VLSI System Design – VLSI System Design – ECES 681ECES 681

Lecture: Interconnect -1 Lecture: Interconnect -1

Prashant BhadriPrashant Bhadripbhadri@ececs.uc.edu

Office: Rhodes Hall - 933COffice: Rhodes Hall - 933C

Department of ECECS, College of Department of ECECS, College of Engineering, University of Engineering, University of

CincinnatiCincinnati

Noise Noise

What is noise?What is noise?– auditory experience of sound that lacks musical quality; ;

sound of any kind (especially unintelligible or dissonant kind (especially unintelligible or dissonant sound)sound)

– Electrical noise may be said to be the introduction of any unwanted Electrical noise may be said to be the introduction of any unwanted energy, which tend to interfere with the proper reception and energy, which tend to interfere with the proper reception and reproduction of transmitted signals.reproduction of transmitted signals.

External SourcesExternal Sources– AtmosphericAtmospheric– IndustrialIndustrial– ExtraterrestrialExtraterrestrial– Solar noiseSolar noise– Cosmic noiseCosmic noise

Internal Noise Internal Noise – This is the noise generated by any of the active This is the noise generated by any of the active

or passive devices found in the receiver.or passive devices found in the receiver.– Can it be a transmitter?Can it be a transmitter?– How about on chip, in a system design, board How about on chip, in a system design, board

design etcdesign etc.

Chip NoiseChip Noise

Circuit noiseCircuit noise includes all the disturbances induced by the includes all the disturbances induced by the circuit’s topology.circuit’s topology.

Interconnect noiseInterconnect noise includes noise coming from capacitive or includes noise coming from capacitive or inductive coupling between interconnects.inductive coupling between interconnects.

Power supply noisePower supply noise, which refers to deviations of the supply , which refers to deviations of the supply and ground voltages from their nominal values.and ground voltages from their nominal values.

Substrate noise Substrate noise in mixed-signal integrated circuits: the charge in mixed-signal integrated circuits: the charge injected in the substrate by the logic gates during the transitions injected in the substrate by the logic gates during the transitions may interfere severely with the operation of sensitive analog may interfere severely with the operation of sensitive analog circuits.circuits.

Reference: Bartolo’s Thesis, Chapter 1

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

Shot NoiseShot Noise

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

Thermal NoiseThermal 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 NoiseFlicker Noise

• Flicker noise dominates the noise spectrum at low frequency.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/http://eeclass.stanford.edu/ee273/

Other IssuesOther Issues

Charge Injection Charge Injection Capacitive Feed-through Capacitive Feed-through

Problem Problem Solution Solution

Charge InjectionCharge Injection

Reference: http://kabuki.eecs.berkeley.edu/~gchien/thesis/Masters/appB/appendixB.pdf

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

Clock Feed-throughClock 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/http://eeclass.stanford.edu/ee273/

Reference: Digital System Engineering http://eeclass.stanford.edu/ee273/http://eeclass.stanford.edu/ee273/

How will you remove noise during How will you remove noise during the chip design phase? the chip design phase?

Any Ideas ??Any Ideas ??

Noise FigureNoise Figure

Used to assess the performance.Used to assess the performance. Additionally compares two devices in Additionally compares two devices in

order to evaluate their performance + order to evaluate their performance + compares the signal and the noise at the compares the signal and the noise at the same point to ensure that noise is not same point to ensure that noise is not excess.excess.

This term is used to describe how noisy This term is used to describe how noisy a device is. a device is.

It is a ratio of the signal to ratio at the It is a ratio of the signal to ratio at the input to the signal to noise ratio at the input to the signal to noise ratio at the output.output.

Reading Assignment

1. Paper Name : Design Methodologies for Noise in Digital Integrated CircuitsAuthor: Kenneth L. ShepardDepartment of Electrical EngineeringColumbia University, New York, NY 10027Website: http://www.cisl.columbia.edu/faculty/shepard/group/dac_noise.pdf