NE570 - onsemi.com

1 Semiconductor Components Industries, LLC, 2006 May, 2006 Rev. 41 Publication Order Number: NE570 /DNE570 CompandorThe NE570 is a versatile low cost dual gain control circuit in whicheither channel may be used as a dynamic range compressor orexpandor. Each channel has a full wave rectifier to detect the averagevalue of the signal, a linerarized temperature compensated variablegain cell, and an operational NE570 is well suited for use in cellular radio and radiocommunications systems, modems, telephone, and satellitebroadcast/receive audio Complete Compressor and Expandor in One IC Temperature Compensated Greater than 110 dB Dynamic Range Operates Down to VDC System Levels Adjustable with External Components Distortion may be Trimmed Out Pb Free Packages are Available*Applications Cellular Radio Telephone Trunk Comandor High Level Limiter Low Level Expandor Noise Gate Dynamic Noise Reduction Systems Voltage Controlled Amplifier Dynamic FiltersMAXIMUM RATINGSR atingSymbolValueUnitMaximum Operating VoltageVCC24 VDCO perating Ambient Temperature RangeTA0 to +70 COperating Junction TemperatureTJ150 CPower DissipationPD400mWThermal Resistance, Junction to AmbientRqJA105 C/WStresses exceeding Maximum Ratings may damage the device.

2 MaximumRatings are stress ratings only. Functional operation above the RecommendedOperating Conditions is not implied. Extended exposure to stresses above theRecommended Operating Conditions may affect device CELL INRECT VTHD TRIMRECT CAPINVERTER INOUTPUT+ R2 20 kWR1 10 kWVARIABLEGAIN30 kW20 kWFigure 1. Block DiagramRECTIFIERR3R3R4*For additional information on our Pb Free strategy and soldering details, pleasedownload the ON Semiconductor Soldering and Mounting TechniquesReference Manual, CONNECTIONSSee detailed ordering and shipping information in the packagedimensions section on page 9 of this data INFORMATION(Top View)SOIC 16 WBD SUFFIXCASE 751 GRECT_IN_1 RECT_CAP_212345678910111213141615 RECT_CAP_1DG_CELL_IN_1 INV_IN_1 GNDRES_R3_1 OUTPUT_1 THD_TRIM_1 RECT_IN_2DG_CELL_IN_2 VCCINV_IN_2 RES_R3_2 OUTPUT_2 THD_TRIM_21 MARKINGDIAGRAM161NE570 DAWLYYWWGA= Assembly LocationWL = Wafer LotYY = YearWW = Work WeekG= Pb Free PackagePlastic Small Outline Package;16 Leads.

3 Body Width mmNE570 FUNCTION DESCRIPTIONPinSymbolDescription1 RECT CAP 1 External Capacitor Pinout for Rectifier 12 RECT IN 1 Rectifier 1 Input3DG CELL IN 1 Variable Gain Cell 1 Input4 GNDG round5 INV. IN 1 Inverted Input 16 RES. R3 1R3 Pinout 17 OUTPUT 1 Output 18 THD TRIM 1 Total Harmonic Distortion Trim 19 THD TRIM 2 Total Harmonic Distortion Trim 210 OUTPUT 2 Output 211 RES. R3 2R3 Pinout 212 INV. IN 2 Inverted Input 213 VCCP ositive Power Supply14DG CELL IN 2 Variable Gain Cell 2 Input15 RECT IN 2 Rectifier 2 Input16 RECT CAP 2 External Capacitor Pinout for Rectifier 2 ELECTRICAL CHARACTERISTICS VCC = +15 V, TA = 25 C; unless otherwise ConditionsSymbolMinTypMaxUnitSupply 24 VSupply CurrentNo SignalICC Current CapabilityIOUT 20 mAOutput Slew RateSR V/msGain Cell Distortion (Note 1)Untrimmed %Resistor Tolerance 5 15%Internal Reference DC Shift (Note 2)Untrimmed 90 150mVExpandor Output NoiseNo signal, 15 Hz to 20 kHz(Note 3) 2045mVUnity Gain Level (Note 4) + Change (Notes 1 and 5)TA = 0 C to +70 C Drift (Note 5)TA = 0 C to +70 C 10mVResistor Drift (Note 5)TA = 0 C to +70 C + , %Tracking Error (measured relative to value at unity gain)equals [VO VO (unity gain)] dB V2 dBmRectifier Input VCC = + VV2 = + dBm, V1 = 0 dBV2 = 30 dBm, V1 = 0 dB + , + Separation 60 dB1.

4 Measured at 0 dBm, Expandor AC input change from no signal to 0 Input to V1 and V2 0 dB = 775 Relative to value at TA = 25 DESCRIPTIONThe NE570 compandor building blocks, as shown in theblock diagram, are a full wave rectifier, a variable gain cell,an operational amplifier and a bias system. The arrangementof these blocks in the IC result in a circuit which can performwell with few external components, yet can be adapted tomany diverse full wave rectifier rectifies the input current whichflows from the rectifier input, to an internal summing nodewhich is biased at VREF. The rectified current is averaged onan external filter capacitor tied to the CRECT terminal, andthe average value of the input current controls the gain of thevariable gain cell. The gain will thus be proportional to theaverage value of the input signal for capacitively coupledvoltage inputs as shown in the following equation.

