158 IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 23, NO. 3, MARCH 2013

20-pJ/Pulse 250 Mbps Low-Complexity CMOSUWB Transmitter for 3–5 GHz Applications

Ming Jian Zhao, Bin Li, Member, IEEE, and Zhao Hui Wu, Member, IEEE

Abstract—This letter presents a CMOS on-off keying 3–5 GHzultra-wideband (UWB) transmitter with low complexity, lowpower and high speed. In the transmitter, a new differentialnarrow triangular pulse generator using push and pull integratingtechnique was designed for reducing quiescent current andcommon-mode interference, and a new complementary switchmode on-off voltage controlled ring oscillator (VCRO) was pro-posed by breaking the oscillation loop instead of breaking thepower to avoid base-band energy without extra shaping filter.Without using delay resistor and capacitor in the VCRO, thetransient response speed of the transmitter can be increased byonly utilizing the parasitic resistances and capacitances. Thedesign was successfully implemented with a 0.18 CMOStechnology. The test results show that the new UWB transmittercan obtain a sidelobe rejection of more than 20 dB, a low energyconsumption of 20 pJ/pulse at 250 Mbps, and a small core chipsize of 0.08 .

Index Terms—CMOS, high speed, low power, narrow triangularpulse, on-off voltage controlled ring oscillator (VCRO), ultra wide-band (UWB) transmitter.

I. INTRODUCTION

T HE ultra-wideband (UWB) communication technologymeets the crucial requirements for future high data-rate

and low-power wireless applications such as wireless com-ponent interconnect and implantable biomedical electronics.According to the U.S. Federal Communications Commission(FCC) spectrum mask regulation, the power levels of a licensedUWB RF signal must be lower than 41.3 dBm/MHz in the3.1 10.6 GHz frequency band [1].There are several methods to generate a licensed UWB RF

signal. One way is to shape or filter out a base-band narrowpulse to satisfy the FCC regulation. However, it needs to inte-grate a large area of LC circuit which is not beneficial to theminiaturization of the devices [2]. Another way is to use anall-digital method to generate licensed UWB RF signal by com-bining multiple base-band single-pulse to meet FCC regulation[3], [4]. Such technique requires an accurate relative delay con-trol of each monocycle, resulting in some design difficulties.The third way is to use a mixer and a voltage controlled oscil-lator (VCO)with a few LC components to transpose a base-bandsignal to a licensed UWB RF signal [5], [6]. Although this way

Manuscript received August 12, 2012; revised December 06, 2012; acceptedJanuary 26, 2013. Date of publication February 25, 2013; date of current versionMarch 07, 2013. This work was supported by the Natural Science Foundationof China (60976026).The authors are with the Institute of Microelectronics, School of Elec-

tronic and Information Engineering, South China University of Technology,Guangzhou, 510640, China (e-mail: phlibin@scut.edu.cn).Color versions of one or more of the figures in this letter are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/LMWC.2013.2245412

Fig. 1. Block diagram of the proposed OOK UWB transmitter.

has good performance in signal peak magnitude and spectral ef-ficiency, it’s not suitable for high-speed design due to its highpower consumption or long oscillation response time. In addi-tion, a digital pulse oscillator operating in switch mode with fasttransient response can generate UWB RF signal, but it needs anextra shaping filter to remove the base-band energy in the outputsignal spectrum.In this letter, a novel low-complexity high-speed on-off

keying (OOK) UWB transmitter is proposed. In the noveltransmitter, a burst operation mode is used to reduce the staticpower consumption. In the design of the key module-voltagecontrolled ring oscillator (VCRO), a new switch mode withbreaking the oscillation loop instead of breaking power isused to avoid ringing and keep high speed at same time. Fur-thermore, the new structure of the designed VCRO can avoidproducing base-band energy even without using extra filter,making the design low power and compact. The proposedtransmitter was implemented by a 0.18 CMOS process andthe tested results show that it is highly compact, low power andhigh speed.

