® BUF600 BUF601 BUF 600 BUF 600 BUF 601 HIGH-SPEED BUFFER AMPLIFIER FEATURES APPLICATIONS ● OPEN-LOOP BUFFER ● HIGH-SLEW RATE: 3600V/µs, 5.0Vp-p ● BANDWIDTH: 320MHz, 5.0Vp-p 900MHz, 0.2Vp-p ● LOW INPUT BIAS CURRENT: 0.7µA/1.5µA ● VIDEO BUFFER/LINE DRIVER ● INPUT/OUTPUT AMPLIFIER FOR MEASUREMENT EQUIPMENT ● LOW QUIESCENT CURRENT: 3mA/6mA ● GAIN FLATNESS: 0.1dB, 0 to 300MHz ● TELECOMMUNICATIONS ● HIGH-SPEED ANALOG SIGNAL PROCESSING ● PORTABLE SYSTEMS ● TRANSMISSION SYSTEMS ● ULTRASOUND DESCRIPTION The BUF600 and BUF601 are monolithic open-loop unity-gain buffer amplifiers with a high symmetrical slew rate of up to 3600V/µs and a very wide bandwidth of 320MHz at 5Vp-p output swing. They use a complementary bipolar IC process, which incorporates pn-junction isolated high-frequency NPN and PNP transistors to achieve high-frequency performance previously unattainable with conventional integrated circuit technology. The BUF601, with 6mA quiescent current and therefore lower output impedance, can easily drive 50Ω inputs or 75Ω systems and cables. The broad range of analog and digital applications extends from decoupling of signal processing stages, impedance transformation, and input amplifiers for RF equipment and ATE systems to video systems, distribution fields, IF/communications systems, and output drivers for graphic cards. V+ = +5V (1) Their unique design offers a high-performance alternative to expensive discrete or hybrid solutions. The BUF600 and BUF601 feature low quiescent current, low input bias current, small signal delay time and phase shift, and low differential gain and phase errors. The BUF600 with 3mA quiescent current is wellsuited for operation between high-frequency processing stages. It demonstrates outstanding performance even in feedback loops of wide-band amplifiers or phase-locked loop systems. VIN (4) VOUT (8) Bias Circuitry BUFFER Simplified Circuit Diagram V– = –5V (5) International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111 Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 ® © 1991 Burr-Brown Corporation PDS-1128F 1 BUF600, 601 Printed in U.S.A. March, 1998 SPECIFICATIONS DC SPECIFICATION At VCC = ±5V, RLOAD = 10kΩ, RSOURCE = 50Ω, and TAMB = +25°C, unless otherwise noted. BUF600AP, AU PARAMETER CONDITIONS INPUT OFFSET VOLTAGE Initial vs Temperature vs Supply (tracking) vs Supply (non-tracking) vs Supply (non-tracking) VCC = ±4.5V to ±5.5V VCC = +4.5V to +5.5V VCC = –4.5V to –5.5V INPUT BIAS CURRENT Initial vs Temperature vs Supply (tracking) vs Supply (non-tracking) vs Supply (non-tracking) TYP MAX ±30 –54 ±15 9 –72 –55 –54 +3.5 0.4 0.15 0.5 20 –2.5/+5 VCC = ±4.5V to ±5.5V VCC = +4.5V to +5.5V VCC = –4.5V to –5.5V INPUT IMPEDANCE INPUT NOISE Voltage Noise Density Signal-to-Noise Ratio f = 100kHz to 100MHz S/N = 20 Log (0.7/(Vn • √5MHz)) TRANSFER CHARACTERISTICS DC Current Output Output Impedance MIN TYP MAX UNITS ±30 –54 ±15 25 –77 –55 –54 mV µV/°C dB dB dB +3.5 0.7 0.3 0.5 20 –5/+10 µA nA/°C µA/V µA/V nA/V 4.8 || 1 2.5 || 1 MΩ || pF 5.2 95 4.8 96 nV/√Hz dB 0.95 V/V V/V V/V Voltage Gain; VIN = ±2.5V RLOAD = 100Ω RLOAD = 200Ω RLOAD = 10kΩ RATED OUTPUT Voltage Output BUF601AU MIN VIN = ±2.7V RLOAD = 100Ω RLOAD = 200Ω DC, RLOAD = 100Ω 0.96 0.99 ±2.5 ±20 0.99 ±2.5 ±2.6 ±4.5 ±2.6 ±5 ±3 V V mA Ω ±20 6.2 POWER