Designing with Super Fast Dual Norton Amplifier ANOTHER NORTON AM

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Designing with Super Fast Dual Norton Amplifier ANOTHER NORTON AM

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Designing with Super Fast Dual Norton Amplifier
Designing with Super Fast Dual Norton Amplifier
ANOTHER NORTON AMPLIFIER current differencing Norton amplifier been widely applied over last years because versatility availability quad Norton amplifiers (the LM3900) These cost quads found today wide variety analog systems primarily medium frequency single supply applications Today brand dual current differencing amplifier LM359 offers spectacular speed improvements which used circuits operating well beyond video frequencies speed improved speed improvement Norton amplifier cascode circuit (Figure Cascode circuits used high frequency singleended amplifier designs because there Miller effect collector-to-base capacitance input transistor Also there collector-to-emitter parasitic feedback common base configured transistor high frequency signal appearing output cascode does reflect back into input Furthermore note that bandlimiting transistors eliminated from signal path here PNPs used only collector loads only high speed maintained high gain also obtained without additional amplification stages
National Semiconductor Application Note Timothy Regan September 1981
HIGH FREQUENCY ACTIVE FILTER STRUCTURE Multiple active filter building blocks very popular because their sensitivities their tunability basic element such filter inverting integrator Usually inverting integrators cascaded third inverter allows closing overall loop with proper phase This idea behind state variable bi-quad filter structures which today fully available cost hybrid forms
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FIGURE Adding Current Mirror Provide Current Differencing Inputs
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FIGURE Basic Cascode Circuit Adding mirror differential inputs make high frequency single-ended amplifier more versatile differential inputs should provided easy current mirror across negative (inverting) input terminal (Figure This method provides current differencing current entering non-inverting input extracted from inverting input current LM359 then current differencing opposed voltage differencing programmable features extend versatility additional feature LM359 programmability speed input impedance output current sinking capability line driver applications control overall power consumption (Figure internal compensation capacitor adequate compensation inverting applications where gain higher additional compensation capacitor added externally reduce undesired bandwidth particular application will discussed later following sections illustrate some design ideas using this fast Norton amplifier
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FIGURE Simplified Schematic LM359 High Speed Current Differencing Amplifier Input Output Speed Characteristics Externally Programmable
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C1995 National Semiconductor Corporation
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RRD-B30M115 Printed
count these filters could reduced (allowing dual instead amps quad) true non-inverting integrator could built with single Unfortunately this cannot done with standard amps trivial task with current differencing amplifiers (Figure Combining non-inverting integrator with inverting high frequency sensitivity active filter building block made (Figure Table shows particular filter structures together with
their design equations which derived from Figure frequency compensation amplifiers asymmetric optimize performance Also since LM359 wide bandwidth amplifier high frequency circuit layout strongly recommended circuit works with single supply output biasing each filter type provided with resistors which should chosen according Table
TABLE Analysis Design Equations Type Notch BandReject (Notch) (LP) (BP) RQCi (HP)
TABLE Biasing Equations (DC) (DC) Type Type Type (DC) (Ri2) (DC)
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FIGURE True Non-Inverting Integrator
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Table Table relate Figure
FIGURE High Performance Amplifier Bi-Quad Filter Half LM359 Acts Non-Inverting Integrator Other Half Acts Inverting Extra Inversion Necessary Provide Proper Phase
operating range active filter estimated comparing center frequency product with gain bandwidth product (GBW) active elements should less than active element factor least higher factor will yield less sensitive filters instance with product filter should exceed reality should even less filters tested with LM359 could extend their product VOLTAGE-CONTROLLED PASS FILTER most unique feature LM359 that provides user with complete control frequency response over very wide range combination both programmable input stage current external compensation capability this flexibility most simple illustrative examples usefulness this capability voltage-controlled pass filter shown Figure corner frequency this filter determined closed loop corner frequency inverting gain amplifier This frequency directly controlled frequency dominant pole amplifier's open loop response which approximated expression ISET CCOMP AVOL
simplest method dynamically control vary ISET through control voltage where ISET RSET 500X
this manner CCOMP should chosen highest desired corner frequency maximum ISET curves illustrating dependence corner frequency ISET different compensation capacitors shown Figure
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where AVOL amplifier's open loop gain equal 026V room temperature ISET input stage programming current CCOMP total compensation capacitance
FIGURE Amplifier Closed Loop Corner Frequency ISET should noted that compensation capacitor increased ISET decreased maximum slew rate amplifier decreased prevent slew rate induced distortion sinusoidal input signals following restriction applies Slew rate ISET peak CCOMP
where peak peak output voltage filter where signal frequency output voltage signal frequencies less than corner frequency filter (within passband) should then restricted peak
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FIGURE Voltage-Controlled Pass Filter Minimum Input Frequency Determined closed loop corner frequency which stated also corner frequency filter AVOL where feedback factor single pole open loop frequency response assumed Combining these expressions corner frequency ISET CCOMP
VIDEO AMPLIFIERS basic principle behind design LM359 provide amplification high frequency signals with ease using standard operational amplifiers most obvious application area this amplifier video area where fair amount gain required frequencies much higher than monolithic amps provide specific application amplification buffering composite video signal distributed monitor system
Figure shows typical connection non-inverting video amplifier whose signal source either detected video from receiver possibly camera signal output stage LM359 programmed shown drive terminated cable Vp-p video line driver color signals differential phase error differential gain error desirably noted Table
TABLE Typical Video Amplifier Performance Bandwidth Differential Phase Error Differential Gain Error Amplifier Output Swing Vp-p
