ANALOG DEVICES FEATURES Low Cost Low Nonlinearity: +0.05% @ 10V pk-pk Output High Gain Stability: +0.0075%/C, +0.001%/1000 hours Isolated Power Supply: +8.5V de @ +5mA, High CMR: 110dB min with 5kQ Imbalance High CMV: +5000V__, 10ms Pulse; +2500V de continuous Small Size: 1.5 x 1.5" x 0.6 Adjustable Gain: 1 to 10V/V; Single Resistor Adjust Meets IEEE Std 472: Transient Protection (SWC) Meets UL Std 544 Leakage: 2.0uA max @ 115V ac, 60Hz APPLICATIONS Biomedical and Patient Monitoring Instrumentation Ground |.oop Elimination in Industrial Control Off-Ground Signal Measurements 4-20mA Isolated Current Loop Receiver GENERAL DESCRIPTION Model 284} is a low cost isolation amplifier featuring isolated power, +8.5V de @ t5mA loads, +2500V de off-ground isola- tion (CMV) and 110dB minimum CMR at 60Hz, 5kQ source imbalance, in a compact 1.5" x 1.5 x 0.6 epoxy encapsulated package. This improved design achieves low nonlinearity of +0.05% @ 10V pk-pk output, gain stability of +0.0075%/C and input offset drift of +15uV/C at G=10V/V. Using modu- lation techniques with reliable transformer isolation, model 284] will interrupt ground loops, leakage paths and high voltage transients to 5kV,, (10ms pulse) providing de to 1kHz (-3dB) response over an adjustable gain range of 1V/V to 10V/V. Model 284)s fully floating guarded input stage and floating isolated power for external input circuitry, offers versatility for both medical and industrial OEM applications. WHERE TO USE MODEL 284J Medical Applications: In all biomedical and patient monitoring equipment such as multi-lead ECG recorders and portable diag- nostic designs, model 284] offers protection from lethal ground fault currents as well as 5kV defibrillator pulse inputs. Low level bioelectric signal recording is achieved with model 284]Js low input noise (8uV p-p) and high CMR (110dB, min). Industrial Applications: In computer interface systems, process signal isolators and high CMV instrumentation, model 284] offers complete galvanic isolation and protection against dam- age from transients and fault voltages. High level transducer interface is afforded with model 284Js 10V pk-pk input signal capability at a gain of 1V/V operation. In portable field designs, model 284Js single supply, low power drain of 85mW @ +12V operation offers long battery operation. Economy, High Performance, Self Contained, Isolation Amplifier A20rA ; CURRENT * t SHIELDED Ls yee MAX ~1hV ISOLATED 4.20mA ANALOG INTERFACE DESIGN FEATURES AND USER BENEFITS Isolated Power: Dual +8.5V dc @ +5mA, completely isolated from the input power terminals (2500V dc isolation), pro- vides the capability to excite floating signal conditioners, front end buffer amplifiers and remote transducers such as thermis- tors or bridges. Adjustable Gain: Model 284]s adjustable gain combined with its 10V pk-pk output signal dynamic range offers compatibility with a wide class of input signals. A single external resistor en- ables gain adjustment from 1V/V to 10V/V providing the flexi- bility of applying model 284] in both high level transducer interfacing as well as low level sensor measurements. Floating, Guarded Front-End: The input stage of model 284] can directly accept floating differential signals, such as ECG biomedical signals, or it may be configured as a high perfor- mance instrumentation front-end to accept signals having CMV with respect to input power common. High Reliability: Model 284] is a conservatively designed, compact module, capable of reliable operation in harsh envi- ronments. Model 284J has a calculated MTBF of over 400,000 hours and is designed to meet MIL-STD-202E environmental testing as well as the IEEE Standard for Transient Voltage Pro- tection (472-1974: Surge Withstand