SUPPLY Rated Voltage Derated Performance Quiescent Current ±2.6 3.6 ±5.5 ±3.4 ±4.5 ±5.4 85 125 –40 –40 ±5 ±6 ±5.5 ±6.6 V V mA 85 125 °C °C MAX UNITS TEMPERATURE RANGE Specification Storage –40 –40 AC SPECIFICATION At VCC = ±5V, RLOAD = 200Ω (BUF600) and 100Ω (BUF601), RSOURCE = 50Ω, and TAMB = +25°C, unless otherwise noted. BUF600AP, AU PARAMETER CONDITIONS MIN TYP BUF601AU MAX MIN TYP FREQUENCY DOMAIN LARGE SIGNAL BANDWIDTH (–3dB) VO = 5Vp-p, COUT = 1pF VO = 2.8Vp-p, COUT = 1pF VO = 1.4Vp-p, COUT = 1pF 320 400 700 320 400 700 MHz MHz MHz SMALL SIGNAL BANDWIDTH VO = 0.2Vp-p, COUT = 1pF 650 900 MHz 250 200 ps 0.4 0.05 % % % % 0.025 0.03 Degrees Degrees Degrees Degrees GROUP DELAY TIME DIFFERENTIAL GAIN DIFFERENTIAL PHASE VIN = 0.3Vp-p, f = 4.43MHz V = 0 to 0.7V BUF600 RLOAD = 200Ω RLOAD = 1kΩ BUF601 RLOAD = 100Ω RLOAD = 500Ω 0.5 0.075 VIN = 0.3Vp-p, f = 4.43MHz V = 0 to 0.7V BUF600 RLOAD = 200Ω RLOAD = 1kΩ BUF601 RLOAD = 100Ω RLOAD = 500Ω 0.02 0.04 ® BUF600, 601 2 AC-SPECIFICATIONS (CONT) At VCC = ±5V, RLOAD = 200Ω (BUF600) and 100Ω (BUF601), RSOURCE = 50Ω, and TAMB = +25°C, unless otherwise noted. BUF600AP, AU PARAMETER CONDITIONS HARMONIC DISTORTION Second Harmonic Third Harmonic Second Harmonic Third Harmonic Second Harmonic Third Harmonic MIN TYP f = 10MHz, VO = 1.4Vp-p BUF601AU MAX MIN TYP MAX UNITS –65 –64 –51 –56 –43 –48 –65 –67 –59 –62 –53 –54 dBc dBc dBc dBc dBc dBc VO = 0.4Vp-p, DC to 30MHz VO = 0.4Vp-p, 30MHz to 300MHz 0.01 0.3 0.005 0.1 dB dB VO = 0.4Vp-p, DC to 30MHz VO = 0.4Vp-p, 30 to 300MHz 5.5 55 3.8 45 Degrees Degrees 10% to 90%, 700ps 1.4Vp-p Step 2.8Vp-p Step 5.0Vp-p Step 0.82 0.97 1.18 0.87 0.95 1.13 ns ns ns VO = 1.4Vp-p VO = 2.8Vp-p VO = 5.0Vp-p 1500 2400 3400 1500 2400 3600 V/µs V/µs V/µs f = 30MHz, VO = 1.4Vp-p f = 50MHz, VO = 1.4Vp-p GAIN FLATNESS PEAKING LINEAR PHASE DEVIATION TIME DOMAIN RISE TIME SLEW RATE FUNCTIONAL DESCRIPTION PIN CONFIGURATION Top View FUNCTION DIP/SO-8 +VCC 1 8 Out NC 2 7 NC NC 3 6 NC In 4 5 –VCC In Out +VCC –VCC DESCRIPTION Analog Input Analog Output Positive Supply Voltage; typical +5VDC Negative Supply Voltage; typical –5VDC ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. BUF600, BUF601 ABSOLUTE MAXIMUM RATINGS ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. Power Supply Voltage .......................................................................... ±6V Input Voltage(1) ......................................................................... ±VCC ±0.7V Operating Temperature ..................................................... –40°C to +85°C Storage Temperature ...................................................... –40°C to +125°C Junction Temperature .................................................................... +150°C Lead Temperature (soldering, 10s) ................................................ +300°C NOTE: (1) Inputs are internally diode-clamped to ±VCC. PACKAGE/ORDERING INFORMATION PRODUCT PACKAGE PACKAGE DRAWING NUMBER(1) BUF600AP BUF600AU BUF601AU Plastic 8-Pin DIP SO-8 Surface Mount SO-8 Surface Mount 006 182 182 TEMPERATURE RANGE –40°C to +85°C –40°C to +85°C –40°C to +85°C NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. ® 3 BUF600, 601 INPUT PROTECTION Static damage has been well recognized for MOSFET devices, but any semiconductor device deserves protection from this potentially damaging source. The BUF600 and BUF601 incorporate on-chip ESD protection diodes as shown in Figure 1. This eliminates the need for the user to add external protection diodes, which can add capacitance and degrade AC performance. +VCC All input pins on the BUF600 and BUF601 are internally protected from ESD by means of a pair of back-to-back reverse-biased diodes to the power supplies as shown. These diodes will begin to conduct when the input voltage exceeds either power supply by about 0.7V. This situation can occur with loss of the amplifier’s power supplies while a signal source is still present. The diodes can typically withstand a continuous current of 30mA without destruction. To insure long term reliability, however, the diode current should be externally limited to 10mA or so whenever possible. ESD Protection Diodes internally connected to all pins. External Pin The internal protection diodes are designed to withstand 2.5kV (using the Human Body Model) and will provide adequate ESD protection for most normal handling procedures. However, static damage can cause subtle changes in amplifier input characteristics without necessarily destroying the device. In precision amplifiers, this may cause a noticeable degradation of offset and drift. Therefore, static protection is strongly recommended when handling the BUF600 and BUF601. Internal Circuitry –VCC FIGURE 1. Internal ESD Protection. TYPICAL PERFORMANCE CURVES At VCC = ±5V, RLOAD = 10kΩ, and TA = 25°C, unless otherwise noted. INPUT BIAS CURRENT vs TEMPERATURE 2 4 1.8 3 1.6 2 1.4 1 Bias Current (µA) Offset Voltage (mV, normalized) OFFSET VOLTAGE vs TEMPERATURE 5 BUF600 0 –1 BUF601 –2 1.2 1 0.8 BUF600 0.6 –3 0.4 –4 0.2 –5 BUF601 0 –40 –20 0 20 40 Temperature (°C) 60 80 100 –40 0 20 40 Temperature (°C) 60 80 100 INPUT IMPEDANCE vs FREQUENCY BUF601 10M 10M 1M 1M Input Impedance (Ω) Input Impedance (Ω) INPUT IMPEDANCE vs FREQUENCY BUF600 –20 100k 10k 1k 100k 10k 1k 100 1k 10k 100k 1M Frequency (Hz) 10M 100 100M ® BUF600, 601 4 1k 10k 100k 1M Frequency (Hz) 10M 100M TYPICAL PERFORMANCE CURVES (CONT) At VCC = ±5V, RLOAD = 10kΩ, and TA = 25°C, unless otherwise noted. INPUT VOLTAGE NOISE SPECTRAL DENSITY BUF600/601 QUIESCENT CURRENT vs TEMPERATURE 100 12 10 Quiescent Current (mA) Voltage Noise (nV/√Hz) 10 BUFF600 BUFF601 BUF601 8 6 BUF600 4 2 1 0 100 1000 10k Frequency (Hz) 100k –40 –20 0 BUF600 TRANSFER FUNCTION 40 60 80 100 BUF600 GAIN ERROR vs INPUT VOLTAGE 14 5 4 BUF600 (Full Temperature Range, RLOAD = 200Ω) RLOAD = 200Ω 12 3 –40°C 10 2 Gain Error (%) Output Voltage (V) 20 Temperature (°C) 1 0 –1 –2 +25°C 8 85°C 6 4 –3 2 –4 0 –5 –5 –4 –3 –2 –1 0 1 Input Voltage (V) 2 3 4 –5 5 –4 –3 –1 0 1 Input Voltage (V) 2 3 4 5 BUF601 GAIN ERROR vs INPUT VOLTAGE BUF601 TRANSFER FUNCTION 14 5 4 BUF601 (Full Temperature Range, RLOAD = 100Ω) RLOAD = 100Ω 12 –40°C +25°C 3 10 2 Gain Error (%) Output Voltage (V) –2 1 0 –1 –2 +85°C 8 6 4 –3 2 –4 0 –5 –5 –4 –3 –2 –1 0 1 Input Voltage (V) 2 3 4 –5 5 –4 –3 –2 –1 0 1 Input Voltage (V) 2 3 4 5 ® 5 BUF600, 601 TYPICAL PERFORMANCE CURVES (CONT) At VCC = ±5V, RLOAD = 100Ω (BUF601), RLOAD = 200Ω (BUF600), and TA = 25°C, unless otherwise noted. GROUP DELAY TIME vs FREQUENCY BUF600/601 GAIN FLATNESS 2 1.5 1 0.5 1 0 Gain (dB) Group Delay Time (ns) 2 0 BUF601 BUF600 –0.5 –1.0 –1.5 –2 RLOAD = 100Ω VO = 0.2Vp-p BUF600 RLOAD = 200Ω BUF601 RLOAD = 100Ω –2.5 –3 300k 1M 10M 100M 1G 3G 300k 1M 10M Frequency (Hz) BUF600 SMALL SIGNAL PULSE RESPONSE 160 VI = 5Vp-p tRISE = tFALL = 1.5ns (Generator) 3 2 VI 40 Voltage (V) Voltage (mV) 80 VO 0 –40 VI 1 VO 0 –1 –80 –2 –120 –3 –160 –4 0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 Time (ns) BUF600 SMALL SIGNAL PULSE RESPONSE 30 35 40 45 50 BUF600 LARGE SIGNAL PULSE RESPONSE 4 VI = 0.2Vp-p tRISE = tFALL = 3ns (Generator) 120 25 Time (ns) 160 VI = 5Vp-p tRISE = tFALL = 3ns (Generator) 3 80 2 40 Voltage (V) Voltage (mV) 1G BUF600 LARGE SIGNAL PULSE RESPONSE 4 VI = 0.2Vp-p tRISE = tFALL = 1.5ns (Generator) 120 100M Frequency (Hz) VI 0 VO –40 1 –2 –120 –3 0 5 10 15 20 25 30 35 40 45 –4 50 0 Time (ns) 5 10 15 20 25 30 Time (ns) ® BUF600, 601 VO –1 –80 –160 VI 0 6 35 40 45 50 TYPICAL PERFORMANCE CURVES (CONT) At VCC = ±5V, RLOAD = 100Ω (BUF601), RLOAD = 200Ω (BUF600), and TA = 25°C, unless otherwise noted. BUF601 SMALL SIGNAL PULSE RESPONSE 160 BUF601 LARGE SIGNAL PULSE RESPONSE 4 VI = 0.2Vp-p tRISE = tFALL = 1.5ns (Generator) 120 2 40 VI Voltage (V) 80 Voltage (mV) VI = 5Vp-p tRISE = tFALL = 1.5ns (Generator) 3 VO 0 –40 0 –1 –80 –2 –120 –3 –160 VO VI 1 –4 0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 Time (ns) BUF601 SMALL SIGNAL PULSE RESPONSE 40 45 50 VI = 5Vp-p tRISE = tFALL = 3ns (Generator) 3 80 2 40 Voltage (V) Voltage (mV) 35 4 VI = 0.2Vp-p tRISE = tFALL = 3ns (Generator) 120 VI 0 VO –40 1 VI 0 VO –1 –80 –2 –120 –3 –160 –4 0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 Time (ns) RIN 4 5 600 8 RS 15 VO COUT 5 RL –10 –15 –20 –25 –30 300k RS COUT f–3dB 1 0Ω 1pF 820MHz 2 30Ω 12pF 425MHz 3 15Ω 33pF 270MHz 4 12Ω 47pF 215MHz 4 3 2 1 –10 –20 –25 10M 35 40 45 50 4 100M 1G –30 300k 3G +5V 1 RS 8 601 VO COUT 5 –5V RL 0 –5 –15 VI = 0.4Vp-p 1M RIN 5 –5V 0 –5 VI 180Ω 10 Gain (dB) 10 1 30 BUF601 BANDWIDTH vs COUT with RECOMMENDED RS 20 +5V VI 180Ω 25 Time (ns) BUF600 BANDWIDTH vs COUT with RECOMMENDED RS 20 Gain (dB) 30 BUF601 LARGE SIGNAL PULSE RESPONSE 160 15 25 Time (ns) RS COUT f–3dB 1 0Ω 1pF 980MHz 2 30Ω 12pF 435MHz 3 15Ω 33pF 260MHz 4 12Ω 47pF 215MHz 4 3 2 1 VI = 0.4Vp-p 1M 10M 100M 1G 3G Frequency (Hz) Frequency (Hz) ® 7 BUF600, 601 TYPICAL PERFORMANCE CURVES (CONT) At VCC = ±5V, RLOAD = 100Ω (BUF601), RLOAD = 200Ω (BUF600), and TA = 25°C, unless otherwise noted. BUF600 BANDWIDTH vs RLOAD 20 BUF601 BANDWIDTH vs RLOAD 20 V1 = 0.2Vp-p 15 15 10 10 5 150Ω 0 Gain (dB) Gain (dB) 5 –5 500Ω –10 –15 –5 –20 –25 –25 –30 10M 100M 1G 100Ω –10 150Ω –15 1kΩ 1M 50Ω 0 –20 300k VI = 0.2Vp-p –30 300k 3G 1M 10M BUF600 BANDWIDTH vs OUTPUT VOLTAGE 10 5Vp-p 2.8Vp-p 5 1.4Vp-p 0 0.6Vp-p –5 –10 10 5Vp-p 2.8Vp-p 5 1.4Vp-p 15 Output Voltage (Vp-p) Output Voltage (Vp-p) 3G 20 15 0.2Vp-p –15 0 –10 –20 –25 –25 10M 100M 1G dB 300k 3G 0.2Vp-p –15 –20 1M 0.6Vp-p –5 1M 10M Frequency (Hz) 100M 1G 3G Frequency (Hz) HARMONIC DISTORTION vs FREQUENCY HARMONIC DISTORTION vs FREQUENCY 0 0 BUF601 RLOAD = 100Ω BUF600 RLOAD = 200Ω –10 –10 Harmonic Distortion (dBc) Harmonic Distortion (dBc) 1G BUF601 BANDWIDTH vs OUTPUT VOLTAGE 20 dB 300k 100M Frequency (Hz) Frequency (Hz) –20 –30 –40 –50 2f –60 3f –70 –80 0.1M 1M 10M Frequency (Hz) –30 –40 –50 2f –60 3f –70 –80 0.1M 100M 1M 