Applications following circuits will illustrate some wide variety appl

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AND8159/D Applications Compandors NE570/SA571
Applications following circuits will illustrate some wide variety applications NE570/SA571. Basic Expandor Figure shows circuit would hooked expandor. Both rectifier cell inputs tied that gain proportional average value (VIN). Thus, when falls gain drops output drops exact expression gain
Gain exp. (avg) Figure Basic Expandor
CIN2
CIN1
VREF
VOUT
CRECT
maximum input that handled circuit Figure peak rectifier input current large V/R1 V/10 cell input current should limited V/R2 V/20 necessary handle larger input voltages than peak, external resistors should placed series with limit input current above values. Figure shows pair input capacitors CIN1 CIN2. necessary both capacitors level tracking accuracy important. tied together share common capacitor, small current will flow between cell summing node rectifier summing node offset voltages. This current will produce error gain control signal levels, degrading tracking accuracy.
output expandor biased gain provided output will bias
VOUTDC VREF
supply voltages higher than shunted with external resistor bias output VCC. Note that possible externally increase decrease This allows great deal flexibility setting system levels. larger input signals handled, increased; larger output required, increased. obtain largest dynamic range this circuit, rectifier input should always large possible (subject "300 peak current restriction).
Semiconductor Components Industries, LLC, 2005
February, 2005 Rev.
Publication Order Number: AND8159/D
AND8159/D
Basic Compressor Figure shows NE570/SA571 compressor. functions expandor feedback loop amp. input rises output rise only increase output level produces increase gain cell, yielding increase feedback current summing node. Exact expression gain
Gain comp. (avg)
CRECT
VREF
VOUT
same restrictions rectifier cell maximum input current still hold, which place limit maximum compressor output. expandor, rectifier cell inputs could made common save capacitor, level tracking accuracy would suffer. Since there feedback path around through cell, must provided externally. pair resistors capacitor must provided. output will bias
VOUTDC 2RDC VREF
Figure Basic Compressor
largest dynamic range, compressor output should large possible that rectifier input large possible (subject "300 peak current restriction). input signal small, large output produced reducing with attendant decrease input impedance, increasing would best increase rather than that rectifier input current reduced.
Distortion Trim Distortion produced voltage offsets cell. distortion mainly even harmonics, drops with decreasing input signal (input signal meaning current into cell). trim terminal provides means trimming offset voltages thus trimming distortion. circuit shown Figure suitable, would other capable delivering into resistor tied
3.6V 6.2kW 20kW Trim 200pF VOUT
Figure Trim Network
CIN1
VREF
VOUT
CIN2
CRECT
Figure Expandor with Level Mistracking
Level Mistracking compandor will follow 2-to-1 tracking ratio down very levels. rectifier responsible errors gain, rectifier input bias current <100 that
produces errors levels. magnitude signal level drops average, bias current will produce error gain. This will occur below maximum input level.
AND8159/D
possible deviate from 2-to-1 transfer characteristic levels shown circuit Figure Either (but both), required. voltage CRECT plus avg. level inputs negligible, assume bias CRECT. placed from CRECT will bleed current V/RA. rectifier average input current less than this value, there will gain control input cell that gain will zero expandor output will zero. input level raised, input current will exceed V/RA expandor output will become active. large input signals, will have little effect. result this that will deviate from 2-to-1 expansion, present high levels, infinite expansion levels where output shuts completely. Figure shows some examples tracking curves which obtained. Complementary curves would obtained compressor, where level signals result would infinite compression. bleed current through will function temperature because drops, level tracking will drift with temperature. negative supply available, would desirable that, rather than ground, increase value accordingly. bleed current will then less sensitive temperature drift.
COMPRESSOR INPUT LEVEL EXPANDOR OUTPUT LEVEL RECTIFIER OUTPUT CURRENT, 100kW 250kW 500kW COMPRESSOR INPUT LEVEL EXPANDOR OUTPUT LEVEL 250kW
EXPANDOR INPUT LEVEL COMPRESSOR OUTPUT LEVEL
Figure Mistracking with
330kW 3.6V 10MW 100kW RECTIFIER INPUT
Figure Rectifier Bias Current Compensation
W/OUT COMP WITH COMP
EXPANDOR INPUT LEVEL COMPRESSOR OUTPUT LEVEL
RECTIFER INPUT LEVEL,
Figure Mistracking with
Figure Rectifier Performance with Bias Current Compensation
will supply extra current rectifier equal (VCC-1.3 V)RB. this case, expandor transfer characteristic will deviate towards 1-to-1 levels. levels expandor gain will stop dropping expansion will cease. compressor, this would lead lack compression levels. Figure shows some typical transfer curves. value approximately would trim level tracking match Bell system trunk compandor characteristic.
