Quadrature Generation Techniques in CMOS Relaxation Oscillators S. - - PowerPoint PPT Presentation

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Quadrature Generation Techniques in CMOS Relaxation Oscillators S. - - PowerPoint PPT Presentation

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Quadrature Generation Techniques in CMOS Relaxation Oscillators S. Aniruddhan Indian Institute of Technology Madras Chennai, India ISCAS 2012 Outline Introduction & Motivation Quadrature Relaxation Oscillators (QRXO)

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Quadrature Generation Techniques in CMOS Relaxation Oscillators

  • S. Aniruddhan

Indian Institute of Technology Madras Chennai, India

ISCAS 2012

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Aniruddhan, IIT Madras ISCAS 2012 2

Outline

  • Introduction & Motivation
  • Quadrature Relaxation Oscillators (QRXO)

– Shunt-coupled QRXO – Series-coupled QRXO

  • Design and Simulation Results
  • Summary
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Aniruddhan, IIT Madras ISCAS 2012 3

Introduction

  • RF oscillator: key block in wireless & wireline

communication systems [1,2]

  • LC VCOs are commonly used

– Low phase noise (high-Q) – Large area (spiral inductors) – Tuning range limited by device parasitics

  • Quadrature LO signals

– Recovery of IQ signal – Image-rejection

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Aniruddhan, IIT Madras ISCAS 2012 4

IQ LO Generation – 1

  • VCO (f0) + polyphase filter

– High frequencies: capacitive parasitics become

comparable to filter C

– Buffers required to drive low impedances = high

power consumption

– Quadrature error ⇐ R & C matching

  • VCO (2f0) + Divide-by-2

– LC oscillator potentially has higher Q at 2f0 – Divider power becomes significant – Quadrature error ⇐ device matching

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Aniruddhan, IIT Madras ISCAS 2012 5

IQ LO Generation – 2

  • Four-stage ring oscillator (f0)

– Tuning range set by stage delays – Quadrature error ⇐ delay matching

  • Quadrature VCO (f0) [1,3,4]

– Power efficient at higher frequencies – Quadrature error ⇐ coupling strength

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Aniruddhan, IIT Madras ISCAS 2012 6

Relaxation Oscillator

  • Schmitt Trigger: Cross-coupled NMOS + R loads
  • Integrator: Capacitor C
  • Tune frequency using I0
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Aniruddhan, IIT Madras ISCAS 2012 7

Quadrature Generation

  • Quadrature Relaxation Oscillator [5,6]

– VC and VOUT are 90° out of phase – Integrator of each oscillator triggers the other

  • Quadrature LC VCO

– Inhibit negative resistance generation for 0° or

180° modes

– Shunt & series injection

  • Quadrature Relaxation Oscillator (this work)

– Suppress Schmitt-trigger operation for 0°/180° – Shunt & Series coupling

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Aniruddhan, IIT Madras ISCAS 2012 8

Shunt Coupled QRXO

  • I=Q (in-phase)

⇒ M5-6 oppose M1-2

– QRXOI dies out

QRXO ⇒

Q too ceases to oscillate

  • I=Q (out-of-phase)

M ⇒

7-8 oppose M3-4

– QRXOQ dies out

QRXO ⇒

I too ceases to oscillate

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Aniruddhan, IIT Madras ISCAS 2012 9

Series Coupled QRXO

  • Series injection through M5-8
  • Coupling devices in triode region
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Aniruddhan, IIT Madras ISCAS 2012 10

Circuit Design & Simulation

  • Quadrature relaxation oscillators designed and

simulated using Spectre (Cadence)

– f0 = 2.4GHz – UMC 0.18µm CMOS process (VDD = 1.8V)

  • Reference 2.4GHz relaxation oscillator

– Total bias current = 6mA – M1-2 = 100µm X 0.25µm – Load resistance R = 100Ω – Integrator capacitance C = 460fF

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Aniruddhan, IIT Madras ISCAS 2012 11

Shunt-coupled QRXO

  • Quadrature coupling validated in simulation
  • Primary design parameter: size of quadrature

coupling devices

– Large W/L

strong coupling, larger parasitics ⇒

– Small W/L

weak coupling, more flicker noise ⇒

– Larger L

less flicker noise, more parasitics ⇒

– M5-8 = 36µm X 0.65µm

  • Total QRXO current = 12mA
  • 1% I-Q mismatch

0.25 ⇒ ° quadrature error

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Aniruddhan, IIT Madras ISCAS 2012 12

Shunt QRXO – Startup

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Aniruddhan, IIT Madras ISCAS 2012 13

