OPA ® OPA660 660 OPA 660 Wide Bandwidth OPERATIONAL TRANSCONDUCTANCE AMPLIFIER AND BUFFER FEATURES APPLICATIONS ● WIDE BANDWIDTH: 850MHz ● BASE LINE RESTORE CIRCUITS ● HIGH SLEW RATE: 3000V/µs ● LOW DIFFERENTIAL GAIN/PHASE ERROR: 0.06%/0.02° ● VERSATILE CIRCUIT FUNCTION ● EXTERNAL IQ-CONTROL ● VIDEO/BROADCAST EQUIPMENT ● COMMUNICATIONS EQUIPMENT ● HIGH-SPEED DATA ACQUISITION ● WIDEBAND LED DRIVER ● AGC-MULTIPLIER DESCRIPTION The OPA660 is a versatile monolithic component designed for wide-bandwidth systems including high performance video, RF and IF circuitry. It includes a wideband, bipolar integrated voltage-controlled current source and voltage buffer amplifier. ● NS-PULSE INTEGRATOR ● CONTROL LOOP AMPLIFIER ● 400MHz DIFFERENTIAL INPUT AMPLIFIER 200Ω 100Ω The voltage-controlled current source or Operational Transconductance Amplifier (OTA) can be viewed as an “ideal transistor.” Like a transistor, it has three terminals—a high-impedance input (base), a lowimpedance input/output (emitter), and the current output (collector). The OTA, however, is self-biased and bipolar. The output current is zero-for-zero differential input voltage. AC inputs centered about zero produce an output current which is bipolar and centered about zero. The transconductance of the OTA can be adjusted with an external resistor, allowing bandwidth, quiescent current and gain trade-offs to be optimized. 3 B R1 6 +1 VO R3 390Ω OTA E 2 IQ = 20mA G=1+ RP 82Ω CP 6.4pF R5 100Ω R3 =3 2R5 XE OPA660 DIRECT-FEEDBACK FREQUENCY RESPONSE 20 Output Voltage (dB) The open-loop buffer amplifier provides 850MHz bandwidth and 3000V/µs slew rate. Used as a basic building block, the OPA660 simplifies the design of AGC amplifiers, LED driver circuits for Fiber Optic Transmission, integrators for fast pulses, fast control loop amplifiers, and control amplifiers for capacitive sensors and active filters. VI 5 8 C The OPA660 is packaged in SO-8 surface-mount, and 8-pin plastic DIP, specified from –40°C to +85°C. 15 5Vp-p 10 2.8Vp-p 5 1.4Vp-p 0 0.6Vp-p –5 –10 0.2Vp-p –15 –20 –25 –30 100k 1M 10M 100M 1G Frequency (Hz) 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 © 1990 Burr-Brown Corporation PDS-1072F Printed in U.S.A. April, 1995 SPECIFICATIONS Typical at IQ = 20mA, VS = ±5V, TA = +25°C, and RL = 500Ω, unless otherwise specified. OPA660AP, AU PARAMETER OTA TRANSCONDUCTANCE Transconductance OTA INPUT OFFSET VOLTAGE Initial vs Temperature vs Supply (tracking) vs Supply (non-tracking) vs Supply (non-tracking) OTA B-INPUT BIAS CURRENT Initial vs Temperature vs Supply (tracking) vs Supply (non-tracking) vs Supply (non-tracking) OTA OUTPUT BIAS CURRENT Output Bias Current vs Temperature vs Supply (tracking) vs Supply (non-tracking) vs Supply (non-tracking) OTA OUTPUT Output Current Output Voltage Compliance Output Impedance Open-Loop Gain BUFFER OFFSET VOLTAGE Initial vs Temperature vs Supply (tracking) vs Supply (non-tracking) vs Supply (non-tracking) BUFFER INPUT BIAS CURRENT Initial vs Temperature vs Supply (tracking) vs Supply (non-tracking) vs Supply (non-tracking) CONDITIONS MIN TYP MAX UNITS VC = 0V 75 125 200 mA/V ±30 55 40 40 +10 50 60 45 48 mV µV/°C dB dB dB –2.1 5 ±5 µA nA/°C nA/V nA/V nA/V VB = 0 VS = ±4.5V to ±5.5V V+ = 4.5V to 5.5V V– = –4.5V to –5.5V