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AD637JR-REEL7 Arkusz danych(PDF) 7 Page - Analog Devices |
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AD637JR-REEL7 Arkusz danych(HTML) 7 Page - Analog Devices |
7 / 20 page AD637 Rev. K | Page 7 of 20 FUNCTIONAL DESCRIPTION FILTER/AMPLIFIER 24kΩ 24kΩ ONE QUADRANT SQUARER/DIVIDER BUFFER AMPLIFIER Q1 Q2 Q3 Q4 125Ω 6kΩ 6kΩ 12kΩ 24kΩ A5 A1 A2 ABSOLUTE VALUE VOLTAGE TO CURRENT CONVERTER I1 I3 I4 A4 A3 BIAS Q5 CAV +VS RMS OUT COMMON CS DEN INPUT OUTPUT OFFSET dB OUTPUT AD637 BUFF OUT BUFF IN –VS 14 1 13 10 4 6 5 3 7 9 11 8 VIN Figure 4. Simplified Schematic The AD637 embodies an implicit solution of the rms equation that overcomes the inherent limitations of straightforward rms computation. The actual computation performed by the AD637 follows the equation ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ = rms V V Avg rms V IN 2 Figure 4 is a simplified schematic of the AD637, subdivided into four major sections: absolute value circuit (active rectifier), squarer/divider, filter circuit, and buffer amplifier. The input voltage (VIN), which can be ac or dc, is converted to a unipolar current I1 by the active rectifiers A1 and A2. I1 drives one input of the squarer/divider, which has the transfer function 3 1 4 I I I 2 = The output current of the squarer/divider I4 drives A4, forming a low-pass filter with the external averaging capacitor. If the RC time constant of the filter is much greater than the longest period of the input signal, then the A4 output is proportional to the average of I4. The output of this filter amplifier is used by A3 to provide the denominator current I3, which equals Avg I4 and is returned to the squarer/divider to complete the implicit rms computation rms I I I Avg I 1 4 1 4 = ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ = 2 and VOUT = VIN rms To compute the absolute value of the input signal, the averaging capacitor is omitted. However, a small capacitance value at the averaging capacitor pin is recommended to maintain stability; 5 pF is sufficient for this purpose. The circuit operates identically to that of the rms configuration, except that I3 is now equal to I4, giving 4 1 I I 2 4 I = I4 = |I1| The denominator current can also be supplied externally by providing a reference voltage (VREF) to Pin 6. The circuit operates identically to the rms case, except that I3 is now proportional to VREF. Therefore, 3 1 I I Avg 2 4 I = and DEN IN OUT V V V 2 = This is the mean square of the input signal. |
Podobny numer części - AD637JR-REEL7 |
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Podobny opis - AD637JR-REEL7 |
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