OPA660

® OPA 660 OPA660 OPA 660 Wide Bandwidth OPERATIONAL TRANSCONDUCTANCE AMPLIFIER AND BUFFER FEATURES q WIDE BANDWIDTH: 850MHz q HIGH SLEW RATE: 3000V/µs q LOW DIFFERENTIAL GAIN/PHASE ERROR: 0.06%/0.02° q VERSATILE CIRCUIT FUNCTION q EXTERNAL IQ-CONTROL APPLICATIONS q BASE LINE RESTORE CIRCUITS q VIDEO/BROADCAST EQUIPMENT q COMMUNICATIONS EQUIPMENT q HIGH-SPEED DATA ACQUISITION q WIDEBAND LED DRIVER q AGC-MULTIPLIER q NS-PULSE INTEGRATOR q CONTROL LOOP AMPLIFIER q 400MHz DIFFERENTIAL INPUT AMPLIFIER 200Ω 8 C 3B OTA E 2 RP 82Ω CP 6.4pF R5 100Ω R3 390Ω 5 +1 6 VO 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. 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. 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. The OPA660 is packaged in SO-8 surface-mount, and 8-pin plastic DIP, specified from –40°C to +85°C. 100Ω VI R1 IQ = 20mA G=1+ R3 =3 2R5 XE OPA660 DIRECT-FEEDBACK FREQUENCY RESPONSE 20 15 10 Output Voltage (dB) 5Vp-p 2.8Vp-p 1.4Vp-p 0.6Vp-p 5 0 –5 –10 –15 –20 –25 –30 100k 1M 10M Frequency (Hz) 0.2Vp-p 100M 1G 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) BUFFER and OTA INPUT IMPEDANCE Input Impedance BUFFER INPUT NOISE Voltage Noise Density, f = 100kHz BUFFER DYNAMIC RESPONSE Small Signal Bandwidth Full Power Bandwidth Differential Gain Error Differential Phase Error Harmonic Distortion, 2nd Harmonic Slew Rate Settling Time 0.1% Rise Time (10% to 90%) Group Delay Time BUFFER RATED OUTPUT Voltage Output Current Output Gain Output Impedance POWER SUPPLY Voltage, Rated Derated Performance Quiescent Current (Programmable, Useful Range) IO = ±1mA RL = 500Ω RL = 5kΩ ±3.7 ±10 0.96 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 CONDITIONS MIN TYP MAX UNITS VC = 0V VB = 0 VS = ±4.5V to ±5.5V V+ = 4.5V to 5.5V V– = –4.5V to –5.5V 75 125 +10 50 60 45 48 –2.1 5 200 ±30 mA/V mV µV/°C dB dB dB µA nA/°C nA/V nA/V nA/V µA nA/°C µA/V µA/V µA/V mA V Ω || pF dB 55 40 40 ±5 ±750 ±1500 ±500 VS = ±4.5V to ±5.5V V+ = 4.5V to 5.5V V– = –4.5V to –5.5V 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 ±10 500 ±10 ±10 ±10 ±15 ±4.7 25k || 4.2 70 ±20 ±25 ±25 ±25 IC = ±1mA f = 1kHz VS = ±4.5V to ±5.5V V+ = 4.5V to 5.5V V– = –4.5V to –5.5V 55 40 40 +7 50 60 45 48 –2.1 5 ±30 mV µV/°C dB dB dB µA nA/°C nA/V nA/V nA/V MΩ || pF nV/√Hz MHz MHz MHz % Degrees dBc V/µs ns ns ns ps V mA V/V V/V Ω || pF ±5 ±750 ±1500 ±500 VS = ±4.5V to ±5.5V V+ = 4.5V to 5.5V V– = –4.5V to –5.5V 1.0 || 2.1 4 850 800 570 0.06 0.02 –68 3000 25 1 1.5 250 ±4.2 ±15 0.975 0.99 7 || 2 ±4.5 ±5 ±3 to ±26 ±5.5 V V mA ® OPA660 2 PIN CONFIGURATION Top View I Q Adjust 1 8 C ABSOLUTE MAXIMUM RATINGS DIP/SO-8 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 NOTE: (1) Inputs are internally diode-clamped to ±VS. E 2 7 V+ = +5V B 3 1 6 Out PACKAGE/ORDERING INFORMATION V– = –5V 4 5 In PRODUCT OPA660AP OPA660AU PACKAGE 8-Pin Plastic DIP SO-8 Surface-Mount PACKAGE DRAWING NUMBER(1) 006 182 TEMPERATURE RANGE –25°C to +85°C –25°C to +85°C 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. 