AD815ARBZ-24

a High Output Current Differential Driver AD815 FUNCTIONAL BLOCK DIAGRAM FEATURES Flexible Configuration Differential Input and Output Driver or Two Single-Ended Drivers Industrial Temperature Range High Output Power Thermally Enhanced SOIC 400 mA Minimum Output Drive/Amp, RL = 10 ⍀ Low Distortion –66 dB @ 1 MHz THD, RL = 200 ⍀, V OUT = 40 V p-p 0.05% and 0.45ⴗ Differential Gain and Phase, R L = 25 ⍀ (6 Back-Terminated Video Loads) High Speed 120 MHz Bandwidth (–3 dB) 900 V/␮s Differential Slew Rate 70 ns Settling Time to 0.1% Thermal Shutdown APPLICATIONS ADSL, HDSL, and VDSL Line Interface Driver Coil or Transformer Driver CRT Convergence and Astigmatism Adjustment Video Distribution Amp Twisted Pair Cable Driver GENERAL DESCRIPTION The AD815 consists of two high speed amplifiers capable of supplying a minimum of 500 mA. They are typically configured as a differential driver enabling an output signal of 40 V p-p on ± 15 V supplies. This can be increased further with the use of a coupling transformer with a greater than 1:1 turns ratio. The low harmonic distortion of –66 dB @ 1 MHz into 200 Ω NC 1 24 NC NC 2 23 NC NC 3 22 NC NC 4 5 THERMAL HEAT TABS +VS* 21 NC AD815 20 6 TOP VIEW 19 7 (Not to Scale) 18 8 THERMAL HEAT TABS +VS* 17 +IN1 9 16 +IN2 –IN1 10 15 –IN2 OUT1 11 14 OUT2 –VS 12 13 +VS NC = NO CONNECT *HEAT TABS ARE CONNECTED TO THE POSITIVE SUPPLY. combined with the wide bandwidth and high current drive make the differential driver ideal for communication applications such as subscriber line interfaces for ADSL, HDSL and VDSL. The AD815 differential slew rate of 900 V/µs and high load drive are suitable for fast dynamic control of coils or transformers, and the video performance of 0.05% and 0.45° differential gain and phase into a load of 25 Ω enable up to 12 back-terminated loads to be driven. The 24-lead SOIC (RB) is capable of driving 26 dBm for full rate ADSL with proper heat sinking. +15V 1/2 AD815 100⍀ TOTAL HARMONIC DISTORTION – dBc –40 –50 VS = ⴞ15V G = +10 VOUT = 40V p-p AMP1 499⍀ –60 VIN = 4Vp-p 110⍀ –70 –80 R1 = 15⍀ G = +10 RL 120⍀ VD = 40Vp-p VOUT = 40Vp-p 499⍀ RL = 50⍀ (DIFFERENTIAL) 100⍀ 1/2 AD815 RL = 200⍀ (DIFFERENTIAL) –90 R2 = 15⍀ AMP2 1:2 TRANSFORMER –15V –100 Figure 2. Subscriber Line Differential Driver –110 100 1k 10k 100k FREQUENCY – Hz 1M 10M Figure 1. Total Harmonic Distortion vs. Frequency REV. D Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/461-3113 © 2015 Analog Devices, Inc. All rights reserved. AD815–SPECIFICATIONS (@ T = +25ⴗC, V = ⴞ15 V dc, R A Model DYNAMIC PERFORMANCE Small Signal Bandwidth (–3 dB) Bandwidth (0.1 dB) Differential Slew Rate Settling Time to 0.1% NOISE/HARMONIC PERFORMANCE Total Harmonic Distortion Input Voltage Noise Input Current Noise (+I IN) Input Current Noise (–I IN) Differential Gain Error Differential Phase Error DC PERFORMANCE Input Offset Voltage S FB = 1 k⍀ and RLOAD = 100 ⍀ unless otherwise noted) Conditions VS Min G = +1 G = +1 G = +2 G = +2 