Precision Rectifiers

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Precision Rectifiers

• CEC

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Contents

• Ordinary Rectifier Limitations.
• Precision Diode.
• Precision Half Wave Rectifier.
• Precision Full Wave Rectifier.
• Pros and Cons.

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Ordinary Rectifier

• Use of silicon diodes for rectification.
• No gain flexibility.
• Diode cut in voltage limitations.
• Cannot rectify signals below 0.6 V.

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Precision Rectifiers

• Gain flexibility.
• Use of OPAMPs to provide amplification.
• Diode cut in voltage limitation minimised.
• OPAMPs high open loop gain (say 104) reduces the
  effect of diode cut in voltage.
• Input amplitude required only .
• Capable of rectifying small signals ( mV).
• Impedance Matching.
• Apprx. 2 x 105 for IC 741C

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Precision Diode
Super diode?
Diode conducts when forward biased.
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Precision Diode

• Diode cut in voltage V? virtually eliminated.
• OPAMPs high open loop gain AOL (apprx. 104)
  minimises the effect of V?.
• Input amplitude Vi required
  60µV.
• When , V0 gt V?, diode
  conducts.
• Circuit as a voltage follower for
  .
• Diode cut off when .
• Capable of rectifying low amplitude signals.
  

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Precision Diode

• Alternates between open loop and closed loop
  configurations.
• Use of high speed OPAMPs recommended.
• Slew rate limitations.
• Rectifiers may use more than one diode.
• OPAMP output to change quickly to switch over the
  conduction from one diode to the other.

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Precision Half Wave Rectifier
Unity Gain Inverter
Rcomp Rf ?? R1
Rf, R1 determine gain.
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Precision Half Wave Rectifier

• Uses two diodes D1 and D2.
• OPAMP in inverting configuration.
• When Vi positive, D1 conducts, V0A goes negative,
  D2 off, V0 0V.
• When Vi negative, D1 off, V0A goes positive, D2
  conducts, V0 gt 0V.
• Gain control by Rf and R1.
• Can amplify low magnitude inputs.

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Precision Full Wave Rectifier
V2
Vi ve, V2 ve, D1 ON, D2 OFF Vi ve, V2 ve, D1
OFF, D2 ON
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Precision Full Wave Rectifier
d
Virtual Ground
va
c
b
va
c, d
A1, A2 act as unity gain inverters, Vo Vi
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Precision Full Wave Rectifier
d
Virtual Ground
a
v
c
b
b, c
b, c
a
A2 as non-inverting amplifier.
A1 as unity gain inverter.
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Precision Rectifiers

• Diode cut in voltage issue overcome.
• Gain flexibility.
• No loading effects.
• Two diodes and OPAMPs.
• OPAMP power supply requirements.
• Slew rate limitations.
• Circuit complexity.

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References

1. Roy D. C. and S. B. Jain, Linear Integrated
   Circuits, New Age International, 3/e, 2010.
2. Your Prescribed Text Books and Online
   References.

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Thank You..