VS = ±4.5V to ±5.5V V+ = 4.5V to 5.5V V– = –4.5V to –5.5V ±750 ±1500 ±500 ±10 500 ±10 ±10 ±10 VB = 0, VC = 0V VS = ±4.5V to ±5.5V V+ = 4.5V to 5.5V V– = –4.5V to –5.5V ±10 ±4.0 f = 1kHz ±30 VS = ±4.5V to ±5.5V V+ = 4.5V to 5.5V V– = –4.5V to –5.5V +7 50 60 45 48 mV µV/°C dB dB dB –2.1 5 ±5 µA nA/°C nA/V nA/V nA/V 55 40 40 VS = ±4.5V to ±5.5V V+ = 4.5V to 5.5V V– = –4.5V to –5.5V VO = ±100mV VO = ±1.4V VO = ±2.5V 3.58MHz, at 0.7V 3.58MHz, at 0.7V f = 10MHz, VO = 0.5Vp-p 5V Step 2V Step VO = 100mVp-p 5V Step Group Delay Time BUFFER RATED OUTPUT Voltage Output Current Output Gain IO = ±1mA ±3.7 ±10 0.96 RL = 500Ω RL = 5kΩ Output Impedance POWER SUPPLY Voltage, Rated Derated Performance Quiescent Current (Programmable, Useful Range) ±4.5 ® OPA660 mA V Ω || pF dB ±750 ±1500 ±500 BUFFER INPUT NOISE Voltage Noise Density, f = 100kHz Differential Gain Error Differential Phase Error Harmonic Distortion, 2nd Harmonic Slew Rate Settling Time 0.1% Rise Time (10% to 90%) ±25 ±25 ±25 µA nA/°C µA/V µA/V µA/V ±15 ±4.7 25k || 4.2 70 IC = ±1mA BUFFER and OTA INPUT IMPEDANCE Input Impedance BUFFER DYNAMIC RESPONSE Small Signal Bandwidth Full Power Bandwidth ±20 2 1.0 || 2.1 MΩ || pF 4 nV/√Hz 850 800 570 0.06 0.02 –68 3000 25 1 1.5 250 MHz MHz MHz % Degrees dBc V/µs ns ns ns ps ±4.2 ±15 0.975 0.99 7 || 2 V mA V/V V/V Ω || pF ±5 ±3 to ±26 ±5.5 V V mA PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS Top View Power Supply Voltage ......................................................................... ±6V Input Voltage(1) ........................................................................ ±VS ±0.7V Operating Temperature ................................................... –40°C to +85°C Storage Temperature ..................................................... –40°C to +125°C Junction Temperature .................................................................... +175°C Lead Temperature (soldering, 10s) ............................................... +300°C DIP/SO-8 I Q Adjust 1 8 C E 2 7 V+ = +5V B 3 6 Out 1 NOTE: (1) Inputs are internally diode-clamped to ±VS. PACKAGE/ORDERING INFORMATION V– = –5V 4 5 PRODUCT PACKAGE PACKAGE DRAWING NUMBER(1) OPA660AP OPA660AU 8-Pin Plastic DIP SO-8 Surface-Mount 006 182 In TEMPERATURE RANGE –25°C to +85°C –25°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. 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. 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. 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 OPA660 TYPICAL PERFORMANCE CURVES IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted. TOTAL QUIESCENT CURRENT vs RQ TOTAL QUIESCENT CURRENT vs TEMPERATURE 1.5 Total Quiescent Current (Normalized) Total Quiescent Current (mA) 100 30 Nominal Device High IQ Device 10 3.0 Low IQ Device 1.0 100 300 1.0k 3.0k 10k 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 R Q — Resistor Value ( Ω) –25 25 50 Temperature (°C) BUFFER AND OTA B-INPUT BIAS CURRENT vs TEMPERATURE OTA C-OUTPUT BIAS CURRENT vs TEMPERATURE 0 75 100 5 Representative Units OTA C-Output Bias Current (µA) Input Bias Current (µA) 0.0 –1.0 –2.0 –3.0 –4.0 Trim Point –40 –5.0 –20 –0 20 40 60 100 80 –20 –0 20 Temperature (°C) OTA C-OUTPUT RESISTANCE vs TOTAL QUIESCENT CURRENT (IQ) 60 80 100 OTA TRANSFER CHARACTERISTICS 