Capability). As an addi- tional assurance of reliability, every model 284J is factory tested for CMV and input ratings by application of 5kV pk, 10ms pulses, between input terminals as well as input/output terminals. ISOLATION AMPLIFIERS 137SPECIFICATIONS (typical @ 25C and Vs = +15V dc unless otherwise noted) MODEL 284] GAIN (NON-INVERTING) : , ree Le tOwy 100K 10.7kQ. + Ry(kQ) Deviation from Formula +3% vs. Time *ys. Temperature (0 to +70C)! +0 001%/1000 Hours 0 0075%/"C *Nonlinearity, G = 1V/V to 10V/V* +0 05% INPUT VOLTAGE RATINGS Linear Differential Range, G = 1V/V t5V min Max Safe Differential [Input Continuous 24)Vums Pulse, }0ms duration, 1 pulse/10 sec Max CMV, Inputs to Outputs AC, 60Hz, 1 minute duration Pulse, }Oms duration, 1 pulse/10 sec With 510kQ2 in series with Guard Continuous, ac or dc CMR, Inputs to Outputs, 60Hz, Rs S 5kQ Balanced Source Impedance 5k92 Source Impedance Imbalance CMR, Inputs to Guard, 60Hz 1k82 Source Impedance Imbalance Max Leakage Current, Inputs to Power Common @ 115V ac, 60Hz 6500Vp4 max 25.00V ams +2500Vp_ max 5)00Vp, max +2500V5, max 114dB 110dB min 78dB 2.0uA rms max INPUT IMPEDANCE Differential Overload Common Mode INPUT DIFFERENCE CURRENT Initial, @ +25C vs. Temperature (0 to +70C) 10 QU70pk 300kQ 10 5x07" ON20pK t7nA max tO.1nALC INPUT NOISE Voltage, G = LOV/V 0.05Hz to 100L2 10Hz to kHz Current 8uy p-p LORY rms 0.05Hz to 100H: 5p.\ p-p FREQUENCY RESPONSE Small Signal, -3dB, G = 1V/V to LOV/V 1k Iz Slew Rate 25:.nV/us Full Power, 10V p-p Output Gain = 1V/V TOOL Gain = 10V/V 200Hz Recovery Time, to 100uV after Application 20)0ms of 6500V, Differential [Input Pulse OFFSET VOLTAGE REFERRED TO INPUT Initial, @ +25C, Adjustable to Zero *vs. Temperature (0 to +70C) (4 + 20/G)m 0. + 150/G)UVPC OUTLINE DIMENSIONS Dimensions shown in inches and (mm). SEE GUARDING TECHNIQUES 1 LO IN/ASC PWR COM + Vs 7 $-$2GAIN fej det h-- 1.51 (38.1) MAX -_| 3 Visa = PWR COM f 4 2 15T 26 (38.1) 284) (18.7) I MAX MAX t \ LO OUT 3 0.20 TO 0.25 HIOUT 10 (57064) 0.04 (1.02) 1A a=] feat j BOTTOM VIEW WEIGHT: 40 Grams al Ja GRID 9.1 (2.54) SHIELDED MOUNTING SOCKET AC1049 INTERCONNECTION AND GUARDING TECHNIQUES Model 284J can be applied directly to achieve rated perform- ance as shown in Figure 1 below. To preserve the high CMR performance of model 284], care must be taken to keep the capacitance balanced about the input terminals. A shield should be provided on the printed circuit board under model 284J as illustrated in the outline drawing above (screened area). The GUARD (Pin 6) should be connected to this shield. This guard-shield is provided with the mounting socket, model AC1049. A recommended guarding technique using model AC1049 is illustrated in Figure 1. To reduce effective cable capacitance, cable shield should be connected to the common mode s:gnal source by connecting the shield as close as possi- ble to the signal low. Offset Voltage Trim Adjust: The trim adjust circuit shown in Figure 1 can be used to zero the output offset voltage over the gain range from 1 to 10V/V. The output terminals, HI OUT and LO OUT, can be floated with respect to PWR COM up to +50V,), max, offering three-port isolation. A 0.1uF capacitor is required from LO OUT to PWR COM whenever the output terminals are floated with respect to PWR COM. LO OUT can be connected directly to PWR COM when output offset trim- ming is not required. vs. Supply Voltage +1 nV/% RATED OUTPUT Voltage, 50kQ. Load +5V min Output Impedance 1k2 Output Ripple, IMHz Bandwidth 5mV pk-pk ISOLATED POWER OUTPUTS Voltage, #5mA Load +8 5V de Accuracy +5 % Current +5 nA min Regulation, No Load to Full Load +0 -15% Ripple, 100k fz Bandwidth 10)mV p-p POWER SUPPLY, SINGLE POLARTI v3 Voltage, Rated Pertormance +15V de Voltage Operating 8 to 15.5)V de Current, Quiescent +1)mA TEMPERATURE RANGE Rated Performance Operating Storage Oto +70C -29C to 485C 55 C10 85C CASE DIMENSIONS 1.6" x 4.5" x 0.62" *Improved performance over earlier design. Gain temperature drift is specified as a percentage of output sijnal level. 