WO2009019639A2

WO2009019639A2 - Crystal-less transceivers

Info

Publication number: WO2009019639A2
Application number: PCT/IB2008/053080
Authority: WO
Inventors: Paulus T. M. Van Zeijl; Neil C. Bird; Alan J. Davie
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-08-06
Filing date: 2008-07-31
Publication date: 2009-02-12
Also published as: TW200926630A; WO2009019639A3

Abstract

The present invention relates to an apparatus and a system having at least one of a transmitter portion or apparatus for transmitting a transmission signal and receiver portion or apparatus for receiving a transmission signal, and to a method of operating such an apparatus and system. A reference frequency is generated at an oscillator circuit (82) which is used for frequency conversion in at least one of the transmitter and receiver portion, and the transmission signal is filtered at a filter circuit (10) before it is input to the transmitter portion or after it is output from the receiver portion. At least one of a physical or electronic coupling of at least one bandwidth parameter at the filter circuit (10) to the oscillator circuit (82) is provided to thereby relax accuracy requirements at said oscillator circuit. Thereby, the oscillator circuit can be configured without crystal resonator element(s) and the size of the apparatus and system can be reduced.

Description

Crystal-less transceivers

FIELD OF THE INVENTION

The present invention relates to an apparatus and a system having at least one of a transmitter portion or apparatus for transmitting a transmission signal and receiver portion or apparatus for receiving a transmission signal, and to a method of operating such an apparatus and system. More specifically, the present invention is directed to - but not limited to - transceiver devices for wireless communication system.

BACKGROUND OF THE INVENTION

A transceiver is a device that has both a transmitter and a receiver which are combined and share common circuitry or a single housing. On a wired telephone, the handset contains the transmitter and receiver for the audio. The whole unit is colloquially referred to as a "receiver." On a mobile telephone or other radio telephone, the entire unit is a transceiver, for both audio and radio.

Fig. 1 shows a schematic block diagram of a conventional transceiver device, wherein an antenna signal passes through a radio frequency (RF) filter 10, which may be a band bass filter, followed by a switch 12 configured to switch either a receiver portion or a transmitter portion to the RF filter 10. The RF filter 10 can be a Surface- Acoustic- Wave (SAW) filter, Bulk- Acoustic- Wave (BAW) filter and/or a ceramic filter. In the receiver portion, a low noise amplifier (LNA) 20 amplifies the received antenna signal, and after down-conversion to an intermediate frequency (IF) in respective I- and Q-mixers 42, 44 of an in-phase (I) branch and a quadrature (Q) branch, amplification (together with Automatic Gain Control, not shown), filtering in respective IF filters 52, 54 (e.g. and pass and/or low pass filters which may be tunable by a tuning signal T) and AD-conversion in respective analog- to-digital converters (ADC) 62, 64, a digital representation of signal is obtained, which can be demodulated e.g. at a digital processing unit 70. The mixers 42, 44 can be image reject mixers or non-image reject mixer. The receiver portion can have a single IF (high-IF, low-IF or zero-IF) or multiple IFs.

The IF filters 52, 54, if realized with on-chip components, may require tuning by the tuning signal T for optimum centre frequency accuracy. This tuning may uses a phase- locked loop (PLL) circuit with a crystal (XTAL) oscillator signal as reference signal. In Fig. 1, the oscillator signal for the mixers 42, 44 is derived from an LC-based voltage controlled oscillator (LC-VCO) 80, which is coupled in the PLL to a reference XTAL oscillator 120. The PLL circuit comprises the LC-VCO 80, a divider circuit 90 for dividing the output frequency of the LC-VCO 80 by an integer number N, a detector 110 (implemented by a mixer or multiplier) for comparing the phase of the down-converted signal with the phase of the a reference signal generated by XTAL oscillator 120.

In the transmitter portion, digital I- and Q-data output by the digital processing unit 70 is DA-converted at respective digital-to-analog converters (DACs) 132, 134, low-pass filtered at respective low-pass filters 142, 144 (which may be tunable by a tuning signal T), and up-converted by respective I- and Q-mixers 46, 48. At RF level the up-converted I- and Q-streams are combined by a combining element 150 (e.g. an adder circuit or the like) and amplified by a power amplifier 30 before being filtered in the RF filter 10 and radiated at the antenna. In this example the transmitter is a zero-IF transmitter. The transmitter may also be realized with multiple IFs or as a polar transmitter.