60 10 50 OTA Output Current (mA) OTA Output Resistance (k Ω) 40 Temperature (°C) 40 30 20 10 5 IQ = 5mA 0 IQ = 10mA –5 IQ = 20mA 0 –10 4 6 8 10 12 14 16 18 20 –60 Total Quiescent Current — IQ (mA) –20 0 20 OTA Input Voltage (mV) ® OPA660 –40 4 40 60 TYPICAL PERFORMANCE CURVES (CONT) IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted. BUFFER AND OTA B-INPUT OFFSET VOLTAGE vs TEMPERATURE BUFFER AND OTA B-INPUT RESISTANCE vs TOTAL QUIESCENT CURRENT (IQ) Buffer and OTA B-Input Resistance (MΩ) 20 Offset Voltage (mV) 15 10 5 0 –5 –10 –15 –20 0 25 50 75 RINOTA 3 RINBUF 2 1 0 –1 100 4 8 10 12 14 16 18 Total Quiescent Current — IQ (mA) BUFFER OUTPUT AND OTA E-OUTPUT RESISTANCE vs TOTAL QUIESCENT CURRENT (IQ) BUFFER SLEW RATE vs TOTAL QUIESCENT CURRENT (IQ) 20 4000 40 3800 3600 30 20 ROUTOTA ROUTBUF 10 Rising Edge 3400 3200 3000 2800 Falling Edge 2600 2400 2200 2000 0 4 6 8 10 12 14 16 18 4 20 6 8 10 12 14 16 18 20 Total Quiescent Current—IQ (mA) Total Quiescent Current—IQ (mA) OTA TRANSCONDUCTANCE vs TOTAL QUIESCENT CURRENT (IQ) OTA TRANSCONDUCTANCE vs FREQUENCY 1000 OTA Transconductance (mA/V) 150 OTA Transconductance (mA/V) 6 Temperature (°C) Slew Rate (V/µs) Buffer Output and OTA E-Output Resistance (Ω) –25 4 100 50 RL = 50Ω IQ = 20mA 106mA/V 100 IQ = 10mA IQ = 5mA 66mA/V 40mA/V 10 0 0 2 4 6 8 10 12 14 16 18 1M 20 10M 100M 1G Frequency (Hz) Total Quiescent Current—IQ (mA) ® 5 OPA660 TYPICAL PERFORMANCE CURVES (CONT) IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted. BUFFER FREQUENCY RESPONSE BUFFER VOLTAGE NOISE SPECTRAL DENSITY 100 20 –3dB Point 2.8Vp-p 10 Output Voltage (dB) Voltage Noise (nV/ Hz) 15 10 5 1.4Vp-p 0 0.6Vp-p –5 –10 0.2Vp-p –15 –20 –25 1 dB 100 1k 10k 100k 1M 10M 100M 200k 1M 10M 100M 1G Frequency (Hz) Frequency (Hz) IQ = 20mA RIN = 160Ω RL = 100Ω BUFFER MAX OUTPUT VOLTAGE vs FREQUENCY TRANSCONDUCTANCE vs INPUT VOLTAGE 160 Transconductance (mA/V) 0 RQ = 250Ω 120 RQ = 500Ω 80 RQ = 1kΩ RQ = 2kΩ 40 0 0.1 1M 10M 100M 1G –40 –30 –20 –10 0 10 OTA PULSE RESPONSE 30 40 OTA PULSE RESPONSE +2.5V VO (V) +0.625V 0V 0V –2.5V –0.625V Input Voltage = 1.25Vp-p, tR = tF = 1ns, Gain = 4 Output Voltage = 5Vp-p ® OPA660 20 Input Voltage (mV) Frequency (Hz) VO (V) Buffer Output Voltage (Vp-p) 10 6 TYPICAL PERFORMANCE CURVES (CONT) IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted. BUFFER LARGE SIGNAL PULSE RESPONSE VO (V) VO (V) BUFFER LARGE SIGNAL PULSE RESPONSE tR = tF = 3ns, VO = 5Vp-p (HDTV Signal Pulse) tR = tF = 10ns, VO = 5Vp-p 160Ω 50Ω 5 VI +1 Network 50Ω Analyzer R6 6 VO 50Ω RIN = 50Ω 50Ω 50Ω R7 RL = R6 + R7||RIN = 100Ω tR = tF = 3ns, VO = 0.2Vp-p Test Circuit Buffer Pulse and Frequency Response BUFFER DIFFERENTIAL GAIN ERROR vs TOTAL QUIESCENT CURRENT (IQ) BUFFER DIFFERENTIAL PHASE ERROR vs TOTAL QUIESCENT CURRENT (IQ) 0.10 Differential Phase Error (Degrees) Differential Gain Error (%) 0.25 0.20 RL = 500Ω VO = 0.7Vp-p f = 3.58MHz 0.15 0.10 0.05 0 4 6 8 10 12 14 16 18 20 RL = 500Ω VO = 0.7Vp-p f = 3.58MHz 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 4 Total Quiescent Current —IQ (mA) 6 8 10 12 14 16 18 20 Total Quiescent Current—IQ (mA) ® 7 OPA660 TYPICAL PERFORMANCE CURVES (CONT) IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted. HARMONIC DISTORTION vs FREQUENCY HARMONIC