a diode used in the feedback loop of an operational amplifier is forward biased by a constant current loop of an op-amp. Antilog is inverse operation of log operation so; antilog amplifiers can be operation. Log Amplifier using Diode. Fig 1. Antilogarithmic Amplifier using Single Transistor. The circuit Here a general purpose NPN transistor is connected to inverting input of op-amp. Basic Antilog Amplifier Using Diode The circuit diagram of basic antilog amplifier using diode As op-amp input current is zero, the current I must be same as If.

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Observe that the left hand side terms of both equation 1 and equation 3 are same. Project Using and 4. You May Also Like. So, the voltage at its inverting input terminal will be zero volts. It is obvious from anp circuit shown above that negative feedback is provided from output to inverting terminal.

The figure of anti-logarithmic ueing using matched diode is shown in figure below. In the circuit shown above, the non-inverting input terminal of the op-amp is connected to ground.

An anti-logarithmic amplifieror an anti-log amplifieris an electronic circuit that produces an output that is proportional to the anti-logarithm of the applied input.

Thus, thermal voltage of amplifjer st transistor will be same to thermal voltage of 2 nd transistor and saturation current of 1 st transistor will be equal to saturation current of 2 nd transistor.


The electronic circuits which perform the mathematical operations such as logarithm and anti-logarithm exponential with an amplification are called as Logarithmic amplifier and Anti-Logarithmic amplifier respectively.

Voltage at inverting pin of op-amp A1 is potentially equal to voltage at non-inverting input of op-amp i. The logarithmic circuit can be redrawn as follows. The circuit arrangement for Antilogarithmic amplifier is illustrated in figure 1. Since the non inverting terminal of opamp is antilof ground potential.

Like logarithmic amplifierantilogarithmic is also a non-linear amplifier. Antilov output is depending upon output current of transistor and feedback resistor. According to the virtual short conceptthe voltage at the inverting input terminal of an op-amp will be equal to the voltage at its non-inverting input terminal.

Your email address will not be published. Applying KCL at inverting node of opamp we get. Easy Electronic Projects 5. Thus we can write. Logarithmic amplifier operation The circuit diagram of logarithmic amplifier is as shown below logarithmic amplifier.

Logarithmic amplifier gives the output proportional to the logarithm of input signal. Assuming both diode and matched thus material constant, thermal voltage of diode and saturation current of diode is also same. Using the concept of virtual short between the input terminals of an opamp the voltage at inverting terminal will be zero volts.

Two matched diodes are used here, where one diode D 1 is connected in antilig path and second diode D 2 is connected to inverting input of op-amp A2 in reverse bias mood as shown in figure 2.


You can connect with me on: Now putting the value of collector current of transistor I C in equation 1. This section discusses about the op-amp based anti-logarithmic amplifier in detail.

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Antilogarithmic Amplifier | Derivation

Hence applying KCL at inverting terminal of opamp, we get. This chapter discusses about the Logarithmic amplifier and Anti-Logarithmic amplifier in detail. In the above circuit, the non-inverting input terminal of the op-amp is connected to ground.

This section discusses about the op-amp based logarithmic amplifier in detail. An op-amp based logarithmic amplifier produces a voltage at the output, which is proportional to the logarithm of the voltage applied to the resistor connected to its inverting terminal.

logarthmic, anti logarthmic amplifiers

So, the voltage at the inverting input terminal will be zero volts. Thus, we can write.

A resistor is connected in feedback path. Two matched transistors amplufier used here as shown in figure, where input is given to the non-inverting amplifier pin of first op-amplifier A1.

Gain of logarithmic amplifier. The figure of anti-logarithm amplifier is shown in figure 3.

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