Int. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015) e-ISSN: 1694-2310 | p-ISSN: 1694-2426

NITTTR, Chandigarh EDIT -2015 18

A LOW POWER, LOW PHASE NOISE CMOSLC OSCILLATOR

1Pankaj Aseri, 2R.C Gurjar1,2Microelectronics and VLSI Design, E&I Department, Shri G. S. Institute of Technology and Science, Indore,

M.P, India1pankajaseri17@gmail.com,2rgurjar@sgsits.ac.in

Abstract:- In this paper a Double Cross Coupled Inductorcapacitor based Voltage Control Oscillator (LC-VCO) isdesigned. In the proposed circuit the phase noise, tuningrange with respect to control voltage, output power and thepower dissipation of the circuit is analysed. Phase noise ofapproximate -96 dBc/Hz at frequency of 1MHz, frequencytuning range of 4.8 to 8.3 GHz (corresponding to 53.0%tuning range) obtained by varying the control voltage from 0to 2.0 V, Output power of circuit -8.92 dBm at 50 Ohmresistance terminal and the power consumption of Circuit is3.8 mW. This VCO are designed for 5.5 GHz. The circuit isdesigned on the UMC 180nm CMOS technology and all thesimulation results are obtained using cadence SPECTRESimulator.

Keywords:- Phase Noise, LC-Tank, CMOS, Voltage controlledOscillator (VCO), Low power.

I. INDTRODCTIONThe typical performance parameters of a VCO are phasenoise, tuning range, output power and DC powerconsumption [1]. The VCO is the most important buildingblock of RF IC design. It play a vital role in manyapplications such as GSM, Bluetooth, WLAN, WirelessPersonal Area Network (WPAN) and Wireless SensorNetwork etc. [2]. The most difficult task is to design theVoltage Control Oscillator in the Front end block of RF-ICdesign. In the today’s world of perfection in technologythere is a need to design and develop the circuit with Lowpower and Low noise at the Higher Frequency. Out of thetotal power consumption of a system the oscillator powerconsumption can be a significant portion. So over- allpower consumption can be reduced by minimizing thepower consumption of the VCO [2]. Some basic oscillatorcircuits such as local oscillator are limited to the Mixercircuits at receiver end. But, at the high frequency thedifferent topology of oscillators are used that are capable toprovide low phase noise and most important term smallerpower at high frequency range i.e. Radio frequency range.For higher quality receivers, an L C oscillator topology ischosen over a relaxation oscillator because the band passnature of the resonant tank in the L C oscillator providesthe lowest phase noise [3]. In this paper, LC VoltageControlled Oscillator is designed, the proposed circuitshows frequency tuning range in Giga Hertz due tovariation in control voltage variation.In the SECTION II and SECTION III of this paperprovides information about the LC-VCO circuitdescription and theoretical analyses of proposed circuit.SECTION IV and SECTION V shows the simulationresults and conclusion.

II. LC-VCO CIRCUIT DESCRIPTIONThe schematic circuit of the double cross coupleddifferential LC-VCO including the differential buffer at theoutput side is shown in Fig.1. The proposed LC-VCO formby the PMOS and NMOS, inductor, and capacitor. ThisLC-VCO is having of Cross Coupled PMOS transistors(M4, M5) and Cross Coupled NMOS transistors (M0, M3).Here PMOS and NMOS pairs are in parallel and due to thisnegative resistance is generated. M14 and M12 transistorsare used as an output buffer. For biasing proposed circuit acurrent mirror technique is used. (M1, M2) transistors arebeing used as a current mirror. The Oscillation frequencycan be obtain from M14 and M12 NMOS transistors. Thisproposed circuit provides better Phase Noise performancemeasure because of double switch Cross Coupledstructure.

Fig: 1. Cross Coupled double switch LC-VCO.

III.THEORITICAL ANALYSES OF PROPOSEDCIRCUIT

The proposed circuit shown in the fig.1 consists ofinductor and voltage controlled capacitor (capacitor designthrough MOS transistor) these two passive element formsor resonant tank circuit. In the proposed circuit MOStransistors (M1, M2) and (M3, M4) are cross coupledtransistors, which forms negative resistance and thisnegative resistance basically compensated the resonatorlosses. Voltage across the tank circuit is given by:-

- ≈ A sin( ) (1)

Where = ωt, ω being the angular frequency of oscillation.

