Bootstrapping (electronics)

Bootstrapping is a technique in the field of electronics where part of the output of a system is used at startup.

A bootstrap circuit is one where part of the output of an amplifier stage is applied to the input, so as to alter the input impedance of the amplifier. When applied deliberately, the intention is usually to increase rather than decrease the impedance.[1]

In the domain of MOSFET circuits, bootstrapping is commonly used to mean pulling up the operating point of a transistor above the power supply rail.[2][3] The same term has been used somewhat more generally for dynamically altering the operating point of an operational amplifier (by shifting both its positive and negative supply rail) in order to increase its output voltage swing (relative to the ground).[4] In the sense used in this paragraph, bootstrapping an operational amplifier means "using a signal to drive the reference point of the op-amp's power supplies".[5] A more sophisticated use of this rail bootstrapping technique is to alter the non-linear C/V characteristic of the inputs of a JFET op-amp in order to decrease its distortion.[6][7]

  1. ^ IEEE Standard 100 Authoritative Dictionary of IEEE Standards Terms (7th ed.). IEEE Press. 2000. p. 123. ISBN 0-7381-2601-2.
  2. ^ Uyemura, John P. (1999). CMOS Logic Circuit Design. Springer. p. 319. ISBN 978-0-7923-8452-6.
  3. ^ Pelgrom, Marcel J.M. (2012). Analog-to-Digital Conversion (2nd ed.). Springer. pp. 210–211. ISBN 978-1-4614-1371-4.
  4. ^ King, Grayson; Watkins, Tim (May 13, 1999). "Bootstrapping your op amp yields wide voltage swings" (PDF). EDN: 117–129.
  5. ^ Graeme, Jerald (1994). "Op-amp distortion measurement bypasses test-equipment limitations". In Hickman, Ian; Travis, Bill (eds.). The EDN Designer's Companion. Butterworth-Heinemann. p. 205. ISBN 978-0-7506-1721-5.
  6. ^ Jung, Walt. "Bootstrapped IC Substrate Lowers Distortion in JFET Op Amps" (PDF). Analog Devices application note AN-232.
  7. ^ Douglas Self (2014). Small Signal Audio Design (2nd ed.). Focal Press. pp. 136–142. ISBN 978-1-134-63513-9.