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AD620AR-REEL7 датащи(PDF) 10 Page - Analog Devices |
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AD620AR-REEL7 датащи(HTML) 10 Page - Analog Devices |
10 / 16 page AD620 REV. E –10– VB –VS A1 A2 A3 C2 RG R1 R2 GAIN SENSE GAIN SENSE R3 400 10k 10k I2 I1 10k REF 10k +IN – IN 20 A 20 A R4 400 OUTPUT C1 Q2 Q1 Figure 33. Simplified Schematic of AD620 THEORY OF OPERATION The AD620 is a monolithic instrumentation amplifier based on a modification of the classic three op amp approach. Absolute value trimming allows the user to program gain accurately (to 0.15% at G = 100) with only one resistor. Monolithic construc- tion and laser wafer trimming allow the tight matching and tracking of circuit components, thus ensuring the high level of performance inherent in this circuit. The input transistors Q1 and Q2 provide a single differential- pair bipolar input for high precision (Figure 33), yet offer 10 × lower Input Bias Current thanks to Super βeta processing. Feed- back through the Q1-A1-R1 loop and the Q2-A2-R2 loop main- tains constant collector current of the input devices Q1, Q2 thereby impressing the input voltage across the external gain setting resistor RG. This creates a differential gain from the inputs to the A1/A2 outputs given by G = (R1 + R2)/RG + 1. The unity-gain subtracter A3 removes any common-mode sig- nal, yielding a single-ended output referred to the REF pin potential. The value of RG also determines the transconductance of the preamp stage. As RG is reduced for larger gains, the transcon- ductance increases asymptotically to that of the input transistors. This has three important advantages: (a) Open-loop gain is boosted for increasing programmed gain, thus reducing gain- related errors. (b) The gain-bandwidth product (determined by C1, C2 and the preamp transconductance) increases with pro- grammed gain, thus optimizing frequency response. (c) The input voltage noise is reduced to a value of 9 nV/ √Hz, deter- mined mainly by the collector current and base resistance of the input devices. The internal gain resistors, R1 and R2, are trimmed to an abso- lute value of 24.7 k Ω, allowing the gain to be programmed accurately with a single external resistor. The gain equation is then G = 49.4 k Ω RG + 1 so that RG = 49.4 k Ω G − 1 .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Figure 31b. Gain Nonlinearity, G = 100, RL = 10 kΩ (100 µV = 10 ppm) .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Figure 31c. Gain Nonlinearity, G = 1000, RL = 10 kΩ (1 mV = 100 ppm) AD620 VOUT G=1 G=1000 49.9 10k * 1k 10T 10k 499 G=10 G=100 5.49k +VS 11k 1k 100 100k INPUT 10V p-p –VS *ALL RESISTORS 1% TOLERANCE 7 1 2 3 8 6 4 5 Figure 32. Settling Time Test Circuit |
Аналогичный номер детали - AD620AR-REEL7 |
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Аналогичное описание - AD620AR-REEL7 |
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