Rectifier Bias Current Cancellation rectifier input bias current between This limits dynamic range rectifier about also limits amount attenuation cell. rectifier dynamic range increased about bias current trim network shown Figure Figure shows rectifier performance with without bias current cancellation.
AND8159/D
-10dB GAIN
-20dB
-30dB TIME CONSTANTS 10kW CRECT
Figure Gain Time Input Steps "10, "20,
AMPLITUDE TIME CONSTANTS 10kW CRECT
output risen units, suggests value 13.5 This corresponds 0.675 figure, which again suggests product. Since CCITT recommendations will CRECT There trade-off between fast response distortion. small CRECT used very fast attack decay, some ripple will appear gain control line produce distortion. rule, CRECT will produce 0.2% distortion kHz. distortion inversely proportional both frequency capacitance. Thus, telephone applications where CRECT ripple would cause 0.1% distortion 0.33% frequency distortion generated compressor would cancelled undistorted) expandor, providing that they have same value CRECT. Fast Attack, Slow Release Hard Limiter NE570/SA571 easily used make excellent limiter. Figure shows typical circuit which requires NE570/SA571, LM339 quad comparator, transistor. small signals, cell nearly off, circuit runs unity gain When output signal tries exceed -1.0 peak, comparator threshold exceeded. turned rapidly charges which activates cell. Negative feedback through cell reduces gain output signal level. attack time product release time determined internal rectifier resistor, which circuit shown attacks less than release time constant trickles about through rectifier prevent from becoming completely discharged. gain cell activated when voltage exceeds diode drops. were allowed become completely discharged, there would slight delay before recharged >1.2 activated limiting action. stereo limiter built NE570/SA571, LM339 transistors. resistor networks R12, R14, R15, which limiting thresholds, could common between channels. gang stereo channels together (limiting channel will produce corresponding gain change second channel maintain balance stereo image), then Pins should jumpered together. outputs comparators then tied together, only transistor capacitor need used. release time will then product since channels being supplied current from External operational amplifiers NE570/SA571 adequate some applications.
Figure Compressor Attack Envelope Step
AMPLITUDE TIME CONSTANTS 10kW CRECT
Figure Compressor Release Envelope Step
Attack Decay Time attack decay times compandor determined rectifier filter time constant CRECT. Figure shows gain will change when input signal undergoes change level. attack time much faster than decay, which desirable most applications. Figure shows compressor attack envelope step input level. initial output level unit instantaneously rises units, then starts fall towards final value units. CCITT recommendation attack decay times telephone system compandors defines attack time when envelope fallen level units, corresponding 0.15 figure. CCITT recommends attack time which suggests product Figure shows compressor output envelope when input level suddenly reduced output, initially level units, drops unit then rises final value units. CCITT defines release time when
AND8159/D
LM339 LM393 NE570/SA571
2,15 10kW 2.2MW 20kW 100kW 10kW 100kW 100kW 5,12 30kW 1.8V 3,14 10kW 43kW 10kW 10kW
180kW
10µF
7,10
100kW
100kW
+15V internal NE570/SA571
Figure Fast Attack, Slow Release Hard Limiter
3,14
6,11
EXTERNAL OUTPUT
5,12 INTERNAL DON'T 7,10 1.8V
2,15 1,16
Figure External
slew rate, bandwidth, noise, output drive capability limit performance many systems. best performance, external used. external powered bipolar supplies larger output swing.