DISTORTION vs FREQUENCY –40 –30 RL = 150Ω VO = 0.5Vp-p IQ = 20mA –50 Harmonic Distortion (dBc) Harmonic Distortion (dBc) –30 2f –60 3f –70 –40 RL = 500Ω IQ = 20mA 3f 2Vp-p –50 3f 0.5Vp-p 2f 2Vp-p –60 2f 0.5Vp-p –70 Measurement Limit Measurement Limit –80 –80 10M 20M 40M 60M 100M 10M 20M Frequency (Hz) 40M 60M 100M Frequency (Hz) APPLICATIONS INFORMATION The OPA660 operates from ±5V power supplies (±6V maximum). Do not attempt to operate with larger power supply voltages or permanent damage may occur. The buffer output is not current-limited or protected. If the output is shorted to ground, currents up to 60mA could flow. Momentary shorts to ground (a few seconds) should be avoided, but are unlikely to cause permanent damage. The same cautions apply to the OTA section when connected as a buffer (see Basic Applications Circuits, Figure 6b). Inputs of the OPA660 are protected with internal diode clamps as shown in the simplified schematic, Figure 1. These protection diodes can safely conduct 10mA, continuously (30mA peak). If input voltages can exceed the power supply voltages by 0.7V, the input signal current must be limited. (7) +VCC = +5V Bias Circuitry VI VO B E C (5) (6) (3) (2) (8) BUFFER OTA 100Ω 50kΩ –VCC = –5V I Q Adj. (1) R Q (ext.) (4) FIGURE 1. Simplified Circuit Diagram. ® OPA660 8 BUFFER SECTION—AN OVERVIEW The buffer section of the OPA660 is an open-loop buffer consisting of complementary emitter-followers. It uses no feedback, so its low frequency gain is slightly less than unity and somewhat dependent on loading. It is designed primarily for interstage buffering. It is not designed for driving long cables or low impedance loads (although with small signals, it may be satisfactory for these applications). QUIESCENT CURRENT CONTROL PIN The quiescent current of the OPA660 is set with a resistor, RQ, connected from pin 1 to V–. It affects the operating currents of both the buffer and OTA sections. This controls the bandwidth and AC behavior as well as the transconductance of the OTA section. RQ = 250Ω sets approximately 20mA total quiescent current at 25°C. With a fixed 250Ω resistor, process variations could cause this current to vary from approximately 16mA to 26mA. It may be appropriate in some applications to trim this resistor to achieve the desired quiescent current or AC performance. TRANSCONDUCTANCE (OTA) SECTION—AN OVERVIEW The symbol for the OTA section is similar to a transistor. Applications circuits for the OTA look and operate much like transistor circuits—the transistor, too, is a voltagecontrolled current source. Not only does this simplify the understanding of applications circuits, but it aids the circuit optimization process. Many of the same intuitive techniques used with transistor designs apply to OTA circuits as well. Applications circuits generally do not show resistor, RQ, but it is required for proper operation. With a fixed RQ resistor, quiescent current increases with temperature (see typical performance curve, Quiescent Current vs Temperature). This variation of current with temperature holds the transconductance, gm, of the OTA relatively constant with temperature (another advantage over a transistor). The three terminals of the OTA are labeled B, E, and C. This calls attention to