Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [log-amplifier]

Logarithmic amplifier ("Log Amp").

A logarithmic amplifier ("Log Amp") provides high sensitivity for low amplitude input signals and gradually reduced sensitivity for higher amplitude signals, making the best use of the dynamic range for signals that follow the natural logarithm function. It requires non-zero, non-negative input.

Circuits typically use an op-amp with a feedback element having a PN junction (such as a diode or an NPN BJT transistor).

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LM394 is obsolete. What is the new standard log amp circuit?

The traditional logarithmic amplifier circuit is described in National Appnote 311: This circuit uses the difference of two transistor currents to generate the log of the input over a pretty wide range. The well-matched transistor pair Q1a and Q1b…
markrages
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Can I compress the dynamic range of ns pulses to better fit ADC range using log amp or mixer?

I have an experiment in which the signal I want to measure is a 1 ns pulse that occurs somewhere around 0-100 ns after a trigger. I want to digitize the pulses to extract the time they occurred and the amplitude. The problem is the amplitude of the…
argentum2f
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Logarithmic amplifier with high slew rate -- mutually exclusive?

Does anyone know if the basic construction of a log amp (with a diode or BJT providing feedback from output to input) is in conflict with any ability to reach high slew rates? I've been looking (octopart, digikey, mouser) for a logarithmic amplifier…
stevegt
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How to increase max input current of logarithmic amplifier 10x-100x safely?

Is it possible to increase max allowed current of logarithmic amplifier to say 1A by some workaround without loosing capabilities in lower range: 0..1ma ? For example the TI part LOG112 has few milliampere input current limit. Obviously, 2 parts can…
user924
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Log amplifier with vacuum tubes

Is there a way to build a log amplifier using vacuum tubes? I would like to have a VU meter (with the proper log response,) but do not want to use solid state components. The output would be to an IN-13 neon indicator which has a linear response…
Pentium100
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Simulation of log configuration for op-amp

I'm quite new to pspice and I'm trying to simulate the dc transfer function of an op-amp in log configuration. Here my circuit. I'm using Kicad and ngspice: R3 and R4 are there because it gave me warnings about a singular matrix. I set the…
Mark
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Why does my diode log amplifier in LTspice not match theory?

I am trying to learn about analog multipliers, and I'm trying to implement one using a log-antilog design. I am currently having some difficulties with the log part because simulating an ideal amplifier gives results that are consistently about 0.4…
Paolo Celati
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Opamp detection of extremely tiny voltage

I am working on a project that requires measuring absorbance of a solution. The circuit consist of an emitter led, a photodiode attached to an opamp with \$10^7\$ gain (TIA). The solution absorbs light from the led and causes different voltages…
Totally New
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Resistor on pin 3 of a Log Amplifier

I'm trying to understand what's the function or R2 resistor in this transdiode log amp configuration. I suppose I've to match the right value to give in order to minimize the effect of input bias current. In a simple inverting configuration I'd put…
Brontolo
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Fine tuning of anti-log op-amp for LED driving

I have a 10-bit DAC that outputs a voltage between 0 and 3V. This signal controls a current-driver for LEDs. I need to compensate the "log" behavior of the LEDs, otherwise the first steps are too much different than the last ones. And, more…
Mark
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Multiplier and divisor using logarithmic and anti-logarithmic op-amps, issue with output

I was tasked to make 4 processes using operational amplifiers: adding, substraction, multiplication, and division. However, only the add and substract operations work: whenever I try to multiplicate or divide MultiSim shows very different values to…
JCorona98
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Analog multiplier using logarithmic and anti-logarithmic opamp output problem

I'm trying to build a analog multiplier that takes in two voltages and produces the product of them. I have tried to simulate a circuit. Simulation with this methods is part of the objectives in the project. However the output doesn't even go as I…
Maulana Falithurrahman
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Sound pressure to db analog

I'm trying to convert an amplified microphone output (it is from 0-5v, biased at 2.5v) to a linear response that correlates with db SPL. From my research, the output of the microphone directly correlates to the sound pressure, which is all fine, but…
Warrick
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AD8304 strange behaviour with low current

I am currently experiencing a strange behaviour from my AD8304. I am using the AD8304 evalboard (the evalboard is described on pages 18 and 19 of the datasheet). To test it, I had connected a Keithley current source to the input and a voltmeter to…
verfelixt
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Simulating voltage divider?

Over the past weeks, I've been looking into an analog method of dividing 2 voltages such that V1/V2=Vout. I found many sources on Google using methods like log and antilog amplifiers or a multiplier, but every time I model one in Falstad or…
Wrig Nine
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