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An Ideal Operational Amplifier Simulation Model
Saturday, August 28th, 2010Summary:
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?
A Summing and Differential Amplifier with One Op Amp
Sunday, April 18th, 2010Summary:
In a comment, one of my readers asked me what is the transfer function of the non-inverting summing amplifier in Figure 1, when R3 is connected to a reference voltage instead of ground. Well, this is a summing amplifier with a differential configuration.
Differential Amplifier Output Common-Mode Voltage Calculator
Sunday, February 28th, 2010Summary:
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.
How to Design a Circuit from its Transfer Function Graph
Sunday, February 21st, 2010Summary:
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?
Design a Bipolar to Unipolar Converter with a 3-input Summing Amplifier
Sunday, January 31st, 2010Summary:
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.
How to Design a Summing Amplifier Calculator
Monday, January 11th, 2010Summary:
In this article, you can download a Summing Amplifier Calculator in the form of a spreadsheet. You can input the voltage range, output range, a reference voltage and a choice of two resistors. The calculator gives you the answer for the remaining resistors. Also, this article explains the mathematical steps towards building the calculator.
How to Derive the Inverting Amplifier Transfer Function
Thursday, November 26th, 2009Summary:
Widely used in Analog Design, the inverting amplifier in Figure 1 has a simple transfer function. What is the proof of this function?
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