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 OPA660 TYPICAL PERFORMANCE CURVES IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted. TOTAL QUIESCENT CURRENT vs RQ 100 1.5 TOTAL QUIESCENT CURRENT vs TEMPERATURE Total Quiescent Current (Normalized) 10k Total Quiescent Current (mA) 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 –25 0 25 50 Temperature (°C) 75 100 30 Nominal Device 10 High IQ Device 3.0 Low IQ Device 1.0 100 300 1.0k R Q — Resistor Value ( Ω) 3.0k BUFFER AND OTA B-INPUT BIAS CURRENT vs TEMPERATURE 0.0 OTA C-OUTPUT BIAS CURRENT vs TEMPERATURE 5 Representative Units Input Bias Current (µA) –1.0 –2.0 OTA C-Output Bias Current (µA) Trim Point –3.0 –4.0 –5.0 –20 –0 20 40 60 80 100 Temperature (°C) –40 –20 –0 20 40 60 80 100 Temperature (°C) OTA C-OUTPUT RESISTANCE vs TOTAL QUIESCENT CURRENT (IQ) 60 OTA TRANSFER CHARACTERISTICS 10 OTA Output Resistance (k Ω) OTA Output Current (mA) 50 40 30 20 10 0 4 6 8 10 12 14 16 18 20 Total Quiescent Current — IQ (mA) 5 0 IQ = 5mA –5 IQ = 10mA IQ = 20mA –10 –60 –40 –20 0 20 40 60 OTA Input Voltage (mV) ® OPA660 4 TYPICAL PERFORMANCE CURVES (CONT) IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted. BUFFER AND OTA B-INPUT OFFSET VOLTAGE vs TEMPERATURE 15 Buffer and OTA B-Input Resistance (MΩ) 20 BUFFER AND OTA B-INPUT RESISTANCE vs TOTAL QUIESCENT CURRENT (IQ) 4 RINOTA 3 RINBUF Offset Voltage (mV) 10 5 0 –5 –10 –15 –20 –25 0 25 50 75 100 Temperature (°C) 2 1 0 –1 4 6 8 10 12 14 16 18 20 Total Quiescent Current — IQ (mA) Buffer Output and OTA E-Output Resistance (Ω) BUFFER OUTPUT AND OTA E-OUTPUT RESISTANCE vs TOTAL QUIESCENT CURRENT (IQ) 40 BUFFER SLEW RATE vs TOTAL QUIESCENT CURRENT (IQ) 4000 3800 3600 30 Slew Rate (V/µs) 3400 3200 3000 2800 2600 2400 2200 2000 Rising Edge 20 ROUTOTA 10 ROUTBUF Falling Edge 0 4 6 8 10 12 14 16 18 20 Total Quiescent Current—IQ (mA) 4 6 8 10 12 14 16 18 20 Total Quiescent Current—IQ (mA) OTA TRANSCONDUCTANCE vs TOTAL QUIESCENT CURRENT (IQ) 150 OTA TRANSCONDUCTANCE vs FREQUENCY 1000 OTA Transconductance (mA/V) OTA Transconductance (mA/V) RL = 50Ω 100 IQ = 20mA 100 IQ = 10mA 66mA/V 106mA/V 50 IQ = 5mA 0 0 2 4 6 8 10 12 14 16 18 20 Total Quiescent Current—IQ (mA) 40mA/V 100M 1G 10 1M 10M Frequency (Hz) ® 5 OPA660 TYPICAL PERFORMANCE CURVES (CONT) IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted. BUFFER VOLTAGE NOISE SPECTRAL DENSITY 100 20 15 BUFFER FREQUENCY RESPONSE –3dB Point 2.8Vp-p 1.4Vp-p 0.6Vp-p Voltage Noise (nV/ Hz) 10 Output Voltage (dB) 5 0 –5 –10 –15 –20 –25 10 0.2Vp-p 1 100 1k 10k 100k Frequency (Hz) 1M 10M 100M dB 200k 1M 10M Frequency (Hz) IQ = 20mA RIN = 160Ω RL = 100Ω 100M 1G BUFFER MAX OUTPUT VOLTAGE vs FREQUENCY 10 Buffer Output Voltage (Vp-p) TRANSCONDUCTANCE vs INPUT VOLTAGE 160 RQ = 250Ω 120 RQ = 500Ω 80 RQ = 1kΩ 40 RQ = 2kΩ 0 Transconductance (mA/V) 0.1 1M 10M 100M 1G Frequency (Hz) 0 –40 –30 –20 –10 0 10 20 30 40 Input Voltage (mV) OTA PULSE RESPONSE OTA PULSE RESPONSE +0.625V +2.5V VO (V) VO (V) 0V 0V –0.625V –2.5V Input Voltage = 1.25Vp-p, tR = tF = 1ns, Gain = 4 Output Voltage = 5Vp-p ® OPA660 6 TYPICAL PERFORMANCE CURVES IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted. (CONT) BUFFER LARGE SIGNAL PULSE RESPONSE BUFFER LARGE SIGNAL PULSE RESPONSE VO (V) VO (V) (HDTV Signal Pulse) tR = tF = 10ns, VO = 5Vp-p tR = tF = 3ns, VO = 5Vp-p 50Ω 50Ω VI 160Ω 5 +1 6 VO R6 Network 50Ω Analyzer RIN = 50Ω 50Ω 50Ω R7 RL = R6 + R7||RIN = 100Ω Test Circuit Buffer Pulse and Frequency Response tR = tF = 3ns, VO = 0.2Vp-p BUFFER DIFFERENTIAL GAIN ERROR vs TOTAL QUIESCENT CURRENT (IQ) 0.25 BUFFER DIFFERENTIAL PHASE ERROR vs TOTAL QUIESCENT CURRENT (IQ) 0.10 Differential Phase Error (Degrees) 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 4 Differential Gain Error (%) 0.20 RL = 500Ω VO = 0.7Vp-p f = 3.58MHz 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 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 –30 RL = 150Ω VO = 0.5Vp-p IQ = 20mA HARMONIC DISTORTION vs FREQUENCY –30 RL = 500Ω IQ = 20mA –50 Harmonic Distortion (dBc) Harmonic Distortion (dBc) –40 –40 3f 2Vp-p 3f 0.5Vp-p 2f 2Vp-p 2f –50 –60 3f –70 Measurement Limit –80 10M –60 2f 0.5Vp-p Measurement Limit –80 –70 20M 40M Frequency (Hz) 60M 100M 10M 20M 40M Frequency (Hz) 60M 100M 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. 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. 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). (7) +VCC = +5V VI (5) VO (6) B (3) E (2) C (8) Bias Circuitry 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). 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. 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. 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. 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. 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. 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). 