Antilog amplifiers along with log amplifiers are used to perform analogue computations on the input signals. The circuit of an antilog amplifier. But if diode current is too low then the OP Amp input offsets become Then finally choose a max temp difference of the log and antilog diodes. EXPERIMENT 8: Log and Antilog Amplifiers. Objectives: To understand the behavior of logarithmic and antilogarithmic amplifiers. Materials and Equipment.

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This chapter discusses about the Logarithmic amplifier and Anti-Logarithmic amplifier in detail.

So, the voltage at its inverting input terminal will loog zero volts. Consider the voltage-input transdiode. To investigate its stability, refer to the incremental model, where the BJT has been replaced by its common-base smallsignal model. The logarithmic circuit can be redrawn as follows. Home Questions Tags Users Unanswered.

Linear Integrated Circuits Applications Log And Anti Log Amplifiers

Then, by taking the antilogarithm, you get the product of the two input voltages as indicated in the following equations: Then a properly working multiplier should give you 20 volts out. Since the non inverting terminal of opamp is at ground potential.


Gain of Anti log amplifier. One usually starts with a spec for Input and Output voltage range and max error vs input. It is well lkg that some processes such as multiplication and division, can be performed by addition and subtraction of logs. A simple Anti log amplifier is shown below.

The final output is developed by an inverting amplifier with a voltage gain of —K2. As such, they can vary over a wide range of values. Documents Flashcards Grammar checker. An op-amp based anti-logarithmic amplifier produces amplicier voltage at the output, which is proportional to the anti-logarithm of the voltage that is applied to the diode connected to its inverting terminal. Then determines the required input bias current and offset must be to achieve this.

Log and AntiLog Amplifiers

Negative voltages or currents can be first rectified and then applied to the log amp, but this adds the errors from the rectifier. Very similar question from a month ago: That means zero volts is applied at the non-inverting input terminal of the op-amp.

By summing the outputs of two log amplifiers, you get the logarithm of the product of the two original input voltages. Does this seem reasonable?

Leave a Reply Cancel reply Your email address will not be published. It is obvious from the circuit shown above that negative feedback is provided from output to inverting terminal. So, the voltage at the inverting input terminal will be zero volts. IC log amps may cost about ten times the components needed to build a discrete-component log amp.


It is called four-quadrant since inputs and output can be positive or negative. But if diode current is too low then the OP Amp input offsets become significant compared the the log1, log2 outputs. D1 protects the base-emitter junction from excessive reverse voltages.

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. The circuit diagram of logarithmic amplifier is as shown below. Gain of logarithmic amplifier. You’ve simulated it, so why do you ask if it works for you?

Please think about what you are doing in your simulation. I know there is problem with the last stage, the last opamp should give me gain: