An%20Improved%20Universal%20CMOS%20Current-Mode%20Analog%20Function%20Synthesizer

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An Improved Universal CMOS Current-Mode Analog
Function Synthesizer

• Muhammad Taher Abuelmaatti
• King Fahd University of Petroleum and Minerals ,
  Saudi Arabia
• and
• Nawal Mansour Al-Yahia
• Girls College of Science, Saudi Arabia

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• Analog nonlinear circuits are widely used in
  instrumentation, communication, neural networks,
  signal processing and medical equipment.
• Diodes and linear resistors, BJTs JFETs, MOSFETs,
  BiCMOS operational amplifiers, current conveyors
  and operational transconductance amplifiers are
  widely used in designing analog nonlinear
  circuits.

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• Numerous nonlinear functions can be
  approximated by

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• For example
• For y1/(1-x), a0 a1 a2 a3 a4 a5 a6
  1
• For yln(1x), a0 0, a1 1, a2 -1/2,
• a3 1/3, a4 -1/4, a5 1/5,
  a6 -1/6
• For ycos(x), a0 1, a1 0, a2 -1/2,
• a3 0, a4 1/24, a5 0, a6
  -1/720

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The traditional class-AB current mirror and its
modification to provide squaring unit (SU) and
current proportional to the input current

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• Using the translinear principle then

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• A normalized current proportional to can be
  obtained using the square-difference identity
  . Additional SUs can be
  used to obtain normalized currents proportional
  to , and .

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Examples with SPICE Simulation Results

• In the following examples the bias current Iq
  1 uA, the input current Iin is changing between
  0 and 1 uA, the DC supply voltages are 2 V and x
  Iin/ Iq.

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Subcircuit for realizing y1/(1-x)

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y1/(1-x)Error lt 1 for xlt0.5
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Subcircuit for realizing ycox(x)

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ycox(x)Error lt 1 for xlt1
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Subcircuit for realizing yln(1x)

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yln(1x) Error lt 1 for xlt0.675
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Conclusion

• The proposed technique is very flexible. Any
  nonlinear function can be realized once its
  Taylor series expansion is obtained.
• Accuracy can be improved by using additional
  terms in the Taylor series.
• No current multipliers are used.