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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Antilogarithmic amplifier is one whose output is antilogarithmic exponential of input. Like logarithmic amplifierantilogarithmic is also a non-linear amplifier. The circuit arrangement for Antilogarithmic amplifier is illustrated in figure 1.

Log And Anti Log Amplifiers

Here a general purpose NPN transistor is connected to inverting input of op-amp. A resistor is connected in feedback path.

The output is depending upon output current of transistor and feedback resistor. As we know that.


Thus, we can write. Now putting the value of collector current of transistor I C in equation 1. The output voltage expression becomes.

From the figure we can also conclude that transistor base emitter voltage V BE is equivalent input voltage V i i. The figure of anti-logarithmic amplifier using matched diode is shown in figure below. 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 antklog bias mood as shown in figure 2. Voltage at inverting pin of op-amp A1 is potentially equal to voltage at non-inverting input of op-amp i.

Assuming both diode and matched thus material constant, thermal voltage of diode and saturation current of diode is also same. The figure of anti-logarithm amplifier is shown in figure 3. 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.

Antilogarithmic Amplifier | Derivation

Assuming both transistors are matched. Thus, thermal voltage of 1 st transistor will be same to thermal voltage of 2 nd transistor and saturation current of 1 ap transistor will be equal to saturation current of 2 nd transistor.


As we know that is very small.

Thus we can write. I edit and author this site. You can connect with me on: Google Plus and Facebook.

Linear Integrated Circuits Applications Log And Anti Log Amplifiers

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