AN6077.2 1969, first triple operational transconductance amplifie
|
|
|
Top Searches for this datasheet
Operational Transconductance Amplifier (OTA) With Power Capability
AN6077.2
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
FIGURE CURRENT MIRRORS USED
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.
NORMALIZED OUTPUT CURRENT 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)
19.2 IABC (mS) (mA) IABC 7.5/IABC (mA) ±IOUT IABC (mA) (mA)
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.
FIGURE EQUIVALENT DIAGRAM
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
4-178
http://www.intersil.com 407-727-9207 Copyright
Intersil Corporation 1999
Application Note 6077
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
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.
DIODE CURRENT 10µA INPUT VOLTAGE (mV) 1.0V 500µA IABC CA3080A RATIO RATIO (dB) RATIO (dB) RATIO (dB)
CA3080A IABC
(PERCENT)
FIGURE
DIODE CURRENT 0.5mA 10µA INPUT VOLTAGE (mV) 500µA IABC CA3080A RATIO
GAIN CONTROL
FIGURE BASIC CONFIGURATION GAIN CONTROL CIRCUIT
(PERCENT)
(PERCENT)
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 [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 obtained with circuit shown Figure Note
FIGURE
DIODE CURRENT DISTORTION PRIMARILY FUNCTION SIGNAL INPUT INPUT VOLTAGE (mV) IABC CA3080A RATIO 10µA 500µA
FIGURE FIGURE PERFORMANCE CURVES CIRCUIT FIGURES
4-179
Application Note 6077
V0.01 IABC (µA) DIODE CURRENT CA3080A GAIN 0.5mA 10µA 100µA DIODE CURRENT
Transistors from CA3046 array. System with extended input range. FIGURE CIRCUIT SHOWING SIGNAL HANDLING CAPABILITY CIRCUIT FIGURE EXTENDED THROUGH CONNECTION DIODES INPUT
FIGURE TOTAL SYSTEM GAIN AMPLIFIER BIAS CURRENT SEVERAL VALUES DIODE CURRENT
Horizontal: 25mV/Div. Vertical: 50µA/Div., IABC 100µA
Horizontal: 0.5V/Div. Vertical: 50µA/Div., IABC 100µA, Diode Current FIGURE CA3080 TRANSFER CHARACTERISTIC CIRCUIT FIGURE
FIGURE CA3080 TRANSFER CHARACTERISTIC 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.
4-180
Application Note 6077
DIFFERENTIAL INPUT OUTPUT
CA3094
CA3094 offers unique combination characteristics that suit ideally programmable gain block audio power amplifiers. transconductance amplifier which gain open-loop bandwidth controlled 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.
DIFFERENTIAL INPUT
OUTPUT
DIFFERENTIAL INPUT OUTPUT
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.
FIGURE SOME TYPICAL DIFFERENTIAL SINGLE ENDED CONVERSION CIRCUITS
IABC
500µA DIFFERENTIAL INPUT CA3080 VOUTPUT
Cost Advantages
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.
500µA, IABC: 10mS. 10mS 100. FIGURE DIFFERENTIAL SINGLE ENDED CONVERSION CIRCUIT WITHOUT PRECISION RESISTORS
4-181
Application Note 6077
ESIG 40mV ESIG ESIG ATOTAL 60dB EQUALIZER AREF 32dB INPUT 10-6 PICKUP ESIG =1mV 10-6 TONE CONTROLS -20dB 10-6 TOTAL GAIN 72dB VOLUME CONTROLS 10-6 BUFFER STAGE INPUT 10-6 POWER SPEAKER 6.23 10-3
6.23 10-3
FIGURE BLOCK DIAGRAM SYSTEM USING "LOSSER" TYPE TONE CONTROL CIRCUIT
ESIG 40mV ESIG 40mV ATOTAL 60dB EQUALIZER AREF 32dB INPUT 10-6 PICKUP ESIG =1mV 10-6 VOLUME CONTROLS AMPLIFIER WITH FEEDBACK TONE CONTROLS 10-6 4.03 10-3
10-6
4.03 10-3
0.5mV
FIGURE SYSTEM WHICH TONE CONTROLS IMPLICIT FEEDBACK CIRCUIT POWER AMPLIFIER
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. 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.
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
where source resistance. input bias current then
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.
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.
4-182
Application Note 6077
"BOOST" (CW) TREBLE 1800 0.001µF 0.001µF 5600 2N6292 680K 0.47 2N6292 0.47 2N6107 0.47 "CUT" (CCW) 0.01µF 120V 26.8VCT
0.12µF
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
15µF
2N6292 1500µF
0.22µF 100K
0.47 2N6292 0.47 2N6107
25µF 1/2VCC 0.2µF
0.47µF
220K
25µF 1/2VCC
FIGURE POWER AMPLIFIER OPERATED FROM SINGLE SUPPLY
4-183
Application Note 6077
Performance
INTERMODULATION DISTORTION 60Hz 60Hz 60Hz 2kHz 7kHz 12kHz
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.
(dB) 1000 100K BASS TREBLE FLAT BASS BOOST TREBLE BOOST
OUTPUT POWER
FIGURE DISTORTION AMPLIFIER WITH UNREGULATED SUPPLY
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 open-loop gain bass boost necessary RIAA 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).
FREQUENCY (Hz)
FIGURE MEASURED RESPONSE AMPLIFIER EXTREMES TONE CONTROL ROTATION
TOTAL HARMONIC DISTORTION 2kHz 4kHz 1kHz 26kHz 16kHz 4kHz OUTPUT POWER 16kHz 26kHz 1kHz
FIGURE TOTAL HARMONIC DISTORTION AMPLIFIER WITH UNREGULATED POWER SUPPLY
4-184
Application Note 6077
120K 5.6K 0.002µF 680pF 1.5M 3.9K 5.6K V120K CA3080 EOUT
derivative Equation with respect yields incremental impedance multiplier:
50µF
(EQ.
where constant transistor found from:
(EQ.