10M Frequency (Hz) ® BUF600, 601 –20 8 100M TYPICAL PERFORMANCE CURVES (CONT) At VCC = ±5V, RLOAD = 100Ω (BUF601), RLOAD = 200Ω (BUF600), and TA = 25°C, unless otherwise noted. IQ vs TIME (Warmup) BUF600, BUF601 GAIN ERROR vs INPUT VOLTAGE 100 5 (Full Temperature Range, RLOAD = 10kΩ) 99 IQ (% of Final Value) Gain Error (%) 4 BUF600 3 2 1 BUF600 98 BUF601 97 96 95 BUF601 94 0 –5 –4 –3 –2 –1 0 1 2 3 4 0 5 Input Voltage (V) 1 2 3 4 5 6 7 8 Time (s) DISCUSSION OF PERFORMANCE The BUF600 and BUF601 are fabricated using a highperformance complementary bipolar process, which provides high-frequency NPN and PNP transistors with gigahertz transition frequencies (fΤ). Power supplies are rated at ±6V maximum, with the data sheet parameters specified at ±5V supplies. The BUF600 and BUF601 are 3-stage open-loop buffer amplifiers consisting of complementary emitter followers with a symmetrical class AB Darlington output stage. The complementary structure provides both sink and source current capability independent of the output voltage, while maintaining constant output and input impedances. The amplifiers use no feedback, so their low-frequency gain is slightly less than unity and somewhat dependent on loading. The optimized input stage is responsible for the high slew rate of up to 3600V/µs, wide large signal bandwidth of 320MHz, and quiescent current reduction to ±3mA (BUF600) and ±6mA (BUF601). These features yield an excellent large signal bandwidth/quiescent current ratio of 320MHz, 5Vp-p at 3mA/6mA quiescent current. The complementary emitter followers of the input stage work with current sources as loads. The internal PTAT power supply controls their quiescent current and with its temperature characteristics keeps the transconductance of the buffer amplifiers constant. The Typical Performance Curves show the quiescent current variation versus temperature. variations in source impedances. A resistor between 100Ω and 250Ω in series with the buffer input lead will usually eliminate oscillation problems from inductive sources such as unterminated cables without sacrificing speed. Another excellent feature is the output-to-input isolation over a wide frequency range. This characteristic is very important when the buffer drives different equipment over cables. Often the cable is not perfect or the termination is incorrect and reflections arise that act like a signal source at the output of the buffer. Open-loop devices often sacrifice linearity and introduce frequency distortion when driving low load impedance. The BUF600 and BUF601, however, do not. Their design yields low distortion products. The harmonic distortion characteristics into loads greater than 100Ω (BUF601) and greater than 200Ω (BUF600) are shown in the Typical Performance Curves. The distortion can be improved even more by increasing the load resistance. Differential gain (DG) and differential phase (DP) are among the important specifications for video applications. DG is defined as the percent change in gain over a specified change in output voltage level (0V to 0.7V.) DP is defined as the phase change in degrees over the same output voltage change. Both DG and DP are specified at the PAL subcarrier frequency of 4.43MHz. The errors for differential gain are lower than 0.5%, while those for