Integrated dc logarithmic amplifiers application note maxim. A log amplifier is an amplifier for which the output voltage vout is k times the natural log of the. For input currents, the circuit will maintain 1% logarithmic. The term logarithmic amplifier generally abbreviated to log amp is something of a misnomer, and. An311theory and applications of logarithmic amplifiers. Log and antilog amplifier pdf antilog amplifiers along with log amplifiers are used to perform analogue computations on the input signals.
An311 theory and applications of logarithmic amplifiers rev. Please note that these amplifiers fall under nonlinear applications. The bulk size and pd rating of the diode affects the amplifidr resistance and bulk resistance or esr, and also junction capacitance and bandwidth. The practical circuit mentioned is displayed below. Integrated dc logarithmic amplifiers application note. Log amplifier is a linear circuit in which the output voltage will be a constant times the natural logarithm of the input. To design a logarithm amplifier circuit, high performance op amps like lm1458, lm771, lm714 are commonly used. A log converter is a circuit that converts an input voltage to an output voltage that is a logarithmic function of. Figure 1 shows an amplifier that provides a logarithmic output for a linear input current or voltage. Low cost, dc to 500 mhz, 92 db logarithmic amplifier data. A log amplifier is an amplifier for which the output voltage v out is k times the natural log of the input voltage v in. Human can recognize in detail for weak signal and roughly for large signal.
Computing the logarithm of a signal is a very useful signal processing technique to compress a large dynamic range into a more manageable smaller range. There are three basic architectures which may be used to produce log amps. This shows that using the log amplifier with base 10 will give less output in the comparison of using the log. Logarithmic amplifier using diode and transistor it produces output which is proportional to logarithmic of input it is a nonlinear amplifier used for amplification or compression of wide range of. There are two basic circuits for logarithmic amplifiers transdiode and diode connected transistor most logarithmic amplifiers are based on the inherent logarithmic relationship between the collector current, ic,and the baseemitter voltage, vbe, in silicon bipolar transistors. This chapter discusses about the logarithmic amplifier and anti logarithmic amplifier in detail. Kuhn march 24, 20 a log converter is a circuit that converts an input voltage to an output voltage that is a logarithmic function of the input voltage. A necessary condition for successful operation of a log amplifier is that the input voltage, vin, is always. In this video, the log and antilog amplifier circuits using opamp and their. The voltage across a silicon diode is proportional to the logarithm of the current through it. Among the classes of logarithmic amplifiers, the dc log amp continues to be a very powerful, costeffective solution for compressing widedynamicrange sensor signals.
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