A System Level Design for a Bluetooth Front-end Receiver Group #789 Supervisor Angela Lin Shekar...

A System Level Design for a Bluetooth Front-end Receiver

Group #789

Supervisor

Angela LinShekar NethiShadi Tawfik

Jan H. Mikkelsen

January 9, 2004

AALBORG UNIVERSITY Department of Communication Technology

Introduction to Bluetooth

Radio Receivers Architectures

Bluetooth Receiver Design

MATLAB Modeling

Working Process

Contents

Conclusion & Future Work

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Unlicensed ISM band (2.4 - 2.4835 GHz)

Bit rate of 1Mbps

Frequency Hopping (1600 Hops/sec)

GFSK Modulation (BT = 0.5, h = 0.28 - 0.35)

Bluetooth is a wireless technology standard intended to be a cable replacement

Introduction to BluetoothDefinition

Short range (10 - 100 m)

Main radio specifications:

Introduction to BluetoothRadio Receivers Architectures


MATLAB Modeling

Working Process

Conculsion & Future Work

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Bluetooth was first originated by Ericsson in 1994, with the main targets being low cost, low power and low form factor

In 1998, the Bluetooth Special Interest Group (SIG) was formed

Currently, average price is around $25

High cost is the main problem delaying the widespread of Bluetooth

Introduction to BluetoothBackground

SIG’s initial target price of a Bluetooth solution $5

Radio part accounts for 80% of the total cost



MATLAB Modeling

Working Process


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The Superheterodyne Receiver

- The Direct Conversion Receiver

Architectures can be classified according to IF used

I/Q Processing Receivers:

Radio Receivers ArchitecturesIntroduction

- The Low IF Receiver

All wireless front-end receivers employ downconversion to an Intermediate Frequency (IF)

Achieve higher Q components

Avoid high power consumption




MATLAB Modeling

Working Process


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avoids desensitization of the receiver

reduces linearity requirements for later blocks

Low Noise Amplifier (LNA)

Minimum noise added during amplification

Mixer

Downconverts RF signal to IF (usually IF = RF/10)

Radio Receivers ArchitecturesThe Superheterodyne Receiver – Operation (1)

RF Band select filter




MATLAB Modeling

Working Process


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RF image-band-reject filter

IF channel select filter

High Q filter for channel selection

Radio Receivers ArchitecturesThe Superheterodyne Receiver – Operation (2)




MATLAB Modeling

Working Process


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Low IF

High IF

Radio Receivers ArchitecturesThe Superheterodyne Receiver – Trade-offs

Razavi-RF Microelectronics




MATLAB Modeling

Working Process


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Bulky external components

Pros High sensitivity and selectivity successive downconversion

Cons

Radio Receivers ArchitecturesThe Superheterodyne Receiver – Pros & Cons

Cannot be integrated

Expensive

High power consumption

VLO1 VLO2

BPF1 BPF2 BPF3 BPF4




MATLAB Modeling

Working Process


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Traditional Downconversion

LO signal contains positive AND negative tones Image rejection before downconversion

Complex Downconversion

LO signal contains positive OR negative tones Image rejection after downconversion

Big Advantage

Introduction to BluetoothIQ Processing Receivers – Theory




MATLAB Modeling

Working Process


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Common disadvantage: IQ mismatches

1% gain and phase mismatch reduces IRR to 35dB

Introduction to BluetoothIQ Processing Receivers – Physical Realization




MATLAB Modeling

Working Process


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Q

I

Image rejection relaxed small IQ mismatches can be tolerated

Radio Receivers ArchitecturesDirect Conversion Receiver – Operation




MATLAB Modeling

Working Process


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DCR can be fully integrated

Radio Receivers ArchitecturesDirect Conversion Receiver – Problems (1)

DC offset

Imperfect isolation between different ports

Distortion of downconverted signal




MATLAB Modeling

Working Process


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Static and dynamic DC offsets

Radio Receivers ArchitecturesDirect Conversion Receiver – Problems (2)

Flicker noise major noise contributor in MOS devices

Even order non-linearities

LO leakage in-band interference for other receivers





MATLAB Modeling

Working Process


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Image rejection Polyphase filter

Radio Receivers ArchitecturesLow IF Receiver – Operation




MATLAB Modeling

Working Process


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IQ mismatches are a major concern

Pros Integrability

DC offsets, flicker noise and even order distortion can be easily removed

Combined advantages of Superheterodyne and DCR

Cons

Radio Receivers ArchitecturesLow IF Receiver – Pros & Cons




MATLAB Modeling

Working Process


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Performance CostPower

ConsumptionForm Factor

SuperheterodyneHigh High High High

Direct Conversion

Low DC offset

Flicker noise Even order distortion

LO leakage

Low Low Low

Low IFLow

IQ mismatches

Low Low Low

Off-chip Components

Full Integration

Full Integration

A low IF architecture is found suitable for a Bluetooth receiver

Radio Receivers ArchitecturesSummary




MATLAB Modeling

Working Process


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Bluetooth Receiver DesignStrategy

Overall Receiver Parameters Calculation

Verification

Block Level Design




MATLAB Modeling

Working Process


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Bluetooth Receiver DesignOverall Parameters – Total Noise Figure

Sensitivity (PMIN) = -70 dBm

Bandwidth (B) = 1 MHz

From Bluetooth radio specifications

NFTOT ≤ 33 dB

(BER)MAX = 10-3

Mapping for GFSK (SNRo)MAX = 21 dB

But, Carrier-to-Co-Channel interferenece (C/ICO-CH) = 11 dB

(SNRo)MAX = 11 dB




MATLAB Modeling

Working Process


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Two interferers

sine signal, PINT1 = -39 dBm

GFSK modulated signal, PINT2 = -39 dBm

IP3i,TOT ≥ – 21dBm

Desired signal (C) = -70 dBm

IM test requirements

Carrier-to-Co-Channel interferenece (C/ICO-CH) = 11 dB

Bluetooth Receiver DesignOverall Parameters – Linearity

PINT = -39 dBm




MATLAB Modeling

Working Process


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Maximum interference power level (PINT,MAX)

Follows from definition of SFDR

Total noise figure (FTOT) = 32 dB

Total 3rd order Intercept Point (IP3iTOT) = -20 dBm

SFDR = 29.3 dB

Sensitivity level (PMIN) = -70 dBm

Bluetooth Receiver DesignOverall Parameters – SFDR

PINT,MAX = -40.6 dBm




MATLAB Modeling

Working Process


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ADC full scale power (PFS,ADC)

ADC Full scale voltage (VFS,ADC) = 0.8 V

ADC Input resistance (Rin,ADC) = 6 k

GTOT,MAX = 57.27 dB

GTOT,MIN = 7.27 dB

Bluetooth Receiver DesignOverall Parameters – AGC Range

Sensitivity level (PMIN) = -70 dBm

Maximum signal level (PMAX) = -20 dBm

PFS,ADC = -12.73 dBm




MATLAB Modeling

Working Process


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Bluetooth Receiver DesignOverall Parameters – In-band Filtering Requirements

In-band blockers test specifies a desired signal power level of - 60 dBm

In-band interferers power levels

Overall filtering requirements for in-band interferers




MATLAB Modeling

Working Process


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Bluetooth Receiver DesignOverall Parameters – Out-of-band Filtering Requirements

Out-of-band blockers test specifies a desired signal power level of - 67 dBm

Out-of-band interferers power levels

Overall filtering requirements for out-of-band interferers




MATLAB Modeling

Working Process


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Main Assumption

Bluetooth Receiver DesignOverall Parameters – Desensitization & Blocking (1)

Overall gain reduction is due to gain reduction in LNA only

FTOT = FLNA+FRx’ – 1

GLNA




MATLAB Modeling

Working Process


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Rx’

G’LNA ≥ 15.5 dB


Typical values for CMOS LNAs

NFLNA = 4 dB

GLNA = 15 dB

NF from test with minimum desired signal power (PSIGNAL)

IM test: PSIGNAL = - 64 dBm

Out-of-band blockers test: PSIGNAL = - 67 dBm

In-band blockers test: PSIGNAL = - 60 dBm

NF = 3 dB




MATLAB Modeling

Working Process


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To obtain 3


3 = 0.6 mV-2

Using a typical value for a CMOS LNA IP3i,LNA = - 9 dBm

| B | ≤ 1.37 mV




MATLAB Modeling

Working Process


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Referring to a 50 load


PBL,MAX = – 17.3 dBm

Referring to a 50 load

BMAX = ±1.37 mV

8 dB attenuation required before LNA




MATLAB Modeling

Working Process


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Bluetooth specifications v1.1

Bluetooth Receiver DesignBlock Level Design – Assumptions

Assumptions for unavailable values

RF band select filter attenuation for f = 6 GHz continues constantly for higher frequencies

Polyphase channel select filter for adjacent channels (f ≥ 3 MHz) extracted from a LPF of the same order

RF band select filter is almost perfectly linear IP3i,RF = 30 dBm




MATLAB Modeling

Working Process


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Bluetooth Receiver DesignBlock Level Design – Parameters




MATLAB Modeling

Working Process


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Bluetooth Receiver DesignSummary and Conclusion

A low cost Bluetooth low IF receiver can be implemented in a standard CMOS process




MATLAB Modeling

Working Process


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Building the front-end receiver in a simulation environment is a further step towards more accurate evaluation of performance

MATLAB ModelingAim and Accomplishments

Previous calculations use approximate formulas

Polyphase filter

The group was able to build behavioral models in MATLAB for the following:

LNA (Mixer)

RF band select filter

RF noise




MATLAB Modeling

Working Process


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fs ≥ 2fmax

MATLAB ModelingRF Simulation Problem

A computer can only deal with discrete time signals

Sampling of input band-pass signal is required

Still bounded with Nyquist Sampling Theorem

For RF signals, sampling frequency would be very high

Huge number of samples

Computationally inefficient

Therefore, use base-band representation of band-pass signals

Model built to deal with base-band form input

Model gives output in base-band form




MATLAB Modeling

Working Process


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is the complex envelope

MATLAB ModelingBase-Band Representation of Band-Pass Signals

Any band-pass (modulated) signal can be written as

Consequently, the band-pass signal can be written as

contains all transmitted information

is a base-band signal

Canonical forms of transmitters and receivers

I(t) and Q(t) are real signals




MATLAB Modeling

Working Process


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m(t)

MATLAB ModelingGFSK Signal Generation – Basic Principle

g()Introduction to Bluetooth



MATLAB Modeling

Working Process


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MATLAB ModelingGFSK Signal Generation - Waveforms

PSD of GFSK signal

Bipolar bits stream Gaussian shaped bitsIntroduction to Bluetooth



MATLAB Modeling

Working Process


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modulation index = 0.35

BT = 0.5

The PSD of white noise is infinite

Direct simulation of white noise is impossible

Usually, we have a limited bandwidth of interest

MATLAB ModelingRF Noise Model – Basic Principle




MATLAB Modeling

Working Process


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MATLAB ModelingRF Noise Model – Algorithm




MATLAB Modeling

Working Process


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MATLAB ModelingRF Noise Model – Results

Simulation parameters

Two sided PSD ≡ NF = 3dB

Center frequency = 200 MHz

Noise bandwidth = 100 MHz

Sampling frequency = 1 GHz

Brick wall filter ≈ 8th order Butterworth LPF

2/)1(2/' oTFkN

PSD of generated RF noise




MATLAB Modeling

Working Process


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Using partial fractions expansion:

MATLAB ModelingRF Filter Model – Basic Principle (1)

General transfer function of any analog filterIntroduction to Bluetooth



MATLAB Modeling

Working Process


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For the RF band-pass signal




MATLAB Modeling

Working Process


Output of RF band-pass filter

Carrier frequency >> bandwidth

Spectrum ≈ zero outside bandwidth

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From previous analysis we can now write




MATLAB Modeling

Working Process


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MATLAB ModelingRF Filter Model – Results



MATLAB Modeling

Working Process



Bandwidth = 10 MHz


Direct Implementation

First order bandpass filter

Bandwidth = 5 MHz


Low-pass equivalent

First order Butterworth LPF

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Model non-linearity power series expansion

Considering only fundamental component at the output

MATLAB ModelingLNA Model – Basic Principle




MATLAB Modeling

Working Process


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MATLAB ModelingLNA Model – Sine Wave Test

0 = 2 = 3 = 0

Test signal: sine wave

Amplitude = 1 V

Perfectly linear LNA

Voltage gain (1) = 15 dBV

Frequency = 5 Hz

Test signal: sine wave

Amplitude = 1 V

Non-linear LNA

Voltage gain (1) = 15 dBV

Frequency = 5 Hz

0 , 2 , 3 ≠ 0




MATLAB Modeling

Working Process


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Perfectly linear LNA

Non-linear LNA

MATLAB ModelingLNA Model – GFSK Signal Test




MATLAB Modeling

Working Process


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MATLAB ModelingPolyphase Filter Model – Basic Principle

Polyphase filter deals with downconverted signal direct simulation

Basic Transformation




MATLAB Modeling

Working Process


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Polyphase filter

MATLAB ModelingPolyphase Filter Model – Results

Test signal: GFSK

Center frequency = 2 MHz Bandwidth = 1 MHz

Sampling frequency = 10 MHz

Bandwidth = 1 MHz





MATLAB Modeling

Working Process


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Conclusion and Future Work




MATLAB Modeling

Working Process


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Conclusions:

A low IF receiver architecture is suitable for Bluetooth

The architecture can be implemented in a low cost standard CMOS process

Behavioral models for RF blocks can be implemented in MATLAB

Future work:

Building a complete low IF receiver in MATLAB to perform more accurate tests

Working ProcessTime Line




MATLAB Modeling

Working Process


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Problems arise from different expectations

Working ProcessAnalysis




MATLAB Modeling

Working Process


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Expectations about working hours

Working style

Supervisor guidance

RF design field

Key points to a good project

Try to learn from each other

Being good listeners

Discussions

Be self motivated

THANK YOU

A System Level Design for a Bluetooth Front-end Receiver Group #789 Supervisor Angela Lin Shekar...

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