SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?1?of?11 voltage?controlled?amplifier?for?electronic?volume?control sip-8 description the?SA2159?is?a?voltage- controlled?amplifier?(vca)?circuit.?the?chip?is?a high-performance? current?in/current-out? devices? including? two? opposing- polarity,? voltage-sensitive? control? ports.? due? to? super? low- noise application,? the? circuit? adopts? high? h fe. c omplementary? npn/pnp? pairs configuration.? it? requires? little? external? support? circuitry? and? selects? a space-efficient? plastic? 8-pin? single?in?line? (sip)? package.? t he? SA2159 vca?combines a?number?of?advantages?such?as?low?noise,?low?distortion, low? offset? and? high? gain- bandwidth? to? offer? discrete? performance? at? ic prices. features *?wide?dynamic?range:>115db *?wide?gain?range:>130db *?logarithmic?gain?control *?low?distortion:(0.008%@0db?gain,?0.035%@15db?gain) *?wide?gain-bandwidth:?6mhz *?single?in?line?package *?dual?gain-control?ports(pos/neg) ordering?informations device package SA2159 sip-8 applications *?faders *?expanders *?compressors *?equalizers *?oscillators *?filters *?automation?systems block?diagram
SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?2?of?11 absolute?maximum?ratings ?(t amb =25 c) characteristic symbol ratings unit positive?supply?voltage v cc +15 v negative?supply?voltage v ee -15 v supply?current i cc 30 ma power?dissipation p d 330 mw operating?temperature?range t op -20~+75 c storage?temperature?range t st -40~+125 c recommended?operating?conditions characteristics symbol test?conditions min typ max unit supply?voltage v cc +4 +12 +15 v supply?voltage v ee -4 -12 -15 v bias?current i set v cc -?v ee =24v - 2 2.4 ma signal?current i in +i out i set =2.4ma - 125 550 m a electrical?characteristics (unless?otherwise?specified,?v cc +=+15v,?v cc -=-15v,?t amb ?=25 c) characteristics symbol test?conditions min typ max unit supply?current i cc no?signal - 2 3 ma equiv.?input?bias?current i b no?signal - 5 20 na input?offset?voltage v off (in) no?signal - +10 - mv output?offset?voltage v off (out) r out =20k w 0?db?gain thd?adj?for?min - 1 mv gain?cell?idling?current i idle - 20 - m a gain-control?constant ec+ ec- t amb =20 c -60db SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?3?of?11 pin?configuration pin?description pin?no. symbol description 1 in signal?input 2 ec+ positive?exponential?control 3 ec- negative?exponential?control 4 ec+(sym)? symmetry?control 5 v- negative?power 6 gnd ground 7 v+ positive?power 8 out output function?description operating?theory the?SA2159?vca?is?designed?for?high?performance?in?audio?frequency?applications?which?requires?exponential gain?control,?low?distortion,?wide?dynamic?range?and?low?dc?bias?modulation.?the?gain?control?part?controls?gain by?converting?an?input? current?signal?to? a?bipolar?logged?voltage,? adding?a?dc?control?voltage?and?reconverting the?summed?voltage?back?to?a?current?through?a?bipolar?antilog?circuit. the? simplified? internal? circuit? diagram? of? the? ic? is? shown? in? figure? 1.? the? ac? input? signal? current? flows? in? the input?pin?1,?which?is?maintained?at?a?virtual?ground?potential?by?the?internal?op?amp. figure?1.?simplified?internal?circuit?diagram
SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?4?of?11 positive?input?currents for? positive? input? currents? (iin? defined? as? flowing? into? pin? 1),? the? op? amp? turns? q1? and? d1? off,? while simultaneously?turns?q3?and?d3?on.?thus,?the?input?signal?current?is?forced?to?flow?through?q3?and?d3. logging?&?antilogging we?know?the?basic?properties?vbe?of?the?transistor?and?the?collector?current?ic?as: vbe?=?v t ?ln?(ic/is?) it?is?assumed?that?d3/q3?and?q4/d4?are?matched,?we?therefore?can?conclude: v3?=?ec-?-?2v t ?in?(ic3?