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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This chapter discusses about the Logarithmic amplifier and Anti-Logarithmic amplifier in detail. V is voltage applied across diode; V t is the voltage equivalent of temperature. Anti log amplifier is one which provides output proportional to the anti log i.

The circuit arrangement for Antilogarithmic amplifier is illustrated in figure 1. Logarithmic amplifier gives the output proportional to the logarithm of input signal. A resistor is connected in feedback path. You May Also Like.

Two matched transistors is used here as shown in figure, where input is given to the non-inverting amplifier pin of first op-amplifier A1. So, the voltage at its inverting input terminal will be zero volts. The output is depending ajplifier output current of transistor and feedback resistor. I edit and author this site.

### Antilogarithmic Amplifier | Derivation

Since the non inverting terminal of opamp is at ground potential. A logarithmic amplifieror a log amplifieris an electronic circuit that produces an output that is proportional to the logarithm of the applied input. Now antilg the ampligier of collector current of transistor I C in equation 1. Logarithmic amplifier operation The circuit diagram of logarithmic amplifier is as shown below logarithmic amplifier. Please note that these amplifiers fall under non-linear applications.

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

In the circuit shown above, amplitier non-inverting input terminal of the op-amp is connected to ground. Observe that the left hand side terms of both equation 1 and equation 3 are same.

The figure of anti-logarithmic amplifier using matched diode is shown in figure below. 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.

## Log And Anti Log Amplifiers

Your email address will not be published. Using the concept of virtual short between the input terminals of an opamp the voltage at inverting terminal will be zero volts. That means zero volts is applied at the non-inverting input terminal of the op-amp. Gain of logarithmic amplifier.

A simple Anti log amplifier is shown below. It is obvious from the circuit shown above that negative feedback is provided from output to inverting terminal. 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. According to the virtual short conceptthe voltage at the inverting input terminal of op-amp will be equal to the voltage present at its non-inverting input terminal.

Hence applying KCL at inverting terminal of opamp, we get. Gain of Anti log amplifier. The output voltage expression becomes. Here a general purpose NPN transistor is connected to inverting input of op-amp. The anti log amplifier can be redrawn as follows. 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.

Applying KCL at inverting node of opamp we get. Like logarithmic amplifierantilogarithmic is also a non-linear amplifier. Usng matched diodes are used here, where one diode D 1 is connected in feedback path and second diode D 2 is connected to inverting input of op-amp A2 in reverse bias mood as shown in figure 2.

## logarthmic, anti logarthmic amplifiers

Thus, we can write. Electronic Game and Fun Projects. The circuit diagram of logarithmic amplifier is as shown below.

Thus, thermal voltage of 1 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. So, the voltage at the inverting input terminal will be zero volts. It means zero volts is applied to its non-inverting input terminal.

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Easy Electronic Projects 5. According to the virtual short conceptthe voltage at the inverting input terminal of an op-amp will be equal to the qntilog at its non-inverting input terminal. From the figure we can also conclude that transistor base emitter voltage V BE is equivalent input voltage V i i.