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. Internal Current Source Circuitry OPA660 V+ 1/2 REF200 100µA 1kΩ R1 100Ω 50kΩ 4 –VCC IQ ≈ 85 • I1 R1 = 85 • (100µA) R2 = 20mA 1 I1 425Ω R2 1/2 (1) OPA1013 RQ = 250Ω sets roughly IQ ≈ 20mA 1 RQ 250Ω RB 3 (25Ω to 200Ω) –5V(1) 470pF + 8 +5V (1) 470pF NOTE: (1) Requires input common-mode range and output swing close to V–, thus the choice of OPA1013. FIGURE 3. Optional Control Loop for Setting Quiescent Current. 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. 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 2 7 + 1 6 Solid Tantalum 10nF 2.2µF 10nF 4 5 RB (25Ω to 200Ω) 2.2µF Solid Tantalum 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. 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. 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. +5V 4.7kΩ Internal Current Source Circuitry 2N2907 OPA660 0/5V Logic In 5V: OPA660 On 100Ω 50kΩ 1 4 IC IC = 0: OPA660 On IC ≈ 1mA: OPA660 Off RQ 250Ω –5V FIGURE 4. Logic-Controlled Disable Circuit. V+ RB RL VO 100Ω VI 8 C 3B OTA E 2 RE RL VO Non-Inverting Gain VOS ≈ 0 VI Inverting Gain VOS ≈ several volts RB RE V– (a) Common-Emitter Amplifier Transconductance varies over temperature. (b) Common-E Amplifier Transconductance remains constant over temperature. FIGURE 5. Common-Emitter vs Common-E Amplifier. V+ V+ 100Ω VI VI RE (b) Common-C Amplifier (Buffer) 3B 8 C OTA E 2 VO VO RE G≈1 VOS ≈ 0.7V G≈1 VOS ≈ 0 G=– RL VO Non-Inverting Gain VOS ≈ several volts 100Ω RL 1 RE + gm ≈– RL RE 8 C OTA E 2 VO Inverting Gain VOS ≈ 0 RL RE VI 3B V– (a) Common-Collector Amplifier (Emitter Follower) G= 1+ 1 gm 1 1 gm ¥ R E ≈1 (a) Common-Base Amplifier VI RE RO = (b) Common-B Amplifier FIGURE 6. Common-Collector vs Common-C Amplifier. ® FIGURE 7. Common-Base vs Common-B Amplifier. OPA660 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. 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. The transconductance of the OTA with degeneration can be calculated by— 1 gm = 1 + RE gm 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). 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. 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. • 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. • Do not extend the ground plane under high impedance nodes sensitive to stray capacitance. • Sockets are not recommended because they add significant inductance. 