Harris Intelligent Power OPERATIONAL TRANSCONDUCTANCE AMPLIFIER (

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Harris Intelligent Power OPERATIONAL TRANSCONDUCTANCE AMPLIFIER (

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AN6077.1
Harris Intelligent Power
OPERATIONAL TRANSCONDUCTANCE AMPLIFIER (OTA) WITH POWER CAPABILITY
Authors: Kaplan Wittlinger 1969, first triple operational transconductance amplifier introduced. wide acceptance this circuit concept prompted development single, highly linear operational transconductance amplifier, CA3080. Because extremely linear transconductance characteristics with respect amplifier bias current, CA3080 gained wide acceptance gain control block. CA3094 improved performance CA3080 through addition pair transistors; these transistors extended current carrying capability 300mA, peak. This device, CA3094, useful extremely broad range circuits consumer industrial applications; this paper describes only many consumer applications.
OUTPUT
INVERTING INPUT AMPLIFIER BIAS CURRENT
NON-INVERTING INPUT
IABC
What OTA?
OTA, operational transconductance amplifier, concept basic transistor; once understood, will broaden designer's horizons boundaries make realizable designs that were previously unobtainable. Figure shows equivalent diagram OTA. differential input circuit same that found many modern operational amplifiers. remainder composed current mirrors shown Figure geometry these mirrors such that current gain unity. Thus, highly degenerating current mirrors, output current precisely defined differential input amplifier. Figure shows output current transfer characteristic amplifier. shape this characteristic remains constant independent supply voltage. Only maximum current modified bias current.
FIGURE CURRENT MIRRORS USED
NORMALIZED OUTPUT CURRETN DEVIATION FROM STRAIGHT LINE -0.2 -0.4 -0.6 -0.8 -1.0 -150 -100 (mV) DIFFERENTIAL AMPLIFIER TRANSFER CHARACTERISTIC
FIGURE OUTPUT CURRENT TRANSFER CHARACTERISTIC SAME THAT IDEALIZED DIFFERENTIAL AMPLIFIER
IOUT (±ein)
IABC
19.2 IABC (mA) (mS) 7.5/IABC (mA)
±IOUT IABC (mA) (mA)
FIGURE EQUIVALENT DIAGRAM
major controlling factor input amplifier bias current IABC; explained Figure total output current controlled this current. addition, input bias current, input resistance, total supply current, output resistance proportional this amplifier bias current. These factors provide performance this most flexible device, idealized differential amplifier, i.e., circuit which differential input single ended output conversion realized. With this knowledge basics OTA, possible explore some applications device.
Copyright
Harris Corporation 1994 11-42
Application Note 6077
Gain Control methods providing gain control functions numerous. Each advantage simplicity, cost, high level control, distortion. Many manufacturers have nothing better offer propose four quadrant multiplier. This analogous using elephant carry twig. elegant takes keep going! When operated gain control mode, input standard transconductance multiplier offset that only half differential input used; thus, half multiplier being thrown away. OTA, while providing excellent linear amplifier characteristics, does provide simple means gain control. this application considered realization ideal differential amplifier which full differential amplifier converted single ended output. Because differential amplifier ideal, directly proportional operating current differential amplifier; maximum output current equal amplifier bias current IABC. Thus, varying amplifier bias current, amplifier gain varied: where output load resistance. Figure shows basic configuration gain control circuit.
SIGNAL INPUT AMPLITUDE MODULATED OUTPUT (PERCENT)
obtained with circuit shown Figure Note improvement linearity transfer characteristic. Reduced input impedance does result from this shunt connection. Similar techniques could used output, then output signal would reduced correction circuitry further removed from source linearity. must emphasized that input circuitry differential.
