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Role of a transmitter

HPMX-2007

The lkhefw wlkhq wilehr

The lkhefw wlkhq wilehr

The lkhefw wlkhq wilehr

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

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esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

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wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

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wklhjr qlih qilh q q3wih q

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wejklh wajkhrqwilu wae.

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esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

wklhjr qlih qilh q q3wih q

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

uP/

DSP

A

A

D

D

Q Data

I Data

Power Supply

Transceiver

Role of a Transmitter

Information

2. add data to carrier

3. shift to high frequency

Modulator

Mixer

0

90

Antenna

Baseband

Processor

Power Amplifier

4. amplify to

broadcast

Oscillator

bias

bias

1. create carrier


Role of a receiver

HPMX-2007

The lkhefw wlkhq wilehr

The lkhefw wlkhq wilehr

The lkhefw wlkhq wilehr

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

wejklh wajkhrqwilu wae.

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

esjlkh qwh wlh lihewrw

wklhjr qlih qilh q q3wih q

wejklh wajkhrqwilu wae.

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wklhjr qlih qilh q q3wih q

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wejklh wajkhrqwilu wae.

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uP/

DSP

A

A

D

D

Q Data

I Data

Power Supply

Role of a Receiver

Information

4. discard carrier and recover data

2. shift to lower frequency (cost and/or performance)

De-Modulator

Baseband

Processor

Mixer

0

90

Antenna

Low Noise Amplifier

1. amplify received signal with min. added noise

Oscillator

bias

bias

bias

3. LO for down conversion


Mixer multiplying up down conversion
Mixer = Multiplying  up/down conversion

  • Frequency translation device

  • Ideal mixer:

    • Doesn’t “mix”; it multiplies

AB

A

B


Image problem converting to if
Image problem converting to IF

A has desired signal at wIF

A1cos(wRFt)

plus an interference at wIM

A2cos(wIMt)

B is at wLO

And:

wRF - wLO = wLO - wIM = wIF

Both converted to IF,

Can’t be cleaned once corrupted




Problem of image signal1
Problem of Image Signal

  • Solution: Image Rejection Filter


Problem of half if
Problem of Half IF

  • Second order harmonic



Multi if stage receivers
Multi IF Stage Receivers

  • Received RF signal is down converted stage by stage until the desired final IF is obtained

  • Frequency conversion ratio of each stage is usually kept lower than 10.

    • For example, RF 1800 MHz  IF1 450 MHz, then  IF290 MHz, and finally  IF3 18 MHz.

    • Corresponding ratios are: 4; 5; 5; total 100.

  • Each stage has it’s own image problem

  • Each stage requires demanding filtering

    • Typically done off chip or using SAW

    • Complicated, bulky, expensive


If and lo frequency selection
IF and LO frequency selection

  • Fixed RF filter before LNA for band selection

    • One for each standard

    • Off-chip, high quality, no freedom

  • IF frequency is selected at design

    • Fixed for each product

  • LO frequency is tuned in real time

    • |RF–LO|=IF

    • Actual RF freq depends on which channel is assigned to device

    • LO tuning range must cover RF bandwidth



Selection of if
Selection of IF

  • If IF is large,

    • better separation between RF and image

    • better image rejection

    • easier image rejection filter design

    • More stages of down conversion

  • Other IF selection criteria

    • Select IF so that image freq is outside of RF band

    • IF >= (RF BW)/2

      • Sometime may not be possible, if (RF BW)/2 is within RF Band



Example am radio
Example: AM Radio freq that meets the requirement |RF–LO|=IF.

  • AM radio band: 530 to 1610 KHz

  • BW/2 = (1610-530)/2=1080/2=540, in band

  • IF has to be lower. Commonly: 455kHz

  • Image can be in AM band

  • If LO is on low side, LO tuning range is:

    • (530 to 1610) – 455 = (75 to 1155)

    • LO lowest to highest is a factor of 15.4

  • If LO is on high side, LO tuning range is:

    • (530 to 1610) + 455 = (985 to 2065)

    • LO lowest to highest is a factor of 2.01


Direct conversion receiver
Direct Conversion Receiver freq that meets the requirement |RF–LO|=IF.

No image problem


Direct conversion receiver1
Direct Conversion Receiver freq that meets the requirement |RF–LO|=IF.

LO is at same frequency as RF

1/f noise here can end up in channel

Self mixing cause DC problem

- Quadrature RF down conversion required

- DC problem

- Typically requires offset or 2x LO to avoid coupling

+ Eliminate IF SAW, IF PLL and image filtering

+ Integration

+ Avoids image problem


Dc offset self mixing
DC Offset (Self-mixing) freq that meets the requirement |RF–LO|=IF.

A

D

w c

0

Saturates the following stages

capacitive coupling

substrate coupling

bondwire coupling

aLO(t)=ALOcos(w c+q)

w c

A

D

w c

0

w c


Dc offset self mixing1
DC Offset (Self-mixing) freq that meets the requirement |RF–LO|=IF.

+

level

DC Offset

t

-


Dc offset cancellation

-A freq that meets the requirement |RF–LO|=IF.

DC Offset Cancellation

  • Capacitive Coupling

    • Requires a large capacitor

  • Negative Feedback

    • Nonlinear

  • TDMA Offset Cancellation

    • Requires a large capacitor


1 f noise effect
1/f freq that meets the requirement |RF–LO|=IF. noise effect

  • CMOS transistors has significant 1/f noise at low to DC frequency

  • Significantly noise performance of direct conversion receivers

Receive signal

1/f noise

f


Even order distortion
Even-Order Distortion freq that meets the requirement |RF–LO|=IF.

Direct feed through

Direct feed through


Mirror signal
Mirror Signal freq that meets the requirement |RF–LO|=IF.

  • Upper sideband and lower sideband are identical


Mirror signal1
Mirror Signal freq that meets the requirement |RF–LO|=IF.

  • Upper sideband and lower sideband are not identical


Mirror signal suppression
Mirror Signal Suppression freq that meets the requirement |RF–LO|=IF.

  • Quadrature Down Conversion

ui(t)

vi(t)

A

I

D

0

90

a(t)

Q

A

D

vq(t)

uq(t)


Quadrature conversion
Quadrature Conversion freq that meets the requirement |RF–LO|=IF.


Quadrature down conversion
Quadrature Down Conversion freq that meets the requirement |RF–LO|=IF.


I q mismatch

Phase & Gain Error freq that meets the requirement |RF–LO|=IF.

I

0

Phase & Gain Error

90

a(t)

Q

Phase & Gain Error

I/Q Mismatch


I q mismatch due to lo errors
I/Q Mismatch due to LO errors freq that meets the requirement |RF–LO|=IF.


Phase error freq that meets the requirement |RF–LO|=IF.

Gain error

Effect of phase mismatch

Effect of gain mismatch


Use of I/Q down conversion recovers the nonsymmetrical freq that meets the requirement |RF–LO|=IF.

receive signal spectrum

But port isolation becomes more challenging

Selfmixing and even order distortion may affect both channels and affect each other, causing additional I/Q mismatch


DC and 1/f freq that meets the requirement |RF–LO|=IF.

cancellation

Base

Band

DSP

A/D

0

90

a(t)

A/D

Phase and gain mismatch

compensation


Summary of direct conversion receiver
Summary of Direct Conversion Receiver freq that meets the requirement |RF–LO|=IF.

  • No need for imager reject filter

  • Suitable for monolithic integration with baseband

  • DC offsets due to crosstalk of input ports of mixer

  • Even order IM direct feed through to baseband

  • Quadrature down conversion suppresses mirror

  • I/Q mismatch due to mismatches in parasitics

  • Low power consumption attributes to less hardware


Low if receiver
Low IF receiver freq that meets the requirement |RF–LO|=IF.

  • - Quadrature RF down conversion required

  • - Require higher performance ADC

  • Additional mixer

  • Slower RF PLL settling

  • Even order distortion still problem

  • Low freq IF filters require large chip area

+ Eliminate IF SAW, IF PLL and image filtering

+ Integration

+ Relaxes image rejection requirements

+ Avoids DC problems, relaxes 1/f noise problem


Low if down conversion
Low-IF Down Conversion freq that meets the requirement |RF–LO|=IF.

Complex

BPF

Mirror signal, needs removal


Mirror signal suppression 1
Mirror Signal Suppression (1) freq that meets the requirement |RF–LO|=IF.

Complex

Bandpass

Filter

I

Q

I

Q

LO1

LO2


Mirror signal suppression 2
Mirror Signal Suppression (2) freq that meets the requirement |RF–LO|=IF.

I

Q

Q

I

LO1

LO2

Both schemes used in heterodyne receivers for image rejection

Mathematical analysis very similar


Image rejection architectures
Image rejection architectures freq that meets the requirement |RF–LO|=IF.

  • Use additional hardware (LO’s, mixers, and filters)

  • Use I/Q channels which process + or – frequencies differently

  • Two steps of I/Q to solve both image and mirror problems

  • Effects limited by I/Q channel/filter matching accuracies


Image reject receiver
Image Reject Receiver freq that meets the requirement |RF–LO|=IF.

  • Hartley Architecture

A

C

-90°

RF

input

IF

output

0

w LO

90

B


Hartley architecture
Hartley Architecture freq that meets the requirement |RF–LO|=IF.

xcos

xsin


Iq error effect
IQ error effect freq that meets the requirement |RF–LO|=IF.

  • Ideal IQ: image completely rejected

  • If signal and image not single tone, 90o shift is not exact

  • Local oscillator’s sine and cosine not matched in magnitude and phase

  • 90o phase shifter may have both gain and phase error

  • All lead to incomplete image rejection


Ipr evaluation and irr lo error
IPR Evaluation and IRR – LO error freq that meets the requirement |RF–LO|=IF.


Input image power ratio freq that meets the requirement |RF–LO|=IF.


Image reject receiver1
Image Reject Receiver freq that meets the requirement |RF–LO|=IF.

Hartley Architecture with simple 90 deg phase shiftor


Gain Mismatch due to R, C errors freq that meets the requirement |RF–LO|=IF.

At w = 1/RC:


Weaver architecture
Weaver Architecture freq that meets the requirement |RF–LO|=IF.


Weaver architecture1
Weaver Architecture freq that meets the requirement |RF–LO|=IF.


Digital if
Digital IF? freq that meets the requirement |RF–LO|=IF.

  • To avoid 0-IF or low-IF issues, IF frequencies can’t be too low

  • Recall: RF-IF ratio within 10

  • Typical RF freq is in 1 to 5 GHz,  IF needs to be more than 100 to 500 MHz

  • But dynamic range requirements requires >= 14 bit resolution

  • No such ADC’s are available

  • But signal bandwidth much smaller,

  •  Subsampling Receivers


  • Example: freq that meets the requirement |RF–LO|=IF.1.8 GHz GSM Specifications: IF carrier frequency = 246 MHz, Channel BW = 200 KHz, Input Dynamic Range = 90 dB.

  • 2 digital low frequency mixers, no noise and distortion.

  • Easier I&Q matching.

  • No DC offset and 1/f noise.

  • More digital means easier integration on a CMOS process.

  • SNR degradation due to noise folding

  • ADC & SH have to run at high clock to minimize noise folding.


Noise folding problem
Noise folding problem freq that meets the requirement |RF–LO|=IF.

White noise

0

IF

……

fs

2fs

……

0

IF

Baseband noise increased by IF/fs factor


  • The aliased noise, once happened, cannot be removed in the digital domain

  • Band pass filtering of IF before sampling can reduce the noise in lower frequency

    • Requires expensive IF filters

    • Against the spirit of moving more things to digital

  • Reduce IF frequency and increase fs frequency so that IF/fs ratio is not large

    • More stringent requirement on RF filtering and image rejection

    • Requires faster ADC


Example
Example digital domain

UMTS/DCS1800 Specifications


Sensitivity

Adjacent Channel Interference digital domain

Co-Channel Interference

Adjacent Channel

Adjacent Channel

Desired Channel

890.4

890.6

890.4

MHz

Sensitivity

890.4

890.4

890.4

890.4

890.4

890.4

890.4


Multi channel multi mode dynamic range dcs1800
Multi-Channel, Multi-Mode Dynamic digital domainRange, DCS1800


Multi channel multi mode dynamic range dcs18001
Multi-Channel, Multi-Mode Dynamic digital domainRange, DCS1800

PB = 13 dBm, Px = -60 dBm

PB:Px = 73 dB

If want FS:1LSB > 73 dB

 >12 bit resolution

If want digital channel selection + filtering,  fs >= 2BW

 fs >= 150MHz

If want noise floor 20 dB below wanted signal

 SFDR >= 13 – (-60) + 20 = 93 dB

Type of ADC needed: 150 MSPS, 13-14 bit, 95-100 dB SFDR


Sensitivity1
Sensitivity digital domain

Desired Signal

Receiver Added Noise

Receiver Thermal Noise


Sensitivity2
Sensitivity digital domain

Power to Antenna: +40 dBm

TX. Antenna Gain: +10 dB

Frequency: 10 GHz

Bandwidth: 100MHz

Rcvr. Antenna Gain: +60 dB

Transmitter:

+ 50 dBm

ERP

-200 dB

Path Losses

60 dB

Rcvr. Ant. Gain

-80 dBm

Power to Receiver

Receiver:

- 174 dBm/Hz

Noise Floor @ 290K

+ 80 dB

Noise in 100 MHz BW

Margin: 4 dB

+10 dB

Receiver N.F.

ERP = +50 dBm

-84 dBm

Receiver Sensitivity

Path Losses: 200 dB

How to increase Margin by 3dB ?


Selectivity

IF Filter digital domain

RF Filter

Ch

1

Ch

2

Ch

3

Ch

n

Ch

1

Ch

2

Ch

3

Ch

n

fIF

freq

freq

fRF

Selectivity

freq

fLO


Selectivity1
Selectivity digital domain

  • IF filter rejection at the adjacent channel

  • LO spurious in IF bandwidth

  • Phase noise of LO

RF Filter

IF Filter

Receiver Added Noise

Receiver Thermal Noise


Noise figure calculation
Noise Figure Calculation digital domain

RF input

Baseband

receiver


E s n o or e b n o
E digital domains/No or Eb/No=?

17!


Ip3 calculation
IP3 Calculation digital domain


Image rejection calculation
Image Rejection Calculation digital domain

PImage

IRrequired

Pdesired

SNRmin

fRF

fIF

fLO

(all in dB’s)


Transmitter architecture
Transmitter Architecture digital domain

  • Direct Conversion Transmitter

  • Two-step Conversion Transmitter

  • Offset PLL Transmitter


Transmit specifications
Transmit Specifications digital domain

  • Transmit spectrum mask


Receiver specifications
Receiver Specifications digital domain

alternate adjacent channel

Adjacent channel

20

20

40

40


Direct-conversion transmitter digital domain

I

0

90

Q

wLO

Pros: less spurious synthesized

Cons: more LO pulling


I

0

90

wLO

w1

Q

w2

Pros: less LO pulling

Cons: more spurious synthesized


I

0

90

w1+w2

cosw1t

cosw2t

Q

Pros: less LO pulling

superior IQ matching

Cons: required high-Q bandpass filter


I

PD/LPF

VCO

0

90

cosw1t

Q

1/N


Weaver architecture2
Weaver Architecture digital domain


Wideband if architecture
Wideband IF Architecture digital domain


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