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Summary:
What is this circuit good for? It creates a single-ended-input-differential-output amplifier, in which VCM is the common mode and the main signal, in this case the average (VA+VB)/2 rides on top of VCM. It is very useful for fully differential circuits in low noise applications, because differential amplifiers help reduce the common mode noise. VCM in this case, sets the common mode to a useful level as required by the design.
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Converting a Differential Amplifier into a Summing Amplifier
Thursday, June 25th, 2009Summary:
Is there any link between a differential amplifier and a summing amplifier? Yes, it is. They can be easily converted one into the other one. While this article shows the conversion, the main purpose is to demonstrate how the same circuit can be viewed as a differential amplifier or as a summing amplifier, depending on the voltage levels in its inputs.
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The Differential Amplifier Common-Mode Error – Part 2
Sunday, June 7th, 2009Summary:
When designing a differential amplifier, part of the art is to manage the errors affecting the precision of the circuit. In The Differential Amplifier Common-Mode Error – Part 1 of this presentation I discussed the common-mode error of a differential amplifier. I also showed that, given the circuit in Figure 1, the common-mode voltage can be viewed as V2, when we consider V1-V2 as a signal that rides on top of V2. The same goes for V1, which can be considered the common-mode voltage of the differential amplifier when -(V1-V2) is the signal that rides on top of V1.
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The Differential Amplifier Common-Mode Error – Part 1
Wednesday, May 20th, 2009Summary:
The common-mode voltage can bring errors in the differential amplifier applications. What is the common-mode voltage? The common-mode voltage is the voltage level common to both inverting and non-inverting inputs of the differential amplifier. In many applications, the differential amplifier is used to amplify the difference between two voltages, for later processing, or to isolate a signal from common-mode noise, or to amplify a signal that rides on top of some large voltage level. If the common-mode voltage is not rejected, it appears as an error at the amplifier output.
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How to Derive the Differential Amplifier Transfer Function
Thursday, May 7th, 2009Summary:
The transfer function of the differential amplifier, also known as difference amplifier, can be found in articles, websites, formula tables, but where is it coming from? Why is the differential amplifier transfer function as in the following mathematical relation? …
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Solving the Differential Amplifier – Part 3
Sunday, May 3rd, 2009Summary:
Designing the differential amplifier by inspection is part of the art in the analog design. Inspecting the circuit and knowing how it works, it really gives you a feeling on what the values of the resistors should be.
Looking back at the example I took in Solving the Differential Amplifier – Part 1 and 2, we need to have an output signal of -1.25V to +2.365V with an input signal of -0.5V to 5.5V. In those two articles I used the differential amplifier transfer function and I applied math to find the resistors.
This time I am going to demonstrate how this circuit can be solved by simple reasoning and knowing how it works. Some calculations are also necessary. Cannot get rid of math totally.
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Solving the Differential Amplifier – Part 2
Friday, May 1st, 2009Summary:
But the resistors’ calculation becomes a bit of a challenge, when one might be faced with designing a differential amplifier with a certain transfer function. The example I took in the first article was as follows: Given an input range of, -0.5V to 5.5V, the output has to swing between, -1.25V and +2.365V. I solved the problem by using the amplifier transfer function and a system of equations.
In this article I am going to write about designing the resistors of this differential amplifier using the method of coefficients identification.
Starting from the differential amplifier transfer function …
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