1. Research Background 4. Proposed VCO with Adaptive-Bias

6. Results and Conclusions

2. Design for High Performance

3. Reliability Issues

A Tail-Current Modulated VCOwith Adaptive-Bias Scheme

Aravind Tharayil Narayanan, Wei Deng, Kenichi Okada, Akira MatsuzawaTokyo Institute of Technology, Japan

1S-19

Transceiver Power Budget

Voltage Controlled Oscillator (VCO)

AIM: High performance VCO with minimum area/power overhead.

Significantly affects TRx noise performance.

Carrier

OFDM signals Impaired OFDM signals

Effects of Phase Noise

Tail-Feedback VCOClass-C VCO

Schematic Diagram

Simulaion Results

High Vbias (>Vth)during start-up. Vbias is gradually reduced for optimum enhancing efficiency.

Chip micrograph.

Performance comparison.

Phase noise plot.

CMOS Process Phase Noise [dBc/Hz]

JSSC2006 250nm -125@1MHz VLSI2009 180nm -109@1MHz JSSC2013 180nm -125@1MHz

180nm -124@1Mhz This Work SimulationMeasurement 180nm -119@1MHz

Frequency[GHz]

1.754.50 4.84

4.80 4.60

Pdc[mW]

2.25 0.16 3.40

7.20 6.80

FoM [dBc/Hz]

-186 -190 -193

-189 -184

Reliable start-up.Enhanced DC-RF conversion efficiency.

The proposed adaptive start-up scheme achieves:

These goals are achieved with very little overhead.

VBias

IB1 IB2

M1 M2

M3

Bias Circuit

Vb

M4Cb Cb

Rb Rb

Cfb Cfb

VDD

VDD VDD

VP VN

VTune

Out

put (

V)

Time (ns)Start-up Steady state

VG,Tail,P

I bia

s

VP VN

VDD

VP VN

VDD

Vth

Vbias

MTail,P MTail,N

Cfb Cfb

VbiasVbias

1K-140

-120

-100

-80

-60

-20

-40

10K 100KOffset Frequency (Hz)

Phas

e no

ise

(dB

c/H

z)

1M 10M

FoMMAX = 174 + 10log (2Q2)

Isolating the noise generated by active circuitry facilitates fair comparison of various VCO architectures.

ENF = FoMMAX – FoM

Small Φ results in larger transistor noise.

Small Φ required for high efficiency.

Vbias must be reduced for small Φ.

VCO fails to start-up at low Vbias.ie.Vbias < Vth(MTAIL,P/MTAIL,N)

One of the most power hungry TRX building blocks.

Class-C VCO

Φ can be reduced without incresing transistor noise.

Tail-Feedback VCO

PFD/CP LPF

÷N

VCORef

530μ

m

530μm

M1 M2 M1 M2

CTailMTail

VTail

Vgbias

ENF = ηP

1 + NL,tr /NL,tank

ENF

[dB

]

30

50

40

20

10

0

Class-C VCOTail-Feedback VCO

Conduction Angle [rad]

Effic

iecn

y

Tran

sist

or N

oise

[dB

]

4� 2�0 4� 2�0

1.0

1.4

1.6

1.2

0.8

0.6

0.4

10

20

30

40

50

60

0

Current EfficiencyVoltage EfficiencyPower EfficiencyNoise

2.2

2.2

2.4

2.5

2.5

2.7

2.1

Current EfficiencyVoltage EfficiencyPower EfficiencyNoise

2�2�

Effic

iecn

y

1.0

1.4

1.6

1.2

0.8

0.6

0.4

Tran

sist

or N

oise

[dB

]

Conduction Angle [rad]

Conduction Angle [rad] 4� 2�0

VG,Tail,N

VG,Tail,P

t

VP

VN

VDD

-� �-2� 2�0

VTH

Vbias

2Φ

- 0

V

V

I

Iω0

Φ

Voltage Controlled Oscillator (VCO) is dominantcomponent in L.O. in terms of area and power.

Low-power, area-efficient VCOs are required for supporting emerging wireless technologies.

RxVCO

45mW 55%

VCO19mW

38% Rx30mW

62%

36mW 45%

J. Boormans, JSSC 2011H. Darabi, JSSC 2011

J. Boormans, JSSC 2011

36mW 45% Rx

H. Darabi, JSSC 2011

19mW 38%

30mW 62%

Rx

5. Tail-Noise Suppression

Constant Tail-Bias Modulated Tail-Bias

VT,eff

0

� 2�0 3� 4� � 2�0 3�

iDS+iN

VmodVTail iN

iDS+iN

iN

iN

4�

VT,eff =(VTail+Vmod)

VTail

VTail Vth