4 Gain nonlinearity is specified as a percentage of 10V pk-pk out ut span. 3 Recommended power supply, ADI model 904, 15V @ 50mA dutput Specifications subject to change without notice. 138 ISOLATION AMPLIFIERS TRANSDUCER AC 1049 eo arne. ne aa _ 2nC (HkS2t - 7 fe 0) fo SHIELO 2B4J TOKS? : [ 20x: 3 OFFSET VOLTAGE L TRIM ADJUST TRA WSDUCER rs GROUND NOT REQUIRED 510ks? [20082 MMO -1N Re O1LF 10ks: NOTE 2 > | ar 22500VDC MAX POWER COM NCTE 1. GAIN RESISTOR, R,, 1%, 50ppm/"C METAL FILM TYPE 1S RECOMMENDED FOR GAIN: 1V/V, LEAVE TERMINAL 2 OPEN FOR GAIN 10V/V, SHORT TERMINAL 2 TO TERMINAL 1 GAIN= 1+ 100K? 10.7kS2 + RilkG2) NCTE 2. GUARD RESISTOR, Rg, REQUIRED ONLY FOR CMV > #2500Vp (25kVpK MAX). Rg MAY BE MOUNTED GN AC 1049 MOUNTING SOCKET USING STANDOFF PROVIDED. (USE % WATT, 5%, CARBON COMPOSITION TYPE; ALLEN BRADLEY RECOMMENDED) NCTE 3. OUTPUT FILTER CAPACITOR, C. SELECT TO ROLLOFF NOISE AND OUTPUT RIPPLE: (e.g. SELECT C = 1.5uF FOR de TO 100Hr BANDWIDTH) Figure 1. Basic Isolator InterconnectionTHEORY OF OPERATION The remarkable performance of model 284] is derived from the carrier isolation technique which is used to transfer both signal and power between the amplifiers guarded input stage and the rest of the circuitry. The block diagram for model 284J is shown in Figure 2 below. The 320kS) input protection resistor limits the differential in- put current during periods of input amplifier saturation and also limits the differential fault current to approximately 354A in case the preamplifier fails. The bipolar input preamplifier operates single-ended (non- inverting). Only a difference bias current flows with zero net bias current. A third wire return path for input bias current is not required. Gain can be set from 1V/V to 10V/V by chang- ing the gain resistor, Rj. To preserve bigh CMR, the gain resistor must be guarded. Best performance is achieved by shorting terminal 2 to terminal 1 and operating model 284J at a gain of 10V/V. For powering floating input circuitry such as buffer amplifiers, instrumentation amplifiers, calibration signals and transducers, dual isolated power is provided. High CMV isolation is achieved by the low-leakage transformer coupling between the input preamplifier, modulator section and the output circuitry. Only the 20pF leakage capacitance between the floating guarded in- put section and the rest of the circuitry keeps the CMR from being infinite. a = | 320K, .BIPOLAR INPUT AMPLIFIER __ DC to tkHe Hi INPUT(S) + { HI > mop I DEMOD [+4 FILTER |-{i9) OUTPUT GAIN M AA i - We VW ll 1 10.7k92 100kS2 1 Low Rist mop L. | 9) OUTPUT & ORIVE-T~ i. DEMOD ' DRIVE LO iN/ INPUT FLT. ~oa (2) vs ISO PWR COM com. cuarD(6) | 60kHz CSCILLATOR t +8.5V V50 85V V0 4 POWER C_ (8) com POWER SUPPLY INPUT SHIELD GAIN =1+ {1V/V TO 10V/V} T00kK2 10.7kQ + RitkQ) Figure 2. Block Diagram Model 284J INTERELECTRODE CAPACITANCE, TERMINAL RATINGS AND LEAKAGE CURRENTS LIMITS Capacitance: Interelectrode terminal capacitance arising from stray coupling capacitance effects between the input terminals and the signal output terminals are each shunted by leakage resistance values exceeding 50kM{2. Figure 3 illustrates the CMR ratings at 60Hz and 5k&2 source imbalance between sig- nal input/output terminals, along with their respective capaci- tance. p TR 70pF Li fo { | 2 I rte coor 2 i 2g 110dB MIN err Che + : @ O BTL GUARD o Po ow ) } *WHEN GUARD TIED TO INPUT COMMON MODE SOURCE O<Ri<~ GUARD PWR COM Figure 3. Model 284/ Figure 4. Model 284J Terminal Capacitance Terminal Ratings and CMR Ratings Terminal Ratings: CMV performance is given in both peak pulse and continuous ac or dc peak ratings. Pulse ratings are intended to support defibrillator and other transient voltages. Continuous peak ratings apply from de up to the normal full power response frequencies. Figure 4 and Table 1 illustrate model 284]Js ratings between terminals. SYMBOL | RATING | REMARKS V1 (pulse) +6500Vpx (10ms) Withstand Voltage, Defibrillator V1 (cont.) 240V ems Withstand Voltage, Steady State V2 (pulse) +2500VpK (10ms) Rc; = 0 Transient V2 (pulse) 5000Vpx (10ms) Rg = 510k&2 | Isolation, Defibrillator V2 (cont,) 2500VpK Isolation, Steady State V3 (cont.) +50Vpx Isolation, DC Z1 5OkMQ\|20pF Isolation Impedance Table 1. Isolation Ratings Between Terminals Leakage Current Limits: The low coupling capacitance between inputs and output yields a ground leakage current of less than 2.0UA rms at 115V ac, 60Hz (or 0.02p:A/V ac). As shown in Figure 5, the transformer coupled modulator signal, through stray coupling, also creates an internally generated leakage cur- rent of about 54A rms @ 60kHz. Line frequency leakage cur- rent levels are unaffected by the power on or off condition of model 284]. For medical applications, model 284] is designed to improve on patient safety current limits proposed by F.D.A., U.L., A.A.M.1. and other regulatory agencies. (e.g. model 284] com- plies with leakage requirements for the Underwriters Labora- tory STANDARD FOR SAFETY, MEDICAL AND DENTAL. EQUIPMENT as established under UL544 for type A and B patient connected equipment reference Leakage Current, paragraph 27.5). In patient monitoring equipment, such as ECG recorders, model 284] will provide adequate isolation without exposing the patient to potentially lethal microshock hazards. Using passive components for input protection, this design limits input fault currents even under amplifier failure conditions. TEST CIRCUITS & MAX. CURRENT LIMITS FOR ANY SWITCH CLOSURE COMBINATION Lo +15v pa fe 284 I ~ INTERNALLY rms im |3500 GENERATED TEST {I} I Lo +15v ~ 4 + 284 LINE INDUCED rms (M inf 5002 TEST (II) ~) ag TIBVAC, 6OHz 10mA 6 4 2 IMmA 6 4 REJECT ACCEPT w YO REGION REGION z 2 | N ui ~ @ 10020 a 2 : ULL. & AAMI zea uw PEA. eouir). LIMITS INTERNALLY GENERATED g 2 L LEAKAGE CURRENT = He 284) | < 6 4 4 LINE INDUCED LEAKAG 3 CURRENT | . | WA iH 6 | i | 1 - M= 5A ems| 4 L= 2.QuA rms : 2 @ 60Hz, 117VAC @ GOkHZ owa (MAX) | (typ. : 1 100 tk 10k 100k FREQUENCY - Hz Figure 5. Model 284J Leakage Current Performance from Line Induced and Internally Generated (Modulator) Operating Conditions ISOLATION AMPLIFIERS 139PERFORMANCE CHARACTERISTICS Common Mode Rejection: Input-to-Output CMR is dependent on source impedance imbalance, signal frequency and ampli- fier gain. CMR is rated at 115V ac, 60Hz and 5k imbalance at a gain of 10V/V. Figure 6 illustrates CMR performance as a function of signal frequency. CMR approaches 146dB at de with source imbalances as high as 5kQ. As gain is decreased, CMR is reduced. At a gain of 1V/V, CMR is typically 6dB lower than at a gain of 10V/V. 140 7 a T GUARANTEED CMR @G = 10V/V : | a 110dB MIN @ 60Hz 120 | Pts 5k&2 SOURCE IMBALANCE 2 T : | Nl | | oT g 100 { 4 { H Pm, 5 I 7] 8 MN vd we 80h PS q @ we ~ IN a 2 cop-- & ! N = Com L = aop z 40 t 8 ' of iH *TEST CIRCUIT 5kS2 EACH RESISTOR CMR VALUE GIVEN FOR WORST CASE RESISTOR COMBINATION va pararin Hacaiariiien 1 10 100 1000 10k FREGUENCY - Hz Figure 6. Common Mode Rejection vs. Frequency Figure 7 illustrates the effect of source imbalance on CMR per- formance at 60Hz and Gain = 10V/V. CMR is typically 120dB at 60Hz and a balanced source. CMR is maintained