIN R3 VR3 VN + - IN+ VR1 IN- VON R1 VR2 R2 FIGURE 51. Although the EL2125 is designed to drive low impedance load, capacitive loads will decrease the amplifier's phase margin. As shown the in the performance curves, capacitive load can result in peaking, overshoot and possible 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 coaxial cable will not add to the capacitive load seen by the amplifier. 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 tantalum capacitor in parallel with 0.1µF ceramic capacitor has been proven to work well when placed at each supply pin. For single supply operation, where pin 4 (VS-) is connected to the ground plane, a single 4.7µF tantalum capacitor in parallel with a 0.1µF ceramic capacitor across pins 7 (VS+) and pin 4 (VS-) will suffice. • IN+ is the amplifier positive input current noise • IN- is the amplifier negative input current noise • VRX is the thermal noise associated with each resistor: 4kTRx where: • k is Boltzmann's constant = 1.380658 x 10-23 • T is temperature in degrees Kelvin (273+ °C) The total noise due to the amplifier seen at the output of the amplifier can be calculated by using the equation below (Figure 52). As the equation shows, to keep noise at a minimum, small resistor values should be used. At higher amplifier gain configuration where R2 is reduced, the noise due to IN-, R2, and R1 decreases and the noise caused by IN+, VN, and R3 starts to dominate. Because noise is summed in a rootmean-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 EL2125 is designed to drive low impedance load. It can easily drive 6VP-P signal into a 100Ω load. This high output drive capability makes the EL2125 an ideal choice for RF, IF, and video applications. Furthermore, the EL2125 is current- V ON = Driving Cables and Capacitive Loads Power Supply Bypassing And Printed Circuit Board Layout • VN is the amplifier input voltage noise V RX = limited at the output, allowing it to withstand momentary short to ground. However, the power dissipation with outputshorted cannot exceed the power dissipation capability of the package. 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 capacitance which will result in additional peaking and overshoot. Supply Voltage Range and Single Supply Operation The EL2125 has been designed to operate with supply voltage range of ±2.5V to ±15V. With a single supply, the EL2125 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 R 2 R 2 R 2 R 1 2 2 2 2 2 2 BW × VN × 1 + ------1- + IN- × R 1 + IN+ × R 3 × 1 + ------1- + 4 × K × T × R 1 + 4 × K × T × R 2 × ------- + 4 × K × T × R 3 × 1 + ------1- R 2 R 2 R 2 R 2 FIGURE 52. 14 FN7045.2 April 21, 2005 EL2125 voltage range. The EL2125 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 supply, the EL2125 has an input voltage range which spans from 0.4V to 3.8V. The output range of the EL2125 is also quite large, on a +5V supply, it swings from 0.4V to 3.6V. All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com 15 FN7045.2 April 21, 2005