AN-1302 APPLICATION NOTE One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com Optimizing the ADuCM350 for 4-Wire, Bio-Isolated Impedance Measurement Applications INTRODUCTION The ADuCM350 is an ultralow power, integrated mixed-signal metering solution that includes a microcontroller subsystem for processing, control, and connectivity. The processor subsystem is based on a low power ARM® Cortex™-M3 processor, a collection of digital peripherals, embedded SRAM and flash memory, and an analog subsystem which provides clocking, reset, and power management capability. This application note details how to set up the ADuCM350 to optimally measure the impedance of an RC type sensor, using 4-wire techniques, while targeting IEC-60601 standards. To target the IEC-60601 standard, the ADuCM350 is used in conjunction with an external instrumentation amplifier (AD8226), to complete high precision absolute measurements using a 4-wire measurement technique. 12168-101 The ADuCM350 has the ability to perform a 2048 point single frequency discrete Fourier transform (DFT). It takes the 16-bit ADC output as input and outputs the real and imaginary parts of the complex impedance. The configurable switch matrix on the ADuCM350 allows you to choose from a 2-wire, 3-wire, or 4-wire impedance measurement. Figure 1. EVAL-ADuCM350EBZ Motherboard and 4-Wire Bio-configuration Daughter Board Rev. 0 | Page 1 of 16 AN-1302 Application Note TABLE OF CONTENTS Introduction ...................................................................................... 1 Sensor Configuration................................................................. 10 Revision History ............................................................................... 2 4-Wire Bio-Isolated Network ................................................... 10 Configurations .................................................................................. 3 AFE Optimization .......................................................................... 11 2-Wire System ............................................................................... 3 Calculate the RLIMIT Resistor ...................................................... 11 4-Wire System ............................................................................... 3 Calculate RTIA .............................................................................. 11 4-Wire Bio-Isolated System......................................................... 3 Calculate RG of the AD8226 ...................................................... 11 Basic 4-Wire Impedance Measurement......................................... 4 Calculate RCAL .......................................................................... 12 The 4-Wire Bio-Isolated Method ................................................... 6 4-Wire Bio-Isolated Measurements ............................................. 13 Basic 4-Wire Theory .................................................................... 6 Hardware Setup For 4-Wire Bio-Configuraton Board .......... 13 4-Wire Bio-Isolated Theory in Application .............................. 6 Software Setup For 4-Wire Bio-Configuration Board............ 13 A 4-Wire Bio-Isolated Solution .................................................. 7 Schematics for the 4-Wire Bio-Configuration Board ................. 14 Example of a 4-Wire Bio-Isolated System ................................... 10 REVISION HISTORY 4/14—Revision 0: Initial Version Rev. 0 | Page 2 of 16 Application Note AN-1302 CONFIGURATIONS The ADuCM350 offers three configurations for measuring the impedance of a sensor. 