Figure shows external connected. non-inverting input must biased about This easily accomplished tying either trim pins, since these pins optional decoupling network shown which will filter noise from NE570/SA571 reference (typically about BW). inverting input external tied inverting input internal amp. output external then used, with internal output left float. external used single supply (+VCC ground), must have input common-mode range down less than
20kW
GAIN TRIM 10kW 10µF LEVEL TRIM 43kW 43kW 10µF ROUT 4.0kW 15µF
600W: 20kW
20kW
1.8kW 30kW
600W
.275 VRMS 600W
.245 VRMS 6000
Figure Compressor
AND8159/D
20kW
600W: 100W
20kW
30kW 16kW 1.8V
GAIN TRIM 150W 600W 150W 200µF ROUT 3.46 VRMS 600W
3.27 VRMS 10µF LEVEL TRIM
10kW
Figure Expandor
Compandor There four primary considerations involved application NE570/SA571 compandor. These matching input output levels, accurate input output impedances, conformance Bell system level tracking curve, proper attack release times. Figure shows implementation compressor. input level 0.245 VRMS stepped 1.41 VRMS matching transformer. input resistor properly terminates transformer. internal resistor (R3) provided, accurate impedance termination external resistor should used. output impedance provided output resistor output transformer. 0.275 VRMS output level requires output level. This provided increasing value with external resistor, which selected fine trim gain. rearrangement compressor gain equation allows determine value
Gain2 1.27
shown Figure this will skew system transfer characteristic levels. rectifier capacitor provides attack release times 13.5 respectively, shown Figures R-C-R network around provides feedback bias output expandor shown Figure input level 3.27 VRMS stepped down 1.33 W:100 transformer, which terminated with resistor accurate impedance matching. output impedance accurately output resistor W:600 output transformer. With this configuration, 3.46 transformer output requires 3.46 output. obtain this output level, necessary increase value with external trim resistor. value found with expandor gain equation.
Gain 1.20
30.3
36.3
external resistance required will thus 36.3 kW-20 16.3 Bell-compatible level tracking characteristic provided level trim resistor from CRECT VCC.
external addition required, this value selected accurately high level gain. level trim resistor from CRECT about provides matching Bell low-level tracking curve, value CRECT provides proper attack release times. resistor from summing node ground biases output VDC.
AND8159/D
Voltage-Controlled Attenuator variable gain cell NE570/SA571 used heart high quality voltage-controlled amplifier (VCA). Figure shows typical circuit which uses external better performance, exponential converter control characteristic -6.0 dB/V. Trim networks shown null distortion shift, fine trim gain with control voltage. transistors form exponential converter generating exponential gain control current, which into rectifier. reference current kW), attenuated factor (6.0 every volt increase control voltage. Capacitor slows down gain changes time constant that abrupt change control voltage will produce smooth sounding gain change. assures that large control voltages circuit will full attenuation. rectifier bias current would normally limit gain reduction about draws excess current rectifier. After approximately attenuation -6.0 dB/V slope, slope steepens attenuation becomes much more rapid until circuit totally shuts about control voltage. should noise high slew rate amp. establish approximately bias A1's output. With control voltage, should adjusted gain. (-6.0 gain) should adjusted minimum distortion with large (+10 dBm) input signal. output bias output) should measured full attenuation (+10 control voltage) then adjusted give same value gain. Properly adjusted, circuit will give typically less than 0.1% distortion gain with output voltage variation only millivolts. clipping level (140 into peak. signal-to-noise ratio obtained. several VCAs must track each other, common exponential converter used. Transistors simply added parallel with control other channels. transistors should maintained same temperature best tracking.
+15V
150kW 3.8V SHIFT TRIM 100kW 220kW 100kW
TRIM
62kW
62kW 220kW
10µF
100kW 2,15 CONTROL VOLTAGE GANGING MULTIPLE CHANNELS -15V 5.45kW 51kW 3,14 20kW NE570/SA571 10kW +15V 150kW 100kW GAIN TRIM -15V 1,16 44MW 30kW
5,12
39pF 36kW
100K
100kW +15V
Figure Voltage-Controlled Attenuator
AND8159/D
Automatic Level Control NE570/SA571 used make very high performance shown Figure This circuit hook-up very similar basic compressor shown Figure except that rectifier input tied input rather than output. This makes gain inversely proportional input level that drop input level will produce increase gain. output will remain fixed constant level. shown, circuit will maintain output level "1.0 input range kHz. Additional external components will allow output level adjusted. Some relevant design equations are:
Output level (avg) where VIN(avg)
(2,15) 10kW (1,16) CRECT
1.11 (for sine wave) (avg)
action very input levels desired, addition resistor will limit maximum gain circuit.
Gain
R1)Rx
time constant circuit determined rectifier capacitor, CRECT, internal resistor.
