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Amplifier Circuits:  Logarithmic
Amplifier -- Main Page          Math Functions -- Main Page

Logarithmic Amplifiers:  #'s - H        I - Z

Last Updated: October 10, 2017 02:34 PM

Circuits Designed by Dave Johnson, P.E. :

Indicate DC Current Flow    -  The circuit below is a simple way to indicate when DC current is flowing through a wire.  The circuit is designed so it will turn on a LED indicator light, whenever the voltage drop across a shunt resistor exceeds about 0.1volts.  The value of the resist . . . Hobby Circuit designed by David A. Johnson P.E.-October 16, 2005

Indicates Battery Charge Current    -  This circuit turns on a LED whenever it detects at least 25ma of battery charge current . . . Hobby Circuit designed by Dave Johnson P.E.-July 23, 2006

Indicator for Acceptable Voltage    -  I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed.  The circuit can also be used to adjust a particular voltage be within specific high or low limits.  The three LEDs will indicate if the voltage is . . . Hobby Circuit designed by David A. Johnson P.E.-February 09, 2002
Precision AC Peak Detector    -  This unique circuit uses a very inexpensive voltage comparator to form a peak detector.  The DC voltage produced tracks the positive peak of the input signal.  It works from about ten millivolts to about 10 volts peak to peak.  The maximum frequency is about . . . Circuit by Dave Johnson P.E.-February 11, 2002

Version 4 of a DC Current Indicator    -  The circuit below uses some common components to turn on an LED whenever DC current above a certain level is detected.  The circuit uses a very popular LM393 dual voltage comparator from National Semiconductor and a common 1N4148 signal diode.  The diode . . . Hobby Circuit designed by Dave Johnson P.E.-December 15, 2008

Wide Band Zero Cross Detector    -  This circuit was designed to convert a low amplitude 40KHz signal into a clean square wave signal.  It will work with inputs as small as 5mv peak-to-peak or as large as 3 volts peak to peak.  The input frequency can range from a few kilohertz to about 150 . . . Circuit by David A. Johnson P.E.-July 18, 2000

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Indicate DC Current Flow -  The circuit below is a simple way to indicate when DC current is flowing through a wire.  The circuit is designed so it will turn on a LED indicator light, whenever the voltage drop across a shunt resistor exceeds about 0.1volts.  The value of the resist . . . Hobby Circuit designed by David A. Johnson P.E.-October, 2005

Indicates Battery Charge Current -  This circuit turns on a LED whenever it detects at least 25ma of battery charge current . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Indicator for Acceptable Voltage -  I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed.  The circuit can also be used to adjust a particular voltage be within specific high or low limits.  The three LEDs will indicate if the voltage is . . . Hobby Circuit designed by David A. Johnson P.E.-February, 2002

Linear potentiometer provides nonlinear light intensity control -  04/28/05  EDN-Design Ideas __ Circuit matches light control to eye’s intensity-response curve __ Circuit Design by Stephan Goldstein, Analog Devices, Wilmington, MA

Log Amp uses capacitor-charging law -  01/10/02 EDN-Design Ideas The novel logarithmic amplifier in Figure 1 relies on the exponential charging characteristics of a simple RC circuit.  The expression for the time, T, required for a capacitor, C, to reach a voltage (VIN–VK) from 0V, when charged through a resistor, R, with an applied voltage of VIN, is VIN–VK=VIN (1–e–T/RC), where VK is a fixed voltage.  The expression for T reduces to T=RCln(VIN/VK), clearly showing an inherent logarithmic characteristic. __ Circuit Design by Jayashree Raghuraman and Ajoy Raman, Aeronautical Development Establishment, Bangalore, India

Mathcad Functions Perform Log Interpolation -  30-Oct-03 EDN-Design Ideas MathCAD provIdeas a number of interpolation and curve-fitting functions, so that, given a set of X-Y data points, you can estimate the Y value for any given X coordinate.  Unfortunately, these functions work poorly with data that is to be displayed in a nonlinear(logarithmic] manner.  Examples of these functions are  Using the built-in "linterp" function, MathCAD estimates and plots the data(Fig __ Circuit Design by James Bach, Delphi Delco Electronics Systems, Kokomo, IN

Microcontroller drives logarithmic/linear dot/bar 20-LED display -  01/18/07  EDN-Design Ideas Do-it-yourself analog-to-LM3914 display driver offers user programmability __ Circuit Design by Dhananjay V Gadre and Anurag Chugh, Netaji Subhas Institute of Technology, New Delhi, India

