Feedback
Feedback2.png

Feedback is a process whereby a fraction of the output signal is sensed (VF) and compared with the input (VIN), generating a very small feedback error term (VE= VIN – VF), thereby making the output an accurate replica of the input.

Example: the typical non-inverting closed loop configuration
It is instructive to identify four elements in the feedback system.

  • The feed forward amplifier (A)
  • A means of sensing the output
  • The feedback network (β)
  • A means of generating the feedback error (Σ)

These elements exist in every feedback system. The pictures on the right describe a general feedback system showing both negative and positive feedback configurations.

Negative and Positive Feedback

There are two kinds of feedback: negative feedback and positive feedback. The block diagrams on the right show that, if the sensed feedback voltage VF has the same phase with the input voltage, then we say it is a negative feedback. Otherwise, it is a positive.

Negative feedback allows high precision signal processing; Positive feedback makes it possible to build oscillators.
Before proceeding to the analysis of feedback circuits, we'll first describe the benefits of negative feedback.

  • Provides gain desensitization. For example, the closed lop gain is much less sensitive to device parameters than the open loop gain is.
  • Controls the input/output impedance; that is, raise or lower the input and output impedances by the selection of an appropriate feedback topology.
  • Increases the amplifier bandwidth.
  • Reduces the noise; that is, minimizes the contribution to the output of unwanted electric signals generated by the circuit components themselves as well as extraneous sources.
  • Reduces nonlinear distortion in an amplifier; that is, makes the output proportional to the input.

20th Annual
Microchip MASTERs Conference 2016
Register now - Deadline: July 29

JW Marriott Desert Ridge Resort-Phoenix, AZ

© 2016 Microchip Technology, Inc.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.