DESIGN AND PARAMETRIC ANALYSIS OF VCOS …2.1[2]. At mm-wave frequencies, gain is rare discouraging...

DESIGN AND PARAMETRICANALYSIS OF VCOS FOR LOW

POWER APPLICATIONS

1Y.Vishwa Sri,Assistant Professor, Department of ECE,

Kommuri Pratap Reddy Institute of Technology2Dr. S. Sreenath Kashyap,

Associate Professor, Department of ECE,Kommuri Pratap Reddy Institute of Technology

Email: [email protected] ,[email protected]

April 27, 2018

Abstract

This paper presents a novel circuit topology of the Switchedcapacitor voltage controlled oscillator, conventional LC tankVCO and active inductor VCO for Multi-standard applica-tions. Recent advances in wireless communication market,a wireless device should be compatible with the standards ofpersonal area network, cellular networks and WLAN. Multistandard VCO is used in receiver section to tune wide rangeof frequency with input control signal. Switched capacitorcircuits are used to operate circuit in discrete time peri-ods, VCO constructed using switched capacitor can attainlow power consumption. The work proposes the design ofall three VCOs and compares result between them. IndexTerms: VCO, Switched capacitor VCO, WLAN, FrequencyModulator, Low power VLSI, WLAN standards.

Index Terms:VCO, Switched capacitor VCO, WLAN,Frequency Modulator, Low power VLSI, WLAN standards.

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International Journal of Pure and Applied MathematicsVolume 118 No. 24 2018ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

1 INTRODUCTION

A voltage-controlled oscillator or VCO is an electronic oscillatordesigned to be controlled in oscillation frequency by a voltage input.The frequency of oscillation is varied by the applied DC voltage,while

modulating signals may also be fed into the VCO to cause fre-quency modulation (FM) or phase modulation (PM). VCOs can begenerally categorized into two groups based on the type of wave-form produced: 1) harmonic oscillators, and 2) relaxation oscilla-tors. Harmonic oscillators generate a sinusoidal waveform. Relax-ation oscillators can generate a saw tooth or triangular waveform.Control of frequency in VCOs

A voltage-controlled capacitor is one method of making an LCoscillator vary its frequency in response to a control voltage. Special-purpose variable capacitance varactor diodes are available withwell- characterized wide-ranging values of capacitance[1]. Such de-vices are very convenient in the manufacture of voltage- controlledoscillators.

VCOs are used in:

• Electronic jamming equipment

• Function generators,

• The production of electronic music, to generate variables,

• Phase-locked loops.

• Frequency synthesizers used in communication equipment.

2 Wideband Receiver

High performance analog blocks and processing chains achievingadequate dynamic range have been published and successful demon-strations of Gb/s communications have been reported.

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International Journal of Pure and Applied Mathematics Special Issue

Fig 2.1: Spectrum allocation

One key aspect of the transceiver is the ability to handle wideanalog bandwidths, challenging for both the linear processing chainand the frequency reference generator. According to inter- nationalregulations, dedicated channels are 2.16 GHz wide and occupy thefrequency range between 57.2 GHz and 65.8 GHz, as shown in Fig.2.1[2]. At mm-wave frequencies, gain is rare discouraging tradinggain for bandwidth. In this work, which extends, we exploit a higherorder filter at the inter-stage between front-end blocks with signifi-cant improvement of the gainbandwidth product at the expense ofa moderate in-band ripple. This technique has been applied to bothLNA and mixer, resulting in an extremely sensitive 65 nm CMOSreceiver with noise

figure (NF)6.5 dB over 13 GHz bandwidth, verified with exper-iments on realized prototypes[3].

The receiver, adopts a sliding IF architecture preferred to a di-rect conversion because it does not require a Quadrature high fre-quency oscillator and to a fixed IF due to a more relaxed synthesizerfrequency range requirement[4]. By judicious choice of the chargepump current and filter components the integrated phase noise from10 kHz to 10 MHz offset is 22.5 dB, enough to assure adequate sig-nal to noise ratios even at highest communications rates.

