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AD637AR 数据表(PDF) 6 Page - Analog Devices |
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AD637AR 数据表(HTML) 6 Page - Analog Devices |
6 / 10 page AD637 REV. E –6– BUFFER AD637 SQUARER/DIVIDER BIAS SECTION FILTER 25k 25k 1 2 3 4 5 6 7 14 13 12 11 10 9 8 CAV –VS +VS + ABSOLUTE VALUE RMS OUTPUT BUFFER OUTPUT ANALOG COM OUTPUT OFFSET + C2 RX 24k BUFFER INPUT NC CHIP SELECT DENOMINATOR INPUT dB 24k FOR 1 POLE FILTER, SHORT RX AND REMOVE C3 SIGNAL INPUT + C3 NC Figure 8. Two Pole Sallen-Key Filter Figure 9a shows values of CAV and the corresponding averaging error as a function of sine-wave frequency for the standard rms connection. The 1% settling time is shown on the right side of the graph. Figure 9b shows the relationship between averaging error, signal frequency settling time and averaging capacitor value. This graph is drawn for filter capacitor values of 3.3 times the averag- ing capacitor value. This ratio sets the magnitude of the ac and dc errors equal at 50 Hz. As an example, by using a 1 µF averag- ing capacitor and a 3.3 µF filter capacitor, the ripple for a 60 Hz input signal will be reduced from 5.3% of reading using the averaging capacitor alone to 0.15% using the single pole filter. This gives a factor of thirty reduction in ripple and yet the set- tling time would only increase by a factor of three. The values of CAV and C2, the filter capacitor, can be calculated for the desired value of averaging error and settling time by using Figure 9b. The symmetry of the input signal also has an effect on the mag- nitude of the averaging error. Table I gives practical component values for various types of 60 Hz input signals. These capacitor values can be directly scaled for frequencies other than 60 Hz, i.e., for 30 Hz double these values, for 120 Hz they are halved. For applications that are extremely sensitive to ripple, the two pole configuration is suggested. This configuration will minimize capacitor values and settling time while maximizing performance. Figure 9c can be used to determine the required value of CAV, C2 and C3 for the desired level of ripple and settling time. INPUT FREQUENCY – Hz 100 0.01 1 100k 10 100 1k 10k 10 1.0 0.1 VALUES FOR CAV AND 1% SETTLING TIME FOR STATED % OF READING AVERAGING ERROR* ACCURACY 2% DUE TO COMPONENT TOLERANCE * %dc ERROR + %RIPPLE (Peak) 100 0.01 10 1.0 0.1 Figure 9a. INPUT FREQUENCY – Hz 100 0.01 1 100k 10 100 1k 10k 10 1.0 0.1 VALUES OF CAV, C2 AND 1% SETTLING TIME FOR STATED % OF READING AVERAGING ERROR* FOR 1 POLE POST FILTER * %dc ERROR + % PEAK RIPPLE ACCURACY 20% DUE TO COMPONENT TOLERANCE 100 0.01 10 1.0 0.1 Figure 9b. INPUT FREQUENCY – Hz 100 0.01 1 100k 10 100 1k 10k 10 1.0 0.1 VALUES OF CAV, C2 AND C3 AND 1% SETTLING TIME FOR STATED % OF READING AVERAGING ERROR* 2 POLL SALLEN-KEY FILTER * %dc ERROR + % PEAK RIPPLE ACCURACY 20% DUE TO COMPONENT TOLERANCE 100 0.01 10 1.0 0.1 Figure 9c. |
类似零件编号 - AD637AR |
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类似说明 - AD637AR |
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