(PERCENT) 10µA 500µA IABC CA3080A RATIO DIODE CURRENT
1.0V
INPUT VOLTAGE (mV)
FIGURE
DIODE CURRENT 0.5mA 10µA INPUT VOLTAGE (mV) 500µA IABC CA3080A RATIO
CA3080A IABC
GAIN CONTROL
FIGURE BASIC CONFIGURATION GAIN CONTROL CIRCUIT
FIGURE
DIODE CURRENT (PERCENT) IABC CA3080A RATIO DISTORTION PRIMARILY FUNCTION SIGNAL INPUT INPUT VOLTAGE (mV) 10µA 500µA
long differential input signal remains under 50mV peak-to-peak, deviation from linear transfer will remain under percent. course, total harmonic distortion will considerably less than this value. Signal excursions beyond this point only result undesired "compressed" output. reason this compression seen transfer characteristic differential amplifier Figure Also shown Figure curve depicting departure from linear line this transfer characteristic. actual performance circuit shown Figure plotted Figure Both signal noise ratio total harmonic distortion shown function signal input. Figures show signal handling capability circuit extended through connection diodes input shown Figure 6[2]. Figure shows total system gain function amplifier bias current several values diode current. Figure shows oscilloscope reproduction CA3080 transfer characteristic applied circuit Figure oscilloscope reproduction Figure
FIGURE FIGURE PERFORMANCE CURVES CIRCUIT FIGURES
11-43
RATIO (dB)
RATIO (dB)
RATIO (dB)
Application Note 6077
V0.01 DIODE CURRENT CA3080A GAIN 10µA 100µA 0.5mA DIODE CURRENT
Transistors from CA3046 array System with extended input range FIGURE CIRCUIT SHOWING SIGNAL HANDLING CAPABILITY CIRCUIT FIGURE EXTENDED THROUGH CONNECTION DIODES INPUT
IABC (µA)
FIGURE TOTAL SYSTEM GAIN FUNCTION AMPLIFIER BIAS CURRENT SEVERAL VALUES DIODE CURRENT
Horizontal: 25mV/Div. Vertical: 50µA/Div. IABC 100µA FIGURE OSCILLOSCOPE REPRODUCTION CA3080 TRANSFER CHARACTERISTIC APPLIED CIRCUIT FIGURE
Horizontal: 0.5V/Div. Vertical: 50µA/Div. IABC 100µA, Diode Current FIGURE OSCILLOSCOPE REPRODUCTION CA3080 TRANSFER CHARACTERISTIC APPLIED CIRCUIT FIGURE
Simplified Differential Input Single Ended Output Conversion more exacting configurations operational amplifiers differential single-ended conversion circuit. Figure shows some basic circuits that usually employed. ratios resistors must precisely matched assure desired common mode rejection. Figure shows another system using CA3080 obtain this conversion without precision resistors. Differential input signals must kept under 126mV better than percent nonlinearity. common mode range that CA3080 differential amplifier. addition, gain characteristic follows standard differential amplifier temperature coefficient -0.3%/oC. Although system Figure does provide precise gain control obtained with standard operational amplifier approach, does provide good simple compromise suitable many differential transducer amplifier applications.
11-44
Application Note 6077
DIFFERENTIAL INPUT OUTPUT
DIFFERENTIAL INPUT
between wide limits. device large reserve output-current capability, breakdown power dissipation ratings sufficiently high allow drive complementary pair transistors. example, power amplifier stage load) driven with peak currents 35mA (assuming minimum output transistor beta supply voltages ±18V. this application, CA3094A operated substantially below supply voltage rating max. dissipation rating 1.6W max. Also this application, high value open-loop gain suggests possibility precise adjustment frequency response characteristics adjustment impedances feedback networks. Implicit Tone Controls addition distortion, large amount loop gain flexibility feedback arrangements available when using CA3094 make possible incorporate tone controls into feedback network that surrounds entire amplifier system. Consider gain requirements phonograph playback system that uses typical high quality magnetic cartridge.[3] desirable system gain would result from output recorded velocity 1cm/s. Magnetic pickups have outputs typically ranging from 10mV 5cm/s. desired output, total system needs about 72dB voltage gain reference frequency. Figure block diagram system that uses passive "losser" type tone control circuit that inserted ahead gain control. Figure shows system which tone controls implicit feedback circuits power amplifier. Both systems assume same noise input voltage equalizer main-amplifier inputs. feedback system shows small improvement (3.8dB) signal-to-noise ratio maximum gain dramatic improvement (20dB) zero gain position. purposes comparison, assumption made that tone controls "flat" both cases. Cost Advantages
OUTPUT
DIFFERENTIAL INPUT
OUTPUT
FIGURE SOME TYPICAL DIFFERENTIAL SINGLEENDED CONVERSION CIRCUITS
IABC
500µA CA3080 OUTPUT
addition savings resulting from reduced parts count circuit size, CA3094 leads further savings power supply system. Typical values power supply rejection common-mode rejection 90dB 100dB, respectively. amplifier with 40dB gain 90dB power supply rejection would require 316mV power supply ripple produce output. Thus, further filtering required other than that given energy storage capacitor output rectifier system.