/?is) where?v3?is?the?voltage?at?the?junction?of?d3?and?d4,?vt?is?the?thermal?voltage,?kt/q,?ic3?is?the?current?in?the collector?of?q3,?and?is?is?the?reverse-saturation?current?of?q3. ?in? typical? applications? (see? typical? applications? diagram.),? pin? 4? is? normally? at? or? very? near? ground.? pin? 8? is connected?to?a?virtual?ground.?in?this?way,?the?voltage?at?the?cathodes?of?d3?and?d4?will?cause?an?exponentially- related?current?to?flow?in?d4?and?q4,?and?out?through?pin?8.?mathematically: v3?=?ec+?-?2v t ?in?(ic4?/?is?) exponential?gain?control it?can?be?derived?from?said?two?equations: v3?=?ec-?-?2v t ?in?(ic3?/?is)?=?ec+?-?2v t ?in?(ic4?/?is) ec+?-?ec-?=?2v t ?in?(ic4?/?is)?-?2v t ?in?(ic3?/?is)?=?2v t ?in?(ic4?/?ic3) rearranging?terms, ic4?=?ic3?e?(ec+?-?ec-)?/?2v t av?=?ic4?/?ic3?=?e?(ec+?-?ec-)?/?2v t where?av?is?the?current?gain,?which?is?exponential?with?the?difference?in?the?voltage?ec+?and?ec- for?pin?4?at?or?very?near?ground,?at?room?temperature,?and?converting?to?a?base?of?10?for?the?exponential,?this reduces?to: av?=?10?-?ec-?/?0.118 another?way?of?expressing?this?relationship?is: gain?=?20?log?av?=?-?ec-?/?0.0059,?where?the?unit?of?gain?is?db. + 30 db - 30 - 90 - 540 - 360 - 180 0 + 180 -e c mv 0 - 60 gain figure?2.?gain?versus?control?voltage?at?25 c
SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?5?of?11 negative?input?currents for? negative?input? currents,? the? operation? of?q1/d1?and?q3/d3?is? symmetric? with?q2/d2? and?q4/d4.? pin?2? is connected? to? ground,? or? very? nearly? ground? potential? (see? the? section? below? on? symmetry? adjustment? for? more detail),? since?the? top? pair? versus?the? bottom? pair? transistors? are?inverted?(npn/pnp)? and?the? bases?are? cross- connected?between?the?input?(left)?half?and?the?output?(right)?half?of?each?pair,?the?polarity?(positive/negative,? in db)?of?the?gain?is?the?same. symmetry?adjustment the?layout?design?construction?of?the?devices?assures?relatively?good?matching?between?the?paired?transistors, but?even?small?vbe?mismatches?can?cause?a?dc?output?current?to?flow?in?pin?8,?which?will?ultimately?manifest?itself as?a?dc?offset?voltage.?the?dc?offset?voltage?will?be?modulated?by?gain?commands,?and?may?become?audible?as ?thumps??if?gain?commands?changes?very?large?and?fast. transistor?matching?also?affects?distortion.?if?the?top?half? of? the?gain?cell?is?perfectly?matched,? while?the?bottom half? is? not? well?match,? then? the? gain? commanded? by? the? voltage? at? pin? 3? will?affect? the? two? halves? of? the? core differently.? since? positive? and? negative? halves? of? input? signals? are? handled? by? separate? parts? of? the? core,? this gives?rise?to?even?order?distortion?production. figure?3.?typical?thd?versus?symmetry?voltage accordingly,? the? base? of? q1? and?q4? are? brought? out? to? pin?2? and? pin?4,? respectively.? this? allows? applying? a small? static? voltage? differential? to? the? two? bases.? the? applied? voltage? differential? must? be? set? to? the? sum? of? the vbe?mismatches?around?the?core.??typical?applications?diagram?includes?a?typical?symmetry?voltage?application circuitry.? the? symmetry?trim?pot? controls? primarily? even-order? harmonic? distortion,? and? is?adjusted?for?minimum distortion?in?the?output?waveform. opposite?polarity?control as?may? be?seen? from? the? equation,?the? bases? of? q1?and?q4? can?also? be? used?as? an? additional?control? port, which? can? be? used? as? opposite? control? port? of? pin? 3.? both? pins? must? be? applied? to? the? control? voltage simultaneously,?while?the?voltage?applied?between?the?two?pins?must?be?small?difference.?(a?typical?connection?is shown? in? figure? 4.)? either? pin? 3,? or? pins? 2? and? 4,? or? both? ports? together? may? be? used? for? gain? control. mathematically:av?=?10 ?-?ec-?/?0.118 ,?or?gain?=?20?log?av?=?-?ec-?/?0.0059,?where?the?unit?of?gain?is?db.
SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?6?of?11 figure?4.?using?both?control?ports?pin?2?and?pin4 control?port?source?impedance the? control? ports? (pin? 2? through? 4)? are? connected? directly? to? the? bases? of? the? logging? and? /or? antilogging transistors.? since? the? collector? currents? of? transistors? are? signal-related,? the? base? currents? will? also? be? signal- related.?if?the?source?impedance?of?the?control?voltage?is?large,?the?signal-related?base?currents?will?cause?signal- related? voltage? to? appear? at? the? control? ports,? which? will? affect? precise?logging?and? antilogging,?in?turn? causing distortion.?at?high?signal?levels,?even?100 w ?can?spoil?the?good?performance?of?these?parts.?due?to?signal?current based?on?a?transistor b ?of?approximately?300(npn)?or?100(pnp),?the?distortion?caused?by?a?specific?and?non-zero source?impedance?by?determining?the?base?voltage?modulation?can?be?estimated. in?SA2159?vca?design,?the?source?impedance?of?pin?2?and?pin?3?are?zero,?while?the?source?impedance?of?pin?4 is?50 w ?because?pin?4?is?intended?for?connection?to?the?symmetry?control. dc?input?signals any?dc?currents?in?the?feedback?loop?of?the?internal?op?amp?will?show?up?as?dc?terms?in?the?output?signal,?and will?be?modulated?by?gain?commands.?the?bias?current?compensation?circuit?inside?the?chip?offers?the?input?bias current? to? the? input? differential? amplifier.? ac? input? coupling? is? strongly? recommended? to? prevent? an? input? dc current?supplied?from?external?application?circuit?of?the?vca. figure?5.?dc?offset?vs.?gain,?after?symmetry?adjustment
SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?7?of?11 current?programming an?external?iset?can?set?the?size?of?the?current?source?at?the?bottom?of?the?core.?iset?is?normally?determined?by a?resistor?between?v-?and?pin?5?(vpin?5?=?-2.7v,?typically).?iset?should?be?200 m a?larger?than?the?total?of?the?peak input?and?output?signal?currents?because?iset?divides?into?two?portions:?approximately?200 m a?is?used?for?internal biasing,?and?the?rest?is?available?for?the?current?source?at?the?bottom?of?the?core. note? that? since? the? sum? of? the? input? and? output? currents? plus? iset? must? be? supplied? through? the? output impedance?of?the?internal?op?amp,?this?impedance?is?approximately?2k w ,?the?voltage?available?to?drive?the?core will?lower. headroom the?logarithmic?characteristics?of?the?core?transistors?also?limit?maximum?signal?currents.?the?devices?used?in the?SA2159?are?specially?designed?to?conform?to?an?ideal?log-linear?curve?over?a?wide?range?of?currents,?but?their limit? value? is? approximately? 1ma.? distortion? will? increase? with? increasing? current? levels? because? of? falling? log conformance.?figure?6?through?8?show?typical?distortion?versus?1?khz?signal?level?for?the?SA2159?at?-15db,?0?db, and? +15db? gain.? thus,? the? maximum? signal? level? for? a? particular? design? will? be? determined? by? the? acceptable distortion. figure?6.?1khz?thd?+noise?vs.?input,-15db?gain figure?7.?1khz?thd+noise?vs.?level,?0db?gain figure?8.?1khz?thd+noise?vs.?input,?+15db?gain
SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?8?of?11 applications input as? mentioned? above,? because? input? and? output? signals? are? currents,? not? voltages,? the? current? input/output mode?provides?great?flexibility?in?application. internal? negative? feedback? loop? provides? a? virtual? ground?to? the? input? pin? 1?(see? figure? 1).?within? the? linear range?of?the?device,?the?input?resistor?(shown?as?20k w ?in?typical? application?circuit)? should? be?scaled?to? convert the? available? ac? input? voltage? to? a? current.? in? order? to? obtain? best? distortion? performance,? peak? input? currents should?be?kept?under?1?ma.?the?input?impedances?must?be?less?than?30k w ?to?assure?the?circuit?stability. the?feedback?impedances?around?the?internal?op?amp?