20 RL1 VO 8 3 OTA Network Analyzer RIN 50Ω Output Voltage (dB) 15 10 5 0 –5 –10 –15 –20 –25 –30 300k 1M 10M 100M 200mVp-p 600mVp-p 2.8Vp-p 1.4Vp-p –3dB Point RL2 100Ω R1 VI 2 rE RL = RL1 + RL2 || RIN RL RE + r E 1 gm RE G= , rE = 1 At IQ = 20mA r E = = 8Ω 125mA/V G= RL RE + 8 Ω at I Q = 20mA 1G 3G Frequency (Hz) IQ = 20mA R1 = 100Ω RE = 51Ω RL = 50Ω Gain = 1 20 15 10 Output Voltage (dB) 20 –3dB Point 2.8Vp-p Output Voltage (dB) 15 10 5Vp-p 2.8Vp-p 1.4Vp-p –3dB Point 5 0 –5 –10 –15 –20 –25 –30 300k 1M 10M 1.4Vp-p 600mVp-p 5 0 –5 –10 –15 –20 –25 600mVp-p 200mVp-p 200mVp-p 100M 1G 3G –30 100k 1M 10M Frequency (Hz) 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. • Use surface-mount components—they generally provide the lowest inductance. • A resistor (25Ω to 200Ω) in series with the buffer and/or B input may help reduce oscillations and peaking. • Use series resistors in the supply lines to decouple multiple devices. OPA660 CURRENT-FEEDBACK C1 56Ω R2 20 5 +1 6 15 VO 5Vp-p 2.8Vp-p 1.4Vp-p 0.6Vp-p 0.2Vp-p –3dB Point 10 Output Voltage (dB) 8 C 3B OTA E 2 R1 47Ω VI R5 22Ω G=1+ R Q = 250Ω (IQ ≈ 20mA) 5 0 –5 –10 –15 –20 –25 –30 100k 200Ω R4 R4 R5 ≈ 10 1M 10M Frequency (Hz) 100M 1G IQ = 20mA R1 = 47Ω R2 = 56Ω R4 = 200Ω R5 = 22Ω Gain = 10 FIGURE 9. Current-Feedback Amplifier. FIGURE 10. Current-Feedback Amplifier Frequency Response, G = 10. C1 100pF 20Ω VIN 5 +1 6 20Ω R2 100kΩ OPA650 25Ω VOUT D1 D1, D2 = 1N4148 RQ = 1kΩ D2 R1 40.2Ω 8 C B 3 20Ω CCII E 2 • 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. • D1 adds a propagation delay to the DC restoration. • R2 and C1 set the decay time constant. FIGURE 11. DC Restorer Circuit. 8 C +IN 3B OTA E 2 RE 2 E –IN 3B OTA C 8 Tuning Coil Magnetic Head Driver Transformer 50Ω IO VI 150Ω 8 C 3B OTA E 2 RE 42Ω 5 +1 6 VO RL 150Ω G= RL R E + rE ≈ +3 R Q = 250Ω (IQ ≈ 20mA) FIGURE 13. Cable Amplifier. FIGURE 12. High Speed Current Driver (bridge combination for increased output voltage capability). ® OPA660 12 C8 +5V R6 47kΩ R8 27kΩ 0.5...2.5pF Offset R2 Trim 10kΩ +5V –5V R3 100Ω 3 RC5 150Ω 5 6 2 C3 7 2.2µF C3 +5V C3 2.2µF R5 47Ω C3 2.2µF VO R1 100Ω VI 8 OTA 4 +1 1 RQ 250Ω R4 150Ω 1 4 BUF600 5 R2 100Ω 2.2µF –5V Propagation Delay Time = 5ns Rise Time = 1.5ns –5V D1 D2 DMF3068A FIGURE 14. Comparator (Low Jitter). +5V 22Ω 22Ω IO = IO1 + IO2 8 IO1 C 3B OTA E 2 RE 50Ω 180Ω 3B 8 IO1 C OTA Diode E 2 RE 50Ω Q1 +IB Q2 180Ω VI 1kΩ Q1, Q2: 2N3906 FIGURE 15. High Speed Current Driver. ® 13 OPA660 180Ω VI 8 C 3B OTA E 2 33pF 47Ω 780Ω VO RE 50Ω Network Analyzer RIN 50Ω VI 3B 8 C OTA E 2 200Ω 27pF 5 +1 6 VO VO ±100mV ±300mV ±700mV ±1.4V ±2.5V f–3dB 351MHz 374MHz 435MHz 460MHz 443MHz G= 1+ 1 1 2gm • (RE + RIN) 50Ω 620Ω 50kΩ 820Ω 1µF ≈ 1; RO = 1 2gm +5V –5V FIGURE 16. Voltage Buffer with Doubled-Output Current. FIGURE 17. Integrator for ns-pulses. 2.2pF +5V 10nF R9 240Ω +5V 7 OPA660 R10 150Ω 1 4 BUF601 5 8 8 22pF R3 51Ω R6 150Ω +VI R6 150Ω –VI 3 10nF R11 51Ω 5 +1 OTA VO R7 51Ω 10nF 4 1 R16 560Ω 6 R8 43Ω C5 18pF 2 Rg G = ––––––––– = 4 R8 + rE rE = 1/gm 10nF 2.2µF –5V 2.2µF –5V FIGURE 18. 