NOTES: 500µA, IABC 10mS 10mS
Power Amplifier Using CA3094
complete power amplifier using CA3094 three additional transistors shown schematically Figure amplifier shown single-channel configuration, power supply values designed support minimum channels. output section comprises complementary epitaxial units connected familiar "bootstrap" arrangement. Capacitor provides added base drive during positive excursions output. circuit operated from single power supply well from split supply shown Figure changes required 14.4V operation with speaker also indicated diagram.
FIGURE DIFFERENTIAL SINGLE ENDED CONVERSION CIRCUIT WITHOUT PRECISION RESISTORS
CA3094
CA3094 offers unique combination characteristics that suit ideally programmable gain block audio power amplifiers. transconductance amplifier which gain open-loop bandwidth controlled
11-45
Application Note 6077
PICKUP =1mV EQUALIZER 32dB INPUT 10-6 40mV TOTAL 60dB TONE CONTROLS -20dB
VOLUME CONTROLS
BUFFER STAGE INPUT 10-6
POWER SPEAKER 6.23 10-6
10-6
10-6 TOTAL GAIN 72dB
10-6
6.23 10-3
FIGURE BLOCK DIAGRAM SYSTEM USING "LOSSER" TYPE TONE CONTROL CIRCUIT
40mV
40mV TOTAL 60dB
EQUALIZER 32dB INPUT 10-6
VOLUME CONTROLS
BUFFER STAGE INPUT 10-6
10-6
10-6
4.03 10-3
4.03 10-3
0.5mV
FIGURE SYSTEM WHICH TONE CONTROLS IMPLICIT FEEDBACK CIRCUIT POWER AMPLIFIER
amplifier also modified accept input from ceramic phonograph cartridges. standard inputs (equalizer preamplifiers, tuners, etc.) 0.047µF, 250k, omitted. ceramic-cartridge inputs, 0.0047µF, 2.5M, jumper across removed. Output Biasing Instead usual two-diode arrangement establishing idling currents "Vbe Multiplier", transistor used. This method biasing establishes voltage between base base constant multiple base emitter voltage single transistor while maintaining variational impedance between collector emitter (see Appendix transistor mounted intimate thermal contact with output units, operating temperature heat sink forces down inversely with heat-sink temperature. voltage bias between bases varies inversely with heat sink temperature tends keep idling current constant. bias arrangement that accomplished lower cost than those already described replaces multiplier with 1N5391 diode series with resistor. This arrangement does provide degree bias stability multiplier, adequate many applications. Tone-Controls tone controls, essential elements feedback system, located sets parallel paths. bass
network includes blocks from feedback network that gain from input feedback takeoff point unity. residual output voltage speaker terminals then
-R12
where source resistance. input bias current then
treble network consists R10, C10. Resistors limit maximum available boost, respectively. boost limit useful curtailing heating finite turn-off time output units. limit also desirable when there tape recorders nearby. limit aids stability amplifier cutting loop gain higher frequencies where phase shifts become significant. cases which absolute stability under load conditions required, necessary insert small inductor output lead isolate circuit from capacitive loads. inductor (1A) parallel with resistor adequate. derivation circuit constants shown Appendix Curves control action versus electrical rotation also given.
11-46
Application Note 6077
"BOOST" (CW) 0.12µF TREBLE 1800 0.001µF 0.001µF
"CUT" (CCW) 0.01µF
120V 26.8VCT
5600 2N6292 680K 0.47 2N6107 0.47 2N6292 0.47 15µF
4700µF
120V
4700
CA3094
1.8M
0.2µF 25µF 0.02µF 0.47µF
BASS "BOOST" (CW) 100K
"CUT" (CCW)
JUMPER
FIGURE COMPLETE POWER AMPLIFIER USING CA3094 THREE ADDITIONAL TRANSISTORS
+36V 1.2M 0.01µF 1.8K 0.001µF 220K 0.02µF 100K BASS CA3094
220K
0.12µF
TREBLE
5.6K
0.22µF 100K
25µF 1/2VCC 0.2µF
220K
25µF 1/2VCC
FIGURE POWER AMPLIFIER OPERATED FROM SINGLE SUPPLY
11-47
15µF
2N6292 1500µF
0.47 2N6292 0.47 2N6107
0.47µF
Application Note 6077
Performance Figure plot measured response complete amplifier extremes tone control rotation. comparison Figure with computed curves Figure (Appendix shows good agreement. total harmonic distortion amplifier with unregulated power supply shown Figure distortion plotted Figure noise typically 700µV output, 83dB down.
EOES (dB) 1000 100K BASS TREBLE FLAT BASS BOOST TREBLE BOOST
Companion RlAA Preamplifier
Many available preamplifiers capable providing drive power amplifier Figure unique characteristics amplifier, power supply, input impedance, gain make possible design RIAA preamplifier that exploit these qualities. Since input impedance amplifier essentially equal value volume control resistance (250k), preamplifier need have high output current capability. Because gain power amplifier high (40dB) preamplifier gain only approximately 30dB reference frequency (1kHz) provide optimum system gain. Figure shows schematic diagram CA3080 preamplifier. CA3080, cost OTA, provides sufficient openloop gain bass boost necessary AIAA compensation. example, 10mS with load resistance 250k provides open-loop gain 68dB, thus allowing least 18dB loop gain lowest frequency. CA3080 operated from same power supply main amplifier with only minimal decoupling because high power supply rejection inherent device circuitry. addition, high voltage swing capability output enables CA3080 preamplifier handle badly over modulated (over-cut) recordings without overloading. accuracy equalization within ±1dB RIAA curve, distortion virtually immeasurable classical methods. Overload occurs output 7.5V, which allows undistorted inputs 186mV (260mV peak).
120K 5.6K 4kHz 0.002µF 680pF 1.5M 26kHz 1kHz 16kHz 4kHz 5.6K 3.9K CA3080 EOUT
FREQUENCY (Hz)
FIGURE MEASURED RESPONSE AMPLIFIER EXTREMES TONE CONTROL ROTATION
TOTAL HARMONIC DISTORTION 2kHz POWER OUTPUT 16kHz 26kHz 1kHz
50µF
FIGURE TOTAL HARMONIC DISTORTION AMPLIFIER WITH UNREGULATED POWER SUPPLY
INTERMODULATION DISTORTION
120K 60Hz 60Hz 60Hz 2kHz 7kHz 12kHz 3.9K 0.002µF 680pF 1.5M CA3080 EOUT
50µF
POWER OUTPUT
FIGURE DISTORTION AMPLIFIER WITH UNREGULATED SUPPLY
FIGURE CA3080 PREAMPLIFIER
11-48
Application Note 6077 Appendix Multiplier
equivalent circuit multiplier shown Figure voltage given
Bass Boost: Bass Cut: Treble Boost Treble
(A1)
asymptotic high-frequency gain obtained letting increase without limit each expression:
Bass Boost: HIGH
Bass Cut: HIGH Treble Boost HIGH
FIGURE EQUIVALENT CIRCUIT MULTIPLIER
value itself dependent emitter current transistor, which turn, dependent input current since:
(A2)
C1C4 Treble Cut: HIGH
derivative Equation with respect yields incremental impedance multiplier:
K3R2
Note that expressions high frequency gain identical both bass circuits, while expressions frequency gain identical treble circuits. Figure shows boost bass treble controls that have characteristics circuits Figure value REFF treble controls Figure derived from parallel combination Figure when control rotated maximum counterclockwise position. When control rotated maximum clockwise position, value equal compute circuit constants, necessary decide advance amounts boost desired. gain expressions Figure indicate that slope amplitude versus frequency curve each case will octave (20dB decade). ratios boosted gain i.e.: Bass Circuit: Boost
(A3)
where constant transistor found from: K3lnI (A4) Equation another form diode equation:
(A5)
Using values shown Figure plus data 2N6292 typical transistor that could used circuit), dynamic impedance circuit total current 40mA found 4.6. actual design multiplier, value must greater than transistor will never become forward biased.