(essentially?q1/d1?and?q3/d3)?are?fixed.?low?values?for the?input?resistor?will?require?more?closed-loop?gain?from?the?op?amp. since?the?open-loop?gain?naturally?falls?off?at?high?frequencies,?this?resistor?should?be?kept?to?10k w ?or?above?in order?to?prevent?high?frequency?distortion?when?the?gain?is?too?much.?distortion?vs.?frequency?for?a?1v?signal?at 0db?gain?with?a?20?k w ?input?resistor?is?shown?in?figure?9. as?mentioned?above,?any?dc?input?currents?will?cause?dc?signals?in?the?output.?the?dc?signals?will?be?modulated by? gain? command,? in? turn? causing? audible? thump.? therefore,? in? order? to? control? quality? audio? applications, capacitive?coupling?must?be?adopted?in?actual?application,?which?can?give?acceptable?low?frequency?performance. figure?9.?typical?thd?vs.?frequency,?0db?gain output the? output? pin? (pin? 8)? should? be? connected? to? a? virtual? ground? node,? so? that? current? flowing? in? it? may? be converted?to?a?voltage.?choose?the?external?op?amp?can?improve?audio?performance. ?a? small? feedback? capacitor? around? the? output? op? amp? is? necessary? to? cancel? the? output? capacitance? of? the vca,?so?that?most?op?amps?can?operate?steadily.?the?capacitance?at?pin?8?is?typically?30?pf. power?supplies the? positive? supply? is? connected? directly? to? pin? 7? without? special? bypassing? circuit,? but? it? is? good? practice? to include?a?small?(~1 m f)?electrolytic?close?to?the?vca?ic?on?the?pcb.?there?is?no?particularly?dependence?between performance? and? supply? voltage.? the? lowest? supply? voltage? is? determined? by? the? sum? of? the? input? and? output currents?plus?iset,?which?must?be?supplied?through?the?resistor?(~2k w )?at?the?top?of?the?core?transistors?while?still allowing?enough?voltage?swing?to?bias?the?internal?op?amp?and?the?core?transistors?themselves.?reducing?signal currents?may?help?accommodate?low?supply?voltages.
SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?9?of?11 the?process?characteristics?and?internal?power?consumption?determine?the?highest?supply?voltage.??+15v?is?the nominal?limit. a? resistive? current? source? determining? the? current? available? for? the? core? is? connected? to? the? negative? supply terminal.? as? mentioned? before,? this? source? must? supply? 200 m a? current? over? the? sum? of? the? required? signal currents? including? input? signal? current,? output? signal? current? and? the? bias? to? run? the? rest? of? the? ic.? 2.4ma? is recommended?for?most?pro?audio?applications?where?+15v?supplies?are?common?and?headroom?is?important. bypassing?at?pin?5?is?not?necessary?because?pin?5?is?a?current?supply,?not?a?voltage?supply. pin?6?is?used?as?a?ground?reference?for?the?vca?which?connect?the?non-inverting?input?of?the?internal?op?amp, as?a?portion?of?the?internal?bias?network.?it?may?not?be?used?as?an?additional?input?pin. voltage?control pin? 3? is? the? primary? voltage? control? pin.? this? point? controls? gain? is? inversely? proportional? to? applied? voltage: positive?voltage?causes?loss,?negative?voltage?causes?gain.?the?current?gain?of?the?vca?is?unity?when?pin?3?is?at 0v?and?varies?with?voltage?at?approximately?-5.9m/db,?at?room?temperature. as?implied?by? the? equation? for? av? at?the? foot?of? page? 3,?the? gain?is? sensitive?to? temperature.? the? constant? of proportionality? is? 0.33%? of? the? decibel? gain? commanded,? per? degree? celsius,? referenced? to? 27 c? (300k).? the formula?is: gain?=?(ec+?-?ec-)?/?(0.0059?*?1.0033?*? ? t). where d t?is?the?difference?between?the?actual?temperature?and?room?temperature?(27 c) for? most? audio? applications,? this? change? with? temperature? is? of? little? consequence.? however,? if? necessary,? it may?be?compensated?by?a?resistor?which?varies?its?value?by?0.33%/ c. when? pin? 3? is? used? for? voltage? control,? pin? 2? is? connected? to? ground? and? pin? 4? is? used? to? apply? a? small symmetry? voltage? (~ 4? mv)? to? correct? for? vbe? mismatches? within? the? vca? ic.? therefore,? in? order? to? obtain optimum? performance,? pin? 4? connects? with? an? external?impedance? of? approximately? 