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AND8160/D Compandor Cookbook
Compandors versatile, cost, dual-channel gain control devices audio frequencies. They used tape decks, cordless telephones, wireless microphones performing noise reduction. Electronic organs, modems mobile telephone equipment compandors signal level control. what companding? all? What happens when Compandor contraction words compressor expandor. There basic reason compress signal before sending through telephone line recording cassette tape: process that signal (music, speech, data) that parts above inherent noise floor transmission medium running into maximum dynamic range limits, causing clipping distortion. diagrams below demonstrate idea; they totally correct because real world electronics tone riding tone. They shown separated better explanation. Figure signal from source. Figure shows noise always transmission medium. Figure shows limits transmission medium what happens when signal larger than those limits sent through Figure result compressing signal (note that larger signal would clipped when transmitted).
1kHz, pk-pk 3kHZ, pk-pk
Figure Wide-Band Noise Floor Transmission Line
SIGNAL AFTER AMPLIFYING ABOVE NOISE
DYNAMIC RANGE PK-PK
Figure
Figure Signal After Compression
Figure Original Signal Input
Semiconductor Components Industries, LLC, 2005
February, 2005 Rev.
Publication Order Number: AND8160/D
AND8160/D
received/playback signal processed (expanded) exactly same only inverted ratio input signal compressed. result clean, undistorted signal with high signal-to-noise ratio. This document been designed give reader basic working knowledge Semiconductor Compandor family. analyses three primary applications will accompanied "recipes" describing select external components (for both proper operation function modification). Schematic artwork application board also provided.
NE570/SA571 INPUT CURRENT CONTROLLED GAIN CELL VREF
basic blocks compandor currentcontrolled variable gain cell (DG), voltage-to-current converter (rectifier), operational amplifier. Each Semiconductor compandor package identical, independent channels with following block diagrams (notice that 570/71 different from 572). operational amplifier main signal path output drive.
SA572 CURRENT CONTROLLED GAIN CELL
OUTPUT
INPUT
OUTPUT
INPUT
VOLT-TO CURRENT CONVERTER
ATTACK TIME CAPACITOR
BUFFER
RELEASE TIME CAPACITOR
ATTACK/RELEASE TIME CONSTANT CAPACITOR
INPUT
VOLTAGE CURRENT
NOTES
Figure Block Diagrams
CURRENT CONTROLLED GAIN CELL
VOLTAGE CURRENT CONVERTER
VOUT
CRECT
VOUT
Figure Basic Compressor
full-wave averaging rectifier measures amplitude signal develops control current variable gain cell.
variable gain cell uses rectifier control current provide variable gain control operational amplifier gain block.
AND8160/D
compandor function Compressor, Expandor, Automatic Level Controller complete compressor/expandor system described following: COMPRESSOR function processes uncontrolled input signals into controlled output signals. purpose this avoid distortion caused narrow dynamic range medium, such telephone lines, satellite transmissions, magnetic tape. Compressor also limit level signal. EXPANDOR function allows user increase dynamic range incoming compressed signal such radio broadcasts. compressor/expandor system allows user retain dynamic range reduce effects noise introduced transmission medium. AUTOMATIC LEVEL CONTROL (ALC) function (like familiar automatic gain control) adjusts gain proportionally with input amplitude. This circuit therefore transforms widely varying input signal into fixed amplitude output signal without clipping distortion. Design Compandor Circuits rest cookbook will provide with basic compressor, expandor, automatic level control application information. SA571 been used circuits. high-fidelity audio separately programmable attack decay time needed, SA572 with noise should used.