5 Note thatfor capacitively coupled inputs there is no offset voltagecapable of producing a gain error. The only error will comefrom the bias current of the rectifier (supplied internally)which is less than |VIN*VREF|avgR1orGT|VIN|avgR1 The speed with which gain changes to follow changes ininput signal levels is determined by the rectifier filtercapacitor. A small capacitor will yield rapid response butwill not fully filter low frequency signals. Any ripple on thegain control signal will modulate the signal passing throughthe variable gain cell. In an expander or compressorapplication, this would lead to third harmonic distortion, sothere is a trade off to be made between fast attack and decaytimes and distortion. For step changes in amplitude, thechange in gain with time is shown by this +10kW CRECTG(t)+(Ginitial*Gfinal)e*tt)GfinalTh e variable gain cell is a current in, current out devicewith the ratio IOUT/IIN controlled by the rectifier.

6 IIN is thecurrent which flows from the DG input to an internalsumming node biased at VREF. The following equationapplies for capacitively coupled inputs. The output current,IOUT, is fed to the summing node of the op +VIN*VREFR2+VINR2A compensation scheme built into the DG cellcompensates for temperature and cancels out odd harmonicdistortion. The only distortion which remains is evenharmonics, and they exist only because of internal offsetvoltages. The THD trim terminal provides a means fornulling the internal offsets for low distortion operational amplifier (which is internallycompensated) has the non inverting input tied to VREF, andthe inverting input connected to the DG cell output as wellas brought out externally.

7 A resistor, R3, is brought out fromthe summing node and allows compressor or expander gainto be determined only by internal output stage is capable of 20 mA output allows a +13 dBm ( VRMS) output into a 300 W loadwhich, with a series resistor and proper transformer, canresult in +13 dBm with a 600 W output bandgap reference provides the reference voltage for allsumming nodes, a regulated supply voltage for the rectifierand DG cell, and a bias current for the DG cell. The lowtempco of this type of reference provides very stable biasingover a wide temperature typical performance characteristics illustrationshows the basic input output transfer curve for basiccompressor or expander circuits.+20+100 10 20 30 40 50 60 70 80 40 30 20 100+10 COMPRESSOR OUTPUT LEVELOREXPANDOR INPUT LEVEL (dBm)COMPRESSOR INPUT LEVEL OR EXPANDOR OUTPUT LEVEL (dBm)Figure 2.

8 Basic Input Output Transfer CurveNE570 , 1541, 165, 128, 97, 106, 11V1V2 VOVCC = 15 VVREF10 mF200 mF +30 kW20 kWDG10 kW20 mF3, mFFigure 3. Typical Test CircuitINTRODUCTIONMuch interest has been expressed in high performanceelectronic gain control circuits. For non critical applications,an integrated circuit operational transconductance amplifiercan be used, but when high performance is required, one hasto resort to complex discrete circuitry with many expensive,well matched components. This paper describes aninexpensive integrated circuit, the NE570 Compandor, whichoffers a pair of high performance gain control circuitsfeaturing low distortion (< %), high signal to noise ratio(90 dB), and wide dynamic range (110 dB).CIRCUIT BACKGROUNDThe NE570 Compandor was originally designed to satisfythe requirements of the telephone system.

9 When severaltelephone channels are multiplexed onto a common line, theresulting signal to noise ratio is poor and companding isused to allow a wider dynamic range to be passed through thechannel. Figure 4 graphically shows what a compandor cando for the signal to noise ratio of a restricted dynamic rangechannel. The input level range of +20 dB to 80 dB is shownundergoing a 2 to 1 compression where a dB input levelchange is compressed into a dB output level change by thecompressor. The original 100 dB of dynamic range is thuscompressed to a 50 dB range for transmission through arestricted dynamic range channel. A complementaryexpansion on the receiving end restores the original signallevels and reduces the channel noise by as much as 45 significant circuits in a compressor or expander arethe rectifier and the gain control element.

10 The phone systemrequires a simple full wave averaging rectifier with goodaccuracy, since the rectifier accuracy determines the (input)output level tracking accuracy. The gain cell determines thedistortion and noise characteristics, and the phone systemspecifications here are very loose. These specs could havebeen met with a simple operational transconductancemultiplier, or OTA, but the gain of an OTA is proportionalto temperature and this is very undesirable. Therefore, alinearized transconductance multiplier was designed whichis insensitive to temperature and offers low noise and lowdistortion performance. These features make the circuituseful in audio and data systems as well as intelecommunications +200 dB 40 80 200 dB 40 80 Figure 4.