Mixed Signal Algorithm Tests Transducers -  04/24/97 EDN-Design Ideas A simple test procedure (Reference 1) allows you to measure damping coefficient beta in electromechanical transducers, such as speakers, microphones, and seismic geophones.  The method is based on stimulating the transducer with a dc step current, IS, and then separately integrating the positive and negative half-waves of the transducer's terminal voltage, V(t), after removing the step current.  The integrals of the positive and negative waveforms contain all the necessary information to calculate beta. __ Circuit Design by Alex Belousov, Rego Park, NY

Model fixed-point DSP arithmetic in C -  03/18/99 EDN-Design Ideas NOTE :  Page includes several designs.  Scroll to find this one.  You can run initial high-level simulations of custom numerical algorithms, such as digital filters, using floating-point numbers in an environment such as C or Matlab.  Unfortunately, you won't see include fixed-point effects, such as truncation due to limited precision and register overflow, until you use a Hardware Design Language (HDL), such as Verilog or VHDL.  However, a technique that models these effects in C—the function "bit_limit" in Listing 1—provIdeas faster execution and better portability than HDLs and allows early exploration of the trade-off between bus width and performance. __ Circuit Design by Roger Maher, SSL Ltd, Dublin, Ireland

Motor-Drive Algorithm Saves Space & Cycle -  02/17/94 EDN-Design Ideas The algorithm embodied in the second subroutine in Listing 1  generates the excitation sequence for most permanent-magnet and hybrid stepper motors.  This subroutine is smaller than subroutines that spring from other algorithms __ Circuit Design by Jose A P Machado da Silva, University of Porto, Porto, Portugal

PIC µC implements CRC-16 algorithm -  02/18/99 EDN-Design Ideas NOTE :  Page includes several designs.  Scroll to find this one.  Detecting errors in serial data can be paramount in completing an embedded-control design.  Determining which algorithm to use for detecting serial-communications errors depends on several factors.  Ideally, the method should require minimal hardware and little computational power from your processor and still provide high-level protection against undetected data errors.  The cyclic redundancy check NOTE :  CRC] __ Circuit Design by Lon Glastner, Solutions Cubed, Chilo, CA

Polarization Dependent Loss Measurements of Passive Optical Components -  Application Note __ Aligent

Precision AC Peak Detector -  This unique circuit uses a very inexpensive voltage comparator to form a peak detector.  The DC voltage produced tracks the positive peak of the input signal.  It works from about ten millivolts to about 10 volts peak to peak.  The maximum frequency is about. . . Circuit by Dave Johnson P.E.-February, 2002

Primer on binary arithmetic rounding -  01/21/99 EDN-Design Ideas NOTE : Page includes several designs.  Scroll to find this one.   As digital communications and data compression/decompression proliferate, signal-processing functions grow in importance.  Whether you’re dealing with hard-wired logic or programmable engines, an understanding of binary-arithmetic rounding is important in getting correct and consistent results.  Before we discuss rounding, consider a binary number(Figure 1) Page includes several designs.  Scroll to find this one __ Circuit Design by Tom Balph, Motorola SPS, Tempe, AZ

Rapid Prototyping Speeds Development of UMTS W-CDMA Algorithms -  Application Note __ Aligent

Routine yields fast bit reversing for DSP algorithms -  09/13/01 EDN-Design Ideas If you need efficient real-time performance in DSP applications, you need an efficient bit-reversing routine.  For several FFT programs, data permutation can take 10 to 50% of the computation time, depending on the input-data dimensions and length.  The idea behind bit reversing is to shuffle the data by flipping the address bits around the middle of the address length so that if the data l __ Circuit Design by Mohammed Aziz, University of Leeds, UK

Simple Circuit Algorithm Nulls DC Offsets In DS -  09/15/94 EDN-Design Ideas One problem associated with converting analog signals to digital samples is ensuring that the zero level of an analog signal   (minus its dc offset, if any) converts to a digital sample of exactly zero.  If the analog signal's zero level does not convert exactly, the converted samples retain a residual dc component, complicating processing. __ Circuit Design by V Solovyov, Rossiya, Russia

Simple Circuit algorithm transforms filter coefficients -  01/21/99 EDN-Design Ideas To synthesize infinite-impulse-response(IIR]-filter functions, expressed as H(z], you commonly use analog prototype-filter functions, expressed as H(s], using the bilinear-z transform.  This operation entails some algebraic complexity in calculating the filter coefficients.  The simple algorithm shown here transforms the prototype-filter coefficients(W0, W1, W2]to the IIR digital-filter coefficients(U0, U1, U2].  These coefficients transform from Page includes several designs.  Scroll to find this one __ Circuit Design by Frank Vitaljic, Bellingham, WA

Single Stage Gives Logarithmic Gain Step -  03-Mar-94 EDN-Design Ideas By placing a variable component in the positive feedback loop of an op amp; you can vary the gain of the stage logarithmically with respect to a linear resistance or conductance. __ Circuit Design by Allen Windhorn, Reliance Electric, North Mankato, MN

Single-cycle logarithms & antilogs -  11/11/13  EDN-Design Ideas Here are some very fast log (and antilog) blocks well-suited to FPGA implementation __ Circuit Design by Michael Dunn

Software Calibrated, 1 MHz to 8 GHz, 60 DB RF Power Measurement System using the AD8318 Logarithmic Detector  -  Software Calibrated, 1 MHz to 8 GHz, 60 dB RF Power Measurement System Using the AD8318 Logarithmic Detector.  A calibration is performed by applying two known signal levels close to the endpoints of the AD8318 linear input range and measuring the corresponding output codes from the ADC.  This deviation is expressed in dB using the equation where CODE_OUT is the ADC output code; SLOPE_ADC is the stored ADC slope in codes/dB; INTERCEPT is the stored intercept; and PIN_TRUE is the exact (and unknown) input level.  , The plots shown in Figure 3 through Figure 8 show the typical system performance that can be obtained using the AD8318 and AD7887BR in an RF power measurement system. __ Analog Devices from the Lab

Software snippet provides improved subset-sum algorithm -  09/25/03  EDN-Design Ideas The subset-sum problem is one of the most frequently occurring NP(nondeterministic, polynomial-time]-complete] problems.  It asks whether a subset of numbers in a set of positive integers adds up exactly to a given value.  A relaxed version of the problem tries to identify a subset of numbers that adds up to a maximum value no greater than a given value __ Circuit Design by Ivan Basov, Brandeis University, Waltham, MA

State of the Art Characterization of Optical Components for Dwdm Applications -  Application Note __ Aligent

Transient Analysis -  One of the most complex and intriguing capabilities of the SPICE algorithm is the Transient Analysis.  How do we take a collection of resistive and energy-storage components, then find its time response to an arbitrary input waveform? Yes, you could formulate and solve the differential equations to get the response versus time, but SPICE is not a differential equation solver (spice design)

Versatile power-supply load uses light bulbs -  02/07/02 EDN-Design Ideas Improvising loads for bench-testing and designing power supplies is often a frustrating and sometimes hazardous experience.  When you push large power resistors to their limit, they tend to burn benches and melt solder connections.  Many electronic loads are on the market but are usually expensive and of laboratory-type precision and often represent overkill for the average designer __ Circuit Design by William Sloot, Computron Display Systems, Mount Prospect, IL

Version 4 of a DC Current Indicator -  The circuit below uses some common components to turn on an LED whenever DC current above a certain level is detected.  The circuit uses a very popular LM393 dual voltage comparator from National Semiconductor and a common 1N4148 signal diode.  The diode . . . Hobby Circuit designed by Dave Johnson P.E.-October, 2005

White LED driver provides 64 step logarithmic dimming -  10-Jun-04 EDN-Design Ideas The circuit of Figure 1 is designed for portable-power applications that require white LEDs with adjustable, logarithmic dimming levels.  The circuit drives as many as four white LEDs from a 3.3V source and adjusts the total LED current from 1 to 106 mA in 64 steps of 1 dB each.  The driver is a charge pump that mirrors the current ISET(sourced from IC3's SET terminal] to produce a current o __ Circuit Design by William Hadden, Maxim Integrated Products, Sunnyvale, CA

Wide Band Zero Cross Detector -  This circuit was designed to convert a low amplitude 40KHz signal into a clean square wave signal.  It will work with inputs as small as 5mv peak-to-peak or as large as 3 volts peak to peak.  The input frequency can range from a few kilohertz to about 150. . . Circuit by David A. Johnson P.E.-February, 2006


Logarithmic Amplifiers:  #'s - H        I - Z

 


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