WO2008069444A1

WO2008069444A1 - Ultra-low power pulse generator for multiband impulse radio-ultra wideband system and method using the same

Info

Publication number: WO2008069444A1
Application number: PCT/KR2007/005268
Authority: WO
Inventors: Jong-Oh Lee; Yoonme Doh; Cheol Sig Pyo; Sang-Gug Lee; Seok-Kyun Han; Phan Yuan Ahn
Original assignee: Electronics And Telecommunications Research Institute
Priority date: 2006-12-06
Filing date: 2007-10-24
Publication date: 2008-06-12

Abstract

Provided are an ultra-low power dispersion pulse generator for a multiband impulse radio (IR)-UWB system and a pulse generation method. The pulse generator includes an oscillation unit generating and outputting a sinusoidal wave; a switch unit activating or deactivating the oscillation unit according to a first control signal; and an adjustment unit adjusting a frequency of the sinusoidal wave. Pulse power spectral density (PSD) of an output pulse matches a Federal Communication Commission (FCC) spectral mask, and a simple switching function can be provided between subbands by changing an oscillation frequency.

Description

ULTRA-LOW POWER PULSE GENERATOR FOR MULTIBAND IMPULSE RADIO-ULTRA WIDEBAND

SYSTEM AND METHOD USING THE SAME

Technical Field

[1] The present invention relates to a pulse generator reqared for ultra-wideband (UWB) communication and a pulse generation method for generating pulse for UWB communication, and more particularly, to an ultra-low power dispersion pulse generator for a multiband impulse radio (IR)-UWB system and a pulse generation method pulse for UWB communication.

[2] The present invention is supported by an information technology (IT) research and development (R&D) program of the Ministry of Information and Communication (MIC) [2005-S-106-02, Development of Sensor Tag and Sensor Node Technologies for Radio Freψency Identification (RFED)/Ubiqitcus Sensor Network (USN)']. Background Art

[3] The Federal Communication Commission (FCC) has defined spectral mask having maximum average eψivalent radiation isotropic power spectral density of -41.25 dBm/MHz and a minimum bandwidth to be 500 MHz for UWB. There are two approaches to an UWB application. That is, multiband orthogonal frecμency division multiplexing (OFDM) UWB and impulse radio (IR)-UWB. Recently, IR-UWB is drawing a lot of attention not only from industries but also from research centers. IR- UWB is one of the most suitable technologies for providing a precise positioning function for inexpensive, low-power consuming and low data rate wireless communication applications and radio frecμency identification (RFID) due to its very short pulse characteristic. In this case, a pulse generator is an essential component of an IR- UWB transceiver.

[4] Previously reported types of pulses of IR-UWB systems may be classified into two types; a pulse for a single band IR-UWB system and a pulse for a multiband IR-UWB system.

[5] For the single band (carrierless) IR-UWB system, a pulse spectrum is designed to occupy an entire allowable freψency band of 3.1 to 10.6 GHz. Hence, a pulse for the single band IR-UWB system reqires very duration (shorter than nanoseconds) having a waveform that is similar to a Gaussian function. Pulses having various waveforms may be used as the pulse for the single band IR-UWB system. Fbwever, a Gaussian pulse is best for satisfying wide bandwidth (??) since a Gaussian pulse and its derivatives include very small sidelobes and provide a sharper roll-off than other types of pulses.. According to theoretical analysis, the higher the derivative order of a Gaussian pulse, the better the roll-off. Hence, the Gaussian pulse can match an FCC spectral mask without reqiring an additional pulse-shaping filter. According to the theoretical analysis, at least 7 derivatives of the Gaussian pulse need to be selected in order to meet pulse power spectral density (PSD) in the FCC spectral mask for outdoor applications. When the order of the derivative or an additionally reqired filter is considered, a Gaussian pulse-based a\ proach is not recommended. In addition, high- and low-frecμency components of the PSD are asymmetric to each other as the order of derivative is increased.

[6] One of the first types of pulse generator used a step recovery diode (SRD) and a transmission line or used a direct synthesis method that took advantages of bipolar junction transistor (BJT) characteristics. However, this type of pulse generator cannot be easily integrated and cannot be implemented in a simple structure and at low costs. Recently, different forms of pulse generator technologies have been developed. Pulses generated using these technologies are generally first or second derivatives of Gaussian pulses and cannot match the FCC spectral mask. Thus, an additional pulse- shaping filter is reqired. In this regard, digital technology including a complicated circuit for generating a pulse using a pulse pattern has been recommended, tbwever, this type of pulse generator consumes a lot of power, does not provide a multiband switching function, and has a complicated structure.

