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# VLSI System Design – ECES 681 PowerPoint PPT Presentation

VLSI System Design – ECES 681. Lecture: Interconnect -1 Prashant Bhadri pbhadri@ececs.uc.edu Office: Rhodes Hall - 933C Department of ECECS, College of Engineering, University of Cincinnati. Noise. What is noise?

VLSI System Design – ECES 681

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## VLSI System Design – ECES 681

Lecture: Interconnect -1

Office: Rhodes Hall - 933C

Department of ECECS, College of Engineering, University of Cincinnati

### Noise

• What is noise?

• auditoryexperienceofsoundthatlacksmusicalquality; soundofanykind (especiallyunintelligibleordissonantsound)

• 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.

• 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

• 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 Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

### 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:

### 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.

• 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 Engineeringhttp://eeclass.stanford.edu/ee273/

### Other Issues

• Charge Injection

• Capacitive Feed-through

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

### 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 Engineeringhttp://eeclass.stanford.edu/ee273/

Reference: Digital System Engineeringhttp://eeclass.stanford.edu/ee273/

### 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.