Compressor
3,14
2,15 1,16 CRECT 5,12
6,11
VREF 7,10 VOUT
Figure Basic Compressor (NE570/SA571 pinout)
Compressor Recipe bias output half between supply ground maximum headroom. circuit Figure designed around system supply thus output level should
VOUT (2RDC R4)) VREF
compressor (see Figure utilizes basic building blocks compandor. this configuration, variable gain cell placed feedback loop standard inverting amplifier circuit. gain equation -RF/RIN. shown above, variable gain cell acts variable feedback resistor (RF) (see Figure input signal increases above crossover level variable resistor decreases value. This causes gain decrease, thus limiting output amplitude. Below crossover level increase input signal causes variable resistor increase value, thereby causing output signal's amplitude increase. compressor configuration, rectifier connected output. complete equation compressor gain
Gain comp. (avg)
VREF external manipulating equation, result
VOUT VREF
where:
where:
VIN(avg) 0.9(VIN(RMS))
Note that C(DC) should large enough totally short this feedback loop. Analyze OUTPUT signal's anticipated amplitude. larger than 2.8V peak, needs increased (see INGREDIENTS section). larger than peak, will also need increased. limiting peak input currents avoid signal distortion. input output coupling caps need large enough attenuate desired frequencies 1/(2pf C)). CRECT should initial setup. This directly affects Attack Release times. input buffer necessary source's output impedance needs matching. Pre-emphasis used reduce noisepumping, breathing, etc., present. SA571 data sheet specific details.
AND8160/D
Distortion (THD) trim pins available already distortion needs further reduced. Refer data sheet trimming network. Note that used, trim pins should have caps ground.
very input signal levels, rectifier's errors become significant reduced with Level Mistracking network. (This technique prevents infinite compression input levels.)
CIN2 VOUT
CURRENT CONTROLLED GAIN CELL
VOUT
CIN1
VOLTAGE CURRENT CONVERTER
CRECT
Figure Basic Expandor Expandor
complete equation expandor gain
Gainexpandor (avg)
EXPANDOR utilizes basic building blocks compandor (see Figure this configuration variable gain cell placed inverting input lead operational amplifier acts variable input resistance, RIN. basic gain equation operational amplifiers standard inverting feedback loop -RF/RIN. input amplitude increases above crossover level dBM, this variable resistor decreases value, causing gain increase, thus forcing output amplitude increase (refer Figure 11). Below crossover level, increase input amplitude causes variable resistor increase value, thus forcing output amplitude decrease.
where:
VIN(avg) (VIN(RMS))
expandor configuration rectifier connected input.
20kW
(6,11)
3,14 20kW VREF 30kW
5,12
VOUT 7,10
2,15 10kW 1,16
CRECT
Figure Basic Expandor (NE570/SA571 pinout)
AND8160/D
Expandor Recipe bias output halfway between supply ground maximum headroom. circuit Figure designed around system supply output level should
VOUT VREF
input amplitude decreases below crossover point, overall system gain increases proportionally, holding output amplitude same constant level. complete gain equation
Gain Output Level where VIN(avg) (avg)
VREF Note that when using supply voltage higher than output level should adjusted. increase output level, recommended that decreased adding parallel resistance (Changing would also affect expandor's gain thus cause mismatch companding system.) Analyze input signal's anticipated amplitude: larger than peak, needs increased (see INGREDIENTS section). larger than peak, will also need increased (see INGREDIENTS). limiting peak input currents avoid signal distortion. input output decoupling caps need large enough attenuate desired frequencies. CRECT should initial setup. input buffer necessary source's output impedance needs matching. De-emphasis would necessary complementary compressor circuit been pre-emphasized tape deck application). Distortion (THD) trim pins available already distortion needs further reduced. Note that used, trim pins should have caps ground. very input signal levels, rectifier's errors become significant reduced with Level Mistracking network. (This technique prevents infinite expansion input levels.) configuration, (Figure 10), variable gain cell placed feedback loop operational amplifier Compressor) rectifier connected input. input amplitude increases above crossover point, overall system gain decreases proportionally, holding output amplitude constant.
where:
1.11 (for sine wave) (avg)
Note that very input levels, desired limit maximum gain, resistor been added. modified gain equation
Gain max.
R1)Rx VREF
((desired gain)
Ingredients [Application guidelines internal external components (and input/output constraints) needed tailor (cook) each three entrees (applications) your taste.] limits input current rectifier. This current should exceed peak value "300 external resistor placed series with input voltage rectifier will exceed "3.0 peak (i.e., limits input current variable gain cell. This current should exceed peak value "140 Again, external resistor placed series with input voltage variable gain cell exceeds "2.8 (i.e., mA). acts conjunction with feedback resistor (RF) (expandor configuration) equation. (R3's value either reduced increased externally.) However, recommended that change when adjusting output level. acts input resistor (RIN) standard non-inverting circuit. (Its value only reduced.)