The conventional transceiver of Fig. 1 uses a crystal resonating element (XTAL) and the XTAL-oscillator 120 to define the frequency of its transmission and/or reception portion. However, such a XTAL is a large component leading to a large form- factor of the complete system. It cannot be integrated on the same piece of silicon as other circuit components, and last but not least it increases complexity and costs of the system.

XTALs are mechanically resonating elements, with a relatively large form factor (e.g. 3.2*2.5*0.7 mm are already very small dimension for an XTAL), in contrast to on-silicon integrated transceivers. These XTALs are also very expensive compared to the silicon- implemented transceivers. In conventional transceivers for systems like GSM (Global System for Mobile communications), WB-CDMA (Wide-Band Code Division Multiple Access), DECT (Digital Enhanced Cordless Telecommunications), Bluetooth, Zigbee, and WLAN (Wireless Local Area Network), radio transceivers without XTAL would be desirable.

The need for transceivers without XTAL is felt hardest in the areas of ultra- low-power radios and wireless consumables. There the form factor and cost of the XTAL is most important.

One of the basic problems in realizing accurate frequencies is the tolerance of active and passive components on silicon. On-chip oscillators can for instance be made from resistors, capacitors and transconductance stages (with a gain factor gm). Such oscillators will have a basic frequency given by /= constant /(R * C) or f=constant*gm/C. A realistic tolerance of +/- 15 % for these components gives a frequency tolerance of 30 %. Conventional systems use a XTAL to lock these on-chip oscillators to. Proposed solutions, such as the one disclosed for example in US5982241, have achieved reductions of this error to approximately 1%, which is however not accurate enough for radio applications.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide modifications for transmitter, receiver or transceiver circuits, by which XTALs can be dispensed with. This object is achieved by a method as claimed in claim 1, an apparatus as claimed in claim 15, and a system as claimed in claim 21.

Accordingly, by providing the coupling arrangement, the bandwidth parameter (which may be a bandwidth-determining parameter of the substrate, such as the acoustic velocity of an acoustic wave or the like, or a measured center frequency and/or bandwidth of the filter circuit, or a detected bandwidth of the received transmission signal) at the filter circuit can be mechanically or electronically linked to or associated with the oscillator circuit. This measure simplifies synchronization or adjustment of the mixing frequency derived from or controlled by the oscillator circuit, so that accuracy requirements of the oscillator circuit can be relaxed and a crystal resonating element (XTAL) is no longer required. According to a first aspect, the coupling arrangement may comprise a common substrate on which the oscillator circuit and the filter circuit are jointly integrated. Thereby, substrate parameters which determine the respective bandwidth and centre frequency of the filter circuit and the oscillator circuit can be linked or matched to each other through the common substrate, so that sufficient accuracy is provided and the XTAL can be dispensed with. According to a specific example, the oscillator circuit and the filter circuit can be implemented based on surface or bulk acoustic wave technology. As an alternative, the oscillator circuit and the filter circuit could be implemented based on a film bulk acoustic resonator technology or a micro-electro-mechanical system technology. The oscillator circuit and the filter circuit may be operated at substantially the same frequency. Alternatively, the oscillator circuit may be operated at twice the frequency of the filter circuit. In the latter case, in-phase and quadrature phase components of a derived local oscillator (LO) signal can simply be generated by using a divide-by-two circuit.

According to a second aspect, the coupling arrangement may comprise a measuring unit for measuring a band-pass characteristic of the filter circuit, and a control unit for adjusting the frequency of the oscillator circuit in response to an output of the measuring unit. This measured characteristic can thus be linked or coupled to the oscillator circuit in order to adjust the reference frequency, so that accuracy requirements of the oscillator circuit can be relaxed and an XTAL is no longer necessary. Additionally, the coupling arrangement may comprise a connecting arrangement for injecting a signal derived from the oscillator circuit to an input of the filter circuit. In a specific example, the connecting arrangement may comprise a switching element which is only closed in a calibration mode of said apparatus. Thereby, the band-pass characteristic can be measured by varying the local oscillator frequency derived from the reference frequency. The measuring unit may for example be adapted to measure a DC voltage generated at a receiving mixer circuit.

According to a third aspect, the coupling arrangement may comprises a detection unit for detecting a temporarily increased bandwidth of a transmission signal received through the filter circuit, and a frequency control unit for controlling the oscillator circuit in accordance with the detection result during a locking operation for capturing a transmission frequency. This approach enables adaptation of the reference frequency of the oscillator circuit to the increased bandwidth of the transmission signal received through the filter circuit. The locking or calibrating procedure of the oscillator circuit can thus be performed with a larger bandwidth, so that accuracy requirements are again reduced and the XTAL is no longer necessary.

The frequency control unit can be adapted to detect a frequency error of the receiver portion and to control the frequency of the oscillator circuit based on the detected frequency error, which could optionally be stored in a memory unit.

Optionally, a feedback measure can be added, wherein the frequency control unit is adapted to transmit an acknowledgment to a transmission end of the transmission signal, if the detected frequency error indicates a frequency locking state of said receiver portion. Then, the transmission end could reduce the bandwidth e.g. after the locking or calibrating operation. A continuous adjustment or adaptation of the reference frequency could be achieved by regularly increasing the bandwidth of the transmission signal and waiting for a feedback from the reception end.

It is noted that the above three alternative aspects of the coupling arrangement may as well be combined in any possible combination of two of the three aspects or all three aspects to thereby improve the relaxation effect for the oscillator circuit. Further modifications of the embodiments may be gathered from the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described based on embodiments with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic block diagram of a conventional transceiver apparatus;

Fig. 2 shows a schematic block diagram of a transceiver apparatus according to a first embodiment;

Fig. 3 shows a schematic block diagram of a transceiver apparatus according to a second embodiment;

Fig. 4 shows a schematic block diagram of a transceiver apparatus according to a third embodiment; and Fig. 5 shows a schematic flow diagram of a frequency locking method according to the third preferred embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, embodiments will be described based on modifications of the initially described transceiver device of Fig. 1.

Fig. 2 shows a schematic block diagram of a transceiver apparatus according to the first embodiment.

In this first embodiment, at least two bulk acoustic wave (BAW) and/or surface acoustic wave (SAW) devices are provided for implementing an RF filter 16 and a reference oscillator 82 and are integrated in a single or common substrate 160 and thus mutually and physically coupled via the common substrate, such that the transceiver has sufficient accuracy to receive and transmit without the use of an XTAL or XTAL-oscillator.

The centre frequency of the SAW and/or BAW RF filter 16 and the SAW and/or BAW reference oscillator 82 is related to or dependent on the acoustic velocity of the acoustic wave in the piezoelectric material of the substrate 160, the physical dimensions of the devices and the "loading" of the device (especially in case of BAW devices).

The production process of SAW and BAW devices allows realization of multiple devices on/in a single substrate. Each device may have two transducers, so that actually it represents a SAW device with one (balanced) input and two (balanced) outputs or vice versa. The SAW and BAW devices may be combined with an integrated bipolar transistor or a CMOS (complementary metal oxide semiconductor) transistor. The centre frequency of the device is defined by the distance between fingers provided in the SAW transducers. The length of the transducers defines the bandwidth of the SAW device in case an SAW transversal filter is provided in the RF filter 16 or the reference oscillator 82. Furthermore, SAW resonators can be implemented in the RF filter 16 or the reference oscillator 82 by using multiple finger-reflectors on the left and right-hand side of a (pair of) SAW transducer(s). Alternatively, SAW delay-lines could be used in the reference oscillator 82 and/or the RF filter 10. The SAW devices could be integrated on silicon (with ZnO as piezoelectric material), quartz, lithium-niobate, or other SAW substrate materials. The implementation of multiple SAW and BAW devices on a single substrate thus gives us an opportunity to obtain crystal-less transceivers, receivers or transmitters.

The RF band-pass filter 10 of Fig. 1 thus has been replaced by the SAW/BAW band-pass filter 16. Additionally, the inductor-capacitor (LC) VCO 80 of Fig. 1 has been replaced by the SAW/BAW VCO as new reference oscillator 82.