VOUT = 20 V p-p, G = +2 10 V Step, G = +2 ± 15 ±5 ± 15 ±5 ± 15 ± 15 100 90 f = 1 MHz, RLOAD = 200 Ω, VOUT = 40 V p-p f = 10 kHz, G = +2 (Single Ended) f = 10 kHz, G = +2 f = 10 kHz, G = +2 NTSC, G = +2, RLOAD = 25 Ω NTSC, G = +2, RLOAD = 25 Ω AD815A Typ Max 120 110 40 10 900 70 MHz MHz MHz MHz V/µs ns ± 15 ± 5, ± 15 ± 5, ± 15 ± 5, ± 15 ± 15 ± 15 –66 1.85 1.8 19 0.05 0.45 dBc nV/√Hz pA/√Hz pA/√Hz % Degrees ±5 ± 15 5 10 ±5 ± 15 20 0.5 0.5 ± 5, ± 15 10 10 ± 5, ± 15 2 ± 5, ± 15 10 800 TMIN – TMAX Input Offset Voltage Drift Differential Offset Voltage TMIN – TMAX Differential Offset Voltage Drift –Input Bias Current TMIN – TMAX +Input Bias Current TMIN – TMAX Differential Input Bias Current TMIN – TMAX ± 5, ± 15 Open-Loop Transresistance TMIN – TMAX INPUT CHARACTERISTICS Differential Input Resistance Output Current1 RB-24 Short Circuit Current Output Resistance MATCHING CHARACTERISTICS Crosstalk POWER SUPPLY Operating Range2 Quiescent Current 2 4 5 90 150 5 5 75 100 5.0 mV mV mV µV/°C mV mV mV µV/°C µA µA µA µA µA µA MΩ MΩ ± 15 ± 15 ±5 ± 5, ± 15 ± 5, ± 15 57 80 ± 15 ±5 ± 15 ± 15 11.0 1.1 21 22.5 11.7 1.8 23 24.5 ±V ±V ±V ±V RLOAD = 10 Ω ± 15 ± 15 ± 15 400 500 1.0 13 mA A Ω f = 1 MHz ± 15 –65 dB ±5 ± 15 ±5 ± 15 ± 5, ± 15 23 30 TMIN – TMAX TMIN – TMAX Single Ended, R LOAD = 25 Ω Differential, R LOAD = 50 Ω TMIN – TMAX TMIN – TMAX TMIN – TMAX Power Supply Rejection Ratio 8 15 30 7 15 1.4 13.5 3.5 65 100 Differential Input Capacitance Input Common-Mode Voltage Range Common-Mode Rejection Ratio Differential Common-Mode Rejection Ratio OUTPUT CHARACTERISTICS Voltage Swing 1.0 0.5 ± 15 +Input –Input Units TMIN – TMAX –55 –66 ± 18 30 40 40 55 MΩ Ω pF ±V ±V dB dB V mA mA mA mA dB NOTES 1 Output current is limited in the 24-lead SOIC package to the maximum power dissipation. See absolute maximum ratings and derating curves. 2 Observe derating curves for maximum junction temperature. Specifications subject to change without notice. –2– REV. D AD815 ABSOLUTE MAXIMUM RATINGS 1 MAXIMUM POWER DISSIPATION Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 18 V Total Internal Power Dissipation2 Small Outline (RB) . . 2.4 Watts (Observe Derating Curves) Input Voltage (Common Mode) . . . . . . . . . . . . . . . . . . . . ± VS Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . ± 6 V Output Short Circuit Duration . . . . . . . . . . . . . . . . . . . . . . Observe Power Derating Curves Can Only Short to Ground Storage Temperature Range RB Package . . . . . . . . . . . . . . . . . . . . . . . –65°C to +125°C Operating Temperature Range AD815A . . . . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +85°C Lead Temperature Range (Soldering, 10 sec) . . . . . . . . 300°C The maximum power that can be safely dissipated by the AD815 is limited by the associated rise in junction temperature. The maximum safe junction temperature for the plastic encapsulated parts is determined by the glass transition temperature of the plastic, about 150°C. Exceeding this limit temporarily may cause a shift in parametric performance due to a change in the stresses exerted on the die by the package. Exceeding a junction temperature of 175°C for an extended period can result in device failure. The AD815 has thermal shutdown protection, which guarantees that the maximum junction temperature of the die remains below a safe level, even when the output is shorted to ground. Shorting the output to either power supply will result in device failure. To ensure proper operation, it is important to observe the derating curves and refer to the section on power considerations. NOTES 1 Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2 Specification is for device in free air with 0 ft/min air flow: 24-Lead Surface Mount: θJA = 52°C/W. It must also be noted that in high (noninverting) gain configurations (with low values of gain resistor), a high level of input overdrive can result in a large input error current, which may result in a significant power dissipation in the input stage. This power must be included when computing the junction temperature rise due to total internal power. PIN CONFIGURATION 24-Lead Thermally-Enhanced SOIC (RB-24) NC 1 24 NC NC 2 23 NC NC 3 22 NC NC 4 21 NC 5 THERMAL HEAT TABS +VS* 6 AD815 20 19 TOP VIEW 7 (Not to Scale) 18 8 MAXIMUM POWER DISSIPATION – Watts 14 THERMAL HEAT TABS +VS* 17 TJ = 150ⴗC 13 12 11 10 9 8 7 6 5 4 +IN1 9 16 +IN2 –IN1 10 15 –IN2 OUT1 11 14 OUT2 1 13 +VS 0 –50 –40 –30 –20 –10 0 10 20 30 40 50 60 AMBIENT TEMPERATURE – ⴗC –VS 12 NC = NO CONNECT *HEAT TABS ARE CONNECTED TO THE POSITIVE SUPPLY. 3 2 θJA = 52ⴗC/W (STILL AIR = 0 FT/MIN) NO HEAT SINK 70 80 90 Figure 3. Plot of Maximum Power Dissipation vs. Temperature CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD815 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. REV. D AD815ARB-24 –3– WARNING! ESD SENSITIVE DEVICE AD815–Typical Performance Characteristics 36 34 10 5 0 5 10 15 SUPPLY VOLTAGE – ⴞVolts VS = ⴞ5V 24 30 60 NO LOAD 20 RL = 50⍀ (DIFFERENTIAL) RL = 25⍀ (SINGLE-ENDED) 40 20 10 0 5 10 15 SUPPLY VOLTAGE – ⴞVolts 40 30 15 VS = ⴞ5V 20 10 27 24 21 2 10 4 6 8 10 12 SUPPLY VOLTAGE – ⴞVolts 16 14 SIDE A, B 0 INPUT BIAS CURRENT – ␮A 20 TA = +25ⴗC Figure 8. Total Supply Current vs. Supply Voltage DIFFERENTIAL OUTPUT VOLTAGE – Volts p-p 50 25 100 30 0 60 VS = ⴞ15V 80 18 0 20 Figure 5. Output Voltage Swing vs. Supply Voltage 30 0 20 40 60 JUNCTION TEMPERATURE – ⴗC 33 TOTAL SUPPLY CURRENT – mA 80 –20 Figure 7. Total Supply Current vs. Temperature DIFFERENTIAL OUTPUT VOLTAGE – V p-p SINGLE-ENDED OUTPUT VOLTAGE – V p-p 26 18 –40 20 40 0 SINGLE-ENDED OUTPUT VOLTAGE – Volts p-p 28 22 Figure 4. Input Common-Mode Voltage Range vs. Supply Voltage 5 30 20 0 10 VS = ⴞ15V 32 15 SUPPLY CURRENT – mA COMMON-MODE VOLTAGE RANGE – ⴞVolts 20 +I B VS = ⴞ15V, ⴞ5V –10 –20 VS = ⴞ5V –30 SIDE B –I B –40 SIDE A –50 SIDE B –60 SIDE A –70 –I B VS = ⴞ15V 0 0 10 100 1k 10k LOAD RESISTANCE – (Differential – ⍀) (Single-Ended – ⍀/2) –80 –40 Figure 6. Output Voltage Swing vs. Load Resistance –20 0 20 40 60 JUNCTION TEMPERATURE – ⴗC 80 100 Figure 9. Input Bias Current vs. Temperature –4– REV. D AD815 0 80 –2 60 –4 40 RTI OFFSET – mV INPUT OFFSET VOLTAGE – mV TA = 25ⴗC VS = ⴞ5V –6 –8 VS = ⴞ15V VS = ⴞ10V 20 VS = ⴞ5V 0 VIN 1/2 f = 0.1Hz 100⍀ AD815 VOUT –20 –10 49.9⍀ VS = ⴞ15V –12 –40 –14 –40 –60 –2.0 –1.6 –1.2 1k⍀ 0 20 40 60 JUNCTION TEMPERATURE – ⴗC –20 80 100 Figure 10. Input Offset Voltage vs. Temperature RL= 5⍀ 1k⍀ 0 –0.8 –0.4 0.4 0.8 LOAD CURRENT – Amps 1.2 1.6 2.0 Figure 13. Thermal Nonlinearity vs. Output Current Drive 750 CLOSED-LOOP OUTPUT RESISTANCE – ⍀ SHORT CIRCUIT CURRENT – mA VS = ⴞ15V 700 SOURCE 650 600 SINK 550 500 450 –60 –40 –20 0 20 40 60 80 100 JUNCTION TEMPERATURE – ⴗC 120 100 10 VS = ⴞ5V VS = ⴞ15V 1 0.1 0.01 140 30k Figure 11. Short Circuit Current vs. Temperature 100k 300k 1M 3M 10M FREQUENCY – Hz 30M 100M 300M Figure 14. Closed-Loop Output Resistance vs. Frequency RTI OFFSET – mV 10 DIFFERENTIAL OUTPUT VOLTAGE – V p-p 15 VS = ⴞ10V TA = 25ⴗC RL = 25⍀ VS = ⴞ5V VS = ⴞ15V 5 0 VIN 1/2 f = 0.1Hz 100⍀ AD815 VOUT –5 49.9⍀ –10 1k⍀ 1k⍀ –15 –20 RL= 25⍀ RL = 100⍀ 30 RL = 50⍀ 20 RL = 25⍀ 10 RL = 1⍀ 0 –16 –12 –8 –4 0 4 VOUT – Volts 8 12 16 0 20 Figure 12. Gain Nonlinearity vs. Output Voltage REV. D TA = 25ⴗC VS = ±15V 40 2 4 10 8 6 FREQUENCY – MHz 12 14 Figure 15. Large Signal Frequency Response –5– AD815 100 100 120 TRANSIMPEDANCE 10 NONINVERTING INPUT CURRENT NOISE INPUT VOLTAGE NOISE 1 10 100 1k FREQUENCY – Hz 100 500 80 0 –50 60 –100 50 –150 40 –200 30 –250 100 Figure 16. Input Current and Voltage Noise vs. Frequency 80 TOTAL HARMONIC DISTORTION – dBc COMMON-MODE REJECTION – dB 10k 100k 1M FREQUENCY – Hz 10M 100M –40 VS = ⴞ15V 70 SIDE B 60 SIDE A 50 562⍀ 562⍀ VOUT VIN 30 562⍀ 1/2 AD815 562⍀ 20 10 10k 100k 1M FREQUENCY – Hz –50 –60 –70 –80 1k 10k 100k FREQUENCY – Hz 1M 10M Figure 20. Total Harmonic Distortion vs. Frequency 10 VS = ⴞ15V G = +2 RL = 100⍀ –30 –40 –PSRR –50 +PSRR –60 –70 –80 –90 –100 0.01 RL = 200⍀ (DIFFERENTIAL) –100 OUTPUT SWING FROM ±V TO 0 – Volts –20 RL = 50⍀ (DIFFERENTIAL) –90 0 –10 VS = ⴞ15V G = +10 VOUT = 40V p-p –110 100 100M 10M Figure 17. Common-Mode Rejection vs. Frequency PSRR – dB 1k Figure 19. Open-Loop Transimpedance vs. Frequency 90 40 PHASE 70 1 100k 10k 100 90 PHASE – Degrees 10 TRANSIMPEDANCE – dB INVERTING INPUT CURRENT NOISE CURRENT NOISE – pA/ √ Hz VOLTAGE NOISE – nV/ √ Hz 110 8 1% 0.1% 6 GAIN = +2 VS = ⴞ15V 4 2 0 –2 –4 –6 1% 0.1% –8 –10 0.1 1 10 FREQUENCY – MHz 100 300 0 Figure 18. Power Supply Rejection vs. Frequency 20 60 40 70 SETTLING TIME – ns 80 100 Figure 21. Output Swing and Error vs. Settling Time –6– REV. D AD815 700 1400 5 1200 500 1000 G = +2 400 800 300 600 200 400 100 200 0 OPEN-LOOP TRANSRESISTANCE – M⍀ 600 DIFFERENTIAL SLEW RATE – V/␮s SINGLE-ENDED SLEW RATE – V/␮s (PER AMPLIFIER) G = +10 0 0 5 10 15 OUTPUT STEP SIZE – V p-p 20 4 SIDE B Figure 22. Slew Rate vs. Output Step Size +TZ SIDE A 2 –TZ SIDE B 