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Fig 2.2: Integrated receiver A. Double-Driven Coupled ResonatorsCognitive radio

A.Double-Driven Coupled Resonators Cognitive radio (CR)has recently emerged as an umbrella term for systems that canadapt to changing conditions so as to dynamically use the spectrumin an opportunistic manner[5]. The adaptation/reconfigurabilityfunctions will be handled by adaptive frequency-agile RF transceivers,which are viewed as the foundation of CR in its most extreme formof a radio that can jump in and out of any band and any operatingmode.

Fig 2.3: Multi-band generation architecture

A number of local-oscillator (LO) frequencies are typically neededto cover such a wide spectrum. The main focus of the research sofar has been on offering multi- band frequency generators based onlocal oscillators with additional processing through frequency di-vision, frequency up- /down-conversion and multiplexing functionsFig 2.3.

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Fig 2.4: Switched capacitor

Fig.4. Simulation of PI controller

This paper details the concept of coupled driven resonators andapplies it to the design of a CMOS VCO that is capable of operatingin two widely separated bands, while simultaneously achieving widetuning range in each band[15].

It can also provide lower current consumption compared to con-tinuous magnetic tuning of transformer loads by utilizing varactortuning within each band and injecting current in the secondarywinding only when switching from one

frequency range to the other.B. Low-Voltage VCOTo reduce the power consumption of a system, low-voltage op-

eration has been a popular method, especially for digital circuitswhere supply voltage has been lowered below the threshold volt-age. In analog and RF circuits, low-voltage operation is difficult

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to achieve due to the reduced signal-to-noise ratio (SNR)[6]. Whilethere are several ways to extend the tuning range such as tank op-timization and a switched tuning scheme, they are not appropriatefor low-voltage VCOs. However, this technique brings about lowimpedance, which, in turn, leads to difficult startup conditions andhigh power consumption. Another way to extend the tuning rangeis to employ a switched tuning scheme.

Fig 2.5: Switch capacitor bank

In this paper, a 0.5-V CMOS VCO with a wide tuning range and lowsensitivity to PVT variations is presented in the 0.18- m process[16].To alleviate the tradeoff between the tuning range and the phasenoise in the

switched tuning scheme, a multistage voltage-boosting circuitis proposed, which is superior to an earlier voltage-boosting circuitproposed by the authors.

3 CONVENTIONAL LC TANK

LC VCOs have the advantage of large transistor voltage swings andlow phase noise. However, their power dissipation is excessive. Atlower frequencies, CMOS VCOs have gained popularity due to theirlow power dissipation brought about by the significantly lower sup-ply voltages[7]. Here, a family of 90-nm CMOS VCOs with recordtuning range and phase noise performance at 3GHz is presented.

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Fig 3.1LC tank VCO

In cross-coupled VCOs, as the parasitic capacitances of transistorsare directly lumped to the tank capacitance, the tuning range islimited by the transistor size[14]. The output buffer further de-grades it, which is always present in cross-coupled VCOs, eitherto drive the 50 test equipment or to distribute the VCO signal tomixers and frequency dividers in an IC. By comparison,the ColpittsVCO requires larger transistor size and current to produce the os-cillation, and hence dissipates more power[8]. Moreover, its tuningrange is mainly determined by the C1: CVAR ratio, which is inde-pendent of the oscillation frequency. Most importantly,fosc dependsprimarily on the passive components (L, C and C), which impliesthat TANK VAR redesigning the VCO to another frequency canbe achieved simply by scaling the passive components of the VCO.

