VLSI System Design

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VLSI System Design ECES 681

• Lecture Interconnect -1
• Prashant Bhadri
• pbhadri_at_ececs.uc.edu
• Office Rhodes Hall - 933C
• Department of ECECS, College of Engineering,
  University of Cincinnati

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Noise

• What is noise?
• auditory experience of sound that lacks musical
  quality sound of any kind (especially
  unintelligible or dissonant sound)
• Electrical noise may be said to be the
  introduction of any unwanted energy, which tend
  to interfere with the proper reception and
  reproduction of transmitted signals.

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• External Sources
• Atmospheric
• Industrial
• Extraterrestrial
• Solar noise
• Cosmic noise
• Internal Noise
• This is the noise generated by any of the active
  or passive devices found in the receiver.
• Can it be a transmitter?
• How about on chip, in a system design, board
  design etc.

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Chip Noise

• Circuit noise includes all the disturbances
  induced by the circuits topology.
• Interconnect noise includes noise coming from
  capacitive or inductive coupling between
  interconnects.
• Power supply noise, which refers to deviations of
  the supply and ground voltages from their
  nominal values.
• Substrate noise in mixed-signal integrated
  circuits the charge injected in the substrate by
  the logic gates during the transitions may
  interfere severely with the operation of
  sensitive analog circuits.

Reference Bartolos Thesis, Chapter 1
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Shot Noise

• In a transistor the major contributor to noise is
  called shot noise.
• The formula for shot noise in a diode is given
  as

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Thermal Noise

• The noise generated by the agitation and
  interaction of electrons is called thermal noise.
  The internal kinetic energy of a particle can be
  expressed through its temperature.
• The kinetic energy of a body is zero at a
  temperature of absolute zero.
• The noise generated by a resistor, for example,
  is proportional to its absolute temperature as
  well as the bandwidth over which the noise is to
  be measured.

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• Any ordinary resistor not connected to a voltage
  source will have a voltage associated with it.
• If the load is noiseless and is receiving the
  maximum noise power generated by our noisy
  resistor then

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Flicker Noise

• Flicker noise dominates the noise spectrum at
  low frequency.

Reference Noise Sources in Bulk CMOS, paper by
Kent H. Lundberg
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Other Issues

• Charge Injection
• Capacitive Feed-through

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Charge Injection
Solution
Problem

• When the switch is on, the voltage across the
  sampling capacitor tracks the time-varying input
  signal within the bandwidth.
• Some charges are present in the MOS channel, this
  is a result of forming a conducting channel under
  the MOS gate.
• When the switch is turned off, charges either
  flow to the input source or to the sampling
  capacitor and create a small voltage which . is a
  function of several parameters which include
  input impedance, source impedance, clock falling
  edge, etc.

Reference http//kabuki.eecs.berkeley.edu/gchien
/thesis/Masters/appB/appendixB.pdf
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Clock Feed-through

• When the clock voltage on the gate switches
  between high and low, this voltage.
• drop is coupled into the signal via the
  capacitor divider.
• The clock feed-through can be corrected to the
  first order by using a differential signal path.
• As long as the error is present on both signal
  inputs and the same magnitude, it can be
  cancelled by taking the input differentially.
• This technique, once again, depends on the
  absolute matching of transistors.

Reference http//kabuki.eecs.berkeley.edu/gchien
/thesis/Masters/appB/appendixB.pdf
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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Reference Digital System Engineering
http//eeclass.stanford.edu/ee273/
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How will you remove noise during the chip design
phase? ? ? ?Any Ideas ??
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Noise Figure

• Used to assess the performance.
• Additionally compares two devices in order to
  evaluate their performance compares the signal
  and the noise at the same point to ensure that
  noise is not excess.
• This term is used to describe how noisy a device
  is.
• It is a ratio of the signal to ratio at the input
  to the signal to noise ratio at the output.

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Reading Assignment

• Paper Name Design Methodologies for Noise in
  Digital Integrated Circuits
• Author Kenneth L. Shepard
• Department of Electrical Engineering
• Columbia University, New York, NY 10027
• Website http//www.cisl.columbia.edu/faculty/shep
  ard/group/dac_noise.pdf