2-WIRE SYSTEM In the presence of varying access resistance to the unknown impedance, this configuration provides relative accuracy measurements for impedance magnitude and impedance phase. For further details on optimizing the ADuCM350 for 2-wire impedance measurements, refer to the AN-1271 Application Note, Optimizing the ADuCM350 for Impedance Conversion. The 2-wire system measures the relative accuracy of Impedance magnitude and phase. 4-WIRE SYSTEM This configuration provides absolute accuracy for both impedance magnitude and impedance phase measurements because access resistances are calibrated out. This configuration does not operate where ac coupling capacitors are required to isolate sensor from device, that is, capacitors in series with the access resistances. Refer to the AN-1271 Application Note, Optimizing the ADuCM350 for Impedance Conversion, for information on optimizing the ADuCM350 for 4-wire measurements. The 4-wire system measures the absolute accuracy of impedance magnitude and phase, however isolation capacitors are not allowed. 4-WIRE BIO-ISOLATED SYSTEM If isolation capacitors are required between sensor and device, then an external instrumentation amplifier is required to measure the differential voltage across the sensor. It is not possible for the ADuCM350 to do this measurement as a single chip solution because the isolation capacitors cause instability when included on the sense (P and N channel) paths. The 4-wire bio-isolated system measures the absolute accuracy of impedance magnitude in the presence of isolation capacitors, however this system is not targeted for accurate phase measurements. Rev. 0 | Page 3 of 16 AN-1302 Application Note BASIC 4-WIRE IMPEDANCE MEASUREMENT To measure the impedance of an unknown sensor, Z, a ratiometric measurement technique is employed using the ADuCM350. EXTERNAL COMPONENTS SWITCH MATRIX RCAL 1 RCAL RACCESS1 RCAL 2 AFE 8 A UNKNOWN Z RACCESS2 AFE 6 4. Calculate the unknown impedance phase on the core using the following equation: ZUNKNOWN PHASE = ZUNK PHASE − RCALPHASE This 4-wire measurement approach to measuring impedances operates if there are no isolation requirements on the sensor. However, if an isolation capacitor, such as CISO, need to be included in series with the access resistor, RACCESS, in a 4-wire measurement, then a single chip solution is not possible. CLOSED LOOP GAIN = 2 DAC_ATTEN_EN EXCITATION AMPLIFIER DACP LOOP DACN 0.6V RCF 50kHz VREFDAC 1.8V 1.0V 12-BIT DAC PGA D GAIN 1/0.025 AFE 7 ZUNK MAG × RCAL RCAL MAG ZUNKNOWN MAG = 0.2V DACCLK REFNHIZ 0.6V P AFE 5 RACCESS3 B RACCESS4 AFE 4 AFE 3 N VBIAS AFE 2 T ADC 16-BITS, 160kSPS DFT 78SPS ×1.5 AFE 1 ×1 AN_A RCAL RCAL RTIA 33kΩ 0.1% IMAG = REAL AND RCAL IMAG RCAL RCAL PHASE = tan–1 Figure 2. 4-Wire Topology for ADuCM350—Measuring RCAL Rev. 0 | Page 4 of 16 2 REAL + RCAL RCAL IMAG RCAL REAL 2 IMAG 12168-001 2. Measure the impedance of a known precision resistor, RCAL, as shown in Figure 2. An excitation voltage is applied at RCAL 1 with associated D and P switches closed in the switch matrix. The resultant excitation current is measured through RCAL 2, with associated T and N switches closed in the switch matrix. This current is converted to a voltage using the TIA amplifier, where RTIA is optimized for the maximum current seen by the ADC, and is converted to a voltage using the ADC. A 2048 point Hann sample is performed on the data to give real and imaginary components of the impedance. Change the switch matrix configuration, as shown in Figure 3, and excite the sensor measuring the response MUX 1. 