1 0 –40 25 SIDE A 3 –20 0 20 40 60 JUNCTION TEMPERATURE – ⴗC 100 Figure 25. Open-Loop Transresistance vs. Temperature –85 15 VS = ⴞ15V VS = ⴞ15V SIDE B –80 14 OUTPUT SWING – Volts +PSRR SIDE A PSRR – dB 80 –75 –70 SIDE A SIDE B –65 RL = 150⍀ +VOUT | –VOUT | 13 +VOUT RL = 25⍀ 12 | –VOUT | 11 –PSRR –60 –40 –20 0 20 40 60 JUNCTION TEMPERATURE – ⴗC 80 10 –40 100 Figure 23. PSRR vs. Temperature –20 0 20 40 60 JUNCTION TEMPERATURE – ⴗC 80 100 Figure 26. Single-Ended Output Swing vs. Temperature 27 –74 –73 26 OUTPUT SWING – Volts CMRR – dB –72 –71 –70 –69 –CMRR VS = ⴞ15V RL = 50⍀ 25 –VOUT +VOUT 24 –68 –66 –40 23 +CMRR –67 –20 0 20 40 60 JUNCTION TEMPERATURE – ⴗC 80 22 –40 100 0 20 40 60 JUNCTION TEMPERATURE – ⴗC 80 100 Figure 27. Differential Output Swing vs. Temperature Figure 24. CMRR vs. Temperature REV. D –20 7– AD815 2 3 4 5 6 7 8 9 2 BACK TERMINATED LOADS (75⍀) 0.010 0.005 0.000 –0.005 –0.010 –0.015 –0.020 –0.025 –0.030 PHASE GAIN GAIN 1 2 PHASE 3 4 5 6 7 8 9 0.12 0.10 0.08 G = +2 0.06 RF = 1k⍀ 0.04 NTSC 0.02 0.00 –0.02 –0.04 10 11 –3 –4 B VIN –0.3 –5 100⍀ –0.4 VOUT –6 ⴞ5V 49.9⍀ –0.5 499⍀ 499⍀ 100⍀ –7 –8 –0.6 1 10 FREQUENCY – MHz 100 –9 300 Figure 31. Bandwidth vs. Frequency, G = +2 1 VS = ⴞ15V G = +2 RF = 499⍀ VS = ⴞ15V, ⴞ5V VIN = 400mVrms RL = 100⍀ SIDE B –50 –60 –70 SIDE A –80 –90 –100 –110 0.03 A A –0.2 NORMALIZED OUTPUT VOLTAGE – dB CROSSTALK – dB –40 –2 B –0.1 –10 –30 –1 0 –0.7 0.1 Figure 28. Differential Gain and Differential Phase (per Amplifier) –20 ⴞ15V 0.1 0 NORMALIZED FREQUENCY RESPONSE – dB 1 ⴞ5V NORMALIZED FLATNESS – dB GAIN 1 ⴞ15V DIFF PHASE – Degrees PHASE 0.5 0.4 0.3 G = +2 RF = 1k⍀ 0.2 0.1 NTSC 0.0 –0.1 –0.2 –0.3 10 11 DIFF PHASE – Degrees DIFF GAIN – % DIFF GAIN – % 6 BACK TERMINATED LOADS (25⍀) 0.04 0.03 0.02 0.01 0.00 –0.01 –0.02 –0.03 –0.04 0.1 1 10 FREQUENCY – MHz 100 0 SIDE A SIDE B –1 –2 –3 VIN 100⍀ 49.9⍀ –5 124⍀ Figure 29. Output-to-Output Crosstalk vs. Frequency 499⍀ 100⍀ –6 –7 0.1 300 VOUT –4 1 10 FREQUENCY – MHz 100 300 Figure 32. –3 dB Bandwidth vs. Frequency, G = +5 2 1 VS = ⴞ15V VIN = 0 dBm SIDE B OUTPUT VOLTAGE – dB 0 100 90 SIDE A –1 –2 –3 VIN 100⍀ VOUT –4 –5 49.9⍀ 562⍀ 10 100⍀ 0% –6 5V –7 –9 0.1 1 10 FREQUENCY – MHz 100 1␮s 300 Figure 33. 40 V p-p Differential Sine Wave, RL = 50 Ω, f = 100 kHz Figure 30. –3 dB Bandwidth vs. Frequency, G = +1 –8– REV. D AD815 RF 562⍀ 10␮F +15V 10␮F +15V 0.1␮F 0.1␮F RS 13 13 1/2 AD815 100⍀ VIN 12 PULSE GENERATOR 50⍀ 1/2 AD815 0.1␮F –15V 50⍀ Figure 38. Test Circuit, Gain = 1 + R F /RS G = +1 RF = 698⍀ RL = 100⍀ SIDE B 5V 20ns 100ns Figure 39. 20 V Step Response, G = +5 Figure 35. 500 mV Step Response, G = +1 SIDE A G = +5 RF = 562⍀ RL = 100⍀ RS = 140⍀ SIDE A SIDE B 100mV RL = 100⍀ 10␮F –15V TR/TF = 250ps Figure 34. Test Circuit, Gain = +1 SIDE A 0.1␮F 12 PULSE GENERATOR 10␮F TR/TF = 250ps 100⍀ VIN RL = 100⍀ G = +1 RF = 562⍀ RL = 100⍀ 562⍀ 10␮F +15V SIDE B 0.1␮F 562⍀ 13 VIN PULSE GENERATOR 55⍀ 1/2 AD815 100⍀ 12 TR/TF = 250ps 0.1␮F RL = 100⍀ 10␮F –15V 1V 20ns Figure 36. 