Logarithmic Amplifier Design with Op Amp, BJT transistor, Thin Film Resistors скачать в хорошем качестве

Logarithmic Amplifier Design with Op Amp, BJT transistor, Thin Film Resistors

How to Design a Logarithmic Amplifier is discussed in this Circuit design example. This Log Amplifier is implemented with two operational amplifiers, a pair of matched BJT Bipolar transistors and two thin film high-precision resistors R and possibly a Temperature compensated TempCo resistor to counteract the positive thermal coefficient of the thermal voltage VT of BJT transistor. For more examples see    • Electrical Engineering, Analog, Digital De...   . The Intuitive operation of the circuit is first discussed in this log amplifier tutorial including the explanation of negative feedback operation in the circuit. Then applying a combination of op amp virtual short, Kirchhoff circuit laws (KVL and KCL) and Shockley PN Junction voltage-current equation, the formula for the output voltage as a function of input voltage is found showing that output voltage of this Log amplifier is proportional to logarithm of input voltage. With proper selection of components, the formula is simplified to Output = 1 - Log10(Input).