The positions of diode and resistance are exchanged as compared to log amplifier circuit. Logarithmic and antilogarithmic amplifiers electronics. A simple anti log amplifier is shown below anti logarithmic amplifier it is obvious from the circuit shown above that negative feedback is provided from output to inverting terminal. However, the feedback element used here is a bipolar junction transistor bjt. Antilog computation may require functions such as ln x, log x or sinhx. Operational amplifiers specialpurpose circuits equations. Computing powers and log ratios general description model 755 is a complete dc logarithmic amplifier consisting of an accurate temperature compensated antilog element, and a low bias current fet amplifier. The log amps output signal, which can represent a manydecade dynamic range of highfrequency input signal amplitudes by a relatively narrow range, is typically used to regulate gain. But the log of 0, to any base, approaches negative infinity. Apr 25, 2012 when working with a log amplifier that uses a diode as the log element, things get more complicated even than the math. Log and antilog amplifiers are nonlinear circuits in which the output voltage is proportional to the logarithm or exponent of the input. The baseemitter junction of a bjt responds similarly to a diode, so the analysis for this circuit is similar to the diode log amplifier.
This type of log amp can be considered to be a video amp with a logarithmic characteristic, and may be known as a logarithmic video log video amplifier or, sometimes, a true log amp. Since the log function is nonlinear, it is clear that. Anti log or exponential generation is simply a matter of rearranging the logarithmic circuitry. Observe that we got the above circuit diagram of active band stop filter by replacing the blocks with the respective circuit diagrams in the block diagram of an active band stop filter. Finally, its the antilog, or exponential amplifier. 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. Aug 10, 2019 antilog amplifiers along with log amplifiers are used to perform analogue computations on the input signals. May 29, 2018 in this video, the log and antilog amplifier circuits using opamp and their applications have been discussed. Jan 18, 2020 then verify your design specs with sweeping voltages on the inputs and compute the gain and offset errors vs input.
Logarithm of a number is defined as the exponent to which another fixed value, the base, must be raised to produce that number. The circuit diagram of basic antilog amplifier using diode is shown in the fig. The circuit diagram below shows the circuitry of the log converted to generate an exponential output from a linear input. There are two other issues with the circuit in figure 1. Logarithmic amplifier gives the output proportional to the logarithm of input signal. The differential input amplifier allows dualpolarity inputs, is selfcompensating for temperature variations, and is relatively insensitive to commonmode noise. The figure below shows a simple embodiment of the analog multiplier. Figure 1 shows an amplifier that provides a logarithmic output for a linear input current or voltage. In this video, the log and antilog amplifier circuits using op amp and their applications have been discussed. What values should be provided to the diode and transistor.
Increase the input voltage in the step of 1v up to 20v. The node a is grounded and hence node b is at virtual ground. I want to design and simulate the basic log amplifier and antilog amplifier circuits both using diode as well as transistor. Each pair is a 15db log subsection, and each input feeds two pairs, for a range of 30db. Anti logarithmic or exponential amplifier or simply antilog amplifier is an op amp circuit configuration, whose output is proportional to the exponential value or antilog value of the input. Jan 22, 2019 antilog amplifiers along with log amplifiers are used to perform analogue computations on the input signals. The emitter of q2 in proportion to the input voltage. Antilog amplifiers along with log amplifiers are used to perform analogue computations on. Log antilog amplifiers pdf new pdf download service. Antilog amplifier does the exact opposite of a log amplifier. The circuit here a general purpose npn transistor is connected to inverting input of opamp. The circuit below is the antilog circuit, and it too is inverting so log and antilog can be cascaded directly. The following topics have been covered in this video. The classic example of this is using a log amp in an automatic gain control loop, to regulate the gain of a variablegain amplifier.
Comparator diagrams and opamp diagrams use the same symbols. There are several applications of log and antilog amplifiers. It is relatively temperature insensitive and not subject to the bias current errors plague most multipliers and circumvents many problems related to the logantilog circuit. Ic log amps may cost about ten times the components needed to build a discretecomponent log amp. Nevertheless, it is quite important not to forget the sign of the signal. The circuit of an antilog amplifier using opamp is shown in the figure below. Be aware that the log response of your circuit is temperature dependent.