3. current. The DFT engine now calculates the real and imaginary components of the unknown impedance, Z. Calculate the unknown impedance magnitude on the core using the following equation: Application Note AN-1302 EXTERNAL COMPONENTS SWITCH MATRIX RCAL 1 RCAL RACCESS1 RCAL 2 AFE 8 CLOSED LOOP GAIN = 2 EXCITATION AMPLIFIER DACP LOOP DACN 0.6V GAIN 1/0.025 0.2V DACCLK REFNHIZ 0.6V P AFE 5 RACCESS3 B RACCESS4 AFE 4 AFE 3 N VBIAS AFE 2 T ADC 16-BITS, 160kSPS DFT 78SPS ×1.5 AFE 1 ×1 AN_A ZUNK ZUNK IMAG = RTIA 33kΩ 0.1% ZUNK Figure 3. 4-Wire Topology for ADuCM350—Measuring Z Rev. 0 | Page 5 of 16 PHASE REAL AND ZUNK IMAG ZUNK REAL2 + ZUNK IMAG2 = tan–1 ZUNK IMAG ZUNK REAL 12168-002 UNKNOWN Z VREFDAC 1.8V 1.0V 12-BIT DAC PGA MUX A AFE 6 RCF 50kHz D AFE 7 RACCESS2 DAC_ATTEN_EN AN-1302 Application Note THE 4-WIRE BIO-ISOLATED METHOD BASIC 4-WIRE THEORY RLIMIT In a classic 4-wire /4-terminal sensing system, a differential current source is used to force a known current into the sensor. This forced current generates a potential difference across the Unknown Z, which is to be measured according to Ohm’s Law where: CISO1 CISO3 RACCESS3 RACCESS1 A V METER V=I×R UNKNOWN Z VAC B When the current is being forced, the access wires to Z also lead to a drop in voltage, which causes inaccuracies in a measurement. To remove this loss from the actual measurement of Z, a differential pair of sense lines are connected to Z at the points labeled A and B in Figure 2. A UNKNOWN Z I METER B 12168-003 V METER Figure 4. Basic 4-Wire Topology The differential sense lines are designed with very high input impedance stages so that no current flows through them and there is no voltage drop across them. The impedance Z is then measured using the equation Z = VMETER/IAC 4-WIRE BIO-ISOLATED THEORY IN APPLICATION An alternative approach is to use a high precision excitation voltage source as the force signal. Apply this voltage to Z and measure the response current using a high accuracy current meter (see Figure 3). The unknown impedance Z is then measured by the equation RACCESS4 RACCESS2 CISO2 I METER 12168-004 CISO4 Figure 5. 4-Wire Bio-Isolated Topology Referring back to Figure 3, it is possible to measure 4-wire impedance using the ADuCM350.The excitation stage excites the sensor with a known voltage, which is accurately differentially sensed using the internal instrumentation loop. The current response is measured through the TIA channel and converted to a voltage. In a real-world application, such as those governed by the IEC-60601 standards, the Z (or sensor) allows a limited dc voltage across it. The restrictions on ac current forced on sensor are more relaxed. The ac voltage source is selected for the force connection to the sensor to utilize the ADuCM350 DFT capability. In Figure 5, CISO1 and CISO2 are discrete isolation capacitors that ensure that no dc voltage appears across the sensor. RACCESS1 and RACCESS2 are access or lead resistance inherent in the connections to the sensor. RLIMIT is an extra level of security to guarantee the maximum allowable excitation current seen by the sensor in a scenario where the RACCESS resistance is removed from the measurement. Z = VMETER/IMETER Rev. 0 | Page 6 of 16 Application Note AN-1302 A 4-WIRE BIO-ISOLATED SOLUTION Referring to Figure 5, the following is required: High Precision Current Meter • • • The ADuCM350 utilizes a TIA amplifier for current to voltage conversion for measurement by the high precision ADC, the gain of which is set by an external resistor, RTIA. The TIA channel sinks the sensor excitation current and the channel is precisely biased on a common mode of 1.1 V. Significant analog and digital filtering is performed on measurement for rejection of interferers and noise. The T and N channels are tied together using the switch matrix for accurate sense capability on the current measured (see Figure 7). Precision ac voltage source High precision current meter Precision differential voltage meter Precision AC Voltage Source The ADuCM350 has a high precision excitation control loop, which drives a precision ac voltage to the sensor. An internal differential sense configuration guarantees the accuracy of the voltage source (see Figure 6). The positive sense, P, is tied to the drive terminal, D, in the configurable switch matrix. A DDS based sine wave generator is used to generate the ac stimulus through a 12-bit DAC. For more information regarding the transmit stage, refer to the ADuCM350 Hardware Reference Manual (UG-587). The ADC converts the current measurement with a 160 kSPS ADC. A 2048 sample point DFT is performed on the data; resulting real and imaginary components for the current measurement are calculated. SWITCH MATRIX CLOED LOOP GAIN = 2 DAC_ATTEN_EN RCAL 1 EXCITATION AMPLIFIER DACP LOOP DACN 0.6V RCAL 2 RCF 50kHz VREFDAC 1.8V 1.0V 12-BIT DAC PGA D GAIN 1/0.025 AFE 8 AFE 7 0.2V REFNHIZ 0.6V P DACCLK AFE 6 AFE 5 ×1.5 AFE 4 ADC 16-BITS, 160kSPS MUX N AFE 3 AFE 2 12168-005 6.2kΩ 1% VAC 22nF CISO1 20% RACCESS3 5kΩ 5kΩ A UNKNOWN Z B RACCESS4 5kΩ 5kΩ 22nF 20% RLIMIT ×1.5 Figure 6. AC Voltage Source on the ADuCM350 EXCITATION AMPLIFIER DACP LOOP DACN 0.6V RCF 50kHz 12-BIT DAC PGA D GAIN 1/0.025 AFE 8 AFE 7 CISO1 AFE 6 RACCESS1 AFE 5 RACCESS2 CISO2 AFE 4 P ADC 16-BITS, 160kSPS ×1.5 N AFE 3 VBIAS AFE 2 AFE 1 DACCLK MUX A UNKNOWN Z B 0.2V REFNHIZ 0.6V VAC ×1.5 T ×1 RTIA Figure 7. High Precision Current Meter Rev. 0 | Page 7 of 16 I METER 12168-006 RLIMIT AN-1302 Application Note data, and resulting real and imaginary components for the voltage measurement are calculated. Precision Differential Voltage Meter To differentially sense the voltage across the sensor, a low power instrumentation amplifier with excellent noise and commonmode rejection is required (see Figure 8). The AD8226 is selected for this application. It is referenced off the common mode of the system set by the VBIAS voltage on the TIA channel. The output of the in-amp is fed back into the ADuCM350 through one of the auxiliary channels, for example, AN_A. 4-Wire, Bio-Isolated Measurement System Block Diagram Figure 9 shows the combination of the following: • • The ADC converts the auxiliary voltage measurement with a 160 kSPS ADC. A 2048 sample point DFT is performed on the Precision ac voltage source (ADuCM350 excitation stage) High precision current meter (ADuCM350 TIA channel stage) Precision differential voltage meter (AD8226 instrumentation amplifier) • EXCITATION AMPLIFIER LOOP EXTERNAL COMPONENTS D AFE 8 RLIMIT AFE 7 CISO1 AFE 6 RACCESS3 RACCESS1 AFE 5 VBIAS VBIAS CISO3 RCM1 A UNKNOWN Z B REF AD8226 RG CISO4 RCM2 RACCESS4 RACCESS2 P AFE 4 N AFE 3 AFE 2 CISO2 VBIAS VAC AFE 1 VBIAS T I METER RTIA 12168-007 V METER Figure 8. High Precision Differential Voltage Meter CLOSED LOOP GAIN = 2 SWITCH MATRIX RCAL 1 RCAL 2 AFE 8 VBIAS RCM1 CISO3 REF AD8226 RACCESS3 RG RCM2 VBIAS CISO4 AFE 7 CISO1 AFE 6 RACCESS1 AFE 5 A UNKNOWN Z B RACCESS4 RACCESS2 CISO2 AFE 4 D 0.2V REFNHIZ 0.6V DACCLK P ×1.5 N VBIAS AFE 3 AFE 2 1.0V 12-BIT DAC PGA GAIN 1/0.025 VREFDAC 1.8V ×1.5 T ADC 16-BITS, DFT 160kSPS 78SPS AFE 1 AN_A ×1 RTIA 12168-008 VBIAS RLIMIT RCF 50kHz MUX EXTERNAL COMPONENTS DAC_ATTEN_EN EXCITATION AMPLIFIER DACP LOOP DACN 0.6V Figure 9. 