A. THEORITICAL DERIVATIONS:

fosc =1

2π√LTANKCeq

Ceq =(C1 + CGS)(CV AR + CSB)

C1 + CV AR + CGS + CSB

+ CGD =C1CV AR

C1 + CV AR

Gm ≥ ω2oscC1CV ARRS

RsωoscLTANK

QLCeq = CV AR + CGS + 4CGD + CDB + CGS M2 + CGD M2

RP = ωoscLTANKQL

L′TANK =

LTANK

k, C

′1 =

C1

k, C

′V AR =

CV AR

k

G′m =

Gm

k

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B. ACTIVE INDUCTOR CMOS VCO Active inductorwhich are constructed using CMOS are used in VCO in LC circuits,since inductor are implemented using CMOS, area can be reduceddrastically, current consumption is also reduced, fabrication in alsovery easy.

Fig 3.2.1: Conceptual VCO

A conceptual illustration of the proposed VCO, where the LC-tankis composed of a tunable active inductor and a varactor for fre-quency control, and the negative conductance is employed to com-pensate for the loss from the LC-tank[9]. In addition, a varactoris included in the LC-tank for fine tuning, maintaining a relativelylow tuning sensitivity to ensure the frequency stability.

Fig 3.2.2: ACTIVE INDUCTOR VCO CRICURIT DAIGRAM

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Instead of using the conventional one-port active inductors, a two-port circuit topology

is adopted, allowing fully differential operation of the VCO. Asa result, a wideband operation with continuous frequency tuningis realized[13]. As for the loss compensation, NMOS cross-coupledtransistors are employed to provide the negative conductance.

C. Switched-Capacitor VCOA great deal of research has focused on the LC-tank VCOs

consisting of passive inductors, transformers, and varactors, whichare available with advancement of CMOS technology. Recently, aVCO using a couple of NMOS and PMOS transistors in the cross-connected pair as a negative conductance generator has been pre-sented[10]. Hence, the topology of switching capacitor is used toenhance the characteristics of phase noise by dividing the wantedfrequency band into four sections.

Fig 3.3: circuit diagram of switched capacitor

The current-reused LC-VCO consists of cross-connected pair tran-sistors M1 and M2, LC- tank and two switched capacitors. Thecurrent-reused VCO must usually be designed carefully to arrive atsymmetrically

differential output signals. Degeneration resistances and degen-eration capacitors are added to enhance the symmetry of the differ-ential output signals[12]. In addition, the source- degenerated RCtopology forms a low-pass filter and is capable of reducing noise.

4 FM - GENERATION BY VCO

A very simple and direct method of generating an FM signal is bythe use of a voltage controlled oscillator. The frequency of suchan oscillator can be varied by an amount proportional to the mag-nitude of an input (control) voltage[11]. Such oscillators, in the

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form of an integrated circuit, have very linear characteristics overa frequency range.

Fig 4.1(a) Block diagram of VCO as FMmodulator, Fig 4.1(b) FM signal

The frequency change is large compared with the unmodulated out-put frequency, and the carrier frequency is only four times that ofthe message.

5 RESULTS ANDDICUSSIONS CON-

VENTIONAL LC VCO SIMULATION

RESULTS

Fig 5.1: Simulation result at control voltage=0.5V

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ACTIVE INDUCTOR VCO SIMULATION RESULTS


SWITCHED CAPACITOR VCO SIMULATION RESULTS


PHASE NOSIE ANALAYSICS:

Fig 5.4: Phase Noise of Conventional VCO

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Fig 5.5: Phase Noise of Active InductorVCO

Fig 5.6: Phase Noise of Switched CapacitorVCO

Fig 5.7: Comparison of Phase Noise of all three circuits

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Fig 5.8: Simulation results of VCO as FM Modulator

6 CONCULSION

In this phase many technical papers have been studied and im-portant parameter to measure VCO performance are been studied.Conventional LC tank VCO, Active inductor VCO and Switchedcapacitor VCO is simulated and parameters frequency and powerhave been measured. An application FM modulator is simulatedusing switched capacitor VCO.

References

[1] B. Min and H. Jeong, 5-GHz CMOS LC VCOs with wide tun-ing ranges, IEEE Microw. Wireless Compon. Lett., vol. 15, no.5, pp. 336 338, May 2005.

