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5 - Current mirrors

Published online by Cambridge University Press:  17 December 2010

Márcio Cherem Schneider  and
Carlos Galup-Montoro
Márcio Cherem Schneider
Affiliation:
Universidade Federal de Santa Catarina, Brazil
Carlos Galup-Montoro
Affiliation:
Universidade Federal de Santa Catarina, Brazil
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Summary

The current mirror is one of the most useful building blocks for analog integrated circuits. It is largely employed as a biasing element and as a load device for amplifier stages. It can also find other uses such as arrays of current sources in D/A converters and current amplifiers in current-mode filters. Basically, a current mirror is a circuit that copies a current flowing through one active device (input) to another active device (output) of a circuit, keeping the output current independent of loading. Current mirrors, from their simplest version to more elaborate circuits, together with analysis of their characteristics, are the subject of this chapter.

A simple MOS current mirror

The ideal current mirror

The simplest configuration of the ideal current mirror is shown in Figure 5.1. Ideally, the current gain AI is independent of the input frequency, and the output current is independent of the output voltage; in other words, the output impedance is infinite. Additionally, the input impedance is zero, i.e., the voltage drop across the input device is zero for any input current. The ideal current mirror is equivalent to a two-port current-controlled current source having a common terminal that connects the input and output ports.

In the section that follows, we will present a first-order analysis of the current mirror implemented with a pair of MOS transistors.

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CMOS Analog Design Using All-Region MOSFET Modeling , pp. 177 - 198
Publisher: Cambridge University Press
Print publication year: 2010

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References

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  • Current mirrors
  • Márcio Cherem Schneider, Universidade Federal de Santa Catarina, Brazil, Carlos Galup-Montoro, Universidade Federal de Santa Catarina, Brazil
  • Book: CMOS Analog Design Using All-Region MOSFET Modeling
  • Online publication: 17 December 2010
  • Chapter DOI: https://doi.org/10.1017/CBO9780511803840.006
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  • Current mirrors
  • Márcio Cherem Schneider, Universidade Federal de Santa Catarina, Brazil, Carlos Galup-Montoro, Universidade Federal de Santa Catarina, Brazil
  • Book: CMOS Analog Design Using All-Region MOSFET Modeling
  • Online publication: 17 December 2010
  • Chapter DOI: https://doi.org/10.1017/CBO9780511803840.006
Available formats
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Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • Current mirrors
  • Márcio Cherem Schneider, Universidade Federal de Santa Catarina, Brazil, Carlos Galup-Montoro, Universidade Federal de Santa Catarina, Brazil
  • Book: CMOS Analog Design Using All-Region MOSFET Modeling
  • Online publication: 17 December 2010
  • Chapter DOI: https://doi.org/10.1017/CBO9780511803840.006
Available formats
×