[7] A pulse for a multiband (carrier-based) IR-UWB system has a longer duration than a pulse for a single band IR-UWB system. Since a pulse for the multiband IR-UWB system includes a plurality of sine wave cycles, it has narrow bandwidth. A multicycle pulse is generated by adjusting the amplitude of an oscillator according to a particular form, for example, a rectangle or a triangle, of an envelope. A center freqiency of the oscillator defines a center freqαency of a pulse spectrum that needs to be adjusted according to subband switching. The pulse spectrum shows different characteristics according to the form of a pulse envelope. Ibr example, a pulse having a triangular envelope can provide a maximum sidelobe suppression fiinction of 26 dB, and only 13dB can be obtained from a rectangular envelope. The size of a sidelobe suppression factor is important for a multiband system in order to prevent interference of adjacent channels. R>r maximum performance the form of the pulse must be symmetrical in a time region. Accordingly, its spectrum is symmetrically concentrated near a center freψency that has maximum equivalent sidelobe suppression.

[8] A pulse may be generated by multiplying a triangular envelope by an output of a voltage controlled oscillator (VCO). This approach illustrated in FIG. 1 provides a sidelobe suppression of more than 20 dB and confines most power to within an effective bandwidth . However, if complexity increases, that is, if the number of fiinctional blocks included in a phase-locked loop (PLL) is increased, chip size is increased, and a lot of direct current is consumed. Thus, this approach is not desirable. Another approach to generation of a multiband pulse is to gate an oscillator. A problem with this technology lies in the fact that an envelope of an output pulse is rectangular. Therefore, additional filtering is reqired for sidelobe rejection performance.

[9] As discussed above, a pulse generator for a multiband IR-UWB system is reqired, wherein the pulse generator can generate a short pulse having a bandwidth of approximately 528 MHz and support a subband switching function. The PSD of a generated pulse must match the FCC spectral mask that has sidelobe rejection performance sufficiently high to endire interference of adjacent channels. In addition, the circuit of the pulse generator must be simple and consume relatively low power so that it can be implemented at low costs. Disclosure of Invention Technical Problem

[10] The present invention provides an apparatus and method for generating a multi-cycle pulse for an ultra-low power consuming multiband impulse radio (IR)-ultra wideband (UWB) system. Technical Solution

[11] According to an aspect of the present invention, there is provided an ultra-low power pulse generator for multiband impulse radio (IR)-ultra wideband (UWB) system. The generator includes an oscillation unit generating and outputting a sinusoidal wave; a switch unit activating or deactivating the oscillation unit according to a first control signal; and an adjustment unit adjusting a freqαency of the sinusoidal wave.

[12] According to another aspect of the present invention, there is provided an ultra-low power pulse generator for multiband impulse radio (IR)-ultra wideband (UWB) system. The generator includes an oscillation unit generating and outputting a sinusoidal wave; a switch unit activating or deactivating the oscillation unit according to a first control signal; an adjustment unit adjusting a freqαency of the sinusoidal wave; a power supply unit supplying current; and a control unit receiving the current and supplying the current or blocking the supply of the current to the oscillation unit, the switch unit and the adjustment unit according to a value obtained by inverting the first control signal. [13] According to another aspect of the present invention, there is provided a method for generating pulse for UWB system. The method includes enerating a sinusoidal wave using an oscillator which can be turned on or off; [14] activating or deactivating the oscillator according to a first control signal; supplying power to the oscillator when the oscillator is activated and blocking the supply of power to the oscillator when the oscillator is deactivated; and [15] adjusting a freφency of the oscillator by changing a value of a capacitor according to a freφency generation reφest which corresponds to a subband.

Advantageous Effects [16] According to the present invention, an ultra-low power pulse generator for multiband

IR-UWB system and a pulse generation method performed using the pulse generator provide a bandwidth of approximately 528 MHz. In addition, the PSD of a final output pulse matches the FCC spectral mask, and a simple switching function can be provided between subbands by changing an oscillation freφency.