greater than 80dB for source imbalances up to 100k22. ] T GUARANTEED CMR @ G = tov/v | : 110dB MIN @ 60Hz AND 5k3: | 1 | SOURCE IMPEDANCE IMBALANCE I . TAK. | La Ss to COMMON MODE REJECTION dB *TEST CIRCUIT EACH RESISTOR ADJUSTED 082 TO 100k? CMR VALUE GIVEN FOR WORST CASE RESISTOR COMBINA SION 10 100 Tk 10k 100k SOURCE IMPEDANCE IMBALANCE Figure 7. Common Mode Rejection vs. Source Impedance Imbalance Input Voltage Noise: Voltage noise, referred to input, is de- pendent on gain and bandwidth as illustrated in Figure 8. RMS voltage noise is shown in a bandwidth from 0.05Hz to the fre- quency shown on the horizontal axis. The noise in a band- width from 0.05Hz to 100Hz is 8uV pk-pk a: a gain of 10V/V. This value is derived by multiplying the rms value at f = 100Hz shown in Figure 8 (1.24%V rms) by 6.6. "t | i ti GAIN = IV/V Tl 1 7 (0.05Hz TO 100Hz) L. # Suv PP tt a) nee _ Py | B INPUT VOLTAGE NOISE ~ uV rms* na GAIN = 10v/V 2 O1 *MULT'PLY BY 66 TO OBTAIN wt 14 i L | PEAK TO PEAK VA! UES poi ig Loi | | 4 | te] 20pV PP (0,05Hz TO 1008 z I 1 10 100 Ik BANDWIDTH (-3d8) - Hz Figure 8. Input Voltage Noise vs. Baiidwidth 140 ISOLATION AMPLIFIERS For lowest noise performance, a low pass filter at the output should be used to selectively roll-off noise, output ripple and undesired signal frequencies beyond the bandwidth of interest (see note 3, Figure 1). Input Offset Voltage Drift: Total input voltage drift is com- posed of two sources, input and output stage drifts and is gain dependen. The curve of Figure 9 illustrates the total input voltage drift over the gain range of 1 to 10V/V. GAIN V/V Figure 9. Input Offset Voltage Drift vs. Gain Gain Nonlinearity: Linearity error is defined as the peak de- viation of the output voltage from the best straight line and is specified as a % of peak-to-peak output voltage span; e.g. non- linearity of model 284J operating at an output span of 10V pk-pk (+5V) is 0.05% or t5mV. In applying model 284J, highest accuracy is achieved by adjustment of gain and offset voltage tc: minimize the peak error over the operating output voltage span. A calibration technique illustrating how to mint mize output error is shown below. In this example, model 284] is operating over an output span of +5V to -V and a gain of 5V/V. GAIN AND OFFSET TRIM PROCEDURE 1. Apply eqy = 0 volts and adjust Ro for eg = 0 volts. 2. Apply ep = +1.000V dc and adjust Rg for eg = +5.000V de. 3. Apply ey = -1.000V de and measure the output error (see curve a). 4. Adjust Rg until the output error is one half that measured in step: 3 (see curve b). 5. Apply epy = +1.000V de and adjust Rg until the output error is one half that measured in step 4 (see curve c). OUTPUT ERROR mV 5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5 VOkS2 7 +15V ZERO Fig LADJUST ~15V - GAIN ADJUST 1 10k? Figure 10. Gain and Offset AdjustrnentGROUNDING PRACTICES The more common sources of electrical noise arise from ground loops, electrostatic coupling and electromagnetic pickup. The guidelines listed below pertain to guarding low level, millivolt signals in hostile environments such as current shunt signals in heavy industrial plants. Guidelines: @ Use twisted shielded cable to reduce inductive and capaci- tive pickup. @ Drive the transducer cable shield, S, with the common mode signal source, Eq, to reduce the effective cable capacitance as shown in Figure 11 below. This is accomplished by con- necting the shield point S, as close as possible to the trans- ducer signal low point B. This may not always be possible. In some cases the shield may be separated from signal low by a portion of the medium being measured (e.g. pressure transducer). This will cause a common mode signal, Em, to be generated by the medium between