1V CMOS Bluetooth Front-End

Fredrik TillmanDepartment of Electroscience

Lund University

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Outline

• Short Introduction to the Bluetooth radio

• Purpose of this work

• Circuit design

• Measured results

• Summary

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The Bluetooth radio

• The ISM band (2.400-2.4835GHz)

• Frequency-hopping modulation– 1600 times per second

• 79 channels of 1MHz– 1Mbit per second

• Packet Radio

• 10m range– Peak output TX power between 0dBm and 20dBm

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Receiver noise requirements

• Complete receiver– Sensitivity at least –70dBm

– Minimum SNR is set to 18dB

– Bandwidth is 1MHz

– 6dB margin

• Front-end alone

-70dBm

-174dBm/Hz

BW=10log(106)

NF + 6dB

SNRmin=18dB

10dBNF ≤⇒

20dBNF ≤⇒

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Receiver linearity requirements

• IIP3 for the complete receiver– 14dB co-channel interference

– 3dB margin

-16dBm3dBdBm402

14dB67dBm40dBm-IIP3 ≈+−++≥

f0 f1 f2

-67dB

-40dB -40dB

2f1-f2

14dB

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Why low voltage?

• Technology scaling– Analog and digital on the same chip

– Electric fields limit VDD

• Reduce dynamic power in digital circuits

• Portable systems, one battery cell

The international technology roadmap for semiconductors, 2001

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Common-gate LNA

• Broad input matching– 1/gm (50Ω)– No external components

• Good isolation– No cascode necessary

• PMOS– Avoide capacitors

• 2.5mA supply current

S11 (differential)

0dB

-10dB

2GHz 2.8GHz

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Passive mixer

• Vt will not scale with technology– Leakage currents (digital)

– Stacking devices not suitable

• CMOS, true voltage switching

• No DC current– No voltage drop

– Minimal 1/f-noise

• Direct conversion

• Low IF

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Design considerations

• Conversion gain– LNA only

• Trade-offs– Gain

– Linearity

– Noise

GainLNA 0 < Gainmixer < 1

Critical capacitance

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Measured noise figure and gain

• Measured at IF = 10MHz– Limitations of the noise

figure meter

2.3 2.4 2.5 2.63

5

7

9

11

13

15

Frequency (GHz)

(dB

)

5

Conversion gain

Differential noise figure (DSB)

(GHz)2.4 2.5 2.6

(dB)

13

7

11

15

101

102

−2.5

−2

−1.5

−1

−0.5

0

0.5

IF (MHz)

(dB

)

Normalized bandwidth

0

-1

-2

(dB)

20 40 60 (MHz)

IF

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Compression

• Compression limit– When no switching occurs

• Limit = -13dBm (Vsw = 0.8V, Vt = 0.6V)

−=20

,

10

)(2LNAG

tswCPIN

VV⇒

50

2log10

2,

,

=

CPIN

CPIN

V

P

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−30 −25 −20 −15 −10 −5 0

−60

−50

−40

−30

−20

−10

0

10

RF input power (dBm)

(dB

m)

Measured linearity and compression

• Third order inter modulation (IM3)– Fundamental IF at 4.0MHz

– IM3 at 4.3MHz

Fundamental (4.0MHz)

IM3 (4.3MHz)

(dBm)-10-15-20

IIP3 = -5dBm

(dBm)

-50

-30

-10

CP1 = -16dBm

CP1 limit

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The hardware

The front-end

1.1mm

0.9mm

• 0.25µm standard CMOS

• Micro-leadframe package

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Summary

• A 1V Bluetooth front-end has been presented

• The measurements comply with the simulationsand fulfill the Bluetooth specification

Measured values Bluetooth requirements

Conversion gain (dB) 14 -

Noise figure (dB) 5 < 10

CP1dB (dBm) -16 > -27

IIP3 (dBm) -5 > -16

Power consumption (mW) 2.5 -

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Publication

• F. Tillman, H. Sjöland, “1 Volt CMOS BluetoothFront-End”, Proc. ESSCIRC, pp. 795-798,September 2002.