[17] The generator and method can also provide a plurality of subbands in a predetermined freφency range (for example, three subbands in the range of 3.1 to 5.1

GHz) and can be used even when the freφency range of applications are extended to or beyond an entire UWB freφency range. [18] An output pulse width can be controlled by changing the duration of an input digital sφare pulse, which can support both pulse position and on-off keying modulation. [19] Furthermore, the pulse generator does not consume direct current and is very suitable for a low-power consuming application. [20] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Description of Drawings [21] The features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: [22] FIG. 1 is a block diagram of a conventional carrier-based pulse generator; [23] FIG. 2 is a diagram for explaining a theory of a pulse generator according to an embodiment of the present invention;

[24] FIG. 3A is an eψivalent circuit diagram of an LC oscillator when turned on;

[25] FIG. 3B is an eψivalent circuit diagram of the LC oscillator when turned off;

[26] FIG. 4 is an output waveform of an oscillator, that is, showing transient waveforms

(indicated by solid lines) when the oscillator is turned on or off and waveforms

(indicated by dotted lines) when the oscillator is in a steady state; [27] FIG. 5 is a block diagram of an ultra-low power pulse generator for multiband impulse radio (IR)-ultra wideband (UWB) system, according to an embodiment of the present invention; [28] FIG. 6 is a circuit diagram of an ultra-low power pulse generator for multiband IR-

UWB system, according to an embodiment of the present invention; [29] FIG. 7 is a circuit diagram of an ultra-low power pulse generator for multiband IR-

UWB system, according to another embodiment of the present invention; [30] FIG. 8 is a circuit diagram of an ultra-low power pulse generator for multiband IR-

UWB system, according to another embodiment of the present invention; [31] FIG. 9 is a timing diagram of waveforms and switching operations of nodes A, B and

C of the ultra-low power pulse generator of FIG. 8); [32] FIG. 10 is a circuit diagram of each of first and second switches according to an embodiment of the present invention;

[33] FTG. 11 illustrates capacitor banks controlled by a 2-bit signal for subband selection;

[34] FIG. 12 illustrates waveforms of an output pulse train according to an embodiment of the present invention; [35] FIG. 13 illustrates a waveform of a signal pulse in detail from among the waveforms illustrated in FIG. 12; [36] FIG. 14 shows that the measured characteristic of power spectrum of a generated pulse is in compliance with a Federal Communication Commission (FCC) spectral mask; [37] FIG. 15 illustrates a case where three subbands completely match the FCC spectral mask in a frecμency range of 3.1 to 5.1 GHz; and [38] FIG. 16 is a flowchart illustrating a method of generating an ultra-low power pulse for multiband IR-UWB system, according to an embodiment of the present invention.

Mode for Invention

[39] The present invention will now be described more fiilly with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth therein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

[40] The detailed description of the configuration and operation of the present invention is referred to in order to gain a sufficient understanding of the present invention, the merits thereof, and the objectives accomplished by the implementation of the present invention.

[41] Hereinafter, the present invention will be described in detail by explaining embodiments of the invention with reference to the attached drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth therein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fiilly convey the concept of the invention to those skilled in the art. Therefore, the attached drawings and the detailed description should be considered in an exemplary sense only and not for purposes of limitation.

[42] The present invention will first be summarized, and then specific embodiments of the present invention will be described.

[43] For a freψency switching function, a voltage-controlled oscillator (VCO) may be used in a generator according to the present invention. However, the present invention is not limited thereto. The VCO is of an indictor-capacitor (LC) tank type, and its oscillation frecμency is determined by a value of a capacitor C and a value of an inductor L.

[44] An output pulse envelope that determines spectral characteristics is provided according to guidelines related to design parameters that are reqired by a system to which the generator according to the present invention is applied.

[45] The VCO includes two n-channel metal oxide semiconductor (NMOS) transistors that generate transconductance. The two NMOS transistors are cross-connected to each other in order to generate negative transcondαctance. The negative transcondictance compensates for parasitic resistance of LC tanks so that the LC tanks can satisfy oscillation conditions.

[46] The present invention further includes a complementary switch having more stable on-resistance. The complementary switch may include a pair of NMOS and p-channel metal oxide semiconductor (PMOS) transistors. When an NMOS gate bias voltage is high and a PMOS gate bias voltage is low, the switch is turned on (closed). On the contrary, when the PMOS gate bias voltage is low and the PMOS gate bias voltage is high, the switch is turned off (opened).

[47] A first switch (indicated by SWl in the drawings is disposed in an LC tank, and a second switch (indicated by SW2 in the drawings) is connected to a current source of the VCO. When the first switch is closed (turned on), the LC tank is short-circuited. Thus, the VCO does not oscillate. When the first switch is opened (turned off), it functions like an open circuit and thus does not affect the operation of the VCO. That is, the VCO oscillates. When the second switch is turned on, the VCO has a direct current bias and oscillates. When the second switch is turned off, the current source is not used, and the VCO is turned off.

[48] The first and second switches are driven by a sψare pulse train. The sψare pulse train passes through two inverters before driving a gate of a switch transistor. This method stabilizes and reduces noise in an actual circuit. Furthermore, the first and second switches are alternately, not simultaneously, turned on and off. A sψare pulse train for driving the NMOS transistor of the first switch and the PMOS transistor of the second switch is selected after passing through a first inverter. In addition, a sψare pulse train for driving the NMOS transistor of the second switch and the PMOS transistor of the second switch is selected after passing through a second inverter.