A log amplifier is an amplifier for which the output voltage v out is k times the natural log of the input voltage v in. Logarithmic amplifier an overview sciencedirect topics. Basic antilog amplifier using diode as follows the circuit diagram of basic antilog amplifier using diode is shown in the fig. Jan 04, 2020 antilog is inverse operation of log operation so. Antilogarithmic amplifier ic with antilog element in input. Figure 1 shows an amplifier that provides a logarithmic output for a linear. Here is a simple analog multiplier provides three quadrant analog multiplication. It is well known that some processes such as multiplication and division, can be performed by addition and subtraction of logs. Log amplifier is a linear circuit in which the output voltage will be a constant times the natural logarithm of the input. The thing to keep in mind is that, even ideally, this amplifier is not taking the log of the input voltage, it is taking the log of the input voltage divided by the product of the thermal voltage and the input resistance and then multiplying that the log of all that stuff by the negative of the thermal voltage. This circuit provides three quadrant analog multiplication which is relatively temperature insensitive and which is not subject to the bias current errors which is plague most multipliers and circumvents many of the problems associated with the logantilog circuit. In this video, the log and antilog amplifier circuits using opamp and their applications have been discussed. Log antilog log and antilog ampllifier circuits include the same elements but arranged in different feedback configurations.
For analog computation to have any repeatability, you will need to use something like the op amp collection circuit with temperature compensation. Since the non inverting terminal of opamp is at ground potential. In most cases a comparator is implemented using a dedicated comparator ic, but opamps may be used as an alternative. We have already seen the circuit diagrams of an active low pass filter, an active high pass filter and a summing amplifier. Log and antilog are important circuits in what is called analog multiplicationcomputation. Although logarithmic the output has the wrong sign for strict correctness. Using the concept of virtual short between the input terminals of an opamp the voltage at inverting terminal will be zero volts. Amplifier circuits electronic circuits and diagram. These can be performed continusely with log amps, and also used for direct db display on a. Unlike the normal digital computers you see these days, the analog. Log and antilog amplifiers explained applications of log. Simulating basic log amplifier and antilog amplifier using. Mar 15, 2020 antilog is inverse operation of log operation so. Use log and antilog calculator to determine the logarithmic and antilogarithmic values with base values of 2 or e or 10.
Spice simulation of voltage multiplier using log and antilog. Input 2 x root of mean of squared value mean figure 2 rms conversion block diagram the, which is the equivalent of taking the square root in the linear domain. It is relatively temperature insensitive and not subject to the bias current errors plague most multipliers and circumvents many problems related to the log antilog circuit. The emitter of q2 in proportion to the input voltage is driven by amplifier a1 in conjunction with transistor q1. A log amplifier is commonly used to compress a signals largeamplitude dynamic range into something more manageable by other circuits such as adcs. Apr 18, 2019 antilog amplifier does the exact opposite of a log amplifier. Notice there is an analog multiplier circuit in there, too.
Antilog or exponential generation is simply a matter of rearranging the logarithmic circuitry. The circuit diagram of logarithmic amplifier is as shown below. For good results the operational amplifier should be a premium part with an input offset voltage well under 100 microvolts and an input bias current less than a few hundred picoamperes. Analog multiplier circuit schematic diagram circuit wiring. This section discusses about the opamp based logarithmic amplifier in detail. Antilog amplifiers along with log amplifiers are used to perform analogue computations on the input signals. Basic antilog amplifier using diode the circuit diagram of basic antilog. If you find a way to use bc547 for the antilog function, this circuit ought to work in simulation. There are many important nonlinear amplifier circuits, including the log amplifier and the antilog amplifier.
One operation can be that, these log and antilog amps can be used for making multipliers. Note that if you put in 0v, then you would have zero current through the diode and,ideally, 0v at the output. They have numerous applications in electronics, such as. The basic output equation of a log amplifier is v vout k ln vinvref. These can be performed continusely with log amps, and also used for direct db display on a digital voltmeter and spectrum analyzer. Similarly for antilog amplifier v 0 r f i s circuit diagram. Then verify your design specs with sweeping voltages on the inputs and compute the gain and offset errors vs input.
94 751 1186 1348 641 515 445 803 191 1436 440 314 289 1456 384 1251 979 129 1000 214 1420 762 98 1180 1260 366 143 825 313 232 476 372 624 1009 753 800 258 1434 614 706 1110 656 1371 868 997 1268