the shield and the signal low. The 78dB CMR capability of model 284J between the input terminals (HI IN and LO IN) and GUARD, will work to suppress the common mode signal, Ey. @ To avoid ground loops and excessive hum, signal low, B, or the transducer cable shield, S, should never be grounded at more than one point. @ Dress unshielded leads short at the connection terminals and reduce the area formed by these leads to minimize inductive pickup. P.C. CARD SHIELD TRANSDUCER TRANSDUCER p 2 _- 7 284 CABLE I FLOATING GUARD TRANSDUCER eT 2tt5v PWR SIGNAL i; ~ th PS R 4 L 284) 2 Pr@ _ a | " MEDIUM L J COMMON MODE ~se VOLTAGE | (TRANSDUCER CONMOR ODE TERMINALS A, B,C) WoC TARE ~ aL GROUND COMMCN MODE = SYSTEM GROUND / TRANSDUCER GROUND VOLTAGE Figure 11. Transducer- Amplifier Interconnection Isolated Power and Output Voltage Swing: Model 284] offers a floating power supply providing +8.5V dc outputs with +5mA output current rating. As shown in Figure 12, the mini- mum voltage output for +Vicg, as well as the maximum load capability, is dependent on the input power supply, +Vg. Fig- ure 12 also illustrates the typical output voltage range as both input supply, +Vg, and the isolated supply loads, +I, , are varied. At t5mA isolated load and Vs = +15V dc, model 284] can provide an output voltage swing of +7.5V. # 8 % 3 W NO LOAD ] ow i= 23m S| Le is bee Os Miso g 5 4 1 MEER. cow, g9 [ #2 up ER ml fa d'ous04 ISOLATED SUPPLY VOLTAGES iMIN) Voits OUTPUT VOLTAGE SWING Volts & Vigo O% 4 1 _t a 1 +7 +8 +9 +100: #190 4720 #130418 15418 POWER SUPPLY (Vs) Votts PWR COM r o 4 Figure 12. Isolated Power (+ Visc) and Output Voltage Swing (Eo) Versus Power Supply Input (Vs) APPLICATIONS IN INDUSTRIAL MEASUREMENT AND CONTROL SYSTEMS Remote Sensor Interface: In chemical, nuclear and metal pro- cessing industries, model 284J can be applied to measure and control off-ground millivolt signals in the presence of +2500V de CMV signals. In interface applications such as pH control systems of on-line process measurement systems such as pollution monitoring, model 284J offers complete galvanic isolation to eliminate troublesome ground loop problems. Iso- lated power outputs and adjustable gain add to the application flexibility of this model. Figure 13 illustrates how model 284] can be combined with a low drift, VvirC max, front-end amplifier, model AD510K, to interface low level transducer signals. Model 284Js isolated 8.5V dc power and front-end guard eliminate ground loops and preserve high CMR (114dB @ 60Hz). O.01uF iowa 499kK82 4990 99 +15V + 6 ADS10K C) | EF oss LT? 0 t5mV 45302 10082 7 +5V O.01NF 70 40s? Ru 7 Owe) * 250 10082 > 284J shir OKs O.0mWF GAIN >a | 9 20k82 ST ADJU , ZERO Lo IN O.1KF ADJUST = 10k{? 6 A 20082 GUARD L BV POWER com Figure 13. Input Signal Conditioning Using Isolated Power for Transducer Buffer Amplifier Instrumentation Amplifier: Model 284] provides a floating guarded input stage capable of directly accepting isolated differ- ential signals. The non-inverting, single-ended input stage offers simple two wire interconnection with floating input signals. In applications where the isolated power is applied to trans- ducers such as bridges which generate differential input signals with common mode voltages measured with respect to the iso- lated power common, model 284] can be connected as shown in Figure 14. To achieve high CMR with respect to the ISO PWR COM, the following trim procedure is recommended. CMR Trim Procedure 1) Connect a 1V pk-pk oscillator between the +IN/-IN and IN COM terminals as shown in Figure 14. 