its similarity to a transistor, yet draws distinction for clarity. It is also possible to vary the quiescent current with a control signal. The control loop in Figure 3 shows a 1/2 of a REF200 current source used to develop 100mV on R1. The loop forces 100mV to appear on R2. Total quiescent current of the OPA660 is approximately 85 • I1, where I1 is the current made to flow out of pin 1. While it is similar to a transistor, one essential difference is the sense of the C output current. It flows out the C terminal for positive B-to-E input voltage and in the C terminal for negative B-to-E input voltage. The OTA offers many advantages over a discrete transistor. The OTA is self-biased, simplifying the design process and reducing component count. The OTA is far more linear than a transistor. Transconductance of the OTA is constant over a wide range of collector currents—this implies a fundamental improvement of linearity. Internal Current Source Circuitry OPA660 V+ BASIC CONNECTIONS Figure 2 shows basic connections required for operation. These connections are not shown in subsequent circuit diagrams. Power supply bypass capacitors should be located as close as possible to the device pins. Solid tantalum capacitors are generally best. See “Circuit Layout” at the end of the applications discussion and Figure 26 for further suggestions on layout. 1/2 REF200 100µA 1kΩ R1 RQ 250Ω 8 2 3 –5V(1) 1 4 FIGURE 3. Optional Control Loop for Setting Quiescent Current. 10nF With this control loop, quiescent current will be nearly constant with temperature. Since this differs from the temperature-dependent behavior of the internal current source, other temperature-dependent behavior may differ from that shown in typical performance curves. 2.2µF 6 5 RB (25Ω to 200Ω) 470pF 2.2µF Solid Tantalum IQ ≈ 85 • I1 R1 = 85 • (100µA) R2 = 20mA NOTE: (1) Requires input common-mode range and output swing close to V–, thus the choice of OPA1013. Solid Tantalum + –VCC 425Ω R2 +5V (1) 470pF + 10nF 4 I1 7 RB (25Ω to 200Ω) 50kΩ 1 1/2 (1) OPA1013 RQ = 250Ω sets roughly IQ ≈ 20mA 1 100Ω The circuit of Figure 3 will control the IQ of the OPA660 somewhat more accurately than with a fixed external resistor, RQ. Otherwise, there is no fundamental advantage to NOTE: (1) VS = ±6V absolute max. FIGURE 2. Basic Connections. ® 9 OPA660 using this more complex biasing circuitry. It does, however, demonstrate the possibility of signal-controlled quiescent current. This may suggest other possibilities such as AGC, dynamic control of AC behavior, or VCO. +5V 4.7kΩ Figure 4 shows logic control of pin 1 used to disable the OPA660. Zero/5V logic levels are converted to a 1mA/0mA current connected to pin 1. The 1mA current flowing in RQ increases the voltage at pin 1 to approximately 1V above the –5V rail. This will reduce IQ to near zero, disabling the OPA660. Internal Current Source Circuitry 0/5V Logic In 5V: OPA660 On 2N2907 OPA660 100Ω 50kΩ BASIC APPLICATIONS CIRCUITS Most applications circuits for the OTA section consist of a few basic types which are best understood by analogy to a transistor. Just as the transistor has three basic operating modes—common emitter, common base, and common collector—the OTA has three equivalent operating modes common-E, common-B, and