AD620 Regardless of the system in which it is being used, the AD620 Note that for the homebrew circuit, the OP07 specifications for provides greater accuracy at low power and price. In simple input voltage offset and noise have been multiplied by √2. This systems, absolute accuracy and drift errors are by far the most is because a three op amp type in-amp has two op amps at its significant contributors to error. In more complex systems inputs, both contributing to the overall input error. with an intelligent processor, an autogain/autozero cycle removes all absolute accuracy and drift errors, leaving only the resolution errors of gain, nonlinearity, and noise, thus allowing full 14-bit accuracy. 10V10k Ω *10k Ω *ROP07DGAD620AR = 350 Ω R = 350 Ω 499 Ω 10k Ω **REFERENCE100 Ω **10k Ω **OP07DR = 350 Ω R = 350 Ω AD620A MONOLITHICINSTRUMENTATIONOP07DAMPLIFIER, G = 10010k Ω *10k Ω *SUPPLY CURRENT = 1.3mA MAX 00775-0-040 "HOMEBREW" IN-AMP, G = 100*0.02% RESISTOR MATCH, 3ppm/ ° C TRACKING**DISCRETE 1% RESISTOR, 100ppm/ ° C TRACKINGPRECISION BRIDGE TRANSDUCERSUPPLY CURRENT = 15mA MAX 00775-0-041 00775-0-039 Figure 37. Make vs. Buy Table 4. Make vs. Buy Error BudgetError, ppm of Full ScaleError SourceAD620 Circuit Calculation“Homebrew” Circuit CalculationAD620Homebrew ABSOLUTE ACCURACY at TA = 25°C Input Offset Voltage, μV 125 μV/20 mV (150 μV × √2)/20 mV 6,250 10,607 Output Offset Voltage, μV 1000 μV/100 mV/20 mV ((150 μV × 2)/100)/20 mV 500 150 Input Offset Current, nA 2 nA ×350 Ω/20 mV (6 nA ×350 Ω)/20 mV 18 53 CMR, dB 110 dB(3.16 ppm) ×5 V/20 mV (0.02% Match × 5 V)/20 mV/100 791 500 Total Absolute Error 7,559 11,310 DRIFT TO 85°C Gain Drift, ppm/°C (50 ppm + 10 ppm) ×60°C 100 ppm/°C Track × 60°C 3,600 6,000 Input Offset Voltage Drift, μV/°C 1 μV/°C × 60°C/20 mV (2.5 μV/°C × √2 × 60°C)/20 mV 3,000 10,607 Output Offset Voltage Drift, μV/°C 15 μV/°C × 60°C/100 mV/20 mV (2.5 μV/°C × 2 × 60°C)/100 mV/20 mV 450 150 Total Drift Error 7,050 16,757 RESOLUTION Gain Nonlinearity, ppm of Full Scale 40 ppm 40 ppm 40 40 Typ 0.1 Hz to 10 Hz Voltage Noise, μV p-p 0.28 μV p-p/20 mV (0.38 μV p-p × √2)/20 mV 14 27 Total Resolution Error 54 67 Grand Total Error 14,663 28,134 G = 100, VS = ±15 V. (All errors are min/max and referred to input.) Rev. H | Page 13 of 20 Document Outline SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION Make vs. Buy: a Typical Bridge Application Error Budget Pressure Measurement Medical ECG Precision V-I Converter GAIN SELECTION INPUT AND OUTPUT OFFSET VOLTAGE REFERENCE TERMINAL INPUT PROTECTION RF INTERFERENCE COMMON-MODE REJECTION GROUNDING GROUND RETURNS FOR INPUT BIAS CURRENTS AD620ACHIPS INFORMATION OUTLINE DIMENSIONS ORDERING GUIDE
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