Shunt QRXO – Phase Noise

  • -99.4dBc/Hz @ 1MHz offset
  • R = 24%; M5-8 (flicker) = 21%; M1-4 (thermal) = 18%
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Aniruddhan, IIT Madras ISCAS 2012 14

Shunt QRXO – Phase Error

15 20 25 30 35 40 45 50

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2.3 2.35 2.4 2.45

  • Quad. Phase Error (deg.)
  • Osc. Freq. (Ghz)

Coupling Device width (um) Quadrature Phase Error (deg.) Oscillation Frequency (GHz)

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Aniruddhan, IIT Madras ISCAS 2012 15

Series-coupled QRXO

  • Quadrature coupling validated in simulation
  • Coupling devices

– Operate in triode region – Weaken cross-coupled NMOS operation

(degeneration)

– Large W/L (M5-8 = 200µm X 0.18µm) – Flicker noise less of a concern

  • Total QRXO current = 16mA
  • 1% I-Q mismatch

0.1 ⇒ ° quadrature error

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Aniruddhan, IIT Madras ISCAS 2012 16

Series QRXO – Startup

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Aniruddhan, IIT Madras ISCAS 2012 17

Series QRXO – Phase Noise

  • -98.3 dBc/Hz @ 1MHz offset
  • M1-4 (flicker) = 70%
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Aniruddhan, IIT Madras ISCAS 2012 18

Series QRXO – Phase Error

160 170 180 190 200 210 220 230 240 250

0.1 0.2 0.3 0.4 0.5 2.05 2.1 2.15 2.2 2.25 2.3 2.35 2.4 2.45 2.5 2.55 2.6 2.65

  • Quad. Phase Error (deg.)
  • Osc. Freq. (Ghz)

Coupling Device width (um) Quadrature Phase Error (deg.) Oscillation Frequency (GHz)

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Aniruddhan, IIT Madras ISCAS 2012 19

Comparison

Shunt coupled QRXO Series coupled QRXO Coupling Devices Saturation (smaller) Triode (larger) Quadrature Error ✕ ✓ Phase Noise ✓ ✕ Current Consumption ✓ ✕

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Aniruddhan, IIT Madras ISCAS 2012 20

Summary

  • Two topologies for quadrature coupling of

relaxation oscillators were presented

  • 2.4GHz quadrature oscillators were designed

and simulated in a UMC 0.18µm CMOS process

– Shunt-coupled

lower current, larger ⇒ quadrature error

– Series-coupled

larger current, lower ⇒ quadrature error

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Aniruddhan, IIT Madras ISCAS 2012 21

References

[1]

  • K. W. Cheng, K. Natarajan, and D. J. Allstot, “A Current Reuse Quadrature GPS Receiver in 0.13 µm

CMOS ,” IEEE Journal of Solid-State Circuits, vol. 45, No.3, pp. 510–523, March 2010. [2]

  • B. G. Perumana, R. Mukhopadhyay, S. Chakarborty, C. H. Lee, and J. Laskar, “A Low-Power Fully

Monolithic Subthreshold CMOS Receiver With Integrated LO Generation for 2.4 GHz Wireless PAN Applications ,” IEEE Journal of Solid-State Circuits, vol. 43, No.10, pp. 2229–2238, October 2008. [3]

  • A. Rofougaran, J. Rael, M. Rofougaran, and A. Abidi, “A 900MHz CMOS LC-Oscillator with

Quadrature Outputs,” IEEE International Solid-State Circuits Conference, Digest of Technical Papers, 1996. [4]

  • P. Andreani, “A 2 GHz, 17% Tuning Range Quadrature CMOS VCO with High Figure-of-Merit and

0.6° Phase Error,” Proceedings of the 28th European Solid-State Circuits Conference, 2002. [5]

  • C. J. M. Verhoeven, “A High-Frequency Electronically Tunable Quadrature Oscillator ,” IEEE Journal
  • f Solid-State Circuits, vol. 27, No.7, pp. 1097–1100, July 1992.

[6]

  • B. Zhou, W. Rhee, and Z. Wang, “Relaxation oscillator with quadrature triangular and square

waveform generation ,” Electronics Letters, vol. 47, No.13, 23rd June 2011. [7]

  • J. R. Fernandes, M. H. L. Kouwenhoven, C. van den Bos, L. B. Oliveira, and C. J. M. Verhoeven,

“The Effect of Mismatches and Delay on the Quadrature Error of a Cross-Coupled Relaxation Oscillator,” IEEE Transactions on Circuits and Systems-I: Regular Papers, vol. 54, No.12,

  • pp. 2592–2598, December 2007.
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Aniruddhan, IIT Madras ISCAS 2012 22

Thank you