2) Set the input frequency at 0.5Hz and adjust R1 for mini- mum eg. 3) Set the input frequency at 60Hz and adjust R2 for mini- mum eg. 4) Repeat steps 2 and 3 for best CMR performance. +IN rt "10 5 JHEINS LIN 200k2 R2 ~ e208 100k2 a+ 1 SEE CMR TRIM 2 |A0308 2 joan PROCEDURE 68pF Fal 7 2K WV PKPK aa ai JRt i! | a TYPLOIN ISO agqy INcom S 100K YT 10.2k02 PwR COM . 7 6lecuarn | 100pF +Viso O 3) Viso J Visa O---_____-______-_4 4] 1 -Viso. Z e9 = 10 [fey -e2} + (21% 22) x 1 Lo O [fei -e2) + ( 2 )* oan ] oe GAIN INPUT CMR ERROR CMR = 94dB SIGNAL Figure 14. Application of 284J as Instrumentation Amplifier ISOLATION AMPLIFIERS 141APPLICATIONS IN BIOMEDICAL DESIGNS Cardiac Monitoring: Heart signals can be masked by muscle noise, electrochemical noise, residual electrode voltages and 60Hz power line pickup. To achieve high performance in cardi- ac monitoring, model 284Js design provides Figh CMR in the de to 100Hz bandwidth and substantial source impedance to 5kQ. An especially demanding ECG requirement is that of fetal heart monitoring as illustrated in Figure 15. The low input noise of model 284] and the dual CMR ratings are exploited in this application to extract the fetal ECG signals. The separa- tion between the mothers and the fetal heartbeat is enhanced by the 78dB of CMR between the input electrodes and guard, while the 110dB of CMR from input to output ground screens out 60Hz pickup and other external interference. ~ MOTHER'S HEART SIGNALS Vu (TYPICALLY Imv) y CABLE TO FETAL HEART Rey MONITOR 5 284) ote heh aa be clan, po \ FETAL HEART SIGNALS Veg (~50uV) cufno OFF-GROUND COMMON MODE VOLTAGE DUE TO PICKUP LEAKAGE, ETC. Vem (= 1mV - 100mv} Vo = Ve + Vm/781B + Von /110dB SHIELDED CABLE +15V FETAL HEARTBEAT Vo TO FETAL 50uV ti " MONITOR NEARTBCAT p11 (i) 284) > | ImV tT 7 7 ey GUARD a PICKUP ImV - 100mV AMPLIFIERS #8dB {NPUT-TO-SHIELD CMR SEPARATES FETAL I4EART BEAT FROM MOTHERS, WHILE 110dB INPUT-TO-GROUND CMR ATTENUATES 60Hz PICKUP. Figure 15. Fetal Heartbeat Monitoring *Visc. -Viso Single Lead ECG Recorder with Leads Off Indicator: In single lead applications model 284J offers simple two-wire hook-up to the ECG signal as illustrated in Figure 16. The floating signal can be connected directly to the HI IN and LO IN terminals using the GUARD tied to the patients right leg for best CMR performance. Using the isolated power from model 284] an inexpensive calibration signal is easily provided. In ECG appli- cations, model 284] provides a simple means to determine whenever a Leads-Off condition exists at the input. A Leads- Off condition (Rg = %) will cause the HI OUT terminal to be at a negative output saturation level; i.e. eg = -8.5V to -9.5V @ Vg = +15V. GUARD BOX AROUND CALIERATION CIRCUIT | 23.2k92 1% + 1@) $1082 > 1% -E OFF CABLE SHIELD Figure 16. Single Lead ECG Recorder with 1mV Calibration Circuit and Leads Off Indicator Multi-Lead ECG Recorder with Right Leg Drive: The small size, economy and isolated power makes model 284J an ideal isola- tion amplifier for application in clinical ECG recorders. Figure 17 illustrates how this new isolator can be applied in a high performance, portable multi-lead ECG recorder. In this applica- tion, model 284Js input is configured as an instrumentation amplifier with high CMR to the floating input common. The right leg drive offers improved CMR between input and isola- ted common by driving to zero any CMV existing between these poirts. The isolated power, tVjsq, is used to drive the lead buffer amplifiers and the front-end, ImV calibration signal. CHEST PATIENT CABLE LA RA CABLE SHIELD o L RESISTANCE NETWORK -Viso a +Viso +3) i i LEAD SELECT SWITCH |-am4 |rl 4 Lm} BUFFER AMPLIFIER <I AL DRIVE 200k ALL AMPLIFIERS: AD308 -iso + USE 1 WATT, 5% CARBON COMPOSITION TYPE; ALLEN BRADLEY RECOMMENDED. Figure 17. Multi-Lead ECG Recorder Application Using Model 284J with Right Leg Drive Output 142 ISOLATION AMPLIFIERS