differential phase are lower than 0.04°. The cross current in the input stage is kept very low, resulting in a low input bias current of 0.7µA/1.5µA and high input impedance of 4.8MΩ || 1pF/2.5MΩ || 1pF. The second stage drives the output transistors and reduces the output impedance and the feedthrough from output to input when driving RLC loads. With its minimum 20mA long-term DC output current capability, 50mA pulse current, low output impedance over frequency, and stability to drive capacitive loads, the BUF601 can drive 50Ω and 75Ω systems or lines. The BUF600 with lower quiescent current and therefore higher output impedance is well-suited primarily to interstage buffering. This type of open-loop amplifier is a new and easy-to-use step to prevent an interaction between two points in complex highspeed analog circuitry. The input of the BUF600 and BUF601 looks like a high resistance in parallel with a 1pF capacitance. The input characteristics change very little with output loading and input voltage swing. The BUF600 and BUF601 have excellent input-to-output isolation and feature high tolerance to ® 9 BUF600, 601 The buffer outputs are not current-limited or protected. If the output is shorted to ground, high currents could arise when the input voltage is ±3.6V. Momentary shorts to ground (a few seconds) should be avoided but are unlikely to cause permanent damage. +5V Pos BUF600AP RIN In CIRCUIT LAYOUT The high-frequency performance of the BUF600 and BUF601 can be greatly affected by the physical layout of the printed circuit board. The following tips are offered as suggestions, not as absolute musts. Oscillations, ringing, poor bandwidth and settling, and peaking are all typical problems that plague high-speed components when they are used incorrectly. 1 4 8 +1 ROUT Out 51Ω 160Ω 5 GND C3 2.2µF C1 470nF • Bypass power supplies very close to the device pins. Use tantalum chip capacitors (approximately 2.2µF); a parallel 470nF ceramic chip capacitor may be added if desired. Surface-mount types are recommended due to their low lead inductance. –5V Neg FIGURE 2. Test Circuit. IMPEDANCE MATCHING The BUF600 and BUF601 provide power gain and isolation between source and load when used as an active tap or impedance matching device as illustrated in Figure 3. In this example, there is no output matching path between the buffer and the 75Ω line. Such matching is not needed when the distant end of the cable is properly terminated, since there is no reflected signal when the buffer isolates the source. This technique allows the full output voltage of the buffer to be applied to the load. • PC board traces for power lines should be wide to reduce impedance or inductance. • Make short and low inductance traces. The entire physical circuit should be as small as possible. • Use a low-impedance ground plane on the component side to ensure that low-impedance ground is available throughout the layout. • Do not extend the ground plane under high-impedance nodes sensitive to stray capacitances, such as the buffer’s input terminals. +5V • Sockets are not recommended, because they add significant inductance and parasitic capacitance. If sockets must be used, consider using zero-profile solderless sockets. 