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Amplifier Circuits:  Variable Gain
Amplifier -- Main Page

Variable Gain Amplifiers:  #'s - K      L - Z

Last Updated: June 02, 2021 01:44 PM

Circuits Designed by Dave Johnson, P.E. :
0VAC to 280VAC Variable Isolated AC Voltage -  I designed and built this circuit about 25 years ago.  It came in handy for many projects that were powered from 120 VAC, 240 VAC and 277 VAC.  It provides complete isolation from the power line.  It uses two 1:1 isolation transformers that are wired in parallel . . . Hobby Circuit designed by Dave Johnson P.E.-July 8, 2000

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


0A to 2A Current Source -  The LT1995 amplifies the sense resistor drop by 5V/V and subtracts that from VIN, providing an error signal to an LT1880 integrator.  The integrated error drives the PMOSFET as required to deliver the commanded current. __ Linear Technology/Analog Devices App Note, Mar 31, 2010

0VAC to 280VAC Variable Isolated AC Voltage -  I designed and built this circuit about 25 years ago.  It came in handy for many projects that were powered from 120 VAC, 240 VAC and 277 VAC.  It provides complete isolation from the power line.  It uses two 1:1 isolation transformers that are wired in parallel . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2000

1 IC Provides Gains of 10 & –10 -  08/07/03  EDN-Design Ideas Real-world data-acquisition systems require amplifying weak signals to match the full-scale input range of an A/D converter.  Unfortunately, when you configure them as gain blocks, most common amplifiers have both gain errors and off__ Circuit Design by Moshe Gerstenhaber and Charles Kitchin, Analog Devices, Wilmington, MA

1A Variable Regulated Power Supply -  A 'must-have' for the experimenter. __ Designed by Peter Parker VK3YE

Balanced Frequency Converter (Suitable for Frequencies up to 50kHz) -  This circuit takes advantage of aliasing that occurs in any time sampled system.  The output signal frequency is the difference in frequency between the input signal and the switch sampling rate.  A 24KHz input signal sampled at 25KHz will be converted to a 1KHz output signal.  In addition by using the LTC1992 fully differential __ Linear Technology/Analog Devices App Note, Mar 16th 2010

Bidirectional Current Source -  The LT1990 is a differential amplifier with integrated precision resistors.  The circuit shown is the classic Howland current source, implemented by simply adding a sense resistor. __ Linear Technology/Analog Devices App Note, Mar 31, 2010

Bipolar, Ground Referenced, Single-Ended Signal Interface to Unipolar, Differential Input ADC -  Differential amplifiers are useful for providing the input to a single supply differential ADC from a bipolar ground referenced input source.  All of the signal level shifting and gain requirements can be adjusted with external resistors. __ Linear Technology/Analog Devices App Note, Mar 16th 2010

Digitally Control Gain over a ±40 DB Range -  09/12/97 EDN-Design Ideas Digitally controlled amplifiers typically take the form of programmable-gain amplifiers (PGAs).  Though useful for many applications, PGAs have the disadvantage of large, discrete gain steps, such as gains of 1, 2, 4, and 8.  For higher resolution gain steps, you must use a different approach.  The circuit in Figure 1 can digitally control an amplifier's gain over a ±40-dB range.  The circuit has a programmable-gain resolution of 1.25 dB and can attenuate or amplify the input signal, depending on the digital code you apply.  You could use this high-resolution PGA as the front end of an ADC and thus obtain increased dynamic range.  The circuit is also useful as a digitally controlled audio preamplifier.   __ Circuit Design by Mark Shill, Burr-Brown Corp, Tucson AZ

Digitally Programmable-Gain Amplifier Uses Divergent-Exponential Curve -  01/08/09  EDN-Design Ideas The divergent-exponential and negative time constants are the core concepts of the DENT (differential-divergent-exponential-negative-time-constant] digitally programmable-gain-amplifier topology__ Circuit Design by W Stephen Woodward, Chapel Hill, NC