II. PROPOSED OOK UWB TRANSMITTER STRUCTURE

The proposed UWB transmitter operating in burst mode isshown in Fig. 1. It consists of a base-band unit, a differentialnarrow triangular pulse generator, an on-off voltage controlledring oscillator (VCRO), and a RF output buffer.Through the base-band unit, the data is transported to narrow

base-band pulse of pulse-width calibrated by VC1 [8].The is changed to a pair of narrow triangular pulsesby a differential narrow triangular pulse generator. Thethen switch the oscillation loop of the on-off VCRO through acomplementary switch mode up-converting the base-band pulseto the OOK UWB RF signal with the amplitude modulated bythe narrow triangular pulse amplitude. Most of the signal energyis confined in the useful bandwidth. The centre frequency of theUWB RF signal can be calibrated by the control voltage VC2.The bandwidth of the UWB RF signal is .Finally, a RF output buffer with a shunt feedback amplifier

and a source follower is used to drive the antenna and adjust thelicensed output power of the UWB RF signal by control voltageVC3 for different applications.

1531-1309/$31.00 © 2013 IEEE

ZHAO et al.: 20 pJ/PULSE 250 Mbps LOW-COMPLEXITY CMOS UWB TRANSMITTER FOR 3–5 GHz APPLICATIONS 159

Fig. 2. Differential narrow triangular pulse generator. (a) The core circuit ofthe narrow triangular pulse generator, (b) The simplified equivalent model of thetransistors M2, M3 and MC. M1-M2 (5.2 um/180 nm), M3-M4 (1.84 um/180nm), MC (16 u/4 u).

III. DESIGN OF KEY CIRCUITS IN THE TRANSMITTER

A. Differential Narrow Triangular Pulse Generator

In order to drive the on-off VCRO and make the UWB RFsignal satisfy the FCC spectral mask and achieve more than20 dB of sidelobe rejection, a differential narrow triangularpulse generator is employed and shown in Fig. 2.In Fig. 2(a), a pair of accurate out-of-phase narrow pulses

and are generated by two exclusive OR gates(XOR1, XOR2) and connected to the gate of the transistorsM1 and M4. M1 and M4 compose a charge pump to drive thefollow-up NMOS-connected capacitor MC for saving area. Inorder to achieve high-performance, the push and pull current ofM1 and M4 are kept equal by designing proper W/L. M2 andM3 operate in linear region with uniform equivalent resistance

. The simplified equivalent model of M2, M3 andMC is shown in Fig. 2(b). and MC are implementedby transistors M2, M3 and MC. When and turn up,M1a and M4b turn off, M1b and M4a turn on in the meantime.On the contrary, when and turn up, M1a and M4bturn on, M1b and M4a turn off in the meantime. By adjustinga suitable RC time constant of the transistors M2, M3 and MC,the narrow base-band pulse can be transposed to the narrowtriangular pulse properly.There is no quiescent current in the differential narrow tri-

angular pulse generator, hence the power dissipation is low. Inaddition, the common-mode interference is restrained by the ca-pacitor MC connecting at both differential output ends.

B. On-off VCRO for UWB RF Signal Generation

The proposed on-off VCRO uses a new switch mode to avoidthe base-band energy. It is driven by a pair of out-of-phasenarrow triangular pulses, implements OOK UWB modulationand gives an output of a licensed UWB RF signal.As shown in Fig. 3, the proposed on-off VCRO consists

of an on-off digital ring oscillator (M5-M8), an output buffer(M9), and a voltage-controlled current source (M10-M12). Thetransistor M8 can implement a new efficiently complementaryswitch mode to control the oscillation loop on or off.When the differential narrow triangular pulse turns up,

the complementary switch (M8) closes the oscillation loop, the

Fig. 3. Core circuit of the on-off VCRO. M5a-M9a (5.2 um/180 nm),M5b-M9b (1.84 um/180 nm).

