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How does a logarithmic amplifier work?
A logarithmic amplifier, or a log amplifier, is an electronic circuit that produces an output that is proportional to the logarithm of the applied input. According to the virtual short concept, the voltage at the inverting input terminal of an op-amp will be equal to the voltage at its non-inverting input terminal.
Which circuit can be used as log amplifier?
The logarithm amplifier gives an output voltage which is proportional to the logarithm of applied input voltage. To design a logarithm amplifier circuit, high performance op-amps like LM1458, LM771, LM714 are commonly used and a compensated logarithm amplifier may include more than one.
What change is required to make it work as logarithmic amplifier?
The necessary condition of the log amplifier to work is that the input voltage always must be positive. It can be seen that Vout = – Vbe. The output of the circuit is, thus, proportional to the log of the input voltage.
What is role of diode in log amplifier?
When a diode is connected in the feedback loop of an inverting amplifier, the output voltage is a logarithmic function of the input voltage. If a diode is used in a noninverting amplifier, the result is an antilog amplifier. There are some problems using diodes in log amplifiers.
What is the output voltage of the log amplifier?
Log amplifier is a linear circuit in which the output voltage will be a constant times the natural logarithm of the input. The basic output equation of a log amplifier is v Vout = K ln (Vin/Vref); where Vref is the constant of normalisation, and K is the scale factor.
How does a log amplifier work in a transistor?
Opamp transistor log amplifier. In this configuration a transistor is placed in the feedback path of an opamp wired in inverting mode. Collector of the transistor is connected to the inverting input of the opamp, emitter to output and base is grounded. The necessary condition for a log amp to work is that the input voltage must be always positive.
How is an opamp circuit made with transistors?
The value had been identified by experimentation. The opamp circuit using transistors appears reasonably linear (reduced distortion) as pointed out in the scope picture listed below. The upper waveform is the ramp input from a function generator, and the bottom waveform is the inverted output of the op-amp having a 50 ohm load.
Which is an opamp diode in a log amplifier?
The schematic of a simple Opamp-diode log amplifier is shown above. This is nothing but an opamp wired in closed loop inverting configuration with a diode in the feedback path.
How is the gain of a logarithmic amplifier compensated?
Temperature sensitive scale factor can be compensated by making the gain of Op-Amp (A2) temperature sensitive. Using temperature dependent resistor R T in such a way that and R T has a opposite effect and the circuit is independent of temperature. Log amplifier using two matched transistors and two op-amps