How much current would have to flow in diode-connected transistor Q4 for V+ to equal V- for U4? In this article, we will see the different antilog amplifier circuits, its working and antilog amplifier applications. $$=>V_{0}=-R_{f}I_{f}.........Equation 4$$, We know that the equation for the current flowing through a diode, when it is in forward bias, is as given below −, $$I_{f}=I_{s} e^{\left(\frac{V_f}{nV_T}\right)}$$, Substituting the value of $I_{f}$ in Equation 4, we get, $$V_{0}=-R_{f}\left \{{I_{s} e^{\left(\frac{V_f}{nV_T}\right)}}\right \}$$, $$V_{0}=-R_{f}{I_{s} e^{\left(\frac{V_f}{nV_T}\right)}}......Equation 5$$, The KVL equation at the input side of the inverting terminal of the op amp will be, Substituting, the value of in the Equation 5, we get −, $$V_{0}=-R_{f}{I_{s} e^{\left(\frac{V_i}{nV_T}\right)}}$$. \$\endgroup\$ – … Banking on our enriched industry experience, we are able to offer a wide gamut of Log and Antilog Amplifier.These high performing Log and Antilog Amplifiers offered by us are non-linear circuits, in which the output voltage is proportional to the logarithm (or exponent) of the input.We take into account the ever changing requirements of different industries and offer innovative range of products. This is the Multiple Choice Questions in Special-Purpose Op-Amp Circuits from the book Electronic Devices – Electron Flow Version and Conventional Current Version 8th Edition by Thomas L. Floyd. Time and Work Formula and Solved Problems. Therefore, the op-amp based anti-logarithmic amplifier circuit discussed above will produce an output, which is proportional to the anti-natural logarithm (exponential) of the input voltage ${V_i}$ when, ${R_fI_s}= 1V$. Log Amplifier using a Single Diode and Op-Amp. From log a a = 1 we have that a 1 = a, which is true for any real number a. Basics of Integrated Circuits Applications. Output : Natural logarithm of 14 is : 2.6390573296152584 Logarithm base 5 of 14 is : 1.6397385131955606 2. log2(a) : This function is used to compute the logarithm base 2 of a. In this article, we will see the different log amplifier circuits, its working and log amplifier applications. A basic anti-log amplifier is shown in Figure \(\PageIndex{3}\). d) 1.214(kT/q)v Answer Questions and Earn Points !!! $V_{T}$ is the diode’s thermal equivalent voltage. View Answer, 3. View Answer, 6. This goes into anti log amp U4. Log and Antilog Amplifier. Anti-logarithmic or exponential amplifier (or simply antilog amplifier) is an op-amp circuit configuration, whose output is proportional to the exponential value or anti-log value of the input. In order to crack any major entrance test, aspirants need to practice solving logarithm questions. Negative voltages or currents can be first rectified and then applied to the log amp, but this adds the errors from the rectifier. The derivation of the input/output Equation is similar to the log … Hence, equate the right hand side term of those two equations as shown below −, $$\frac{V_i}{R_1}=I_{s}e^{\left(\frac{-V_0}{nV_T}\right)}$$, $$\frac{V_i}{R_1I_s}= e^{\left(\frac{-V_0}{nV_T}\right)}$$, Applying natural logarithm on both sides, we get −, $$In\left(\frac{V_i}{R_1I_s}\right)= \frac{-V_0}{nV_T}$$, $$V_{0}=-{nV_T}In\left(\frac{V_i}{R_1I_s}\right)$$. The operational amplifier circuit configurations which can perform mathematical operations such as log and antilog (exponential), including an amplification of the input signal provided to the circuit, are known as Logarithmic amplifier and Antilogarithmic amplifier respectively. Find the circuit used for compensating dependency of temperature in the output voltage? How to provide saturation current and temperature compensation in log-amp? Observe that the output voltage ${V_0}$ is having a negative sign, which indicates that there exists a 1800 phase difference between the input and the output. Participate in the Sanfoundry Certification contest to get free Certificate of Merit. The log amp gives an indication of the instant-by-instant low-frequency changes in the envelope, or amplitude, of the signal in the log domain in the same way that a digital voltmeter, set to "ac volts", gives a steady (linear) reading when the input is connected to a constant amplitude sinewave and follows any adjustments to the amplitude. 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. They have numerous applications in electronics, such as: c) Applying input and reference voltage to separate log-amps Anti log amplifier is one which provides output proportional to the antilog i.e. In other words, if by = x then y is the logarithm of x to base b. c) VO = -(kT/q)×ln(Vref/Vi) exponential to the input voltage. That means zero volts is applied at the non-inverting input terminal of the op-amp. So, the voltage at the inverting input terminal will be zero volts. • It is well known that some processes such as multiplication and division, can be performed by addition and subtraction of logs. 293-321 I ntroduction Log and Antilog Amplifiers are non-linear circuits in which the output voltage is proportional to the logarithm (or exponent) of the input. According to the virtual short concept, the voltage at the inverting input terminal of op-amp will be equal to the voltage present at its non-inverting input terminal. Find the output voltage of the log-amp? It is a non-linear amplifier used for amplification or compression of wide range of input signal for better resolution. C. 10. b) 0.597(kT/q)v The circuit diagram of an op-amp based logarithmic amplifier is shown in the following figure −. In the circuit shown above, the non-inverting input terminal of the op-amp is connected to ground. $V_{f}$ is the voltage drop across diode, when it is in forward bias. c) 0.405(kT/q)v An antilog amplifier has a _____ in series with the input. 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. © 2011-2021 Sanfoundry. here is complete set of 1000+ Multiple Choice Questions and Answers, Prev - Linear Integrated Circuit Questions and Answers – Very High Input Impedance Circuit, Next - Linear Integrated Circuit Questions and Answers – Multiplier and Divider – 1, Linear Integrated Circuit Questions and Answers – Very High Input Impedance Circuit, Linear Integrated Circuit Questions and Answers – Multiplier and Divider – 1, Chemical Engineering Questions and Answers, Electrical Measurements Questions and Answers, Instrumentation Transducers Questions and Answers, Design of Electrical Machines Questions and Answers, Electrical Machines Questions and Answers, Wireless & Mobile Communications Questions & Answers, Electronic Devices and Circuits Questions and Answers, Basic Electrical Engineering Questions and Answers, Linear Integrated Circuits Questions and Answers, Linear Integrated Circuit Questions and Answers – Input Bias Current, Linear Integrated Circuit Questions and Answers – Basic DAC Techniques – 2, Linear Integrated Circuit Questions and Answers – Input Offset Current and Total Output Offset Voltage, Linear Integrated Circuit Questions and Answers – Instrumentation Amplifier – 2, Linear Integrated Circuit Questions and Answers – Peak Detector, Sampling & Hold Circuit and Absolute Value Output Circuit. 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