[49] The present invention further includes capacitor banks (indicated by Cl through C3 in FIG. 11) for a band switching or subband selection function. A 2-bit control signal generates four combinations Jfcwever, three (indicated by reference characters AO through A2 in the drawings) of the four combinations are used to select capacitors using a switch (indicated by reference character SW in the drawings) for selecting

CAP resonant freψencies of three bands (indicated by reference characters f 1 through f3 in the drawings). Output freψencies (indicated by reference characters f 1 through f3 in the drawings) correspond to capacitor banks (indicated by reference characters Cl through C3 in the drawings), respectively. The number of subbands is not limited to the above example and can be increased according to applications.

[50] FIG. 2 is a diagram for explaining a theory of a pulse generator 210 according to an embodiment of the present invention. Referring to FIG. 2, the pulse generator 210 according to the current embodiment of the present invention includes a first control signal 211 and an oscillator 213. The oscillator 213 is internally controlled by an input digital data sψare pulse train, that is, the first control signal 211. When the oscillator 213 is on, it operates normally and generates a sinusoidal wave. When the oscillator 213 is turned off, it does not generate a signal,,and an output pulse 220 is generated and then transmitted via an antenna 230. That is, the output pulse 220 is generated at the output of the oscillator 213. The duration and duty cycle of the generated output pulse 220 are identical to those of the input sψare pulse train. A center freqiency of pulse power spectral density (PSD) is identical to a oscillation frequency of the oscillator 213 . In particular, since the frequency of the oscillator 213 can be converted by a second control signal 215, the center freqiency of the PSD of the output pulse 220 may also be different. Therefore, the pulse generator 210 according to the current embodiment of the present invention can support a multiband switching fiinction.

[51 ] According to an embodiment of the present invention, the pulse generator 210 may include an LC tank-based oscillator for a switching operation. FTG. 3A is an eqivalent circuit diagram of an LC oscillator when turned on, and FlG. 3B is an eqivalent circuit diagram of the LC oscillator when turned off. Referring to FIGS. 3 A and 3B, L and C indicate resonant tanks, R indicates eqivalent parasitic resistance of an LC tank, -R indicates negative resistance provided by active devices, R indicates the total eqivalent resistance of the LC tank while the LC oscillator is turned off.

[52] Referring to FIG. 3A, when the LC oscillator is turned on, the LC tank disperses energy using eqivalent parallel loss resistance R . Thus, the losses need to be compensated for using negative resistance -R. In order to drive the LC oscillator, I-RI must be smaller than R .

T

[53] In the case of a differential LC oscillator, current i provided by negative resistance -

R may be represented by a non-linear polynomial expression in which even-order products are cancelled. In short, the current i approximates to a 3 ^r order non-linear fiinction of an output voltage V and can be obtained using Eqjation 1 below.

OUT

[54] i = av + bv³ , ...(1) s OUT OUT

[55] where a and b indicate first and third coefficients, respectively. In Eqjation 1, a indicates a linear portion of negative transconductance of active devices. [56] Eqjation 2 below can be obtained from FIG. 3A.

[57] i + i + i + i = 0 ...(2). s L C T

[58] If Eqjation 2 is differentiated, Eqjation 3 below can be obtained.

[59] [Math.l]

...(3). [60] Using Eψation 3, the output voltage V can be obtained as follows.

[61] [Math.2]

, ...(4)

[62] Where

[63] [Math.3]

indicates a peak voltage in a steady state, [Math.4]

U₀ = VlTiC indicates a resonant frequency of the LC oscillator, A =aR indicates an open-loop gain, [Math.5]

indicates a characteristic component of the LC tank, and t and φ indicate initial o o time and phase values, respectively. Eψation 4 is a time function including start-up transients and represents an output voltage waveform of the LC oscillator. It can be understood from Eψation 4 that an oscillator output waveform includes t\*o components, that is, oscillation and envelope portions, at ω (a turn-on period). In FIG. 4, waveforms indicated by solid lines represent a combination of transient waves of an oscillator output when turned on and turned off. In addition, waves indicated by dotted lines are the oscillator output when in a steady state. [64] Since an envelope of the pulse determines spectral characteristics, it is useful to obtain the functional dependence of the envelope as a function of design parameters. It can be understood from FIG. 4 that, for a turn-on portion of the pulse, an output voltage swing is small daring a start-up phase. Therefore, the envelope portion in Eψation 4 approximates to Eψation 5 below. [65] [Math.6]

em-rise ^ " peak-steady*

] , ...(5) [66] where v indicates a voltage envelope of an output waveform during the turn-on

period. The time recμired for an output envelope voltage obtained using Equation 5 may be obtained using Eψation 6 below. [67] [Math.7]