400MHz Differential Amplifier 10 –10 –20 0 –30 Gain (dB) –10 without C5 with C5 –40 –50 –60 –20 –30 300k 1M IQ = 20mA, G = +4V/V 10M 100M 1G 3G –70 Frequency (Hz) FIGURE 19. CMRR and Bandwidth of the Differential Amplifier ® OPA660 14 CMRR C 3 B C 2 B E R2 C 1 B E R1 C1 B E R1M C 8 C 4 B E RB R1S RB B E R2S C 5 RB B E R3S VO C 6 R2M C2 7 B E Lowpass Highpass Bandpass R2 = R3 = ∞ R1 = R2 = ∞ R1 = R3 = ∞ R1 = R1S, R2 = –R2S, R3 = R3S R3 F(p) = VO VI = E TRANSFER CHARACTERISTICS R1M 1 R2M + s2C1C2R1M R3 + sC1 R2 R1 s2C1C2R1M R2M + sC1 R1M 1 + R2S R1S R3S C VI Band Rejection R2 = ∞, R1 = R3 Allpass FIGURE 20. High Frequency Universal Active Filter. 120Ω 8 C 3B OTA E 2 665Ω(1) VRED 340Ω(1) VGREEN 1820Ω(1) VBLUE 5 +1 6 VLUMINANCE 150Ω 200Ω 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 8 3 OTA 10Ω VO INT 15nF IN6263 220Ω 2 +5V 8 VI 1µF 100Ω 7 5 +1 4 20kΩ 6 1 180Ω IN6263 220Ω 100Ω +5V 180Ω 7 5 +1 4 6 –VO 3 OTA 1.2kΩ 1.2kΩ 2 –5V 12kΩ 220Ω + 5kΩ Offset Trim – 33pF 390Ω –5V FIGURE 22. Signal Envelope Detector (Full-Wave Rectifier). 120Ω 8 C 3 B OTA E 2 RP 82Ω CP 6.4pF XE R5 100Ω R2 R3 390Ω 5 +1 6 VO 200Ω R4 R6 68Ω Network Analyzer 50Ω RIN VO ±100mV ±300mV ±700mV ±1.4V ±2.5V f–3dB 331MHz 362MHz 520MHz 552MHz 490MHz 100Ω VI R1 IQ = 20mA R3 + R5 R3 2 G= =1+ 1 2R5 R5 + 2 • gm FIGURE 23. Direct-Feedback Amplifier. ® OPA660 16 OPA660 DIRECT FEEDBACK 20 15 10 Output Voltage (dB) 5Vp-p 2.8Vp-p 1.4Vp-p 0.6Vp-p VO (V) Gain = 3, tR – tF = 2ns, VI = 100mVp–p 5 0 –5 –10 –15 –20 –25 –30 100k 1M 10M Frequency (Hz) +150mV 0V 0.2Vp-p –150mV 100M 1G 0 5 10 15 20 25 30 35 40 45 50 R1 = 100Ω R2 = 120Ω R3 = 390Ω R4 = 200Ω R5 = 100Ω R6 = 68Ω IQ = 20mA Rp = 82Ω Cp = 6.4pF Time (ns) FIGURE 24. Frequency Response Direct-Feedback Amplifier. FIGURE 25. Direct-Feedback Amplifier Small-Signal Pulse Response. Gain = 3, VI = 2Vp-p, tR = tF = 2ns R1 160Ω VI 3B E 2 8 C VO 180Ω R2 Network Analyzer 56Ω R3 50Ω RIN +3V OTA IQ = 20mA R4 51Ω VO(V) 0V R4P 75Ω C4P VO ±100mV ±300mV ±700mV ±1.4V ±2.5V f–3dB 351MHz 374MHz 435MHz 460MHz 443MHz –3V 5.6pF 0 5 10 15 20 25 30 35 40 45 50 FIGURE 27. Forward Amplifier. SPICE MODELS Time (ns) FIGURE 26. Direct-Feedback Amplifier Large-Signal Pulse Response. OPA660 OTA FORWARD AMPLIFIER 20 15 10 Output Voltage (dB) 5Vp-p 2.8Vp-p 1.4Vp-p 0.6Vp-p 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. 5 0 –5 –10 –15 –20 –25 –30 100k 1M 10M 0.2Vp-p 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 +1 6 R6 470Ω BUF Out R7 56Ω R2 24Ω OTA Out R1 100Ω OTA In 8 C 3B OTA E 2 C1 2.2µF R4 51Ω C2 3.3nF 10nF 2.2µF 10nF 2.2µF 1N4007 7 4 R3 51Ω +5V –5V RQC 820Ω 1 470pF 470pF FIGURE 30. Evaluation Circuit Diagram. ® OPA660 18