Express log 4 (10) in terms of b.; Simplify without calculator: log 6 (216) + [ log(42) - log(6) ] / log(49) b) VO = Vref+(10-k’vi) a) VO = Vref/(10-k’vi) Sanfoundry Global Education & Learning Series – Linear Integrated Circuits. You are allowed to answer only once per question. Negative voltages or currents can be first rectified and then applied to the log amp, but this adds the errors from the rectifier. Join our social networks below and stay updated with latest contests, videos, internships and jobs! The circuit diagram of an op-amp based logarithmic amplifier is shown in the following figure −. https://www.theengineeringknowledge.com/log-and-antilog-amplifiers 1. 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. a) VO = -(kT)×ln(Vi/Vref) Antilog amplifier does the exact opposite of a log amplifier. 1. This section discusses about the op-amp based logarithmic amplifier in detail. Which of the following functions does the antilog computation required to perform continuously with log-amps? If V in is the input signal applied to a Anti log amplifier then the output is V o = K * exp (a * V i) where K is proportionality constant, a is constant. A logarithm of a number is the power to which a given base must be raised to obtain that number. 1) ... What part of the characteristic curve of a diode is useful for log amplifiers? View Answer, 4. $V_{T}$ is the diode’s thermal equivalent voltage. d) 1.214(kT/q)v Answer & Explanation Most Popular Articles. 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. a) In(x) c) 0.405(kT/q)v A. If in the logarithm the base is 10, then instead of log 10 we write lg. 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. 9. Though evolution of digital technology makes it easier to express real large numbers, but logarithm questions and solutions have not lost their relevance in the academic world. You may also like: Antilogarithmic Amplifier. b) VO = -(kT/q)×ln(Vi/Vref) The derivation of the input/output Equation is similar to the log … 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. Find the circuit that is used to compress the dynamic range of a signal? In the above circuit, the non-inverting input terminal of the op-amp is connected to ground. It can be used direct db display on spectrum analyzer. b) log(x) Calculate the base voltage of Q2 transistor in the log-amp using two op-amps? In other words, if by = x then y is the logarithm of x to base b. This goes into anti log amp U4. shorthand/stand for the repeated multiplication of a variable D. 4. c) 3.3v 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. If you are looking for a reviewer in Electronics Engineering this will definitely help. Therefore, the op-amp based logarithmic amplifier circuit discussed above will produce an output, which is proportional to the natural logarithm of the input voltage ${V_T}$, when ${R_1I_s}=1V$. Note that, in the above equation the parameters n, ${V_T}$ and $I_{s}$ are constants. This current then feeds $$R_f$$, which produces the output voltage. Basically it performs mathematical operation of an anti-logarithm. A current-to-voltage converter produces a A(n) ________ amplifier provides "a barrier" between the input and output for the protection of human life or sensitive equipment. This set of Linear Integrated Circuit Multiple Choice Questions & Answers (MCQs) focuses on “Log and Antilog Amplifier”. Output of summing amp U3 is 1.2V then. $$=>V_{0}=-R_{f}I_{f}.........Equation 4$$, 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 −, $$V_{0}=-R_{f}{I_{s} e^{\left(\frac{V_i}{nV_T}\right)}}$$. From log a a = 1 we have that a 1 = a, which is true for any real number a. Multiple Choice Questions and Answers on Amplifiers with Negative Feedback. a) Applying reference voltage alone to two different log-amps An op-amp based anti-logarithmic amplifier produces a 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. 7. You can now earn points by answering the unanswered questions listed. View Answer, 2. In this article, we will see the different log amplifier circuits, its working and log amplifier applications. Displays more accurate result than log(a,2). We would like to show you a description here but the site won’t allow us. How to provide saturation current and temperature compensation in log-amp? It is well known that some processes such as multiplication and division, can be performed by addition and subtraction of logs. To practice all areas of Linear Integrated Circuits, here is complete set of 1000+ Multiple Choice Questions and Answers. $V_{f}$ is the voltage drop across diode, when it is in forward bias. The compression of any wide-range input signal, analog computing circuits, linearization of exponential sources, such as transducers, certain types of audio circuits, compression and expansion circuits for voice communications. \$\endgroup\$ – … c) Sinh(x) Multiple Choice Questions and Answers on Op-Amp ( Operational Amplifier ) In addition to reading the questions and answers on my site, I would suggest you to check the following, on amazon, as well: Question Bank in Electronics & Communication Engineering by Prem R Chadha In addition to reading the questions and answers on my site, I would suggest you to check the following, on amazon, as well: Question Bank in Electronics & Communication Engineering by Prem R Chadha d) VO = (kT/q)×ln(Vi/Vref) Log amplifier or logarithmic amplifier is an electronic circuit that produces output that is proportional to the logarithm of the applied input. This section discusses about the op-amp based anti-logarithmic amplifier in detail. 