-LOW
Treble Circuit: HIGH Boost
HIGH
Appendix Tone Controls
Figure shows four operational amplifier circuit configurations gain expressions each. asymptotic frequency gain obtained letting approach zero each case:
then following relationships result:
Bass Circuit: 10R2 99R2 Treble Circuit: 10C4 10C4
11-49
Application Note 6077
R2R3 R1R3 SR3C1
R2R3 R1R3 R2R3
FREQUENCY
FREQUENCY
FIGURE (A). BASS BOOST
REFF
FIGURE (B). BASS
REFF
FREQUENCY
FREQUENCY
FIGURE (C). TREBLE BOOST
FIGURE (D). TREBLE
FIGURE FOUR OPERATIONAL AMPLIFIER CIRCUIT CONFIGURATIONS GAIN EXPRESSIONS EACH
unaffected portion gain high bass control treble control) each case. make controls work symmetrically, high frequency break points must equal both boost cut. Thus:
Bass Control:
make controls work circuit Figure breaks were 1000Hz: base control
0.1C1R1 1000
treble control R1C3 1000 Response Control Rotation practical design, desirable make "flat" response correspond rotation position control, have aural sensation smooth variation response either side mechanical center. easy show that "flat" position bass control occurs when wiper advanced total resistance. amplitude response treble control however, never completely "flat"; computer used generate response curves controls were varied. Figure plot response with bass treble tone controls combined various settings both controls. values shown practical ones used actual design. Figure shows information Figure replot-
since 10C1 Treble Control:
R2C3
since 100C2 10C4
11-50
Application Note 6077
function electrical rotation. ideal taper each control would complement 100Hz plot bass control 10kHz response treble control. mechanical center should occur crossover point each case.
GAIN (dB) ELECTRICAL ROTATION BASS CONTROL 1000Hz 100Hz 31.6Hz
FIGURE (A). BASS CONTROL
GAIN (dB) 1kHz 10kHz
FIGURE (B). TREBLE CONTROL FIGURE BOOST BASS TREBLE CONTROLS THAT HAVE CHARACTERISTICS CIRCUITS FIGURE
0.12µF 1.8K 0.001µF EO/ES (dB) 100K 0.98 0.96 0.99 0.001 0.01µF
0.02
0.99 .914 0.85 0.98 0.96
0.75
0.92 0.05 1000
FREQUENCY (Hz)
FIGURE PLOT RESPONSE CIRCUIT FIGURE WITH BASS TREBLE TONE CONTROLS COMBINED VARIOUS SETTINGS BOTH CONTROLS
100K
FIGURE (A).
31.6kHz
ELECTRICAL ROTATION TREBLE CONTROL
FIGURE (B). FIGURE INFORMATION FIGURE PLOTTED FUNCTION ELECTRICAL ROTATION
References
AN6668, "Applications CA3080 CA3080A High Performance Operational Transconductance Amplifiers," Wittlinger, Harris Semiconductor. Wide-Band Amplifier Technique," Gilbert, IEEE Journal Solid State Circuits, Vol. SC-3, December, 1968. "Trackability," James Kogar, Audio, December, 1966.
11-51

Harris Intelligent Power OPERATIONAL TRANSCONDUCTANCE AMPLIFIER (

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