4 V Step Response, G = +1 SIDE A Figure 40. Test Circuit, Gain = –1 SIDE A G = +1 RF = 562⍀ RL = 100⍀ SIDE B SIDE B 2V 100mV 50ns Figure 37. 10 V Step Response, G = +1 REV. D G = –1 RF = 562⍀ RL = 100⍀ 20ns Figure 41. 500 mV Step Response, G = –1 –9– AD815 Choice of Feedback and Gain Resistors SIDE A The fine scale gain flatness will, to some extent, vary with feedback resistance. It therefore is recommended that once optimum resistor values have been determined, 1% tolerance values should be used if it is desired to maintain flatness over a wide range of production lots. Table I shows optimum values for several useful configurations. These should be used as starting point in any application. G = –1 RF = 562⍀ RL = 100⍀ SIDE B Table I. Resistor Values 1V 20ns G= Figure 42. 4 V Step Response, G = –1 THEORY OF OPERATION The AD815 is a dual current feedback amplifier with high (500 mA) output current capability. Being a current feedback amplifier, the AD815’s open-loop behavior is expressed as transimpedance, ∆V O /∆I –IN , or T Z . The open-loop transimpedance behaves just as the open-loop voltage gain of a voltage feedback amplifier, that is, it has a large dc value and decreases at roughly 6 dB/octave in frequency. 562 499 499 499 1k ⬁ 499 499 125 110 As to be expected for a wideband amplifier, PC board parasitics can affect the overall closed-loop performance. Of concern are stray capacitances at the output and the inverting input nodes. If a ground plane is to be used on the same side of the board as the signal traces, a space (5 mm min) should be left around the signal lines to minimize coupling. POWER SUPPLY BYPASSING T Z (S ) VO =G× VIN T Z (S ) + G × RIN + RF Adequate power supply bypassing can be critical when optimizing the performance of a high frequency circuit. Inductance in the power supply leads can form resonant circuits that produce peaking in the amplifier’s response. In addition, if large current transients must be delivered to the load, then bypass capacitors (typically greater than 1 µF) will be required to provide the best settling time and lowest distortion. A parallel combination of 10.0 µF and 0.1 µF is recommended. Under some low frequency applications, a bypass capacitance of greater than 10 µF may be necessary. Due to the large load currents delivered by the AD815, special consideration must be given to careful bypassing. The ground returns on both supply bypass capacitors as well as signal common must be “star” connected as shown in Figure 44. where: RF RG RIN = 1/gM ≈ 25 Ω G = 1+ RF RG RIN RG (⍀) PRINTED CIRCUIT BOARD LAYOUT CONSIDERATIONS Since RIN is proportional to 1/gM, the equivalent voltage gain is just TZ × gM, where the gM in question is the transconductance of the input stage. Using this amplifier as a follower with gain, Figure 43, basic analysis yields the following result: RN +1 –1 +2 +5 +10 RF (⍀) VOUT +VS VIN +IN Figure 43. Current Feedback Amplifier Operation RF Recognizing that G × RIN