pulses that processed data separating decoding circuitry amplifiers single LM359 package combined variety ways provide basic blocks playback channel very high rates level signals they cascaded optimize overall gain bandwidth product already shown Figure single-ended playback signals (non center-tapped head) amplifier used gain stage other differentiating stage convert recovered signal peaks into bi-directional zero crossing signals then properly drive comparator with regard direction flux changes disc tape this simplifies decoding phase-encoded data differential playback signals (center-tapped head) amplifier used provide gain each output signal individually retain differential signal single amplifier difference perform differential single-ended conversion other amplifier perform differentiation single-ended signal multichannel parallel recorded data overall component count playback system minimized using amplifier LM359 channel Combining gain with constant delay filtering Another important application LM359 data recovery systems that filtering most desirable prevent high frequency noise spikes from being coupled through sensing stage causing erroneous readings
general purpose wideband amplifiers availability amplifiers single package allows cascading gain stages achieve very high gain bandwidth products shown Figure DISC MAGNETIC TAPE MEMORY SENSING digital data recovery from magnetic storage medium such disc magnetic tape there exists need high gain bandwidth amplifiers convert level voltage transients from output playback head (caused magnetic flux reversal tape disc) digital
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FIGURE Typical Application this Fast Norton Amplifier High Perfomance Video Amplifier Driving Line
eOUT 1000 Circuit
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FIGURE General Purpose High Gain Wideband Amplifiers Obtained Cascading Norton Amplifiers Available Single Chip
pass filter used must induce time delays valid data signals which will decoded their time relationship each other This immediately implies constant group delay pass filter Bessel filter approximation which implemented with active components also provide signal gain Figure shows fourth order gain Bessel filter Here because requirements Bessel filter simple (Sallen-Key) filter structure been chosen over previously discussed higher performance structures Note however that constant group delay filtering amplification performed with single package HANDLE INPUT NOISE programmability amplifier's input stage current ability ``shut off'' non-inverting input current
mirror allows significant improvements noise characteristics inverting application where non-inverting input would only used biasing purposes alternate biasing scheme nVBE biasing used shown Figure This allows ``shutting off'' input current mirror which itself will reduce input noise factor addition input stage programming current increased further reduce noise voltage expense increase input noise current frequency noise which problem input impedance wideband amplifiers typical effect noise input stage current illustrated Figure
eOUT Time delay
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FIGURE Fourth Order Bessel Filter Data Recovery Systems Filtering Function Done with Single Package
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FIGURE nVBE Biasing Reduce Input Noise Voltage
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Effect ``Shutting Off'' Input Mirror
Noise Performance Figure
FIGURE Programmability Provides Handle Input Noise MAKING FAST JFET INPUT current mirror input stage LM359 used active load differential JFET stage form super fast (Figure This circuit combines high frequency performance programmability LM359 with high input impedance bias currents discrete JFET input stage External compensation LM359 generally required accommodate additional phase shift input stage ``pole-splitting'' configuration shown works quite well speed performance shown Table Note that this should mainly used very high speed single supply coupled circuits This because input offset voltage depends mainly matching discrete JFETs TABLE Typical Amplifier Performance HIGH COMMON-MODE INPUT VOLTAGE DIFFERENCE AMPLIFIER inherent feature current differencing input stage that voltages from which input currents derived limited only maximum input current mirror current) amplifier size input resistors application that takes advantage this high commonmode voltage difference amplifier Figure this circuit LM359 will amplify difference voltage between inputs both inputs riding common-mode level high approximately without exceeding maximum mirror current addition resistor Figure14 allows adjustment common-mode rejection ratio adjusting inverting input bias current programmable input stage current ISET This bias current error most significant lower common-mode input voltage levels making bias current directly proportional input level CMRR improvement possible adjusting maximum CMRR maximum input common-mode voltage
null (VOS typically IBIAS
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FIGURE Combining Norton Amplifier with Discrete P-Channel JFETs Make Fast Voltage Mode
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FIGURE High Input Common-Mode Voltage Difference Amplifier
FIGURE Using Fast Make High Frequency Ultra Linear
diodes 1N914 Metal film Polypropylene Mylar
2N5038
Full-scale adjust made with Zero adjust made with
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FIGURE Complete Schematic Ultra Linear Decade MHz)
Designing with Super Fast Dual Norton Amplifier
BUILDING FAST ULTRA LINEAR CONVERTER Linear fast voltage-to-frequency converters very difficult build especially when standard design techniques used solution this problem fast phase locked loop (PLL) which driven medium frequency ultra linear (the LM331) Figure This high frequency operation obtained frequency divider inserted into loop linearity overall circuit closely approximates linearity medium frequency input high frequency quasi linear error amplifier designed using sections LM359 output frequency which also output system divided compared with output driving digital phase detector overall circuit shown Figure Following zero full-scale adjust works well over decades frequency non-linearity below shown Figure REFERENCES Fredericksen Howard Sleeth ``The LM3900 Current-Differencing Quad Input Amplifiers'' AN-72 National Semiconductor Corporation
Nortronics Design Digest Digital Recording Application Factors Consider Magnetic Heads 1976 Pease ``New Phase-Locked-Loops Have Advantages Frequency Voltage Converters (and more)'' AN-210 National Semiconductor Corporation
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FIGURE Typical Performance
LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT NATIONAL SEMICONDUCTOR CORPORATION used herein Life support devices systems devices systems which intended surgical implant into body support sustain life whose failure perform when properly used accordance with instructions provided labeling reasonably expected result significant injury user critical component component life support device system whose failure perform reasonably expected cause failure life support device system affect safety effectiveness
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Designing with Super Fast Dual Norton Amplifier ANOTHER NORTON AM

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