Differential Amplifier

Differential Amplifier - DIFFERENTIAL AMPLIFIER The advent...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
ECE 414 1 M H Miller DIFFERENTIAL AMPLIFIER The advent of the integrated circuit led to the development of circuit configurations complementing the strengths of the technology and bypassing weaknesses. The high degree to which the characteristics of like components on the same substrate can be matched led to extensive use of symmetry as a filtering mechanism. The differential amplifier circuit configuration in particular has assumed considerable prominence in this respect. Physical and Electrical Symmetry The 'Differential Amplifier' is associated closely with integrated circuit technology; this technology provided both incentives for use of the circuit configuration as well as the means to construct effective circuits of this type. The differential amplifier is used extensively in modern monolithic electronic circuitry. The figure below illustrates the general character of a differential device. The circuit, a specific circuit configuration need not be specified for the present purpose, is assumed to be a linear circuit and to have physical mirror symmetry. The half-circuits on either side of the mirror symmetry line correspond both in topology and also in the properties of respective corresponding circuit elements. The currents I A and I B represent corresponding currents flowing within their respective half-circuits. V A and V B are corresponding voltages (relative to a common ground) in the respective half-circuits. On the other hand I a and I b are currents flowing out of one respective half-circuits, and into the other. The application of symmetry to circuit behavior is based on a philosophical assumption that nature is not maliciously perverse, and so similar circuit elements operated under similar conditions will behave similarly. Two special cases illustrate certain properties of the sort of symmetrical arrangement illustrated that are of special interest. Suppose input signals S 1 and S 2 are provided to the circuit. (The actual signal might be S 1 -S 2 , i.e., applied between the input terminals, but it is convenient here to reference each separately to a common ground point). Two cases of particular interest correspond to the inputs having certain general symmetry properties. In the one case, the 'common-mode' case, both signals are the same, i.e., S 1 =S 2 . In the other case, the 'differential-mode' case, the signals are electrically antisymmetrical, i.e., S 1 = -S 2 . Consider the common-mode case first. Because of the physical symmetry of the two half-circuits and the electrical symmetry of the input signals corresponding voltages and currents in each half circuit will be equal. Thus, for example, I a = I b , and KCL requires I a + I b = 0, i.e., both currents must be zero. A general conclusion is that there is no common-mode current flowing between the two halves even if there are physical connections between them.
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern