Amplitude and phase noise in nano scale rf circuits
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Amplitude and Phase Noise in Nano-scale RF Circuits. Reza Navid May 14, 2007. Today, 45nm technology node is available for commercial production design. Several other nano-scale devices are also becoming available. Channel Length (Micron). Number of MOSFETs. CMOS Scaling Since Early 70s.

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Amplitude and Phase Noise in Nano-scale RF Circuits

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Amplitude and phase noise in nano scale rf circuits

Amplitude and Phase Noise in Nano-scale RF Circuits

Reza Navid

May 14, 2007


Cmos scaling since early 70s

Today, 45nm technology node is available for commercial production design.

Several other nano-scale devices are also becoming available.

Channel Length (Micron)

Number of MOSFETs

CMOS Scaling Since Early 70s

4004 Intel Processor

2,250 10m-MOSFETs

386 Intel Processor

275,000 1m-MOSFETs

Pentium IV Intel Processor

169,000,000 90n-MOSFETs


Scaling problem at nanometer scales

Physical length

Drain Noise level

Ro

Long-channel

prediction

1986

1994

1996

1999

Year

Scaling Problem at Nanometer Scales

Reliability:

Mismatch:

Intrinsic Gain:

Small output resistance

Low intrinsic gain

Noise:

Short-channel MOSFETs

are noisier that Long-channel ones


Noise in rf receivers

LNA Noise

Phase Noise

Noise in RF Receivers

Electrical noise strongly impacts the overall performance.

Input Noise

Output Noise

IF Filter

Mixer

LNA

Transmission

No Signal

LO


Outline

Outline

  • Amplitude Noise in MOSFET

    • Noise in MOSFETs

    • Physical and Compact Models

    • Noise Performance of Ballistic MOSFETs

  • Jitter and Phase Noise in Oscillators

    • Indirect Noise Characterization Using Phase Noise

    • Time-Domain Formulation of Phase Noise

    • Experimental Results

  • Directions for Further Research

  • Conclusions


Outline1

Outline

  • Amplitude Noise in MOSFET

    • Noise in MOSFETs

    • Physical and Compact Models

    • Noise Performance of Ballistic MOSFETs

  • Jitter and Phase Noise in Oscillators

    • Indirect Noise Characterization Using Phase Noise

    • Time-Domain Formulation of Phase Noise

    • Experimental Results

  • Directions for Further Research

  • Conclusions


Noise sources in mosfets

Noise Sources in MOSFETs

  • There are two noise sources in a MOSFET:

    • Drain current noise (ind)

    • Induced gate noise (ing)

Gate

Drain

Drain

ing

gg

Cgs

gmvgs

go

ind

Gate

Source

Source

1/f noise

White noise

  • Gate Noise: Carrier fluctuations

  • coupled to gate through Cgs

  • 1/f Noise: Unknown origin, believed to be due to traps

We study the white noise part of the drain noise in saturation.


Classical mosfet noise formulation

Noise transfer

function (Impedance)

dx

dR

Classical MOSFET Noise Formulation

  • Classical long-channel formulation

    • Impedance Field Method [Van Der Ziel, 1970]:

      • Divide the channel into small pieces

      • Calculate noise of each piece (assuming equilibrium noise)

      • Integrate (assuming independence)

G

S

D

N+

N+

dR

It accurately predicts noise in long-channel MOSFETs.


Deficiency of the long channel model

Deficiency of the Long-Channel Model

  • Excess noise has been reported for 20 years now:

g

7.9

Abidi (0.7mm)

3.3

Triantis (0.7mm)

Jindal (0.75mm)

2.9

Scholten (0.35mm)

Tedja (1mm)

1.1

Long-channel

prediction

0.67

1996

1986

1994

1999

Year

Several methods are proposed to study this excess noise.


Excess noise in short channel fets

Our approach

Ballistic Mode:

Ind=2qId

Today’s FETs, 50% Ballistic

Ballistic FETs

Long-Channel FETs

Model revision

Short-Channel

Model: Ind=4kTgshgdo

Excess Noise in Short-Channel FETs

  • Researchers have tried to explain excess noise:

    • Local heating effects [Traintis, 1996]

    • Hydrodynamic simulations [Goo, 1999, Jungemann 2002]

    • Montecarlo analysis [Jungemann, 2002]

Usual approach

Short-Channel

Model: Ind=ks(2qId)

Long-Channel Model:

Ind=4kTggdo

Model revision

  • MOSFETs are moving towards ballistic limit.

We present a model based on ballistic MOSFET model.


Outline2

Outline

  • Amplitude Noise in MOSFET

    • Noise in MOSFETs

    • Physical and Compact Models

    • Noise Performance of Ballistic MOSFETs

  • Jitter and Phase Noise in Oscillators

    • Indirect Noise Characterization Using Phase Noise

    • Time-Domain Formulation of Phase Noise

    • Experimental Results

  • Directions for Further Research

  • Conclusions


Phase noise in oscillators

Phase Noise in Oscillators

  • Device noise leads to frequency fluctuations.

    • Example: Ring Oscillators

Output

t

Time Domain

I

Phase Noise

f

fo

Frequency Domain

t

Phase noise characterizes the frequency fluctuations.


Phase noise formulation and measurement

Phase Noise: Formulation and Measurement

  • Phase noise definition:

    • PSD of signal divided by power

    • Hard to formulate

    • Easy to measure

PN (dBc/Hz)

fo

fo+Df

f

  • Phase noise measurement helps estimate device noise:

  • Need accurate formulation for specific oscillators.

