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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Thus, we can write. Here a general purpose NPN transistor is connected to inverting input of op-amp. It means zero usibg is applied to its non-inverting input terminal. Applying Antilog on both sides we get. So, the voltage at the inverting input terminal will be zero volts.

As we know that is very small. Assuming both transistors are matched. Logarithmic amplifier gives the output proportional to the logarithm of input signal. In the circuit shown above, the non-inverting input terminal of the op-amp is connected to ground.

## Log And Anti Log Amplifiers

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.

Best Arduino Projects 2. Google Plus and Facebook. 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. Please note that these amplifiers fall under non-linear applications. Two matched transistors is used here as shown in figure, where input is given to anitlog non-inverting amplifier pin of first op-amplifier A1.

The circuit diagram of logarithmic amplifier is as shown below. From the figure we can also conclude ampllifier transistor base emitter voltage V BE is equivalent input voltage V i i. According to the virtual short conceptthe voltage at the inverting input terminal of an op-amp will be equal to the voltage ampoifier its non-inverting input terminal.

## logarthmic, anti logarthmic amplifiers

If you have any comments or suggestions please use our contact page We strictly ignore emails regarding post helps or explanation of circuits and projects ; for those purpose please use our comment feature ; We will surely help you by replying to your comment; It may helps other too. Two 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.

Applying KCL at inverting node of opamp we get. Gain of Anti log amplifier. You May Also Like.

Easy Electronic Projects 5. Gain of logarithmic amplifier. Now putting the value of collector current of transistor I C in equation 1. The electronic circuits which perform the mathematical operations such as logarithm and anti-logarithm exponential with an amplification are called as Logarithmic anilog and Anti-Logarithmic amplifier respectively. Project Using and 4. Since the non inverting terminal of opamp is at ground potential.

### logarthmic, anti logarthmic amplifiers | ECE Tutorials

Voltage at inverting pin of op-amp A1 is potentially equal to voltage at non-inverting input of op-amp i. The output is depending upon output current of transistor and feedback resistor.

Using the concept of virtual short between the input terminals of an opamp the voltage at inverting terminal will be zero volts. Assuming ampkifier diode and matched thus material constant, thermal voltage of diode and saturation current of diode is also same.

The circuit arrangement for Antilogarithmic amplifier is illustrated in figure 1. Thus, thermal voltage of 1 amlpifier 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.

### Antilogarithmic Amplifier | Derivation

The figure of anti-logarithm amplifier is shown in figure 3. A simple Anti log amplifier is shown below.

Your email address will not be published. This section discusses about the op-amp based logarithmic amplifier in detail. Complete Electrical Symbol 3. A resistor is connected in feedback path. The logarithmic circuit can be redrawn as follows. Hence applying KCL at inverting terminal of opamp, we get.