4-Wire Measurement System using the ADuCM350 and the Instrumentation Amplifier (AD8226) Rev. 0 | Page 8 of 16 Application Note AN-1302 How to Calculate the Unknown Z After obtaining the current and voltage DFT measurements, the part can exit the AFE Sequencer and calculate the impedance of the sensor using the following equations: Voltage measurement magnitude = SQRT(r2 + i2) Voltage measurement phase = ATan(i/r) Current measurement magnitude = SQRT(r2 + i2) The 1.5 gain in the equation is the ratio between the gain of the ADuCM350 current measurement channel, which is 1.5, vs. the gain of the ADuCM350 voltage measurement channel which is 1. The gain of the in-amp is determined by the selection of RG. For the AD8226, this is determined by Current measurement phase = ATan(i/r) where r and i are the real and imaginary components from the voltage and current DFT measurements, respectively. To calculate the Impedance Z, use Ohm’s law by dividing the voltage magnitude by the current magnitude while taking into account the gains of the signal chain. Z(Magnitude) = (Voltage magnitude/Current magnitude) × (1.5/1.494) × RTIA The current measurement value is converted to a voltage, using the RTIA, for measurement purposes. This gain needs to be taken into account. RG = (49.4 kΩ)/(G − 1) Choosing RG = 100 kΩ results in a gain of 1.494. Note that these equations are taken into account in the example provided in the software development kit. Rev. 0 | Page 9 of 16 AN-1302 Application Note EXAMPLE OF A 4-WIRE BIO-ISOLATED SYSTEM SENSOR CONFIGURATION 4-WIRE BIO-ISOLATED NETWORK In the example described in this application note, measure the impedance of an RC type sensor, with the configuration shown in Figure 10, for a 30 kHz excitation signal. Note that TOL indicates tolerance. For this 4-wire example, select the following components: The sensor details are as follows: • • • CS = 220 pF RS = 20 kΩ RP = 100 kΩ • A lead access resistor, RACCESS = 4.99 kΩ • An isolation capacitor, CISO, of 47 nF If Z is close to or less then RACCESS, a potential divider effect occurs which limits the bandwidth of the ADuCM350 thus degrading accuracy (see Figure 11). RLIMIT CISO3 47nF 20% A RS = 20kΩ TOL = 0.1% RP = 100kΩ TOL = 0.1% CISO1 RACCESS3 4.99kΩ RACCESS1 3kΩ 1% 47nF 20% 4.99kΩ A RC SENSOR Figure 10. RC Sensor to be Measured Calculate the complex sum of RS + CS = Zs = 34962 ∠ −55.11 2. B RACCESS2 CISO2 4.99kΩ 47nF 20% Figure 11. 4-Wire, Bio-Isolated Measurement Network The total impedance of the sensor needs to be calculated to verify the system accuracy. 1. RACCESS4 4.99kΩ 12168-010 B CISO4 47nF 20% 12168-009 CS = 220pF TOL = 1% Calculate Zs || with Rp = ZT = 28337.15 ∠ −41.66 This is the total impedance of the RC sensor to be measured. Rev. 0 | Page 10 of 16 Application Note AN-1302 AFE OPTIMIZATION Optimizing the ADuCM350 consists of the following steps: Note the following: 1. Calculate the RLIMIT resistor. 2. Calculate RTIA. • • 3. Calculate RG of the AD8226. 4. Calculate RCAL. • • CALCULATE THE RLIMIT RESISTOR When calculating the RLIMIT resistor, note that Maximum output voltage from ADuCM350 = 600 mV peak Maximum allowed ac current at 30 kHz is To prevent overranging of the ADC, put in a safety factor of 1.2, that is, the minimum impedance is 1.2 times less than the specified minimum impedance of 300 μA rms (targeting IEC-60601) = 424 μA peak Being conservative, set the maximum allowable ac current to 200 μA peak (<50%). 