, ...(6) [68] where v indicates an envelope voltage at t=0, which may be the amplitude of a env-rise,0 noise signal of an LC tank when initialized. Using Eψation 6, delay and setup times t d and t and the time recμired by an output voltage to reach 10 to 90 percent of a peak voltage Vpeak can be obtained by setting venv-rise = O.lVpeak and 0.9Vpeak, respectively. Therefore, a rising time t may be obtained using Equation 7 below. [69] [Math.8]

•••(7).

[70] The bandwidth of a pulse is in inverse proportion to the cycle thereof. Therefore, the rising time t estimated slightly less than half of a pulse period Tpulse (see FIG. 4) r should be within a nanosecond range that is greater than a bandwidth of 500 MHz . It can be understood from Eqjation 7 that the rising time t can be reduced by redicing a r value of Q and increasing a value of A . Since A is also proportional to Q, the delay

OL OL and rising times t and t can both be effectively reduced by increasing d r transcondictance of the active devices, which generally reqires higher direct current. [71] In FIG. 4, the remaining half of the pulse is composed of a turn-off transient output of the oscillator. In order to represent a turn-off transient output waveform of the oscillator when turned off, the eqivalent circuit illustrated in FIG. 3B may be used. The eqivalent circuit of FIG. 3B includes an LC tank having a resistor R connected in parallel. In a turn-off transient state, the operation of the oscillator is similar to damped oscillation with initial amplitude of the peak voltage Vpeak. Based on an analysis of the disclosed damped oscillation, an output waveform may be defined by Ecμation 8. [72] [Math.9]

, -.(8) [73] where τ =2CR indicates a time constant,

D

[Math.10]

[74] indicates a decaying oscillation freqjency, and φ indicates an initial phase. Due to d weak damping, the time constant [Math.11]

is generally far greater than a period of an LC resonant frecjiency. That is, [Math.12]

W W 0

. Using Ecμation 8, a falling envelope Venv-fall of the oscillator may be defined as follows. [75] [Math.13]

...(9).

[76] Based on Eψation 9, the time required for pulse envelope output amplitude to decrease to an arbitrary value Vout may be obtained using Equation 10 below. [77] [Math.14]

...(10). [78] Referring to FIG. 4, a falling time t is defined as the time required for the amplitude of the envelope to decrease to 90 to 10 percent of the peak voltage Vpeak and can be obtained using Equation 11 below. [79] [Math.15] t_f~x\n9=439CR_D

...(H).

[80] It can be understood from Eψation 11 that the falling time t can be controlled by changing R when a value of C is determined according to a given value t .

D r

[81] In order to obtain symmetry pulse spectrum with a maximum sublobe suppression the falling and rising times of the pulse illustrated in FIG. 4 must be eψal. [82] A condition for satisfying t =t obtained using Eψations 7 and 11 may be defined by r f

Eψation 12 below. [83] [Math.16]

R

R n=

A π OLr - 1

...(12).

[84] In the case of conventional monolithic LC tanks, a value of R tends to be dependent on a characteristic component (a Q-factor) of an on-chip inductor. Therefore, since R > R according to Eψation 12, the value of A must be equal to or greater than 2. In

D OL order to satisfy A >2, R must be smaller than R . Thus, the LC tanks must include

OL D T additional short-circuit resistance daring the turn-off period. [85] Using the concept described above, embodiments for generation of an output pulse will hereinafter be described. [86] Hrst of all, each component of the present invention will be described with reference to FIGS. 5 and 16. Then, specific embodiments of the present invention will be described with reference to FIGS. 6 through 14. FIG. 5 is a block diagram of an ultra- low power pulse generator for multiband IR-UWB system, according to an embodiment of the present invention. FIG. 16 is a flowchart illustrating a method of generating an ultra-low power pulse for multiband IR-UWB system, according to an embodiment of the present invention.

[87] Referring to FIG. 5, the ultra-low power pulse generator for multiband IR-UWB system according to the current embodiment of the present invention includes an oscillation unit 510, a switch unit 520, a control unit 530, a power supply unit 540 and an inverter 550. The oscillation unit 510, which includes an LC resonant tank 511, a transconductance unit 515, an adjustment unit 517, and a subband generation unit 513, generates an output pulse.

[88] Referring to FIGS. 5 and 16, the LC resonant tank 511 has a predetermined frecμency and oscillates, thereby generating a desired output pulse in operation S 1610.

[89] The switch unit 520 activates or deactivates the oscillation unit 510 in response to an input first control signal 211 . That is, the switch unit 520 controls generation of an output pulse in operation S 1620.

[90] The adjustment unit 517 minutely adjusts a freψency of the output pulse. The freψency of the output pulse is adjusted by values of L and C of the LC resonant tank 511, capacitance of the subband generation unit 513, and the adjustment unit 517.

[91] The transcondictance unit 515 generates and outputs transconductance having a negative value, thereby compensating for energy dispersion in the LC resonant tank 511 as described above.

[92] Controlled by the control unit 530, which receives a signal obtained after the first control signal is inverted by the inverter 550, the power supply unit 540 supplies current or blocks the supply of current to the oscillation unit 510. The control unit 530 may be implemented as a complementary switch similar to the switch unit 520. The first control signal is inverted by the inverter 550, and the switch unit 520 indicated by SWl in FTG. 9 and the control unit 530 indicated by SW2 in FIG. 9 operate in opposite on/off states in response to the signal obtained after the first control signal is inverted in operation S 1630.

[93] The subband generation unit 513 includes one or more capacitors as illustrated in

FIG. 11. A switch SW (see FIG. 11) is turned on or off by a second control signal,

CAP thereby controlling a value of each capacitor. Accordingly, an output pulse having an oscillation frecμency that corresponds to a subband can be generated in operation S 1640. [94] FIG. 6 is a circuit diagram of an ultra-low power pulse generator for multiband IR- UWB system, according to a specific embodiment of the present invention . In this circuit, a VCO is adopted to generate an output pulse and is controlled by a first switch SWl (640) in an LC tank. A center tapped indictor 630 is an inductor that forms the LC tank. A first control signal 610 is a square pulse train and turns the first switch SWl (640) on or off using an inverter 620. R>r the duration of the sψare pulse, due to the inverter 620, a voltage for driving the first switch SWl (640) has a logic signal 'low' (¹O'), and the first switch SWl (640) is turned off . In this case, the first switch SWl (640) does not affect the LC tank, and, accordingly, the oscillation occurs normally. After the duration of the sqjare pulse, only a logic signal 'low' exists in the remaining pulse. Due to the inverter 620, the voltage for driving the first switch SWl (640) becomes high. Accordingly, the first switch SWl (640) is turned on and fimctions as a short circuit. In this case, the LC tank is short-circuited, and oscillation doesn't occur. Hence, during the remaining period of the sqjare pulse , no output signal is detected. Conseqjently, a desired pulse waveform can be obtained by turning on or off the VCO in response to the square pulse train. The output pulse has the same duration and period as the input sqjare pulse train. A pulse envelope, which determines pulse spectral characteristics, can be adjusted by selecting a proper operating time of the first switch SWl (640) based on the above analysis. Therefore, the spectrum of the output pulse may match the FCC spectral mask that has high sidelobe rejection performance. Referring to FIG. 6, varectors Cvar 651 and 652 correspond to the adjustment unit 517 of FIG. 5, a capacitor bank 660 corresponds to the subband generation unit 513 of FIG. 5, two NMOS transistors 671 and 672 correspond to the transconductance unit 517, and a power supply unit 680 corresponds to the power supply unit 540 of FIG. 5.

[95] FIG. 7 is a circuit diagram of an ultra-low power pulse generator for multiband IR-

UWB system, according to another embodiment of the present invention . An output pulse is generated by turning on or off a current source I 770 of a VCO. The current source I is controlled by an input sqjare pulse train 710 and using a second switch

SW2 760. During the duration of a sqjare pulse of the input sqjare pulse train 710, if a high voltage corresponding to a logic signal 'high' turns on the second switch SW2 760, current is supplied to the circuit of the pulse generator, and the VCO oscillates normally. After the duration of the sqjare pulse, the input sqjare pulse train 710 is logic 'low' in the remaining period of the sqjare pulse . In this case, the second switch SW2 760 is turned off, and no current flows in the circuit. Thus, the VCO does not oscillate. Accordingly, no output signal is detected during the remaining period of the sψare pulse. Conseψently, a desired output pulse can be obtained in response to the input sφare pulse train 710. Therefore, the output pulse has the same duration and period as the input square pulse train 710. In this way, the pulse generator does not consume direct current. Descriptions of components 720, 731, 732, 740, 751 and 752 identical to those of FIG. 6 will not be included.