Equation another form diode equation:
(EQ.
0.002µF 680pF 1.5M 3.9K CA3080 EOUT
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.
50µF
Appendix Tone Controls
Figure shows four operational amplifier circuit configurations gain expressions each. asymptotic frequency gain obtained letting approach zero each case:
Bass Boost: Bass Cut: Treble Boost:
FIGURE CA3080 PREAMPLIFIER
Appendix Multiplier
equivalent circuit multiplier shown Figure voltage given
(EQ.
Treble Cut:
asymptotic high-frequency gain obtained letting increase without limit each expression:
Bass Boost: HIGH
Bass Cut: HIGH Treble Boost: HIGH Treble Cut: HIGH
FIGURE EQUIVALENT CIRCUIT MULTIPLIER
value itself dependent emitter current transistor, which turn, dependent input current since:
(EQ.
4-185
Application Note 6077
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 Treble Circuit: HIGH Boost HIGH
then following relationships result:
Bass Circuit: Treble Circuit:
FREQUENCY FIGURE (A). BASS BOOST
FREQUENCY FIGURE (B). BASS
REFF
REFF
FREQUENCY FIGURE (C). TREBLE BOOST
FREQUENCY FIGURE (D). TREBLE
FIGURE FOUR OPERATIONAL AMPLIFIER CIRCUIT CONFIGURATIONS GAIN EXPRESSIONS EACH
4-186
Application Note 6077
unaffected portion gain (AHIGH bass control ALOW treble control) each case. make controls work symmetrically, high frequency break points must equal both boost cut. Thus:
Bass Control:
since
FIGURE (A). BASS CONTROL
10C1
Treble Control:
since 100C make controls work circuit Figure breaks were 1000Hz:
base control 0.1C 1000 1000
FIGURE (B). TREBLE CONTROL FIGURE BOOST BASS TREBLE CONTROLS THAT HAVE CHARACTERISTICS CIRCUITS FIGURE
treble control
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.
EO/ES (dB) 0.12µF 1.8K 0.001µF 100K 0.98 0.96 0.99 0.001 0.01µF
0.02
Figure plot response with bass treble tone controls combined various settings both controls. values shown practical ones used actual design. Figure shows information Figure replotted 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.
0.99 =0.914 0.85 0.98 0.96
0.75
0.92 0.05 1000
100K
FREQUENCY (Hz)
FIGURE PLOT RESPONSE CIRCUIT FIGURE WITH BASS TREBLE TONE CONTROLS COMBINED VARIOUS SETTINGS BOTH CONTROLS
4-187
Application Note 6077
GAIN (dB) GAIN (dB) ELECTRICAL ROTATION BASS CONTROL 1000Hz 100Hz 31.6Hz 1kHz 10kHz 31.6kHz
ELECTRICAL ROTATION TREBLE CONTROL
FIGURE (A).
FIGURE (B). FIGURE INFORMATION FIGURE PLOTTED FUNCTION ELECTRICAL ROTATION
References
Intersil documents available internet, site http://www.intersil.com/ Intersil AnswerFAX (407) 724-7800. AN6668 Application Note, "Applications CA3080 CA3080A High Performance Operational Transconductance Amplifiers," Wittlinger, Intersil Corporation. Wide-Band Amplifier Technique," Gilbert, IEEE Journal Solid State Circuits, Vol. SC-3, December, 1968. "Trackability," James Kogar, Audio, December, 1966.
Intersil semiconductor products manufactured, assembled tested under ISO9000 quality systems certification.
Intersil semiconductor products sold description only. Intersil Corporation reserves right make changes circuit design and/or specifications time without notice. Accordingly, reader cautioned verify that data sheets current before placing orders. Information furnished Intersil believed accurate reliable. However, responsibility assumed Intersil subsidiaries use; infringements patents other rights third parties which result from use. license granted implication otherwise under patent patent rights Intersil subsidiaries.
information regarding Intersil Corporation products, site http://www.intersil.com
Sales Office Headquarters
NORTH AMERICA Intersil Corporation 883, Mail Stop 53-204 Melbourne, 32902 TEL: (407) 724-7000 FAX: (407) 724-7240 EUROPE Intersil Mercure Center 100, Fusee 1130 Brussels, Belgium TEL: (32) 2.724.2111 FAX: (32) 2.724.22.05 ASIA Intersil (Taiwan) Ltd. 7F-6, Hsing North Road Taipei, Taiwan Republic China TEL: (886) 2716 9310 FAX: (886) 2715 3029
4-188
Other recent searches
uPA1803 - uPA1803 uPA1803 Datasheet
TLHB440 - TLHB440 TLHB440 Datasheet
SJ4983 - SJ4983 SJ4983 Datasheet
RB420D - RB420D RB420D Datasheet
POS-1400+ - POS-1400+ POS-1400+ Datasheet
PG05DBTFC - PG05DBTFC PG05DBTFC Datasheet
PD54008L-E - PD54008L-E PD54008L-E Datasheet
NJU3712A - NJU3712A NJU3712A Datasheet
NJU3711A - NJU3711A NJU3711A Datasheet
MR16R0824 - MR16R0824 MR16R0824 Datasheet
EP2SGX30 - EP2SGX30 EP2SGX30 Datasheet
Privacy Policy | Disclaimer
© 2012 Datasheet Archive