common-C. See Figures 5, 6, and 7. IC 1 4 RQ 250Ω IC = 0: OPA660 On IC ≈ 1mA: OPA660 Off –5V FIGURE 4. Logic-Controlled Disable Circuit. V+ RB RL VO 100Ω VI Inverting Gain VOS ≈ several volts VI RB VO 8 C 3 B OTA Non-Inverting Gain VOS ≈ 0 RL E 2 RE RE V– (b) Common-E Amplifier (a) Common-Emitter Amplifier Transconductance varies over temperature. Transconductance remains constant over temperature. FIGURE 5. Common-Emitter vs Common-E Amplifier. V+ 8 C V+ 100Ω VI 3 B G=– RL OTA G≈1 VOS ≈ 0 Non-Inverting Gain VOS ≈ several volts VO VO G≈1 VOS ≈ 0.7V RE RE 100Ω RE (b) Common-C Amplifier (Buffer) 3 B V– 1+ (a) Common-Collector Amplifier (Emitter Follower) RO = 1 gm ¥ R E ≈1 (a) Common-Base Amplifier RL RE 8 C OTA VO Inverting Gain VOS ≈ 0 RL RE VI 1 gm (b) Common-B Amplifier FIGURE 6. Common-Collector vs Common-C Amplifier. FIGURE 7. Common-Base vs Common-B Amplifier. ® OPA660 ≈– E 2 VI 1 G= 1 RE + gm VO E 2 VI RL 10 A positive voltage at the B, pin 3, causes a positive current to flow out of the C, pin 8. Figure 5b shows an amplifier connection of the OTA, the equivalent of a common-emitter transistor amplifier. Input and output can be ground-referenced without any biasing. Due to the sense of the output current, the amplifier is non-inverting. Figure 8 shows the amplifier with various gains and output voltages using this configuration. It is recommended to use a low value resistor in series with the B OTA and buffer inputs. This reduces any tendency to oscillate and controls frequency response peaking. Values from 25Ω to 200Ω are typical. Figure 7 shows the Common-B amplifier. This configuration produces an inverting gain, and a low impedance input. This low impedance can be converted to a high impedance by inserting the buffer amplifier in series. Just as transistor circuits often use emitter degeneration, OTA circuits may also use degeneration. This can be used to reduce the effect that offset voltage and offset current might otherwise have on the DC operating point of the OTA. The E-degeneration resistor may be bypassed with a large capacitor to maintain high AC gain. Other circumstances may suggest a smaller value capacitor used to extend or optimize high-frequency performance. CIRCUIT LAYOUT The high frequency performance of the OPA660 can be greatly affected by the physical layout of the circuit. The following tips are offered as suggestions, not dogma. • Bypass power supplies very close to the device pins. Use a combination between tantalum capacitors (approximately 2.2µF) and polyester capacitors. Surface-mount types are best because they provide lowest inductance. The transconductance of the OTA with degeneration can be calculated by— 1 gm = 1 + RE gm • Make short, wide interconnection traces to minimize series inductance. • Use a large ground plane to assure that a low impedance ground is available throughout the layout. Figure 6b shows the OTA connected as an E-follower—a voltage buffer. The buffer formed by this connection performs virtually the same as the buffer section of the OPA660 (the actual signal path is identical). • Do not extend the ground plane under high impedance nodes sensitive to stray capacitance. • Sockets are not recommended because they add significant inductance. RL1 20 VO OTA 100Ω R1 RIN 