[96] FIG. 8 is a circuit diagram of an ultra-low power pulse generator for multiband IR-

UWB system, according to another embodiment of the present invention . Specifically, FIG. 8 illustrates a circuit of a pulse generator that generates an output pulse by controlling the operation of an LC-VCO having two switches. FTG. 9 is a timing diagram of waveforms and switching operations in major nodes A, B and C of the ultra-low power pulse generator of FIG. 8 .

[97] When the VCO operates, a sinusoidal wave (an output pulse) is generated through an output at an oscillation. In this case, the oscillation freψency is determined by a capacitance including values of a varector Cvar 851 and a selected capacitor bank 860, and an inductance of an inductor Ltank 830. Two complementary switches are used. Each of the complementary switches may include a pair of NMOS and PMOS transistors as illustrated in FIG. 10.

[98] A first switch SWl 840 controls an LC bank, and a second switch SW2 880 controls a voltage source I 890 of the VCO. The first and second switches SWl and SW2 840 and 880 operate in an alternating fashion. That is, when one of the first and second switches SWl and SW2 840 and 880 is turned on, the other one of the first and second switches SWl and SW2 840 and 880 is turned off. An input sψare pulse train 810 at node A has a duration and period determined by a data rate of the multiband IR-UWB system . The input sψare pulse train 810 is supplied from a baseband portion (not shown) of the multiband IR-UWB system . The input sψare pulse train 810 passes through two inverters, i.e., first and second inverters 821 and 822. After passing through the first inverter 821, the input sψare pulse train 810 is inverted. Then, after passing through the second inverter 822, the inverted input sψare pulse train 810 becomes identical to the input sψare pulse train 810 at node C. The input sψare pulse train 810 that has passed through the first inverter 821 drives the NMOS transistor of the first switch SWl 840 and the PMOS transistor of the second switch SW2 880 in the LC tank. The input sψare pulse train 810 that has passed through the second inverter 822 drives the NMOS transistor of the second switch S W2 880 and the PMOS transistor of the first switch SWl 840. Waveforms at nodes A, B and C are shown in FIG. 9. During the duration of a sψare pulse of the input sψare pulse train 810, a high voltage corresponding to a logic signal 'high' turns on the second switch SW2 880, and current is supplied to the VCO. In this case, a voltage of the NMOS gate of the first switch SWl 840 becomes a logic signal 'low,' and the first switch SWl 840 is turned off. The first switch SWl 840 does not affect the LC tank. Therefore, the VCO operates normally. After the duration of the sqjare pulse, the input sψare pulse train 810 is logic 'low' in the remaining period of the sqjare pulse. In this case, the second switch SW2 880 is turned off, and no current flows in the circuit. If the first switch SWl 840 is turned on, it can fiinction as a short circuit. Thus, the LC tank short- circuits, and the VCO does not oscillate. Hence, during the remaining period of the scμare pulse, no output signal is detected. Consecμently, the VCO generates the sinusoidal wave only during the duration of the sqjare pulse . During this duration, a desired output pulse is obtained. The output pulse has the same duration and period as the input sqjare pulse train 810. The PSD of the output pulse has the same center frequency as the oscillation frecμency. In addition, a pulse width is in inverse proportion to a controllable pulse period. Current is supplied to the pulse generator for the duration of the sqjare pulse, and the pulse generator is turned off in the remaining period of the sqjare pulse. Thus, since the pulse generator according to the present embodiment does not consume direct current, it consumes dynamic current using the second switch SW2 880. The first switch SWl 840 can provide a design parameter which can obtain an output pulse envelope that matches the FCC spectral mask having maximum sidelobe rejection performance.

[99] In the pulse generator according to the present embodiment, a band switching fiinction is realized by a 2-bit control signal (a second control signal) for subband selection and the capacitor bank 860. The 2-bit control signal generates output combination signals AO, Al and A2 to select corresponding capacitor values from three capacitor banks Cl through C3 of FIG. 11. The output combination signals AO through A2 turn the switch SW , which connects capacitors (the capacitor banks Cl

CAP through C3), on or off. When the switch SW is turned off, a capacitor band of a

CAP capacitor connected to the turned-off switch SW is not selected. When the switch

CAP

SW is turned on, a corresponding capacitor band is used, and a corresponding resonant freqiency at an output is determined by the selected capacitor band and the varectors Cvar 851 and 852. The varectors Cvar 851 and 852 are for freqjency adjustment. [100] The pulse generator according to the present embodiment may generate a pulse having the same duration and duty cycle as the input sqjare pulse train 810. The pulse generator of FIG. 8 does not consume direct current and operates at a voltage of 1.5 V or greater. Dynamic current is proportional to the dαty cycle of the input scμare pulse train 810.