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. If log 3 [log 2 (x 2 – 4x – 37)] = 1, where ‘x’ is a natural number, find the value of x. Please note that these amplifiers fall under non-linear applications. A basic anti-log amplifier is shown in Figure $$\PageIndex{3}$$. Log-Antilog Log and antilog amp circuits include the same elements but arranged in different feedback configurations. • It is well known that some processes such as multiplication and division, can be performed by addition and subtraction of logs. In order to crack any major entrance test, aspirants need to practice solving logarithm questions. An anti-logarithmic amplifier, or an anti-log amplifier, is an electronic circuit that produces an output that is proportional to the anti-logarithm of the applied input. Observe that the output voltage $V_{0}$ has a negative sign, which indicates that there exists a 1800 phase difference between the input and the output. The nodal equation at the inverting input terminal’s node is −, $$=>I_{f}=\frac{V_i}{R_1}......Equation 1$$, The following is the equation for current flowing through a diode, when it is in forward bias −, $$I_{f}=I_{s} e^{(\frac{V_f}{nV_T})} ......Equation 2$$. In the circuit shown above, the non-inverting input terminal of the op-amp is connected to ground. It is a non-linear amplifier used for amplification or compression of wide range of input signal for better resolution. b) Applying input and reference voltage to same log-amps 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, ${R_fI_s}= 1V$. In this article, we will see the different antilog amplifier circuits, its working and antilog amplifier applications. Questions on Logarithm and exponential with solutions, at the bottom of the page, are presented with detailed explanations.. According to the virtual short concept, the voltage at the inverting input terminal of an op-amp will be equal to the voltage at its non-inverting input terminal. Here, y > 0, b > 0, and b ≠ 1. Log and Antilog Amplifier. 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 −, $$In\left(\frac{V_i}{R_1I_s}\right)= \frac{-V_0}{nV_T}$$, $$V_{0}=-{nV_T}In\left(\frac{V_i}{R_1I_s}\right)$$. For example, if 24 = 16, then 4 is the logarithm of 16 with the base as 2. The input voltage, 6v and reference voltage, 4 v are applied to a log-amp with saturation current and temperature compensation. b) 0.597(kT/q)v An antilog amplifier has a _____ in series with the input. So, the output voltage ${V_0}$ will be proportional to the anti-natural logarithm (exponential) of the input voltage ${V_i}$, for a fixed value of feedback resistance ${R_f}$. log a 1 = 0 and log a a = 1. AntiLog amplifier or anti–logarithmic amplifier is an electronic circuit that produces output that is proportional to the anti-logarithm of the applied input. c) Applying input and reference voltage to separate log-amps Log Amplifier using a Single Diode and Op-Amp. 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. $I_{s}$ is the saturation current of the diode. b) 5.3v d) All of the mentioned A logarithmic amplifier, or a log amplifier, is an electronic circuit that produces an output that is proportional to the logarithm of the applied input. They have numerous applications in electronics, such as: d) None of the mentioned When we are solving some logarithm, any part can be unknown. The KVL equation around the feedback loop of the op amp will be −, Substituting the value of $V_{f}$ in Equation 2, we get −, $$I_{f}=I_{s} e^{\left(\frac{-V_0}{nV_T}\right)} ......Equation 3$$, Observe that the left hand side terms of both equation 1 and equation 3 are same. 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. a) 8.7v It means zero volts is applied to its non-inverting input terminal. How much current would have to flow in diode-connected transistor Q4 for V+ to equal V- for U4? Find the output voltage of the log-amplifier 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. B. The electronic circuits which perform the mathematical operations such as logarithm and anti-logarithm (exponential) with an amplification are called as Note that in the above equation, the parameters n, ${V_T}$ and $I_{s}$ are constants. This chapter discusses about the Logarithmic amplifier and Anti-Logarithmic amplifier in detail. So, the voltage at its inverting input terminal will be zero volts. Figure 2: Anti-logarithmic Amplifier IC with antilog element in input. Applications of Anti-logarithmic Amplifier IC. 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. 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. So, the output voltage $V_{0}$ will be proportional to the natural logarithm of the input voltage $V_{i}$ for a fixed value of resistance $R_{1}$. We can write it as 4 = log 2= 16. Anti log amplifier is one which provides output proportional to the antilog i.e. Find the output voltage of the log-amp? 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