50Ω RL2 rE RL = RL1 + RL2 || RIN VI 2 G= RE RL RE + r E , rE = G= RE + 8 Ω 1.4Vp-p 0 600mVp-p –5 –10 200mVp-p –15 –25 –30 300k 1M 10M 100M 1G 3G Frequency (Hz) at I Q = 20mA IQ = 20mA R1 = 100Ω RE = 51Ω RL = 50Ω Gain = 1 20 20 15 –3dB Point 10 Output Voltage (dB) 5 1.4Vp-p 0 –5 600mVp-p –10 –15 200mVp-p –5 –15 –25 100M 1G –30 100k 3G Frequency (Hz) 600mVp-p –10 –25 10M 1.4Vp-p 0 –20 1M 2.8Vp-p 5 –20 –30 300k –3dB Point 5Vp-p 15 2.8Vp-p 10 Output Voltage (dB) 5 –20 1 gm 1 At IQ = 20mA r E = = 8Ω 125mA/V RL –3dB Point 2.8Vp-p 10 Output Voltage (dB) 3 15 Network Analyzer 8 200mVp-p 1M 10M 100M 1G Frequency (Hz) IQ = 20mA R1 = 100Ω RE = 51Ω RL = 100Ω Gain = 2 IQ = 20mA R1 = 100Ω RE = 51Ω RL = 500Ω Gain = 10 FIGURE 8. Common-E Amplifier Performance. ® 11 OPA660 • Use low-inductance components. Some film resistors are trimmed with spiral cuts which increase inductance. • A resistor (25Ω to 200Ω) in series with the buffer and/or B input may help reduce oscillations and peaking. • Use surface-mount components—they generally provide the lowest inductance. • Use series resistors in the supply lines to decouple multiple devices. OPA660 CURRENT-FEEDBACK C1 20 5 6 +1 VO Output Voltage (dB) 56Ω R2 8 C 3 B OTA E 2 200Ω R1 47Ω VI G=1+ R4 R5 5Vp-p 10 2.8Vp-p 5 1.4Vp-p 0 –5 0.6Vp-p –10 0.2Vp-p –15 –3dB Point –20 R4 R5 22Ω 15 –25 –30 100k ≈ 10 1M 10M 100M 1G Frequency (Hz) R Q = 250Ω (IQ ≈ 20mA) IQ = 20mA R1 = 47Ω R2 = 56Ω R4 = 200Ω R5 = 22Ω Gain = 10 FIGURE 9. Current-Feedback Amplifier. 20Ω VIN FIGURE 10. Current-Feedback Amplifier Frequency Response, G = 10. 5 +1 6 C1 100pF 20Ω VOUT OPA650 R2 100kΩ D1 25Ω D1, D2 = 1N4148 RQ = 1kΩ D2 R1 40.2Ω • The OTA amplifier works as a current conveyor (CCII) in this circuit, with a current gain of 1. • R1 and C1 set the DC restoration time constant. CCII 8 C 2 E • D1 adds a propagation delay to the DC restoration. B • R2 and C1 set the decay time constant. 3 20Ω FIGURE 11. DC Restorer Circuit. 8 C 3 B +IN OTA IO VI 150Ω E 2 3 B OTA RL 150Ω E 2 RE 50Ω Tuning Coil Magnetic Head Driver Transformer G= RL R E + rE R Q = 250Ω (IQ ≈ 20mA) FIGURE 13. Cable Amplifier. 3 B OTA C 8 FIGURE 12. High Speed Current Driver (bridge combination for increased output voltage capability). ® OPA660 6 +1 RE 42Ω 2 E –IN 5 8 C 12 VO ≈ +3 C8 0.5...2.5pF +5V R8 27kΩ R6 47kΩ Offset R2 Trim 10kΩ +5V –5V R1 100Ω VI R3 100Ω +5V 7 3 RC5 150Ω 2.2µF C3 R4 150Ω 8 5 +1 6 OTA 2 4 C3 R2 100Ω C3 2.2µF 1 4 BUF600 1 5 RQ 250Ω R5 47Ω C3 2.2µF VO 2.2µF –5V –5V Propagation Delay Time = 5ns Rise Time = 1.5ns D1 D2 DMF3068A FIGURE 14. Comparator (Low Jitter). +5V 22Ω IO = IO1 + IO2 180Ω VI 8 IO1 C 3 B OTA 8 IO1 C 3 B Q1 +IB 22Ω Q2 1kΩ OTA Diode E 2 E 2 RE 50Ω RE 50Ω 180Ω Q1, Q2: 2N3906 FIGURE 15. High Speed Current Driver. ® 13 OPA660 8 C 180Ω 3 B VI 200Ω 33pF OTA 47Ω E 2 VO f–3dB ±100mV ±300mV ±700mV ±1.4V ±2.5V 351MHz 374MHz 435MHz 460MHz 443MHz 8 C 780Ω VI Network Analyzer VO RE 50Ω 3 B RIN 50Ω OTA 820Ω 620Ω 1µF 50kΩ 1 G= 1+ ≈ 1; RO = 1 2gm • (RE + RIN) 1 2gm +5V FIGURE 16. Voltage Buffer with Doubled-Output Current. 10nF +5V 7 R6 150Ω –VI FIGURE 17. Integrator for ns-pulses. R9 240Ω R3 51Ω R6 150Ω –5V +5V 2.2pF +VI 22pF 8 OPA660 3 5 10nF R10 150Ω OTA +1 1 4 BUF601 8 5 R7 51Ω 4 1 R16 560Ω 10nF 6 R8 43Ω 2 10nF Rg G = ––––––––– = 4 R8 + rE C5 18pF 2.2µF 2.2µF rE = 1/gm –5V –5V FIGURE 18. 