Diode compensates distortion in Amplifier stage -  09/16/04 EDN-Design Ideas The voltage amplifier in Figure 1 exhibits smaller nonlinear distortion than does the conventional amplifier in Figure 2.  Diode D1 compensates for the distortion inherent in the npn transistor.  The voltage gain of a common-emitter amplifier depends on the transconductance of the transistor.  The transconductance of the bipolar transistor is as follows  where e is the charge of an electron,__ Circuit Design by Chekcheyev, Pridnestrovye State University, Moldova

Dual-Rail Variable DC Power Supply -  Simple add-on for a single-rail supply; ±2.5V to ±15V output __ Contact: Flavio Dellepiane, fladello @ tin.it

Find resistor values for arbitrary programmable-amplifier gains -  08/03/06  EDN-Design Ideas Roll your own custom programmable-gain amplifiers__ Circuit Design by Sid Levingston, DML Engineering Inc, Aloha, OR

Fixture Statically Tests Programmable-Gain Amplifiers -  06/26/08  EDN-Design Ideas Using a simple fixture having a common ground point, you can statically test digital gain-programmable amplifiers__ Circuit Design by Marián Štofka, Slovak University of Technology, Bratislava, Slovakia

Force/sense connection eliminates multiplexer on-resistance error -  22-Jan-04 EDN-Design Ideas Digitally controlled gain is an everyday analog-design element.  You frequently find this element in an op-amp-based, transimpedance current-to-voltage converter.  When you design digital gain control into such a converter, the usual scheme is to arrange things such that a digital multiplexer selects the appropriate feedback resistor for each gain figure__ Circuit Design by Stephen Woodward, Marine Sciences, Chapel Hill, NC

Full-Bridge Load Current Monitor -  The LT1990 is a micropower precision difference amplifier with a very high common mode input voltage range.  It has pin selectable gains of 1 or 10.  The LT1990 operates over a ±250V common mode voltage range on a ±15V supply.  The inputs are fault protected from common mode voltage transients up to ±350V and differential voltages __ Linear Technology/Analog Devices App Note, Apr 5th 2010

Full-Wave Active Rectifier Requires No Diodes -  A full-wave rectifier can be built without using any diodes.  It exploits the fact that the output voltage of certain single- supply op amps is effectively clamped to ground (0 V) when the input signal goes negative. __ Designed by Anthony H. Smith

Full-wave rectifier has programmable gain -  11/09/00 EDN-Design Ideas The traditional approach to the design of a full-wave rectifier(Figure 1) is to set the gains of IC1 and IC2 to 1 and use the.   PDF contains multiple circuits, scroll to find the one of interest__ Circuit Design by Chuck and Chris Wojslaw, Xicor Inc, Milpitas, CA

Gain-programmable offers performance & flexibility -  25-Nov-04 EDN-Design Ideas You can use a standard precision instrumentation amplifier, such as the INA118 or AD623, as a gain-programmable amplifier with high accuracy and wide gain range.  However, the gain range of such parts is fixed at certain values, limiting their flexibility.  To solve the problem, a usual way is to use a gain-adjustable circuit controlled by a microcomputer (Figure 1)__ Circuit Design by Luo Bencheng, Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences

High-Frequency VGA has Digital Control -  07/18/96  EDN-Design Ideas You can use variable-gain amplifiers (VGAs) in many types of systems, such as radio receivers, in which the input signal voltage depends on an uncontrolled variable, such as distance to the transmitter.  In this type of system, you can use a VGA to ensure that the input signal amplitude matches the input voltage range of key components, such as ADCs and DACs, thereby maximizing the converters' dynamic range.__ Circuit Design by Ron Mancini, Harris Semiconductor, Melbourne, FL

Instrumentation Amplifier extends DSO -  01/05/06 EDN-Design Ideas Elusive current waveforms required scope documentation.  To determine the specifications of a solar-generating plant, I needed to accurately measure the load current a product consumed.  The product switched several internal devices on and off during an interval of several seconds.  An ammeter showed that the current transitions occurred too quickly for visual logging, and my managers had requested an oscilloscope photo of the current waveform's peaks__ Circuit Design by Bob Perrin, Sacramento, CA

Variable Gain Amplifiers:  #'s - K      L - Z

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