Transcript noise (Bhadri) - Department of Electrical Engineering and

VLSI System Design – ECES 681
Lecture: Interconnect -1
Prashant Bhadri
[email protected]
Office: Rhodes Hall - 933C
Department of ECECS, College of
Engineering, University of Cincinnati
Noise
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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.
Chip Noise
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Circuit noise includes all the disturbances induced by the
circuit’s 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: Bartolo’s Thesis, Chapter 1
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Shot Noise
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In a transistor the major contributor to noise is called shot noise.
The formula for shot noise in a diode is given as:
Thermal Noise
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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:
Flicker Noise
• Flicker noise dominates the noise spectrum at low frequency.
Reference: Noise Sources in Bulk CMOS, paper by Kent H. Lundberg
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Other Issues
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Charge Injection
Capacitive Feed-through
Charge Injection
Problem
Solution
•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
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
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/
How will you remove noise during
the chip design phase?   
Any Ideas ??
Noise Figure
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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.
Reading Assignment
1. 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/shepard/group/dac_noise.pdf