50 w .? a? trim? pot? is? used? to adjust?the?voltage?between?pin?4?and?pin?2?as?shown?in?typical?application?circuit.?voltage?adjustment?range?is 4 mv. pin?2?and?pin4?can?be?used?together? as?an?opposite?sense?voltage?control?port?(see?figure?4).?pin?3?may?be grounded?and?pin?2?driven?against?the?symmetry-adjustment?voltage.?the?change?of?voltage?at?pin?4?does?have?a small?effect?on?the?symmetry?voltage,?but?this?is?of?little?practical?consequence?in?most?applications. the?chip?can?combine?all?control?ports?together?with?differential?drive?(see?figure?10).?while?the?driving?circuitry is?more?complex,?this?configuration?offers?better?performance?at?high?attenuation?levels?(<-90db)?where?the?single control?port?circuits?begin?to?saturate?q1?(for?ec-?drive)? or?q3?(for?ec+?drive).?when?either?of?these?transistors saturates,? the? internal? op? amp? will? accommodate? the? change? in? current? demand? by? responding? with? a? small change?in?its?input?offset? voltage.? this?leads?to?an?accumulation? of? charge?on?the?input? capacitor,?which?in?turn can? cause? thump? when? the? high? attenuation? is? suddenly? removed(e.g.,? when? a? muted? channel? is? opened). differential?control?drive?avoids?the?large?dc?levels?otherwise?required?to?command?high?attenuation?(+600mv?or?- 100db?gain?at?pin?3?alone,?vs. 300mv?when?using?both?pin?3?and?pins?2?and?4). control?port?drive?impedance in? order?to?reduce?distortion,?it?is?necessary?to?use?low?source?impedance?at?the?control?port.?thus,?this?often suggests? an? op? amp? is? used? to? drive? the? control? port?directly? (see? below? under? noise? considerations).? however, due?to?falling?loop?gain?at?high?frequencies,?the?closed-loop?output?impedance?of?an?op?amp?typically?rises.?the output? impedance? is? therefore? inductive? at? high? frequencies.? excessive? inductance? can? cause? the? vca? to
SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?10?of?11 oscillate?internally.?in? such?cases,?a?100 w ? resistor?in? series?with? a? 1.5nf?capacitor? between? the? control?port? and ground?will?usually?suffice?to?prevent?the?instability. in v+ v- gnd e c+ e c+(sym) e c- input output 10 - 20k +15v out 5.1k 20k 47p lf351 +15v 50k sym adj -15v 150k rsym 51 -15v 5 6 2 4 8 3 7 1k 1k e c+ SA2159 vca figure?10.?using?both?control?ports?(differential?drive) noise?considerations for?good?audio?designers,?it?is?important?to?consider?the?effects?of?noisy?devices?on?the?signal?path.?as?is?well known,? this? includes? not? only? active? devices,? but? also? impedance.? high? value? resistors? have? inherent? thermal noise.?and?the?wrong?choice?of?impedance?levels?will?easily?bring?on?the?noise?performance?of?an?otherwise?quiet circuit?being?spoiled. however,?the?effect?of?noisy?circuitry?and?high?impedance?levels?in?the?control?path?of?voltage-control?circuitry?is easily?neglected.? when? no? signal?is? present? at? the? signal?input,? the? SA2159? vca?noise? at? the? control?input? is rejected? like? double-balanced?multipliers.? most? everyone?measures? noise? in?the? absence? of? signal,? so?noise? of control?circuitry?is?often?neglected.?however,?noise?at?the?control?port?of?these?parts?will?cause?noise?modulation of?the?signal.?if?driving?the?control?ports?is?not?quiet?signals,?this?problem?will?become?very?grave. quiet? electronics? throughout? be? control-voltage? circuitry? can? be? used? to? avoid? excessive? noise.? one? useful technique?is?to?process?control?voltages?at?a?multiple?of?the?eventual?control?constant?(e.g.,?59mv/db??ten?times higher? than? the? vca? requires).? and? then? attenuate? the? control? signal? just? before? the? final? drive? amplifier.? it? is necessary?to?pay?attention?to?impedance?levels?and?noisy?op?amps. figure?11.?typical?frequency?response?vs.?gain figure?12.?typical?noise?(20khz?nbw)?vs.?gain
SA2159 hangzhou?silan?microelectronics?co.,ltd ?????rev:?1.0??????2005.04.22 http:?www.silan.com.cn??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????page?11?of?11 typical?application?circuit package?outline sip-8 unit:?mm
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