Outline Motivation Front-end architecture and interference - - PowerPoint PPT Presentation

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection

• A. Bevilacqua, A. Gerosa and A. Neviani

UNIVERSITY OF PADOVA UWB for Sensor Network Workshop Lausanne – 4 November 2005

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 1/17

Outline

• Motivation
• Front-end architecture and

interference rejection concept

• Circuit design
• Measurement results

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 2/17

Introduction

• UWB is 7.5 GHz of unlicenced spectrum for:

– High data-rate comm. → wireless USB – Low data-rate comm. → sensor networks

• Broadband sets new design challenges
• We developed a UWB receiver front-end:

– Tailored for high data-rate MB-OFDM – Focused on low-power, low-cost technology and interference rejection

• Results show general UWB receiver feasibility

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 3/17

Front-end architecture

IN

RF LO

LO Buffer O/P Buffer LO Buffer

LO OUT

I

OUT

Q I Q O/P Buffer

Notch Filter LNA

• Direct conversion for higher integration

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 4/17

UWB spectrum

3960 4488 5016 5544 6072 6600 7128 7656 8184 8712 9240 3432 9768 10296 f [MHz] WLAN bands

Group #2 Group #1 Group #3 Group #4 Group #5

• Severe WLAN interference in 4.9–5.825 GHz range

– Use of that range for UWB is prevented – Either operate on a small portion of the spectrum, e.g. “Group #1” only – Or broadband system with interference filtering

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 5/17

Interference rejection

Several possible approaches:

• Off-chip prefilter

– Increases cost and losses in the signal path

• Highly linear front-end

– Stringent circuit level specs

• Wideband integrated filter

– Trade-off btw. roll-off and filter complexity

• Tunable integrated notch filter

– Needs automatic tuning

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 6/17

Integrated tunable notch filter

Basic idea:

• Front-end linearity is limited by the largest interferer
• Suppress the largest blocker by just 10 dB

⇒ strongly improve linearity performance

• WLAN band is fragmented ⇒ the spectrum where

the largest fraction the interference is concentrated can be notched out – Automatic tuning circuit not addressed in this work – Solutions already reported in the literature

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 7/17

LNA design

Vcas Vbias

L b C1 C2 L L RL L e L 2

Vcc

Q1

Vin

Q2

Vcc

Q3 notch filter Cc Rc Cc

Vout Zin

1

L

• LC-ladder input network to noise/power match

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 8/17

Notch filter design

L 3 Cvar

Vtune

Q4 C4 Q1 Q2

Ven

M1 C3

Notch Filter

Vcc

LNA

Inotch

• Current is steered away from signal path at notch

frequency

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 9/17

Mixer design

Q5 Q6 Q7 Q10 Q9

Vcc Vcc

Rd Cm Q8 RFin Ibias,mix C5 R1 R2 R3 L 4 Cm

Vcc

Rm Rm

Vo,mix

LO port

• Single-balanced mixer with modified bias network

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 10/17

Chip microphotograph

• 0.35µm SiGe BiCMOS technology
• Die area is 2.1×1.7 mm2 including pads

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 11/17

Input match

2 4 6 8 10 12 −40 −30 −20 −10 10 S11 [dB] Frequency [GHz]

At board connector On wafer

• QPAD < 10 for f > 3.8 GHz impairs the input match
• On wafer meas. show that input net. works properly

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 12/17

Conversion gain

3 5 7 9 11 8 10 12 14 16 18 20 22 Frequency [GHz] G [dB]

• Peak conversion gain is 21.5 dB
• −3 dB bandwidth is 3.1–8 GHz

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 13/17

DSB noise figure

4 6 8 10 12 4 6 8 10 12 14 16 Frequency [GHz] NFDSB [dB]

• Noise figure is less than 6.6 dB for f < 7.4 GHz

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 14/17

Notch filter operation

0.8 1 1.2 1.4 −13 −12 −11 −10 −9 −8 −7 −6 −5 Vtune [V] Amax [dBc] 0.8 1 1.2 1.4 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 fN [GHz]

• Notch filter tuning range covers

the entire WLAN band

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 15/17

Cross-band gain desensitization

4 6 8 10 x 10

9

−30 −25 −20 −15 −10 Frequency [GHz] P−1dB,CB [dBm]

Notch Filter ON Notch Filter OFF

• Notch filter improves P−1 dB,CB by as much as 9.8 dB

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 16/17

Summary of performance

Maximum gain [dB] 21.5 Bandwidth [GHz] 3.1–8 Minimum NFDSB 4.8 I & Q matching [dB] 0.5

P−1dB,CB, IIP3#3, IIP3#7 [dBm] −11.3⋄†,> −4.7†,> −6.5† ICP, IIP2IB, IIP3IB [dBm] > −22, > 29.2∗,> −14.6

Power consumption [mW]

49.2 from VCC = 1.8 V

Die area [mm2]

2.1×1.7

⋄ at 3.5 GHz † notch filter on ∗ simulation result

A 0.35µm SiGe BiCMOS Ultrawideband Receiver Front-End with Integrated Interference Rejection – p. 17/17