32.985 kΩ = 27 k Ω RTIA with safety factor included = 41.2 kΩ/1.2 RTIA = 34.3 kΩ RLIMIT ~= 600 mV peak/200 μA peak = 3 kΩ. This calculation ignores CISO due to its small size. Note that 33 kΩ is used for this example. CALCULATE RTIA RTIA is the feedback resistor on the TIA to convert the current to a voltage. CALCULATE RG OF THE AD8226 The maximum impedance of sensor Minimum impedance/maximum current seen by the TIA is ZUNKNOWN MAX Z PNMIN = (Real) 2 + (Sumofimaginary) 2 (R (XC LIMIT + R ACCESS1MIN + ZUNKNOWN MIN + R ACCESS 2 MIN ISO1MIN + XC ISO 2 MIN ) 2 Maximum voltage swing is 600 mV peak. Highest signal current into TIA = 600 mV peak/32.98 kΩ = 18.19 μA peak. Peak voltage at output of TIA (maximum allowed by the ADuCM350) = 750 mV peak. RTIA resistor to give peak 750 mV voltage for peak signal current is as follows: RTIA = 750 mV/18.19 μA RTIA = 41.2 kΩ ) 2 + = 28.337 kΩ A safety factor is incorporated on the RTIA to prevent the ADC from overranging. The same needs to be done here thus the maximum peak current is divided across differential inputs of AD8226 by a factor of 1.2. Peak current seen at VIN(AD8226) = Assume 20 kΩ is the minimum impedance of ZUNKNOWN. (18.19 μA peak)/1.2 = 15.16 μA peak RACCESS1 = RACCESS2 = 4.99 kΩ RLIMIT = 3 kΩ VIN(AD8226) = 15.16 μA peak × 28.337 kΩ = 439.6 mV peak XCISO1 = XCISO2 = 289.37 Ω AD8226 G = 750 mV peak/(439.6 mV peak) = 1.706 ZPNMIN = 32.985 kΩ If a further safety factor of 1.1 is used on the peak-to-peak of the voltage (this may be unnecessary for the application), then AD8226 G = 750 mV peak/(1.1 × 439.6 mV peak) = 1.55 AD8226 G = 1 + (49.4 kΩ/RG) = 1.55 RG = (49.4K)/(1.55 − 1) = 89.8 kΩ Select an RG of 100 kΩ since it is a standard value. AD8226G = 1 + (49.4 kΩ/RG) = 1 + (49.4 kΩ/100 kΩ) = 1.494 Note that the AD8226 has bandwidth limitations. For a frequency of 50 kHz, the gain is limited to 10 (see Figure 12). Rev. 0 | Page 11 of 16 AN-1302 Application Note CALCULATE RCAL 70 60 VS = 2.7V GAIN = 1000 The calibration of the auxiliary channel and TIA channel must take into account the gain through the system. 50 GAIN = 100 • For the voltage measurement channel, the auxiliary channel is calibrated. • For the current measurement channel, the temperature sensor is calibrated and the results are loaded to the offset and gain registers of the TIA channel. This ensures that the difference between the voltage and current gain is exactly 1.5. 30 20 GAIN = 10 10 0 GAIN = 1 –10 –20 –30 100 1k 10k 100k FREQUENCY (Hz) 1M 10M 12168-111 GAIN (dB) 40 All this is done for the user in the 4-wire bio-isolated example code in the software development kit. Figure 12. Gain vs. Frequency of AD8226 at 2.7 V Rev. 0 | Page 12 of 16 Application Note AN-1302 4-WIRE BIO-ISOLATED MEASUREMENTS HARDWARE SETUP FOR 4-WIRE BIOCONFIGURATON BOARD 1. When setting up the EVAL-ADuCM350EBZ motherboard 2. 3. 4. • • For the voltage measurement, insert LK1 (Auxiliary Channel A). Open LK6. For the ADuCM350 4-wire bio-configuration board • • Insert LK7, LK8, LK9, and LK10. To measure the network shown in Figure 10 and Figure 11, insert LK16, LK17, and LK21. The result should appear as shown in Figure 13. By default, the 4-wire configuration seen in Figure 10 and Figure 11 is setup on the 4-wire bio-configuration board. After downloading the software development kit, go to C:\Analog Devices\ADuCM350BBCZ\EVALADUCM350EBZ\examples. Click the BioImpedanceMeasurement_4Wire folder. Click the .eww file in IAR. During the download and debug stage, open the Terminal I/O window to read the returned results. Measurement Results