    • Time-domain phase noise analysis method

This method is most suitable for formulation of phase noise in switching-base oscillators.


Time domain phase noise analysis

  • Jitter characterization:

Without low-frequency poles

T1

Ti

T2

0

i-j

0

i-j

DTiDTjhas necessary andsufficient information for phase noise calculation.

With white noise

(presented here)

With colored noise

(presented elsewhere)

Time-Domain Phase Noise Analysis

  • Formulation of phase noise:

    • 1) Calculate jitter

    • 2) Calculate phase noise using jitter-phase-noise relationships


Jitter in switching based oscillators 1

Jitter in Switching-Based Oscillators (1)

  • Switching-based oscillators:

    • Energy-injecting elements act like ideal switches.

in

in

vC

vout

vref

vout

vC

in

C

R

Passive noisy network

Ideal noise-free switch

Calculate jitter during each switching; Add them up to find total jitter.


Jitter in switching based oscillators 2

Jitter in Switching-Based Oscillators (2)

  • Calculation procedure:

    • Calculate voltage variance at the switching time.

    • Divide by the square of voltage slope to get jitter.

2Dvc

vc

Slope=S

vref

vref

vC

in

C

R

2Dvc

2DT

t

This is suitable for switching-based oscillators.


Jitter phase noise relationships 1

Jitter-Phase-Noise Relationships (1)

  • If all covariance terms are zero [Navid, 2005],

Variance of one period

PN(dBc/Hz)

Df (Hz)

Df (Hz)

The 1st harmonic

The 3rd harmonic

Phase noise has peaks around odd harmonics, as expected.


Jitter phase noise relationships 2

Jitter-Phase-Noise Relationships (2)

  • It can be approximated by a Lorentzian Function.

    • Consistent with the results for sinusoidal signals [Herzel, 1999]

Exact

phase noise

  • Usually:

PN(dBc/Hz)

Lorentzian

Df (Hz)

Jitter-phase-noise relationship for nonzero jitter covariance is presented elsewhere [Navid, 2004].


Phase noise in ring oscillators

Phase Noise in Ring Oscillators

  • Time-domain phase noise analysis:

    • Treat invertors as ideal switches.

    • Use long-channel noise formulation.

A

B

B

A

On State:

Off State:

Use time-domain jitter analysis for switching-based oscillators.


Phase noise in ring oscillators cont

Phase Noise in Ring Oscillators (cont.)

  • Using jitter-phase-noise relationships [Navid, 2005]:

Dynamic Power

Very simple equations, but how accurate?


Phase noise in ring oscillators1

Phase Noise in Ring Oscillators

  • Measured results form Hajimiri, JSSC 1999 compared to our formulation:

DPN (dB)

Lmin (mm)

Df=1MHz

The difference is only a few dB; it increases in short-channel devices.


Oscillators for noise characterization

Oscillators for Noise Characterization

  • Need an oscillator with predictable phase noise, not necessarily low phase noise: an unsymmetrical ring oscillator.

The unsymmetrical ring oscillator is only one of many possibilities.


The unsymmetrical ring oscillator

The Unsymmetrical Ring Oscillator

  • Chip photo:

Ring oscillators for functionality test

MIM Capacitors

OSC1, L=.18mm

OSC2, L=.38mm

OSC3, L=.54mm

Fabricated in National Semiconductor’s 0.18mm CMOS process.


Mosfet noise characterization

MOSFET Noise Characterization

  • Frequency spectrum of the oscillators:

The oscillator with longer transistors has better spectral purity.


Mosfet noise characterization cont

MOSFET Noise Characterization (Cont.)

  • Phase noise of the oscillators:

Oscillator with Longer transistors has 7dB smaller phase noise.


Device noise parameters

OSC3

Long-channel prediction

Device Noise Parameters

  • Device noise parameters can be extracted from phase noise data.

Full shot noise

OSC1

Extracted device noise parameters are consistent with our prediction.


Further research on phase noise

Charge

Pump

Further Research on Phase Noise

  • Indirect device noise characterization for Nanotubes and Nanowires:

  • Ring oscillators built with these devices are already available (Z. Chen et al, Science 24 March 2006).

  • Time-domain phase noise analysis:

  • Jitter/phase noise calculation for various oscillators/PLL systems.

VCO

Fref

Loop

Filter

PFD

:N

Vb


Noise for device engineering

Noise for Device Engineering

  • Non-equilibrium noise carries unique device information

    • Device engineering based on noise characterization

    • Examples:

    • Examine carrier transport using noise data

    • Nano-tubes, Nano-wires, MOSFETs, …

    • Design new devices based on noise measurement

    • Bio-analytical devices

Use noise data to improve existing devices and build new ones.


Other scaling problems

Physical length

Drain Noise level

Ro

Long-channel

prediction

1986

1994

1996

1999

Year

Other Scaling Problems

Reliability:

Mismatch:

Intrinsic Gain:

Small output resistance

Low intrinsic gain

Noise:

Short-channel MOSFET

are noisier that Long-channel ones


Conclusions

Conclusions

  • Efficient CMOS analog design calls for a careful study of noise in MOSFETs, which has been a mystery for two decades.

  • Time domain phase noise analysis method accurately predicts the phase noise in switching-based oscillators.

  • Device noise can be characterized through phase noise measurement, facilitating process characterization.

  • Noise can be useful.


Acknowledgment

Acknowledgment

This work is supported under an SRC customized research project from Texas Instruments and MARCO MSD center.

We would like to thank National Semiconductor Inc. for the fabrication of test chips.


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