Tag Archives: OPAMP

Sensing current on the high side


Michael Dunn@ edn.com discuss about current sense on the high side of power source.

At their heart, the majority of DC current sense circuits start with a resistance in a supply line (though magnetic field sensing is a good alternative, especially in higher-current scenarios). One simply measures the voltage drop across the resistor and scales it as desired to read current (E = I × R (if I didn’t include this, someone would complain)). If the sense resistor is in the ground leg, then the solution is a simple op-amp circuit. Everything stays referenced to ground, and you only have to be careful about small voltage drops in the ground layout.

Sensing current on the high side – [Link]

Lux Meter Module


LUX Meter project has been design to measure the illumination. Illumination is luminous flux falling on surface area of photo diode. This illumination converted to corresponding voltage using Op-Amp circuit.


  • Supply 9 VDC PP3 Battery @ 20 mA
  • Onboard Photo Diode
  • Onboard preset for calibration
  • Range selection via jumper 10mV/LUX, 1mV/LUX, 0.1mV/LUX
  • Interfacing is via berg connector
  • Power-On LED indicator
  • Four mounting holes of 3.2 mm each
  • PCB dimensions 53 mm x 38 mm

Lux Meter Module – [Link]

Increasing cable length in precision video applications


Maurizio tipped us about his latest article. In this article he talks about the different ways of transmitting video signal over large distances. He writes:

Traditionally, the physical environment for transmitting video signals over long distances has been the shielded coax cable. Its quality and advantages are well known, and many times designers looking for off-the-shelf solutions do not know that long distance video transmission can be achieved with the same quality but for a much lower price.

Increasing cable length in precision video applications – [Link]

Understanding silicon circuits: inside the ubiquitous 741 op amp


Ken Shirriff’s blog looks inside the famous 741 OPMAP and discuss how it’s made and how it’s working:

The 741 op amp is one of the most famous and popular ICs[1] with hundreds of millions sold since its invention in 1968 by famous IC designer Dave Fullagar. In this article, I look at the silicon die for the 741, discuss how it works, and explain how circuits are built from silicon.

Understanding silicon circuits: inside the ubiquitous 741 op amp – [Link]

Introduction to OPAMPs and Applications

Operational amplifiers (OPAMPs) are high performance differential amplifiers in integrated form that can be used in many different ways. A typical OPAMP has a non-inverting input, an inverting input, two dc power pins, one output pin and a few other fine-tuning pins. On the following image you can see a typical diagram of an operational amplifier.

The basic OPAMP operation is simple. If the voltage applied to the inverting input is greater than the voltage applied to the non-inverting input then the output saturates to the negative supply voltage. In addition, if the voltage applied to the non-inverting input is greater than the voltage applied to the inverting input, then the output saturates at positive supply voltage.

This operation mode is limited and doesn’t give us the full idea behind OPAMP operation. The trick to make an OPAMP more useful is to provide negative feedback from the output to the inverting input. In the image below we see an OPAMP with negative feedback working as an inverting amplifier.

In this configuration a part of the output voltage is fed back to the inverting input and thus the gain of the OPAMP can be controlled and output isn’t saturating. The gain of such an amplifier is controlled by the two resistors Rf and Rin. The minus means that the output is inverted relative to input.

By adding more components on the feedback loop, different OPAMP circuits can be made, such voltage regulator circuits, current to voltage converters, oscillators, filters etc.

Beside the negative feedback, a positive feedback can be used. This way the OPAMP is driven toward saturation and works in either +Vs or –Vs output range. Applications of positive feedback is on comparator circuits and oscillators. Continue reading Introduction to OPAMPs and Applications

Passive Infrared Detector Circuit

The infrared (IR) is invisible radiant energy, electromagnetic radiation that we cannot see with our eyes, but we can sometimes feel on our skin as heat. The infrared light falls just outside the visible spectrum, beyond the edge of what we can see as red. Most of the thermal radiation emitted by objects near room temperature is infrared.

The circuit uses a MCP6032 microchip operational amplifier. The MCP6032 operational amplifier (op amp) has a gain bandwidth of 10kHz with a low typical operating current of 900nA and an offset voltage that is less than 150uV. The MCP6032 uses Microchip’s advanced CMOS technology, which provides low bias current, high-speed operation, high open-loop gain and rail-to-rail input and output swing. The MCP6032 operates with a single supply voltage that can be as low as 1.8V, while drawing less than 1uA of quiescent current. The MCP6032 is available in standard 8-lead SOIC and MSOP packages. It also includes, a PID20 integrated circuit and a few electronic components. The size of the output signal of PID20 is determined by the task at pins 3 and 4. The output signal at pin 3 is compared with a reference voltage equal to half the supply voltage. The reference voltage is taken from the voltage divider R2-R3-R4-R5. When approaching an object warmer than the surrounding environment, or to remove an object colder than the environment, the output voltage increases. The variation of the sensor output will be compared, the IC2a and IC2b, located voltage of 0.5V under and over voltage reference respectively. Depending on the output, one of the comparators calculates and activates T1.

This basic circuit is used in night-vision devices with infrared illumination, which allows people or animals to be observed without the observer being detected. The infrared light is also used in industrial, scientific, and medical applications as well as in consumer devices.

Passive Infrared Detector Circuit – [Link]

Build an op amp with three discrete transistors


by Lyle Russell Williams:

You can use three discrete transistors to build an operational amplifier with an open-loop gain greater than 1 million (Figure 1). You bias the output at approximately one-half the supply voltage using the combined voltage drops across zener diode D1, the emitter-base voltage of input transistor Q1, and the 1V drop across 1-MΩ feedback resistor R2.

Build an op amp with three discrete transistors – [Link]

Measure small currents without adding resistive insertion loss


by Maciej Kokot @ edn.com:

In most cases, you measure current by converting it into a proportional voltage and then measuring the voltage. Figure 1 shows two typical methods of making the conversion. In one method, you insert a probing resistor, RP, in series with the current path and use differential amplifier IC1 to measure the resulting voltage drop (Figure 1a). A second method is a widely known operational amplifier current-to-voltage converter in which inverted IC1’s output sinks the incoming current through the feedback resistor (Figure 1b).

Measure small currents without adding resistive insertion loss – [Link]

Simple Acoustic Guitar Sound Receiver

This design of acoustic sound receiver features low power operational amplifier. It has rail-to-rail input/output and 0.85mA supply current per amplifier. It uses piezo speaker as its microphone that can be attached to easily due to its size and dimension.

The circuit is comprised of MCP6L91RT-E/OT 10 MHz, 850 µA operational amplifier that is used to amplify the sound signal. The low-pass filter is used to allow low frequency signal to pass while attenuating high frequency signal or above cut-off frequency of the system to prevent distortions and unnecessary signal. The piezo speaker is used as a microphone or a sound receiver in this circuit. Its size and dimensions is well suited for this application.

The circuit is suitable for different types of acoustic guitar. Since it can be attached easily, the old and other traditional instruments can be developed and modified so that it can continue its service even for the digital era. It can be interfaced to different applications which is not limited to musical instrument.

Simple Acoustic Guitar Sound Receiver – [Link]