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In electronics, '''power supply rejection ratio''' or '''PSRR''' is a term widely used in the [[electronic amplifier]] (especially [[operational amplifier]]) or [[voltage regulator]] datasheets; used to describe the amount of [[noise]] from a [[power supply]] that a particular device can reject.
 
The PSRR is defined as the ratio of the change in supply voltage in the [[op-amp]] to the equivalent (differential) output voltage it produces,<ref>[http://www.maximintegrated.com/glossary/definitions.mvp/term/PSRR/gpk/240 Maxim Integrated's glossary definition of PSRR]</ref> often expressed in [[decibel]]s.<ref>Allen, Phillip; Holberg, Douglas, ''CMOS Analog Circuit Design'', Oxford University Press, Inc, cc 1987.</ref><ref>Franco, ''Design With Operational Amplifiers and Analog Integrated Circuits'', McGraw-Hill, Inc, cc 1988.</ref><ref>Jung, Walt; ''Op Amp Applications Handbook'', Newnes, 2006, page 86 http://www.analog.com/library/analogdialogue/archives/39-05/Web_Ch1_final_R.pdf#page=93</ref> An ideal op-amp would have infinite PSRR. The output voltage will depend on the feedback circuit, as is the case of regular input offset voltages. But testing is not confined to [[Direct current|DC]] (zero frequency); often an operational amplifier will also have its PSRR given at various frequencies (in which case the ratio is one of [[Root mean square|RMS]] amplitudes of [[sinewave]]s present at a power supply compared with the output, with gain taken into account). Unwanted [[oscillation]], including [[Motorboating (electronics)|motorboating]], can occur when an amplifying stage is too sensitive to signals fed via the power supply from a later [[power amplifier]] stage.
 
<math>
PSRR(dB) = 20 \log_{10}\left({\Delta V_\mathrm{supply} \over {\Delta  V_\mathrm{out}}} \cdot A_v\right)\mbox{dB}
</math>
 
For example: an amplifier with a PSRR of 100 dB in a circuit to give 40 dB closed-loop [[gain]] would allow about 1 [[millivolt]] of power supply ripple to be superimposed on the output for every 1 [[volt]] of ripple in the supply. This is because
 
<math>100-40 = 60\ \mathrm{dB} </math>.
 
And since thats 60 dB of rejection, the sign is negative so:
 
<math> 1\ \mathrm{V} \cdot 10^\frac{-60}{20} = .001\ \mathrm{V} = 1\ \mathrm{mV} </math>
 
Note:
* The PSRR doesn't necessarily have the same poles as A(s), the open-loop gain of the op-amp, but generally tends to also worsen with increasing frequency (e.g. [http://focus.ti.com/lit/ds/symlink/opa2277.pdf]).{{Citation needed|date=September 2010}}
* For amplifiers with both positive and negative power supplies (with respect to earth, as [[op-amp]]s often have), the PSRR for each supply voltage may be separately specified (sometimes written: PSRR+ and PSRR-), but normally the PSRR is tested with opposite polarity signals applied to both supply rails at the same time (otherwise the [[common-mode rejection ratio]] (CMRR) will affect the measurement of the PSRR).
* For voltage regulators the PSRR is occasionally quoted (confusingly; to refer to ''output'' voltage change ratios), but often the concept is transferred to other terms relating changes in output voltage to input: Ripple Rejection (RR) for low frequencies, Line Transient Response for high frequencies, and Line Regulation for DC.
* Sometimes k<sub>SVR</sub> (or simply SVR) is used to denote the Power Supply Rejection Ratio  (e.g. [http://focus.ti.com/lit/ds/symlink/tl071.pdf])
 
==References==
<references/>
 
==External links==
* [http://www.analog.com/static/imported-files/tutorials/MT-043.pdf Operational Amplifier Power Supply Rejection Ratio (PSRR) and Supply Voltages by Analog Devices, Inc. Definition and measurement of PSRR.]
* [http://www.commsdesign.com/design_corner/showArticle.jhtml?articleID=12804251 Testing an A/D's power supply rejection ratio by Rob Reeder, Senior design engineer, Analog Devices Inc., Multi-Chip Products Group, Greensboro, N.C.]
* [http://www.omicron-lab.com/bode-100/application-notes-know-how/application-notes/psrr-measurement.html Application Note on PSRR Testing of Linear Voltage Regulators], by Florian Hämmerle (OMICRON Lab) and Steven Sandler (Picotest)
 
{{DEFAULTSORT:Power Supply Rejection Ratio}}
[[Category:Power supplies]]

Revision as of 13:41, 14 September 2013

Template:Multiple issues

In electronics, power supply rejection ratio or PSRR is a term widely used in the electronic amplifier (especially operational amplifier) or voltage regulator datasheets; used to describe the amount of noise from a power supply that a particular device can reject.

The PSRR is defined as the ratio of the change in supply voltage in the op-amp to the equivalent (differential) output voltage it produces,[1] often expressed in decibels.[2][3][4] An ideal op-amp would have infinite PSRR. The output voltage will depend on the feedback circuit, as is the case of regular input offset voltages. But testing is not confined to DC (zero frequency); often an operational amplifier will also have its PSRR given at various frequencies (in which case the ratio is one of RMS amplitudes of sinewaves present at a power supply compared with the output, with gain taken into account). Unwanted oscillation, including motorboating, can occur when an amplifying stage is too sensitive to signals fed via the power supply from a later power amplifier stage.

For example: an amplifier with a PSRR of 100 dB in a circuit to give 40 dB closed-loop gain would allow about 1 millivolt of power supply ripple to be superimposed on the output for every 1 volt of ripple in the supply. This is because

.

And since thats 60 dB of rejection, the sign is negative so:

Note:

  • The PSRR doesn't necessarily have the same poles as A(s), the open-loop gain of the op-amp, but generally tends to also worsen with increasing frequency (e.g. [1]).Potter or Ceramic Artist Truman Bedell from Rexton, has interests which include ceramics, best property developers in singapore developers in singapore and scrabble. Was especially enthused after visiting Alejandro de Humboldt National Park.
  • For amplifiers with both positive and negative power supplies (with respect to earth, as op-amps often have), the PSRR for each supply voltage may be separately specified (sometimes written: PSRR+ and PSRR-), but normally the PSRR is tested with opposite polarity signals applied to both supply rails at the same time (otherwise the common-mode rejection ratio (CMRR) will affect the measurement of the PSRR).
  • For voltage regulators the PSRR is occasionally quoted (confusingly; to refer to output voltage change ratios), but often the concept is transferred to other terms relating changes in output voltage to input: Ripple Rejection (RR) for low frequencies, Line Transient Response for high frequencies, and Line Regulation for DC.
  • Sometimes kSVR (or simply SVR) is used to denote the Power Supply Rejection Ratio (e.g. [2])

References

  1. ↑ Maxim Integrated's glossary definition of PSRR
  2. ↑ Allen, Phillip; Holberg, Douglas, CMOS Analog Circuit Design, Oxford University Press, Inc, cc 1987.
  3. ↑ Franco, Design With Operational Amplifiers and Analog Integrated Circuits, McGraw-Hill, Inc, cc 1988.
  4. ↑ Jung, Walt; Op Amp Applications Handbook, Newnes, 2006, page 86 http://www.analog.com/library/analogdialogue/archives/39-05/Web_Ch1_final_R.pdf#page=93

External links

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