A Tail-feedback VCO with Self-Adjusting Current Modulation Scheme

Aravind Tharayil Narayanan, Wei Deng, Kenichi Okada, and Akira Matsuzawa

Matsuzawa& Okada Lab.

Matsuzawa Lab.Tokyo Institute of Technology

Matsuzawa& Okada Lab.

Matsuzawa Lab.Tokyo Institute of Technology

Tokyo Institute of Technology, Japan

2

Contents

u  Motivation u  High Efficiency VCOs u  Reliable Power-Efficient Solutions u  Startup issue in Tail-Feedback VCO u  Proposed VCO u  Tail-Bias Vs Class-C u  Measurement Results u  Conclusion

3

Motivation

9.1mW

32.5mW

76.1%

21.9%

VCO

Others

[1] L. Vercesi, JSSC 2012.

Aim: §  Low-power §  High-purity §  Long lifetime

Ø Low-power VCO needed for longer battery-life

VCO

PDref LPF

N

4

High Efficiency VCOs

Class-C Class-D Class-F

High current efficiency High voltage efficiency

VP VN

VDD

M1 M2

M3 CTailVTail

Vgbias VP VN

VDDLDO

M1 M2

M1 M2

VP VNKM

VDD

VDD

M3 CTailVTail

[2] P. Andreani, JSSC 2008. [3] L. Fanori, JSSC 2013. [4] M. Babaie, JSSC 2013.

5

ηI × ηV

High Efficiency VCOs – Contd.

u ENF = FoMMAX – FoM

[5] M. Garampazzi, ESSCIRC 2014.

Excess Noise Factor5 (ENF)

FoMMAX : Only depends on Q ENF : Only depends on topology

u ENF ∝ 1 ηI : Current efficiecny

✓ High ηI : §  Good candidate for practical high efficiency VCO

✗ High ηV : §  Loading effects §  Reliability issues.

ηV : Voltage efficiecny

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VTune

I M1

I M2

VP VN

VDD

M1 M2

M3

I Tail

CTailVTail

Vgbias

t

t

VP VN

VDD

VG,M2

VG,M1

ϖ 2ϖ 3ϖ 4ϖ0

IM1 IM2

Iω0 ≈ IBias

VTH

Class-C VCO

Ø Impulse-shaped current for high efficiency [2] A. Mazzanti and P. Andreani, JSSC 2008.

7

VTuneVP VN

VDD

M1 M2

M3 M4 t

t

VP VN

VDD

VG,M3

VG,M4

ϖ 2ϖ 3ϖ 4ϖ0

IM1 IM2

Iω0 ≈ IBias

Cfb

VTail

Cfb

VTail

I M1

I M2

VTHVTail

Φ

Tail-Feedback VCO

Ø High efficiency can be achieved if 𝚽 is small. [6] A. Musa, IEICE 2013.

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Startup Issue Ø  Large oscillation amplitude for better phase noise

9060300012345

Conduction Angle (degrees)Ph

ase N

oise I

mpro

vmen

t (dB

)t

t

VTHVTail

VDDVDS

IDS

VT,eff

-ϖ ϖ0

Iω0 ≈ IBias

Ø  VCO fails to startup at low tail-bias voltage.

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Proposed VCO VDD

VBias

VTune

IB1 IB2M1 M2

M3

Bias Circuit

VP

Vb

I M1

VN

M4M6M5Cb Cb

Rb Rb

I M2

VDDVDD Cfb Cfb

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Self-Adjusting Tail-Current Modulation

Ø  Ensures robust startup

11

Self-Adjusting Tail-Current Modulation

Ø  Optimizes ‘𝚽’ for better phase noise

12

Contents

u  Motivation u  High Efficiency VCOs u  Reliable Power-Efficient Solutions u  Startup issue in Tail-Feedback VCO u  Proposed VCO u  Tail-Bias Vs Class-C u  Measurement Results u  Conclusion

13

!!"# =!!! − (!!" − !!")

!

Efficiency and MOS Sizing in Class-C

[2] A. Mazzanti and P. Andreani, JSSC 2008. Ø Large MOS required for better efficiency (class-C)

VDS

VDD

VTH

IDS1

Imax1

Imax2

IDS2ϖ-ϖ ϖ-ϖ 0

2 2

−Φ2 −Φ2

VGS

Small MOS

Large MOS

−Φ1 Φ1

-0.3 0.0 0.3 0.6-115

-110

-105

-100

Phas

e No

ise [d

Bc/H

z]

Vgbias[V]

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Fixed Tail Bias ϖ 2ϖ0 3ϖ 4ϖ

VTail IDS

Noise

iN

iDS+iN VTHVTail

ISF

0

Tail Noise Factor: Fixed Tail Bias

Ø Continuous Tail-Noise Up-Conversion in Class-C [7] S.L.J. Geirkink, JSSC 1999.

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Tail Noise Factor: Modulated Tail Bias

Modulated Tail Bias ϖ 2ϖ0 3ϖ 4ϖ

Vmod

VTail

VT,eff =(VTail+Vmod)

IDS

Noise

iN

iDS+iN VTHVT,eff

ISF

VTail

Ø Reduced Tail-Noise Up-Conversion [7] S.L.J. Geirkink, JSSC 1999.

16

In Brief

Tail-feedback VCO compared to class-C VCO Ø  Better tuning range.

Ø  Similar if not better noise performance.

Ø  Start-up issue is solvable.

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Contents

u  Motivation u  High Efficiency VCOs u  Reliable Power-Efficient Solutions u  Startup issue in Tail-Feedback VCO u  Proposed VCO u  Tail-Bias Vs Class-C u  Measurement Results u  Conclusion

18

Measurement

Technology 180nm CMOS

FOSC 4.6GHz

PN@1MHz -119dBc/Hz

Power 6.8mW FoM -184dBc/Hz

245𝛍M

530𝛍M

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Measurement

1K

-140

-120

-100

-80

-60

-20

-40

10K 100KOffset Frequency (Hz)

Phas

e noi

se (d

Bc/H

z)

1M 10M

20

Conclusion u  VCO topologies for high-efficiency is briefly

analyzed. u  Current-efficient topology is identified as a viable

candidate for practical design. u  Tail-feedback VCO is capable of achieving similar if

not better performance compared to class-C VCO. u  The start-up issues present in tail-feedback VCO is

briefly discussed. u  A bias mechanism is presented for solving startup

issues. u  A VCO is implemented in 180nm CMOS process

incorporating the proposed bias scheme.

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APPENDIX

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Analysis: Class-C VCO

Cgs,m1 Cgd,m1

Cgd,m3

Cgs,m3 CTL C

CL

VTail

VDD

M1

M3M3

Cdc

CL

Cgd,m3Cgs,m1

Cgs,m3

Cgd,m1

VP

VDD

C LVP

Conventioanl Class-C equivalent circuit

CT

Ø CGS has prominent effect on tank impedance

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VDD

M1

M3

Cfb

CL

VTail

VP

VDD

C L

Cgd,m3Cgs,m1

Cgs,m3

Cgd,m1

Tail bias equivalent circuit

Cgs,m1

Cgd,m3

Cgs,m3

CfbCgd,m1

L C

CL

VP

Analysis: Tail-Feedback VCO

Ø Cross-couple size is independent of ‘𝚽’