400MHz Differential Amplifier –10 10 –20 0 without C5 –10 –40 with C5 –50 –20 –60 IQ = 20mA, G = +4V/V –30 300k 1M 10M 100M Frequency (Hz) FIGURE 19. CMRR and Bandwidth of the Differential Amplifier ® 14 –70 1G 3G CMRR Gain (dB) –30 OPA660 +1 27pF E 2 50Ω 5 R11 51Ω VO 6 VO C 3 B C E TRANSFER CHARACTERISTICS 2 B R3 E F(p) = R2 VI = R1M 1 R2M + s2C1C2R1M R3 + sC1 R2 R1 s2C1C2R1M R2M + sC1 R1M 1 + R2S R1S R3S C C VI VO 7 1 B C2 C E Lowpass B E 6 B C1 R1 R2M R2 = R3 = ∞ Highpass R1 = R2 = ∞ Bandpass R1 = R3 = ∞ Band Rejection R2 = ∞, R1 = R3 E Allpass R1 = R1S, R2 = –R2S, R3 = R3S R1M VO C 8 C B C 4 E 5 B B E RB RB R3S E RB R1S R2S FIGURE 20. High Frequency Universal Active Filter. 120Ω 150Ω 5 +1 6 VLUMINANCE 8 C 3 B OTA E 2 665Ω(1) 200Ω VRED 340Ω(1) VGREEN 1820Ω(1) VBLUE RQ = 500Ω (IQ ≈ 20mA) NOTE: (1) Resistors shown are 1% values that produce 30%/59%/11% R/G/B mix. FIGURE 21. Video Luminance Matrix. ® 15 OPA660 +VO 290Ω VO INT 8 3 OTA 10Ω IN6263 +5V IN6263 +5V 220Ω 180Ω 8 VI 7 7 1µF 100Ω 5 6 +1 180Ω –VO 3 15nF 2 220Ω 100Ω 5 +1 6 OTA 1 4 4 1.2kΩ 20kΩ –5V 12kΩ –5V 220Ω + 1.2kΩ 2 390Ω – 5kΩ Offset Trim 33pF FIGURE 22. Signal Envelope Detector (Full-Wave Rectifier). 120Ω 100Ω VI 8 C 3 B 5 +1 200Ω 6 VO R2 OTA IQ = 20mA R1 E 2 RP 82Ω R5 100Ω 50Ω RIN VO f–3dB ±100mV ±300mV ±700mV ±1.4V ±2.5V 331MHz 362MHz 520MHz 552MHz 490MHz R3 + R5 R3 2 G= =1+ 1 2R5 R5 + 2 • gm CP 6.4pF XE FIGURE 23. Direct-Feedback Amplifier. ® OPA660 R4 R6 68Ω R3 390Ω Network Analyzer 16 OPA660 DIRECT FEEDBACK 15 5Vp-p 10 2.8Vp-p 5 Gain = 3, tR – tF = 2ns, VI = 100mVp–p 1.4Vp-p +150mV 0 0.6Vp-p –5 VO (V) Output Voltage (dB) 20 –10 0.2Vp-p –15 0V –20 –25 –30 –150mV 1M 100k 10M 100M 1G Frequency (Hz) 0 R1 = 100Ω R2 = 120Ω R3 = 390Ω R4 = 200Ω R5 = 100Ω R6 = 68Ω IQ = 20mA Rp = 82Ω Cp = 6.4pF 5 10 15 20 30 VO Gain = 3, VI = 2Vp-p, tR = tF = 2ns 8 C R1 160Ω +3V VI 0V Network Analyzer 56Ω 15 20 25 30 35 40 R3 50Ω RIN OTA IQ = 20mA R4 51Ω C4P 10 45 50 3 B R4P 75Ω –3V 5 40 180Ω R2 E 2 0 35 FIGURE 25. Direct-Feedback Amplifier Small-Signal Pulse Response. FIGURE 24. Frequency Response Direct-Feedback Amplifier. VO(V) 25 Time (ns) 5.6pF VO f–3dB ±100mV ±300mV ±700mV ±1.4V ±2.5V 351MHz 374MHz 435MHz 460MHz 443MHz FIGURE 27. Forward Amplifier. 45 50 Time (ns) SPICE MODELS FIGURE 26. Direct-Feedback Amplifier Large-Signal Pulse Response. Computer simulation using SPICE models is often useful when analyzing the performance of analog circuits and systems. This is particularly true for video and RF amplifier circuits, where parasitic capacitance and inductance can have a major effect on circuit performance. SPICE models are available from Burr-Brown. OPA660 OTA FORWARD AMPLIFIER Output Voltage (dB) 20 15 5Vp-p 10 2.8Vp-p 5 1.4Vp-p 0 0.6Vp-p –5 –10 0.2Vp-p –15 –20 –25 –30 100k 1M 10M 100M 1G Frequency (Hz) IQ = 20mA R1 = 160Ω R4 = 51Ω R2 = 180Ω R3 = 56Ω R4p = 75Ω C4p = 5.6pF FIGURE 28. Frequency Response Forward Amplifier. ® 17 OPA660 FIGURE 29. Evaluation Circuit Silk Screen and Board Layouts. R5 160Ω BUF In 5 6 +1 R6 470Ω BUF Out R7 56Ω R2 24Ω OTA Out R1 100Ω OTA In 8 C 3 B R3 51Ω OTA –5V +5V RQC 820Ω 1 470pF 470pF E 2 C1 2.2µF R4 51Ω C2 3.3nF 10nF 10nF 2.2µF 2.2µF 1N4007 7 FIGURE 30. Evaluation Circuit Diagram. ® OPA660 18 4