Datenblatt-Suchmaschine für elektronische Bauteile |
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AD538BD Datenblatt(PDF) 6 Page - Analog Devices |
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AD538BD Datenblatt(HTML) 6 Page - Analog Devices |
6 / 11 page AD538 –6– REV. C 25k 25k LOG RATIO 100 25k 25k ANTILOG LOG OUTPUT 100 AD538 INTERNAL VOLTAGE REFERENCE I VO IZ VZ B +10V –VS +VS +2V IY A D IX VX C PWR GND SIGNAL GND VY 118 17 16 15 14 13 12 11 10 2 3 4 5 6 7 8 9 Figure 9. Functional Block Diagram FUNCTIONAL DESCRIPTION As shown in Figures 9 and 10, the VZ and VX inputs connect directly to the AD538’s input log ratio amplifiers. This subsec- tion provides an output voltage proportional to the natural log of input voltage VZ , minus the natural log of input voltage VX. The output of the log ratio subsection at B can be expressed by the transfer function: V B = kT q ln V Z V X where k = 1.3806 × 10–23 J/K, q = 1.60219 × 10–19 C, T is in Kelvins. The log ratio configuration may be used alone, if correctly tem- perature compensated and scaled to the desired output level (see Applications section). Under normal operation, the log-ratio output will be directly connected to a second functional block at input C, the antilog subsection. This section performs the antilog according to the transfer function: V O = VY e VC q kT As with the log-ratio circuit included in the AD538, the user may use the antilog subsection by itself. When both subsections are combined, the output at B is tied to C, the transfer function of the AD538 computational unit is: V O = VY e kT q q kT ln VZ VX ; V B = VC which reduces to: VV V V OY Z X = Finally, by increasing the gain, or attenuating the output of the log ratio subsection via resistor programming, it is possible to raise the quantity VZ/VX to the m th power. Without external programming, m is unity. Thus the overall AD538 transfer function equals: V O = VY V Z V X m where 0.2 < m < 5. When the AD538 is used as an analog divider, the VY input can be used to multiply the ratio VZ /VX by a convenient scale factor. The actual multiplication by the VY input signal is accomplished by adding the log of the VY input signal to the signal at C, which is already in the log domain. INPUT FREQUENCY – Hz 150 100 10 1.0 0.1 1k 10k 100k 1M 100 VX = 10V VY = 5V +5V SIN t VOLTS VZ = 0V Figure 7. VY Feedthrough vs. Frequency DC OUTPUT VOLTAGE – Volts 100 0.01 10 1 0.10 0.01 0.1 1 10 FOR THE FREQUENCY RANGE OF 10Hz TO 100kHz THE TOTAL RMS OUTPUT NOISE, eo, FOR A GIVEN BANDWIDTH Bw, IS CALCULATED eo = en Bw VX = 10V VX = 0.01V Figure 8. 1 kHz Output Noise Spectral Density vs. DC Output Voltage |
Ähnliche Teilenummer - AD538BD |
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Ähnliche Beschreibung - AD538BD |
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