[101] FIG. 12 illustrates waveforms of an output pulse train according to an embodiment of the present invention. The duration of the output pulse train is 3.5 ns, and a period thereof is 25 ns. A waveform of the output pulse train has a peak-to-peak amplitude of 160 mV. The duration of output pulse train corresponding to a bandwidth of 520 MHz at -10 dB is 3.5 ns. FIG. 13 illustrates a waveform of a signal pulse in detail from among the waveforms illustrated in FIG. 12. FIG. 14 shows a case where a power spectrum of a generated pulse matches a Federal Communication Commission (FCC) mask. The center frequency is identical to an oscillation freqμency at 3.8 GHz. A maximum spectrum power level is -42 dBm at a bandwidth of 520 MHz. In order to avoid interference of adjacent channel bands, a pulse spectrum completely matches the FCC spectral mask, and sidelobe refusal performance is greater than 25 dB.

[102] After a capacitor value is selected in a capacitor bank using the 2-bit control signal, the oscillation frecμency is changed, and the center frequency of a subband is shifted. Conseqμently, frequency switching is realized. FIG. 15 illustrates a case where three subbands completely match the FCC spectral mask. The number of subbands may be increased using the same theory.

[103] The present invention can also be implemented as computer-readable code on a computer-readable recording medium. The computer-readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer-readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet).

[104] The computer-readable recording medium can also be distributed over network- coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. Also, functional programs, code, and code segments for accomplishing the present invention can be easily construed by programmers skilled in the art to which the present invention pertains.

Claims

[1] An ultra-low power pulse generator for multiband impulse radio (IR)-ultra wideband (UWB) system, the generator comprising: an oscillation unit generating and outputting a sinusoidal wave; a switch unit activating or deactivating the oscillation unit according to a first control signal; and an adjustment unit adjusting a frecμency of the sinusoidal wave.

[2] The generator of claim 1, further comprising: a power supply unit supplying current; and a control unit receiving the current and supplying the current or blocking the supply of the current to the oscillation unit, the switch unit and the adjustment unit according to a value obtained by inverting the first control signal.

[3] The generator of claim 1, further comprising a subband generation unit comprising one or more capacitors, which selects an oscillation frecμency corresponding to a subband, and transmits the selected oscillation frecμency to the oscillation unit.

[4] The generator of claim 3, wherein the subband generation unit adjusts a capacitance of the subband generation unit by connecting or disconnecting the capacitors to or from each other according to a second control signal.

[5] The generator of claim 1, wherein the oscillation unit is a fixed frecμency oscillator or a voltage controlled oscillator (VCO).

[6] The generator of claim 5, wherein the VCO is an LC-VCO.

[7] The generator of claim 1, wherein the first control signal is a scμare pulse having a duration and duty cycle according to a bandwidth and a data rate recμired by multiband impulse wireless UWB system.

[8] The generator of claim 7, wherein the first control signal is a signal which has been modulated using on/off keying or pulse position modulation.

[9] The generator of claim 1, wherein the oscillation unit comprises: an LC resonant tank; and a transconductance unit connected to the LC resonant tank and outputting a negative transconductance value.

[10] The generator of claim 9, wherein the transconductance unit comprises two n-channel metal oxide semiconductor (NMOS) transistors cross-connected to each other.

[11] The generator of claim 1, wherein the adjustment unit comprises at least one varectors connected to each other.

[12] The generator of claim 1, wherein each of the switch unit and the control unit is a complementary switch comprised of a pair of NMOS and p- channel metal oxide semiconductor (PMOS) transistors.

[13] A method of generating an ultra-low power pulse for multiband IR-UWB system, the method comprising: generating a sinusoidal wave using an oscillator which can be turned on or off; activating or deactivating the oscillator according to a first control signal; supplying power to the oscillator when the oscillator is activated and blocking the supply of power to the oscillator when the oscillator is deactivated; and adjusting a freqiency of the oscillator by changing a value of a capacitor according to a frecμency generation reqiest which corresponds to a subband.

[14] The method of claim 13, wherein the oscillator is controlled by logic values.

[15] The method of claim 13, wherein the first control signal is a signal which has been modulated by on/off keying or pulse position modulation.

[16] The method of claim 13, wherein the adjusting of the frequency of the oscillator comprises: forming a capacitor bank using at least one capacitors; receiving a second control signal, which connects the capacitors to each other, in order to select an oscillation freqiency corresponding to the subband; and adjusting a capacitance of the capacitor bank by connecting or disconnecting the capacitors to or from each other according to the second control signal. [17] The method of claim 13, wherein the first control signal is a sψare pulse whose duration and duty cycle allow a bandwidth and a data rate reqired by multiband impulse wireless UWB system.