OBSOLETE. r-. ANALOG W DEVICES. . UltraLow Voltage Noise 1.3nV1v1tz

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1 ANALOGDEVCES FAXONDEMANDHOTLNE Page 11 r. ANALOG W DEVCES ~low NoiseMicrophone Preamplifier FEATURES. UltraLow Voltage Noise 1.3nV1v1tz Wide Bandwidth G = High Slew Rate, 8V/jlS Very Low Harmonic Distortion %@ G =. Excellent CMR db. True Differential nstrumentation Type nputs Programmable nput Stage Optimizes en vs RN. Low Cost SSM2015 The SSM2015 also offers high slew rate of about8v/s and full DC coupling without any crossover distortion. This device is packaged in a 14pin epoxy DP and is guaranteed overthe operating temperature range of C to +S5 C. PN CONNECTON ORDERNG NFORMATON SSM2015P Storage Temperature GENERAL DESCRPTON OPERATNG TEMPERATURE RANGE C to...ss.'c 55'C to., 25 C The SSM.2015 is an ultra.low noise audio preamplifier particularly suited to microphone preamplification. Gains from toover 0 can be selected withwide bandwidth and lowdistortion over the full gain range. The SSM.2015's true differential inputs with high commonmode rejection provide easy interfacing to flotation transducers such as balanced microphone outputs. as well as single ended devices. BLOCK DAGRAM.v 14PN EPOXY DP (PSuffix) ABSOLUTE MAXMUM RATNGS Supply Voltage :t18v Operating Temperature Range ' 1 O~C to +55 C Junction..Temperature...150C Storage Temperature 55C to +5 C Lead Temperature Range (Soldering. 60 sec), +300<C PACKAGETYPE EliA(Note) elc 14PinPlastic DP(P) NOTE: UNTS 'C.w 1. e,a is specified forworst case mounting condtions. 'e. e,a is s~cll'ed lor device n socket for P.DP package.. 1W CaMP 13 ~.NULL NULL.N~ Z. N t1.0 1!1kU 4kU 4k11 u AS v The very lowvoltage noise performance (1.3nVfRZ)oftheSSM 2015 is enhanced by a programmable input stage which allows overall noise to be optimized for source impedances of up to 4kQ.

2 ANALOGDEVCES faxondemand HOTLNE Page SSM2015 ELECTRCAL CHARACTERSTCS at Vs =:t15v,ta = 25 C, RetAS=33kn. unless otherwise noted. 55M2015 PARAMETER SYMBOL CONDTONS MN TYP MAX UNTS Total Harmonic Distortion nput Referred Voltage Noise nput Current Noise THO Eo n VOUT 7V RMS. RL ko GOOO f.lkhz 1.ka G.. 1kHz = khz G. f 1kHz. khz nputs Shorted to GND 20kHz Bandwidth R8'~S 33KO G0 G G. RQ.~s. 150kO alooo G. G. 20kHzBandwidth Ral~s33kO Ra'As 68kO RB'As.150kO R,A2kO G Error From Gain Equation.1.0 G 0.1 db G % uv RMS pa RMS nput Offset Voltage nput Bias Current Vos e A2 ko G VCA. OV RaJAs. 33kO Aa'As.150kO mv ua nput Offset Current CommonMode Relection Aatio Power Supply Rejection Ratio CommonMode Vollage Range CommonMode nput mpedance DifferentialMode nput mpedance Output Voltage Swing Output Current (Note 2) 3dB Bandwidth Slew Rate Supply Current 'as CMRR PSRR CMVA A'NCtA R'N Vo lout GBW SA 'Sy VelA= OV Ra1As.33kO RB,~s.'50kn R,A2lOkO G 0 G. G VS:ttO:t17V G 0 G G At 2k'. Source Sink G 0 G Gw :t.s \ :t4 ;;: :t SO B wa db ab v M 1 Ml n y A.HZ... v..>. Ạ. NOTES:,. Parameter Ssample tested maximum limits. 2. Output is protected rom short circuits to ground or either supply. Specifications subject to change; consult latest data sheet j

3 ANALOGDEVCES faxondemand HOTLNE Page 13 SSM2015,1Jt{).., C. Vovr 21MC. 3 lout.null Mf'VT.,V SSMo201S R 11. Lv. 0 F0.,1' c;.v 'COMP2 NPUT 8Gp 7 COMP 3 VOLTAOi!JAN. ~. 3.1 AO R... 15V FGURE 1: Typical Application APPLCATONS NFORMATON PRNCPLEOF OPERATON Figure 1 shows a typical application for the SSM2015. This device operates as a true differential amplifier with feedback returned directly to the emitters of the input stage transistors by. This system produces both optimum noise and commonmode rejection while retaining a very high input impedance at both input terminals. An internal feedback loop maintains the input stage current at a value controlled by an external resistor (AetAs) from pin 14 to V. This provides a programmability function which allows noise to be optimized for source impedances of up to 4kO. GAN SETTNG The nominal gain of the SSM2015 is given by: G == + R2 + At + Rz + 1 or RG 8kU 20kU G = RG For At. Rz = ku At and A2 should be equal to kq for best results (see Figure 1). t is vital that good quality resistors be used in the gain setting network, since low quality types (notably carbon composition) can generate significant amounts of distortion and, under some conditions, low frequency noise. The SSM2015 will function at gains down to 3.5, but the best performance is obtained at gains above. Table 1gives Aavaluesfor mostcommonlyusedgains. TABLE1: AGValues for Commonly Used Gains RG = At + Rz G. 3.5 GAN Ra 3kO ERROR +0.14dB +O.OO2dB +O.3dB +O.28dB +O.O3dB FREQUENCY COMPENSATON Referring to Figure 1, C3 (50pF) provides compensation for the input stage current regulator, while C, and C2 compensate the overall amplifier.the latter two depend on the value 01 AetAS chosen. Table 2 shows the recommended values for C, and C2 at various AajAS levels. These values are valid for all gain settings. TABLE 2: Recommended Compensation Values RBAS C, 27kQ 47kQ 47kQ68kQ 68kU 150kQ 30pF C2 pf 5pF

4 ANALOGDEVCES faxondemand HOTLNE Page 1~ SSM2015 The SSM2015 has a bandwidth of at least 70kHz under worst case conditions (G = 0. RalAs = 150kQ) and considerably greater at higher set currents and lower gains. This excellent performance is supplemented by a highly symmetric slew rate for optimum large signal audio performance. The SSM2015 provides stable operation with load capacitances of up to 150pF; larger capacitances should be decoupled with a 1oon resistor in series with the output ( in Figure 1 should remain connected to pin 3). 2CO l i 00 0:! ~ S 27 \0 log k SOlAC AESO$TAHC ( < NOSE The programmability 01the SSM2015 provides close to optimum performance for source impedances of up to 4kQ, and S within 1dBofthetheoreticai minimum value between soon and 2.5kQ. Figure 2 shows the recommended bias resistor (AatAs) versus source impedance. lor balanced or singleended inputs. NPUTS Although the SSM2015 inputs are fully floating, care must be exercised to ensure that both inputs have a DC bias connection capable of maintaining them within the input commonmode range. The usual method of achieving this is to ground one side of the transducer as in Figure 3(a), but an alternative way is to float the transducer and use two resistors to set the bias point as in Figure 3(b). The value of these resistors can be up to kil. but they should be kept as small as possible to limit commonmode noise. Noise generated in the resistors themselves is negligible since it is attenuated by the transducer impedance. Balanced transducers give the best noise immunity, and mterlace directly as in Figure 3(c). TRMMNG The gain of the SSM2015 can be easily trimmed by adjustment of AG' However, two further trims may be desirable: OHset Voltage and Commonmode Rejection, although the SSM2015 provides excellent untrimmed performance in both respects. FGURE 2: Optimum RBASliS. Source Resistance _20 1! C ' {U.VEmHG ~, :: 3 T'NSDUC~, 5 SSM20'5 T ~ r1 TRAHSDUCER (8) (~V.RTNO 1 J 1! \A 13 (c) _2015 L...,..p' TAHSOUC (b) FGURE 3: Three Ways of nterfacing Transducers for High Noise 'mmunity (a) Sing'e Ended (b) Pseudo Differentia' (c) True Differentia' j ~

5 ANALOGDEVCES faxondemand HOTLNE Page 15 SSM loni.!.! The offset trim can also be used to null out the gain control feedthrough. The output offset at low gains S determined by matchingof the feedback resistors while at high gains t Sdeter. mined by the matching of the input resistors t the gain setting S changed rapidly. the output shift can cause an (audible) click or thump. To reduce or eliminate this. the offset at high gains S adjusted to be equal to the offset at low gains. +V. SSM2O15 TABLE 3: Recommended Values for the Offset Voltage Trim AO V RetAS 6!. 27kQ 47kn 47k.68kQ 68kn 150kU.,. VR2' G = 500kn 250kU 250kU... FGURE 4: Trimming the SSM2015 ' V soou = VR2' G= 500k!1 kf1 1OOk{ VR2' G = 0 250kU ku 50kn Figure 4 shows the trimming method for both parameters. VA' is the CMR trim and should be adjusted for minimum output with an 8Vpp amplitude 60Hz Sine Wave common to both inputs. VR2is the offset voltage trim, and should be selected from Table 3. The offset trim should follow the CMR trim, since there is a small (nonreciprocal) interaction. The offset trim can also be used to null out the gain control PHANTOM POWER A recommended circuit for phantom microphone powering S shown in Figure 5. Z, through Z4 provide transient overvoltage protection forthe SSM2015 whenever microphones are plugged n and out.,~ SSM2O1, 11 1<\1 e. 6 2OOpf' Z,Z,5.6V4OQmW c, 5.8kU1%.NPUT +UV A. OOU 8.8kti 1'to ~ 47' onpvt c, c. n,sov TANTALUM :: FGURE 5: SSM2015 with Phantom Power