Impedance Magnitude Measured result = 28405 Ω Theoretical value measured ZT = 28337 Ω However, the Cs of 220 pF used in the calculation had a tolerance of 1%. Upon analysis, the capacitor measured closer to 221 pF. SOFTWARE SETUP FOR 4-WIRE BIOCONFIGURATION BOARD In theory, a Cs of 221 pF would give a ZT of 28416 Ω vs. the measured result of 28405 Ω. Firmware Example Code available in the ADuCM350 software development kit is designed to be used with the 4-wire bio-configuration board to validate the solution discussed in this application note. Impedance Phase The current 4-wire-bio-isolated configuration is not capable of measuring accurate phase measurements. If an absolute phase measurement is required, use a single chip ADuCM350 4-wire measurement configuration. Note that this configuration does not have isolation capacitors (CISO). 12168-011 The Readme.txt in the example folder provides more details on the measurement. For more details, refer to the Sensor Configuration section. Figure 13. 4-Wire Measurements Display on Terminal I/O Rev. 0 | Page 13 of 16 AN-1302 Application Note SCHEMATICS FOR THE 4-WIRE BIO-CONFIGURATION BOARD MOTHERBOARD CONNECTOR - ALIGN J8 AND J9. J8-21 J8-2 J8-41 AFE6 J8-22 P4.2 J8-3 J8-43 J8-23 J8-4 J8-45 J8-25 J8-6 AFE7 J8-26 P0.10 J8-7 J8-27 J8-8 AFE3 REF_EXCITE_1 J8-29 J8-10 AFE8 J8-30 J8-11 J8-31 J8-12 J8-32 AFE4 J8-13 RCAL1 J8-33 J8-14 RCAL2 J8-34 J8-15 J8-35 J8-46 TIA_I J9-4 J9-24 J9-5 J9-25 J9-45 J9-6 J9-26 J9-46 J9-7 J9-27 J9-47 J9-8 J9-28 J9-48 J9-44 J9-49 J8-50 J9-50 J8-51 J9-11 J9-31 J9-51 J8-52 J9-12 J9-32 J9-52 J8-53 J9-13 J9-33 J9-53 J8-54 J9-14 J9-34 J9-54 J8-55 J9-15 J9-35 J9-55 J8-56 J9-16 J9-36 J9-56 J9-17 J9-37 J9-57 VBIAS_1 J9-18 J9-38 J9-58 J9-19 J9-39 J9-59 VREF_1 J9-20 J9-40 J9-60 J8-58 TIA_O J9-43 J9-29 J8-38 J8-40 VCCM_ANA J9-23 3.3V_BOARD J9-30 J8-57 J8-39 J9-42 J9-3 J9-41 J9-9 J8-37 J8-20 J9-21 J9-22 J9-10 J8-17 J8-19 J9-1 J9-2 J8-49 J8-36 AFE5 AN_D_1 J8-48 J8-16 J8-18 AN_C_1 J8-47 J8-28 J8-9 AN_B_1 J8-44 J8-24 AFE2 J8-5 AN_A_1 J8-42 3.3V_BOARD J8-59 J8-60 12168-012 AFE1 J8-1 Figure 14. Motherboard Connector 4-WIRE BIO IMPEDANCE CONFIGURATION ISOLATION + LEAD LK8 AFE8 R32 RLIMIT (3.0kΩ) R24 R25 47nF 4.99kΩ UNCOMITTED CONFIGURATION ISOLATION +LEAD R1A DNI R1 DNI R2A AFE2 LK2 DNI R2 DNI SENSOR R3A AFE3 18nF 3 R17 R30 DNI R4 2K R15 DNI LK4 R5A AFE5 LK20 LK19 VBIAS_1 4 R12 100kΩ INAMP_M R9 20kΩ R31 10MΩ 1 2 100kΩ –IN 8 +VS RG U3 7 OUT AD8226 REF RG 6 –VS +IN 5 AFE4 LK5 DNI R5 10µF 10MΩ R6A LK21 R16 DNI 0Ω R13 R10 INAMP_P 220pF AFE6 LK6 DNI R6 6.8K LK22 ISOLATION +LEAD LK10 INAMP_M R26 R29 47nF 4.99kΩ ISOLATION + LEAD LK7 AFE7 R19 R27 47nF 4.99kΩ Figure 15. 4-Wire and Uncommitted Schematics Rev. 0 | Page 14 of 16 12168-013 VBIAS_1 DNI R3 R4A C3 0.1µF AN_A_1 LK17 LK16 VBIAS_1 LK3 LK18 VCCM_ANA LK13 4.99kΩ 47nF LK1 LK11 AFE1 LK12 R28 R23 LK14 LK9 LK15 INAMP_P Application Note AN-1302 RCAL RCAL2 1kΩ R18 TEST POINTS RCAL1 TP5 TP1 TP4 TP6 TP12 M20-9991246 HARWIN 3.3V_BOARD J1-4 M20-9991246 HARWIN REF_EXCITE_1 J1-1 M20-9991246 HARWIN VBIAS_1 J1-5 M20-9991246 HARWIN VREF_1 J1-6 M20-9991246 HARWIN VCCM_ANA J1-12 TP2 TP3 M20-9991246 HARWIN P0.10 J1-3 M20-9991246 HARWIN P4.2 TP10 TP9 TP8 J1-2 TP7 IV GAIN M20-9991246 HARWIN AN_A_1 33kΩ J1-10 M20-9991246 HARWIN AN_B_1 J1-9 M20-9991246 HARWIN AN_C_1 TIA_I AN_D_1 R7 J1-8 M20-9991246 HARWIN J1-7 TP11 DNI M20-9991246 HARWIN J1-11 TIA_O Figure 16. Miscellaneous Schematics Rev. 0 | Page 15 of 16 12168-014 R11 AN-1302 Application Note NOTES ©2014 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. AN12168-0-4/14(0) Rev. 0 | Page 16 of 16