Fig. 4. (a) Die micrograph of the fabricated UWB transmitter, (b) The photo-graph of the transmitter bonding on a PCB to test.

is up-converted to UWBRF frequency band and the outputhas an smooth triangular-like envelope.In the traditional solution, when the oscillation turns off, the

output of the on-off VCRO will be connected to the power orthe ground, inducing a high base-band energy corresponding tothe base-band switch pulse.In this design, in order to solve above problem, besides using

complementary switch (M8) to break the oscillation loop, afeedback resistor is employed to achieve the self-biased voltageat input and output of the output buffer (M9). In this way, Whenthe M8 turns off, though the drain of the M8 and the gate of theM5 connected to the gate of the M9, there is no direct currentpath connecting the gate of the M9 except for the self-biasedresistor Rs. So the output baseline voltage of the M8 and M9 isdecided by the self-biased resistor Rs, normally at the middlelevel of the oscillation voltage. Therefore, the base-band energycan be avoided without extra shaping filter in the output of theon-off VCRO.The transmission delay of the on-off digital ring oscillator

is determined by parasitic resistances and capacitances in eachoutput of the inverters (M5, M6 and M7) and the direct currentof M10 . Hence, the ring oscillator has a fasttransient response ensuring a sufficient oscillation during veryshort pulse duration (can be even as short as a nanosecond). Theoscillation frequency which is the center frequency of UWB RFsignal can be calibrated by the control voltage VC2. Finally, theon-off VCRO outputs a UWB RF signal falling into the FCCspectral mask with favorable spectral efficiency and low powerdissipation.

IV. MEASUREMENT RESULTS

The proposed UWB transmitter was fabricated using 0.18CMOS process, shown in Fig. 4(a). The transmitter is compactand highly integrated without inductor. The core chip size is0.08 excluding pads. For testing convenience, the UWB

160 IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 23, NO. 3, MARCH 2013

Fig. 5. Output PSD in compliance with FCC mask.

Fig. 6. Time domain response of the output signal.

TABLE ICOMPARISONS WITH PREVIOUSLY REPORTED UWB TX

Excluding the output buffer power consumption.

transmitter chip was bond on a PCB directly and tested with thecables, as shown in Fig. 4(b).The transmitter operates with 1.8 V supply, and the input data

is unipolar non-return-to-zero (NRZ) pseudo random code at250 Mbps. The output power spectral density (PSD) was ob-tained by a spectrum analyzer (Anritsu MS2665C), shown inFig. 5. The Black dotted line is simulation result. It is seen thatthe output UWB RF signal satisfies the FCC spectral mask:2 GHz 10 dB bandwidth from 3 to 5 GHz. It has favorable

spectral efficiency with more than 20 dB sidelobe rejection andlow base-band energy of less than 75 dBm.The time domain measurement result is obtained by an os-

cilloscope (Agilent 86100A), as shown in Fig. 6. The Vpp ofthe UWB RF signal on a 50 ohm output load is 260 mV withpulse-width of 1 ns. The pulse repetition period of the signal is4 ns, indicating a data rate of 250 Mps. The simulation resultmarked in blue is provided for comparison.The tested power consumption of the transmitter is 5 mW at

250 Mbps, correspondent to a low energy consumption of 20 pJper pulse, showing that the burst operation mode can save thepower efficiently. Table I shows the performances in compar-ison with previously reported UWB transmitter [7]. It demon-strates that the design with fast transient response is suitablefor applications of low power consumption, high speed and lowcost.

V. CONCLUSION

A low-complexity 3 5 GHz UWB transmitter is proposed.The novel UWB transmitter works at a burst operation mode toreduce the static power consumption. When designing the keymodule-voltage controlled ring oscillator (VCRO), breaking theoscillation loop is used to replace breaking the power, makingthe VCRO avoid ringing but still keep high speed, and not pro-duce base-band energy even without using extra filter. The newdesign methods make the power of the transmitter lower than20 pJ/pulse at 250 Mbps and the chip area only 0.08 . Tri-angular pulses are produced by a new complementary push andpull narrow triangular pulse generator and used to control theVCRO on and off, improving the sidelobe rejection of the UWBoutput signal to more than 20 dB. The test results of the chipshow that the new UWB transmitter meets requirements of lowpower, high speed, and is suitable for using in potential wirelesscomponent interconnect and implantable electronic systems ap-plications.

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