Because the two SAW/BAW devices have been realized on the same substrate 160, the centre frequencies of these BAW devices will be very close. It is assumed that the BAW RF filter 16 has a centre frequency of 850 MHz, and a bandwidth of 1 MHz. The BAW resonator and the reference oscillator 82 using the BAW-resonator can be made to oscillate within this 1 MHz bandwidth by proper design. The antenna signal, after down-conversion, falls within this +/- 0.5 MHz bandwidth. Assuming the ADCs 62, 64 being able to completely convert the +/- 0.5 MHz bandwidth into the digital domain, the digital signal processing unit 70 can be used to find the desired signal and demodulate it. It is also possible to use a second conversion (in the analog and/or digital domain) if required. Various digital signal processing techniques can be used to exactly estimate the centre frequency of the signal, as commonly known in digital receiver design. Alternatively, the ideas presented in the below second and third embodiments can be used to find the exact centre frequency of the transmitted signal. Because the reference oscillator 82 for the down-conversion does not rely on integrated LC components but on a SAW/BAW resonator, and because the BAW resonator is at least as accurate as the SAW/BAW RF filter, no reference XTAL-oscillator is required, so that it can been removed from the transceiver circuit. Consequently, other parts of the PLL that controlled the VCO frequency in Fig. 1, have been deleted, thus reducing overall power consumption, which is of course also a big advantage, especially for ultra low power radio devices. Only the divider circuit 90 is still present to generate a clock signal for the digital circuitry. If the digital circuitry would be implemented asynchronously, this divider circuit 90 could also be removed.

It is noted that the SAW/BAW resonator of the reference oscillator has a higher Q than the integrated LC. This will lead to a lower power consumption of the reference oscillator 82, which is very beneficial for applications like Ultra-Low-Power radios.

In the case the receiver has been realized as described above, a voltage of the tuning signal T for the IF filters 52, 54 can no longer be derived from the XTAL reference oscillator 120 of Fig. 1. However, the SAW/BAW oscillator signal (directly, or divided by some number) can be used as an alternative.

Optimum layout of the RF filter 16 and the resonator of the reference oscillator 82 should be applied to minimize the resonator-oscillator signal leaking to the antenna. Isolation and screening techniques applied in printed circuit board (PCB) or normal application specific integrated circuit (ASIC) design can be used here also.

In the implementation example of Fig. 2, the BAW RF filter 16 and the BAW resonator of the reference oscillator 82 may have approximately the same frequency. Depending on the freedom in production and the specific transceiver requirements the frequencies can also be further apart. For instance, having the BAW resonator at twice the frequency of the BAW RF filter 16 could be very useful in the transmitter and receiver part. The I (0 degree) and Q (90 degrees) LO-signal components for the receive and transmit mixers 42, 44, 46, and 48 can then very easily be derived from the BAW reference oscillator 82 by a divide-by-two circuit.

Instead of SAW/BAW devices, other devices like multiple FBAR and/or MEMS devices can be used to realize the functionality of the first embodiment.

Fig. 3 shows a schematic block diagram of a transceiver apparatus according to a second embodiment.

In the second embodiment, the RF filter 10 and the reference oscillator 162 are electronically coupled, so that the RF filter 10 can be used as a frequency reference. The band-pass characteristic is "measured" by using an on-chip local oscillator 80 and/or an on- chip RC-oscillator 162. The measured centre frequency and bandwidth of the RF filter 10 can be used to centre the reference frequency of the receiver and thus also the transmit frequency.

It is recognized that if the XTAL reference oscillator 120 is removed from the receiver portion shown in Fig. 1, the only accurate (mechanical) component is the RF (band- pass) filter 10. According to Fig. 2 it is proposed to couple (e.g. inject or leak) a signal from the LC-VCO 80 to the RF filter 10 e.g. via a switch 14 which may only be closed in a calibration mode provided for calibrating the receiver portion. Via the receiver chain a (DC- )voltage after the receiving mixers 42, 44, or preferably after the ADCs 62, 64, can be measured by a (DC)measuring unit or functionality 74 incorporated in the digital processing unit 72 or provided as a separate unit. Now, by varying the frequency of the LC-VCO 80, the transfer characteristic of the RF filter 10 can be measured. Or reversely, when the characteristic of the RF filter 10 is known, the LC-VCO frequency can be related or coupled to that of the RF filter 10. The normalized attenuation of an n^th-order (Butterworth) bandpass filter as a function of frequency f is given by:

/f = -10 *

wherein f_c is the centre frequency of the filter and ft_w denotes the 3 dB bandwidth of the filter (for other filters than a Butterworth filter, like Chebyshev, Gaussian filter, similar equations can be found in the literature). The centre frequency and the bandwidth of the filter are defined by the specifications of the filter and are known a priori. Although in Fig. 3 the reference frequency of the PLL/LC-VCO 80 is obtained from the RC-like reference oscillator 162 with +/- 30% inaccuracy, and the LC-VCO 80 in the PLL is expected to have a tolerance of +/-8%, the overall tolerance can be in the order of +/-38%. But, still the PLL/LC-VCO 80 can be programmed to several frequencies and thus measure the transfer or bandwidth characteristic of the RF filter 10. The point of maximum transfer can be defined as the centre frequency of the RF filter 10. Especially when the passband of the RF filter 10 is flat, the measured centre frequency will be quite inaccurate. By also measuring the frequencies at which the RF filter 10 starts to attenuate at 3 dB from maximum transfer the 3 dB frequencies fi and f₂ are also known. These can be related to the centre frequency and the bandwidth of the RF filter 10 by:

J fl - — Jfc - Jfbw /' ^Δ2 ⁽²⁾ Now, the known centre frequency and bandwidth of the RF filter 10 can be related or coupled to the settings in the PLL/LC-VCO 80 and/or the RC reference oscillator 162. These settings of the PLL/LC-VCO 80 and/or the RC reference oscillator 162 can be used for setting the reference frequency for reception and transmission. The correction of the PLL/LC-VCO 80 and the RC reference oscillator 162 can be adjusted such that optimum adjustment of the PLL/LC-VCO for receiving each channel in the band can be easily achieved. The measurement error can be reduced by doing multiple measurements.

As example, it can be expected that the tolerance on the LC-VCO 80 is in the order of +/-8% or +/- 64 MHz at 800 MHz centre frequency (assuming +/-1% in the inductor and +/-15% in the capacitances). Assuming the RF filter 10 to have a tolerance of +/- 1 MHz, the tolerance on the combined LC-VCO 80 and RC reference oscillator can be reduced down to +/- 1 MHz.

A combination of the approaches of the first and second embodiments can be used to further reduce the frequency error. By using the disclosed principles above, the frequency error can be reduced a lot, such that it is much easier to find the proper frequency.

In the text above, the low- frequency oscillator is denoted as RC reference oscillator 162. This oscillator may as well be implemented as gmC-oscillator, ring-oscillator or LC-oscillator. The injection of local oscillator signal at the antenna should not be too high to prevent spurious emissions. For instance in the GSM (Global system for Mobile communications) standard a maximum emission of -57 dBm is allowed. This level is far above the noise floor of the receiver so it can be detected easily. The measurements of the RF filter 10 can be relative measurements, which means that the frequency is detected, at which the attenuation is 3 dB more than the attenuation at the centre of the frequency band.

Fig. 4 shows a schematic block diagram of a transceiver apparatus according to the third embodiment.

In this third embodiment, a variable bandwidth of a transmission signal is used to "capture" the frequency of transmission. An initially increased bandwidth is followed by a smaller bandwidth for the actual data transfer. If the increased or enhanced bandwidth received via the RF filter 10 is detected and coupled to the reference oscillator 162 at the receiver portion, a transceiver can be realized, which does not need a XTAL and/or XTAL- oscillator, thus reducing complexity and cost of the overall system. The basic idea is that the transmission end or transmitter having a master function uses a wideband transmission at the start of the transmission. After the receiver having a slave function has coupled the enhanced bandwidth to the reference oscillator 162 and finally found the transmitted frequency, it can notify the master which reduces the transmitted bandwidth in response to the notification or acknowledgement.

In the following, this master-slave principle will be explained based on a practical numerical example.