2.2µF 470nF • Use low-inductance and surface-mounted components. Using all surface-mount components will offer the best AC performance. 1 VI 4 160Ω • A resistor (100Ω to 250Ω) in series with the input of the buffers may help to reduce peaking. BUF 8 75Ω 75Ω 2.2µF 470nF –5V FIGURE 3. Impedance Converter. ® 10 VO 5 300Ω • Plug-in prototype boards and wire-wrap boards will not function well. A clean layout using RF techniques is essential—there are no shortcuts. BUF600, 601 C4 2.2µF C2 470nF DRIVING CABLES The most obvious way is to connect the cable directly to the output of the buffer. This results in a gain determined by the buffer output resistance and the characteristic impedance of the cable, assuming it is properly terminated. Direct Drive +5V ZO AV = 1 4 VI 150Ω ZO 8 BUF ZO + RO Double termination of a cable is the cleanest way to drive it, since reflections are absorbed on both ends of the cable. The cable source resistor is equal to the characteristic impedance less the output resistance of the buffer amplifiers. The gain is –6dB excluding of the cable attenuation. VO 5 ZO ZO –5V VIDEO DISTRIBUTION AMPLIFIER In this broadcast quality circuit, the OPA623 provides a very high input impedance so that it may be used with a wide variety of signal sources including video DACs, CCD cameras, video switches or 75Ω cables. The OPA623 provides a voltage gain of 2.5V/V, while the potentiometer of 200Ω allows the overall gain to be adjusted to drive the standard signal levels into the back-terminated 75Ω cables. Back matching prevents multiple reflections in the event that the remote end of the cable is not properly terminated. +5V ROUT = ZO – RO 1 4 VI 150Ω ZO 8 BUF VO ROUT 5 ZO ZO –5V AV = – 6dB Double Matched FIGURE 4. Driving Cables. +5V 2.2µF 470nF 120Ω 1 4 BUF601 68Ω 8 VO 5 470nF 120Ω 2 BUF601 OPA658 –5V 68Ω 8 VO 470nF 2.2µF +5V 470nF 2.2µF –5V 6 4 75Ω 2.2µF 5 7 3 150Ω 470nF 1 4 +5V VI 2.2µF +5V 200Ω 120Ω 1 4 –5V BUF601 68Ω 8 VO 5 250Ω 100Ω 470nF 2.2µF –5V FIGURE 5. Video Distribution Amplifier. ® 11 BUF600, 601 +5V 2.2µF 470nF 120Ω 3 VI 1 100Ω 8 4 BUF601 DT OPA660 8 VO 5 2 +5V 470nF 2.2µF 100Ω R1 150Ω 7 5 + DB –5V 6 4 1 R2 150Ω –5V RQ 250Ω G = +2 = 1 + R2 R1 –5V FIGURE 6. Inside a Feedback Loop of a Voltage Feedback Amplifier (BUF601 and OPA660). +5V 2.2µF 470nF 1 VO 150Ω 8 100Ω 3 4 BUF601 R2 240Ω DT 75Ω 8 VO 5 2 2.2µF +5V 470nF 2.2µF OPA660 10nF –5V 470pF 100Ω VI R1 42Ω 7 5 DB 1 75Ω 6 4 470pF 250Ω 10nF G≈– 2.2µF R2 2 (R1 + ROUT) –5V FIGURE 7. Output Buffer for an Inverting RF-Amplifier (Direct Feedback). ® BUF600, 601 12 = –2.031 = VO VI +5V 68nF 150Ω VI 75Ω 4 1 8 BUF600/1 5 VO 47kΩ –5V 1kΩ +5V 1kΩ CA 3080 10kΩ –5V 0.1µF 2N3904 Clamp Pulse 47kΩ 1N 4148 4Vp-p 560kΩ –5V FIGURE 8. Input Amplifier with Baseband Video DC Restoration. +5V Generator 50Ω In RIN 160Ω 1 4 DUT 8 ROUT 51Ω Out 50Ω Network Analyzer RIN = 50Ω 5 RIN 50Ω 50Ω –5V Test Fixture FIGURE 9. Test Circuit Frequency Response. +5V Pulse Generator 50Ω In RIN 160Ω 1 4 DUT 8 ROUT 51Ω Out 50Ω Digitizing Scope RIN = 50Ω 5 RIN = 50Ω 50Ω –5V Test Fixture FIGURE 10. Test Circuit Pulse Response. ® 13 BUF600, 601 +5V +5V Generator 75Ω In RIN 160Ω 1 4 DUT 8 ROUT 75Ω Out 120Ω 2 5 RIN = 75Ω 75Ω Test Fixture 7 3 OPA681 4 75Ω –5V –5V 4.43MHz 400Ω VDC 400Ω FIGURE 11. Test Circuit Differential Gain and Phase. ® BUF600, 601 14 6 75Ω 75Ω Video Analyzer RIN = 75Ω