VOUT R4)) VREF (for Expandor) VOUT (2RDC R4)) VREF (for Compandor, ALC)
[The purpose these biasing equations allow designer output halfway between supply rails largest headroom (usually some positive voltage ground).]
AND8160/D
CIN1 (2,15) 10kW (1,16)
CRECT
20kW (3,14)
CIN2 39kW 33kW 10µF
(5,12) 30pF CIN3 (6,11) 30kW 1.8V (7,10) VOUT 20kW
Figure Automatic Level Control (NE570/SA571 pinout)
acts shunt ground totally remove biasing resistors from gain equation. CIN, caps signal coupling caps. CRECT acts rectifier's filter directly affects response time circuit. There trade-off, though, between fast attack decay times distortion. time constant CRECT. total harmonic distortion (THD) approximated
(1.0 CRECT) (1.0 freq.) 0.2%
System Levels Complete Companding System Figure demonstrates compressing expanding functions: Point represents wide dynamic range signal with maximum amplitude minimum amplitude Point represents compressor output showing reduction dynamic range (-40 increased example). Point also seen dynamic range transmission medium. Transmission noise present level from Point Point Point represents input signal expandor. Point represents output expandor. signal transformation from Point represents expansion.
NOTES: SA572 differs from 570/571 that: There internal amp. attack release times programmed separately.
AND8160/D
NE570/SA571 SYSTEM LEVEL
LEVEL COMPRESSION (COMPRESSOR OUT) 4.9V 3.1V 775mV EXPANDOR (EXPANDOR
LEVEL
+16dB
+16.0 +12.0
-20dB
77.5mV
-40dB
7.75mV
-60dB
775µV
-80dB
77.5µV
Figure System Levels Complete Companding System
Application Board Shown below schematic (Figure NE570/SA571 evaluation/demo board. This board provides
(OPTIONAL PRE-EMPHASIS) 33kW 10µF 20kW 30kW 10µF EXPANDOR INPUT 2.2µF (JUMPER) 20kW 2.2µF
36kW
SHOWN COMPRESSOR (OPTIONAL DE-EMPHASIS) (SPDT SWITCH) 2.2µF 2.2µF
(OPTIONAL PRE-EMPHASIS) 200pF 2.2µF
COMPRESSOR/ALC INPUT
TRANSMISSION MEDIUM 20kW 12kW 200pF 10µF
channel Expansion channel Compression (which switched Automatic Level Control).
(OPTIONAL DE-EMPHASIS) 20kW
30kW 10µF
EXPANDOR
Figure
AND8160/D
Semiconductor registered trademarks Semiconductor Components Industries, (SCILLC). SCILLC reserves right make changes without further notice products herein. SCILLC makes warranty, representation guarantee regarding suitability products particular purpose, does SCILLC assume liability arising application product circuit, specifically disclaims liability, including without limitation special, consequential incidental damages. "Typical" parameters which provided SCILLC data sheets and/or specifications vary different applications actual performance vary over time. operating parameters, including "Typicals" must validated each customer application customer's technical experts. SCILLC does convey license under patent rights rights others. SCILLC products designed, intended, authorized components systems intended surgical implant into body, other applications intended support sustain life, other application which failure SCILLC product could create situation where personal injury death occur. Should Buyer purchase SCILLC products such unintended unauthorized application, Buyer shall indemnify hold SCILLC officers, employees, subsidiaries, affiliates, distributors harmless against claims, costs, damages, expenses, reasonable attorney fees arising directly indirectly, claim personal injury death associated with such unintended unauthorized use, even such claim alleges that SCILLC negligent regarding design manufacture part. SCILLC Equal Opportunity/Affirmative Action Employer. This literature subject applicable copyright laws resale manner.
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AND8160/D

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