Equations for bias current ( ) in NMOS and PMOS pair isas follows:-

Int. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015) e-ISSN: 1694-2310 | p-ISSN: 1694-2426

19 NITTTR, Chandigarh EDIT-2015

+ = (2)And also for PMOS pair

+ = (3)

If transconductance PMOS and NMOS are gmp and gmn

respectively, from the small signal behaviour and analysewe can relate negative resistance Rnegative with thetranscondutances of NMOS and PMOS shown below:-= − (4)

If gmp = gmn = gm. Then we have> (5)

The transistors (M5, M6) are current mirror which provideor maintain the tail current of VCO and provide currentmirror action. Transistor (M7, M8) act as common drainoutput buffer and having large input impedance.

IV.SIMULATION RESULTSIn this section, we have shown all simulation results ofdouble cross coupled LC-VCO. This VCO is designedusing UMC 180nm CMOS technology and is simulatedwith Cadence Spectre simulator. This work has usedestimated value of inductance as L= 2nH and a variableMOS based capacitor. For all measurements, we havechosen following parameters as Vdd (power supply) = 1.8Vand biasing current Ibias, M1 = 1mA. The DC powerconsumption of about <= 3.8 mW is obtained. Fig. 2 showsthe Oscillation waveform of LC-VCO. This Oscillation isproduced by the tank circuit, i.e. inductor (L) andCapacitor (Ceq) in parallel connection forms the parallelRLC circuit.

Fig: 2 Oscillation Waveform of LC VCO

Fig: 3 Oscillation of frequency at two output nodes Vout+and Vout- of LC-VCO.

Fig. 4 The Phase Noise performance of circuit.

Fig: 5 The Tuning range response of circuit.

Fig: 4 The Phase Noise performance of circuit.Fig: 5 The Tuning range response of circuit i.e. graphbetween Frequency v/s Vcn (Control Voltage).By varying of Control Voltage from 0 Volts to 2 Volts, theOscillation frequency varies from 4.8 GHz to 8.3 GHz.The percentage tuning is measured to be 53%.

Int. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015) e-ISSN: 1694-2310 | p-ISSN: 1694-2426

NITTTR, Chandigarh EDIT -2015 20

TABLE.1 COMPARISON AND PERFORMANCESUMMARY OF LC-OSCILLATOR WITH EARLIER

WORKSParameters This

Work[1] [4] [5]

Process (nm) 180 250 180 180

OscillationFrequency

(GHz)

5.5 5.5 4.2 4.25

Core Current(mA)

1 0.83 6 4

Supply voltage(V)

1.8 2.5 1 2

PowerDissipation(m

W)

3.8 2.075 6.0 8.0

Tuning range(%)

53 16.9 42 30

Phase Noise(dBc/Hz)

-95.6@1MH

z

-89.77@1MH

z

-116@1MH

z

-114@1MH

z

V.CONCLUSIONThis design shows improved performance of Double crosscoupled LC-VCO. The integrated CMOS LC-VCO usesdouble cross coupled transistor, an inductor and a capacitor(using MOS varactors). This CMOS LC-VCO isimplemented using UMC 180nm CMOS technology and issimulated using Cadence SPECTRE simulator. This designhas measured phase noise performance of -95.6 dBc/Hz at1MHz and -116.3 dBc/Hz at 3MHz. It consume 3.8mWpower at 1.8V DC voltage supply. The tuning range of thiscircuit is from 4.3 GHz to 8.3 GHz for 0V to 2V controlVoltage respectively i.e. about 53% tuning range. Thisdesign finds its application in RF field because of its lowpower, low area and high speed. Comparison andperformance summary of this work and earlier Oscillatorwork is shown in Table.1

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Small Area, Fully Integrated 5.5 GHz CMOS LC-VCO,Microelectronics and Electronics (PRIME), 2014 10th Conferenceon Ph.D. Research in IEEE 2014, pp. 1-4.

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7) M. Ebrahmzadeh, "Design of an Ultra-Low Power Low Phase NoiseCMOS LC Oscillator," International Scholarly and ScientificResearch & Innovation, vol. 5, IEEE 2011, pp. 931-934,

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