[2] R. S. Rana, X. D. Zhou, and Y. Lian, An

optimized 2.4 GHz CMOS LC-tank VCO with

0.55%/V frequency pushing and 516 MHz tuning range, inIEEE Int. Circuits Syst. Symp., May 2005, pp. 48114814.

[3] B. De Muer, N. Itoh, M. Borremans, and M. Steyaert, A 1.8-GHz highly-tunable low-phasenoise CMOS VCO, in IEEECustom Integr.

Circuits Conf., May 2000, pp. 585588.

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[4] A. D. Berny, A. M. Niknejad, and R. G. Meyer, A 1.8-GHzLC VCO with 1.3-GHz tuning range and digital amplitudecalibration, IEEE J. Solid-State Circuits, vol. 40, no. 4, pp.909917, Apr. 2005.

[5] A wideband low-phase-noise CMOS VCO, in IEEE CustomIntegr. Circuits Conf., Sep. 2003, pp. 555558.

[6] F. Herzel, H. Erzgraber, and N. Ilkov, A new approach to fullyinte- grated CMOS LC- oscillators with a very large tuningrange, in IEEE Custom Integr. Circuits Conf., May 2000, pp.573576.

[7] Z. Li and K. K. O, A 1-V low phase noise multi-band CMOSvoltage controlled oscillator with switched inductors and ca-pacitors, in IEEE Radio Freq. Integr. Circuits Symp. Dig., Jun.2004, pp. 467470.

[8] J.-S. Ko and K. Lee, Low power, tunable active inductor andits applications to monolithic VCO and BPF, in IEEE MTT-S Int. Microw. Symp. Dig., Jun. 1997, pp. 929932.

[9] T. Y. K. Lin and A. J. Payne, Design of a low-voltage, low-power, wide-tuning integrated oscillator, in IEEE Int. CircuitsSyst. Symp., May 2000, pp. 629632.

[10] R. Mukhopadhyay, Y. Park, P. Sen, N. Srirattana, J. Lee, C.-H. Lee, S. Nuttinck, A. Joseph, J. D. Cressler, and J. Laskar,Reconfigurable RFICs in Si-based technologies for a compactintelligent RF front- end, IEEE Trans. Microw. Theory Tech.,vol. 53, no. 1, pp. 8193, Jan. 2005.

[11] D. Ham and A. Hajimiri, Concepts and

methods in optimization of integrated LC

VCOs, IEEE J. Solid-State Circuits, vol. 36, no.

6, pp. 896909, Jun. 2001.

[12] A. Hajimiri and T. H. Lee, Design issues in CMOS differentialLC oscillators, IEEE J. Solid-State Circuits, vol. 34, no. 5, pp.717724, May 1999.

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[13] A general theory of phase noise in electrical oscillators, IEEEJ. Solid-State Circuits, vol. 33, no. 2, pp. 179194, Feb. 1998.

[14] L. Jia, J.-G. Ma, K. S. Yeo, and M. A. Do, 9.310.4-GHz-bandcross- coupled complementary oscillator with low phase-noiseperformance, IEEE Trans. Microw. Theory Tech., vol. 52, no.4, pp. 12731278, Apr. 2004.

[15] Y.-H. Chuang, S.-L. Jang, J.-F. Lee, and S.- H. Lee, A lowvoltage 900 MHz voltage controlled ring oscillator with widetuning range, in IEEE AsiaPacific Circuits Syst. Conf., Dec.2004, pp. 301304.

[16] Y. A. Eken and J. P. Uyemura, A 5.9-GHz voltage-controlledring oscillator in 0.18-m CMOS, IEEE J. Solid-State Circuits,vol. 39, no. 1, pp. 230233, Jan. 2004.

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DESIGN AND PARAMETRIC ANALYSIS OF VCOS …2.1[2]. At mm-wave frequencies, gain is rare discouraging...

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