Articles Tagged ‘op amp’

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Build an Op Amp SPICE Model from Its Datasheet – Part 1

Monday, October 11th, 2010

Summary:

Why do you need to build your own Op Amp model? Most Op Amp manufacturers have SPICE models for their components and make them available for free. Then why should you know how to build one? Well, not everything has a model and that is why, sometimes, you have to build your own. Also, it may be necessary to study a circuit to see what happens if you change the Op Amp slew rate or bandwidth, offset, and so on. Sometimes the manufacturer own model does not work, as a user found out and posted a question in this forum. I told him that the model does not work and advised him to build his own. …

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Categories: Analog Design

An Ideal Operational Amplifier Simulation Model

Saturday, August 28th, 2010

Summary:

You worked hard on your schematic, you calculated everything, you feel confident that it will work. To be sure though, before committing the schematic to copper, you want to simulate it. You develop a SPICE simulation schematic and, surprise, things don’t work. What’s going on?

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Categories: Analog Design

Using the Summing Amplifier as an Average Amplifier

Sunday, July 4th, 2010

Summary:

The summing amplifier can output the average of two, three or more signals. This is different than a signal average. The summing amplifier cannot, for example, output the average of a triangle signal. For that, you need an integrator to perform the average in the analog realm, or you need to sample the signal and calculate the average with a microcontroller. This type of average is the signal average in the time domain. I will write an article about the average of a signal in a near future.

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Categories: Analog Design, Electronic Circuits Examples, Summing Amplifier, Waveforms

Differential Amplifier Output Common-Mode Voltage Calculator

Sunday, February 28th, 2010

Summary:

A differential amplifier frequent use is the amplification of the voltage difference between its input signals, while rejecting the common-mode level. However, the output common-mode level cannot be zero. The operational amplifier technological limitations, as well as the outside resistor tolerances let the common-mode voltage to make it to the amplifier output as an output error. As a consequence, the amplifier output voltage is the input signal difference times gain, plus the output common-mode voltage.

Based on the resistor tolerances, this calculator will show the output common-mode voltage, Vocm, and the total voltage, Vout, at the differential amplifier output. Vocm will alter the ideal output voltage, which can be calculated when the resistors are perfectly matched.

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Categories: Analog Design, Calculators, Differential Amplifier

How to Design a Circuit from its Transfer Function Graph

Sunday, February 21st, 2010

Summary:

Sometimes all we know about a circuit is its transfer function graph. The transfer function might look like the one in Figure 1. How can we design a circuit so that its input-output behavior will match the graph?

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Categories: Analog Design, Differential Amplifier, Electronic Circuits Examples

Differential Amplifier Calculator

Sunday, February 7th, 2010

Summary:

If you need to design a differential amplifier, here is a handy calculator. All you need to define are the input range, the output range and a choice of a voltage reference. The default values for this calculator are set for a unipolar to bipolar converter.

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Categories: Analog Design, Calculators, Differential Amplifier

Design a Bipolar to Unipolar Converter with a 3-input Summing Amplifier

Sunday, January 31st, 2010

Summary:

Since the publication of Design a Bipolar to Unipolar Converter to Drive an ADC, several readers contacted me with requests to help in solving their particular converter. The common problem they had was the fact that the components’ calculation resulted in a negative value for at least one resistor.

To provide a solution, first we need to understand the root cause of the problem. Let’s take one of the circuits I received and analyze it.

The reader wrote that he would like to drive an ADC with the input range of 0 to 2.5V from a signal with the range of –5V to +5V, connected at V1.

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Categories: Analog Design, Electronic Circuits Examples, Summing Amplifier

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