CRECT
Response time made faster expense distortion. Distortion approximated equation:
CRECT freq. 0.2%
Gain
20kW
(3,14)
33kW 10µF 33kW
(5,12) 30pF (6,11) 30kW 1.8V VOUT (7,10) 20kW
Figure Automatic Level Control
AND8159/D
Variable Slope Compressor-Expandor Compression expansion ratios other than achieved circuit shown Figure Rotation dual potentiometer causes circuit hook-up change from basic compressor basic expandor. center rotation, circuit 1:1, neither compression expansion. (input) output transfer characteristic thus continuously variable from compression, through expansion. fixed compression expansion ratio desired, proper selection fixed resistors used instead potentiometer. optional threshold resistor will make compression expansion ratio deviate towards levels. wide variety (input) output characteristics created with this circuit, some which shown Figure
OUTPUT LEVEL
10dB/DIV
10dB/DIV INPUT LEVEL
Figure Typical Input-Output Tracking Curves Variable Ratio Compressor-Expandor
COMPRESSION DUAL EXPANSION
30pF 39kW (6,11) 20kW 20kW (3,14) 30kW 1.8V 10kW (2,15) VOUT (7,10) (5,12) 10µF 39kW
THRESHHOLD
(1,16) CRECT
Figure Variable Slope Compressor-Expandor
Hi-Fi Compandor NE570/SA571 used construct high performance compandor suitable with music. This type system used noise reduction tape recorders, transmission systems, bucket brigade delay lines, digital audio systems. circuits described contain features which improve performance, required applications. major problem with simple NE570/SA571 compressor (Figure limited gain high frequencies. weak input signals, compressor circuit operates high gain NE570/SA571 simply runs
loop gain. Another problem with NE570/SA571 limited slew rate about V/ms. This limitation expandor, since expandor more likely produce large output signals than compressor. Figure circuit high fidelity compressor which uses external high gain wide bandwidth. input compensation network required stability. Another feature circuit Figure that rectifier capacitor (C9) grounded, tied output circuit. This circuit, built around LM324, speeds compressor attack time signal levels. response times simple expandor
AND8159/D
compressor (Figures become longer signal levels. time constant simply CRECT, really:
0.026 IRECT CRECT
When rectifier input level drops from dBm, time constant increases from 10.7 CRECT 32.6 CRECT. systems where there unity gain between compressor expandor, this will cause overall error. Gain loss between compressor expandor will mistracking signal dynamics. circuit with LM324 will greatly reduce this problem systems which cannot guarantee unity gain. When compressor operating high gain, (small input signal), suddenly with signal, will overload until reduce gain. Overloaded, output will attempt swing rail rail. This compressor limited approximately VP-P output swing brute force clamp diodes diodes cannot placed feedback loop because their capacitance would limit high frequency gain. purpose limiting output swing avoid overloading succeeding circuit such tape recorder input.
time takes compressor recover from overload determined rectifier capacitor smaller capacitor will allow faster response transients, will produce more frequency third harmonic distortion gain modulation. value seems good compromise value yields good subjective results. course, expandor should have exactly same value rectifier capacitor proper transient response. Systems which have good frequency amplitude phase response compandors with smaller rectifier capacitors, since third harmonic distortion which generated compressor will undistorted expandor. Simple compandor systems subject problem known breathing. system changing gain, change background noise level sometimes heard. compressor Figure contains high frequency pre-emphasis circuit (C2, R14), which helps solve this problem. Matching de-emphasis expandor required. More complex designs could make pre-emphasis variable further reduce breathing.
LM324
NE570/SA571 10kW 3.6V 30kW 30kW 68kW +7.5V 47kW 10µF 47kW 220kW COMPRESSOR 100kW 100kW D.C. SHIFT TRIM
+3.6V 220kW 100kW TRIM
20kW
COMPRESSOR .005 62kW 20kW 100kW 270pF 2.2kW
Figure Hi-Fi Compressor with Pre-emphasis
AND8159/D
expandor complement compressor shown Figure Here external used high slew rate. Both compressor expandor have unity gain levels Trim networks shown distortion (THD) shift. distortion trim should done first,
+3.6V +7.5V 100kW D.C. SHIFT TRIM 100kW 220kW T.H.D. TRIM SA570 EXPANDOR 100kW .01µF 30kW 20kW 30kW 10kW 270pF 2.2kW +2µF EXPANDOR 68kW 20kW 62kW 0.005µF
with input kHz. shift should adjusted minimum envelope bounce with tone bursts. When applied consumer tape recorders, subjective performance this system excellent.
220kW
100kW
LM325
Figure Hi-Fi Expandor with De-emphasis
AND8159/D
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AND8159/D

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