The transmission frequency received from the master is assumed to be 800 MHz. The slave reference oscillator 162 has an in-accuracy of +/-20%, so somewhere between 800+/-20% or between 640 and 960 MHz. Assuming that the slave reference oscillator 162 is at 960 MHz (the wideband transmission of the master should have at least some signal power at 960 MHz), the slave receives the 800 MHz signal at the edge of its range and demodulates it. From this demodulated signal the master centre frequency can be derived (800 MHz). The slave may now store the deviation or error in frequency, and tunes its receiving frequency to 800 MHz, so that the slave "locks" to or captures the master's frequency. After frequency locking, the transmission bandwidth can be reduced. In case the slave wants to transmit, it uses the stored frequency correction and uses this correction for its reference oscillator 162 when transmitting. This can be a small-bandwidth or a wide- bandwidth transmission. Fig. 5 shows a schematic flow diagram of the above procedure according to the third embodiment for an exemplary transmission between a base station (master) and a mobile station (slave).

In step S201, the base-station (master) transmitter uses a (low- frequency) wide-bandwidth modulation of its carrier frequency, so that it spreads over a wide- bandwidth. A simple way of doing this, is by using a high-modulation index (» 2.4) in an old-fashioned frequency modulation (FM). Other modulations are of course also possible. The bandwidth should be wide enough to fall within the receiver and demodulator bandwidth of the mobile station (slave).

Then, in step S202, the mobile station (slave) detects the wide-bandwidth modulation and couples it to the reference oscillator in order to provide a wide-bandwidth demodulation, thereby detecting the transmit frequency of the base station. In order to detect the wideband modulation of the base station, some extra receiver functionality (like a wideband frequency demodulator 66, temporarily removal of any filtering in the receive path, etc ...) can be implemented. In Fig. 4 this is shown by an additional block FD 66, both connected in front of and after the IF filtering circuits 52, 54.

A frequency error detected by a frequency control unit or function 77 provided in the digital processing unit 70 or as a separate unit, may be stored in step S203 in a memory 78, which may be a digital memory.

In step S204, the reference oscillator (in Fig. 4 shown as an RC oscillator 162, but it could be as well implemented as a gmC-, LC- or ring-oscillator) which replaces the crystal reference oscillator 120 of Fig. 1, is programmed with or controlled based on the frequency correction. In principle, also the local oscillator (LC-VCO 80) can be programmed with or controlled based on the frequency correction.

Then, in step S205, the mobile station (slave) transmits (now on the correct frequency) towards the base station, and acknowledges a "locked" state to the base station.

Dependent on changes in the frequency of the reference oscillator 162, this procedure may be repeated every hour or day or week. In order to lower the number of calibration cycles, once slave and master are locked, the master could, regularly, transmit over a wide-bandwidth (not necessarily as wide as during the initial calibration) to keep its slaves at the correct frequency.

When (all) slaves know the required frequency deviation, future transmissions may use a smaller bandwidth. Also, regular updates (e.g. once per hour or day) can be used to counteract frequency drift and aging in the devices.

The explained principle can also be applied to polar transmitter architectures, or any other transceiver architecture.

It is likely that on the system level multiple slaves will be associated with one master. If the sequence for capturing and locking is used regularly for several devices, also the non-active devices (i.e. devices that have no need for the data to be received) can receive the wide-band transmission and extract the correct frequency reference.

In order to minimize receiver complexity, the transmitted signal can have a simple modulation format, maybe even so simple that it can be demodulated in the analog domain, instead of requiring (high-speed) AD conversion which usually requires higher power consumption.

The above measures of the third embodiment can of course be combined with the measures of the first and second embodiments to further reduce or relax accuracy requirements of the reference oscillator. The extra complexity in receiver design of the third embodiment can very easily be realized in integrated circuit technology. The above example has been given for a master transmitting the wide- bandwidth signal. However, also the reverse situation (the slave transmitting the wide-band signal) can be a valid application scenario.

The large bandwidth required for locking the slave onto the master's frequency should be used wisely. For instance, a large output power can most probably not be tolerated over a large bandwidth due to regulatory requirements of standardization bodies. If a large amount of redundancy is applied in this wide bandwidth, the transmit power can be lowered also to stay below the regulatory maximum emissions.

Several possibilities can be used for realizing a very wide bandwidth transmission. For example, a wide bandwidth FM transmission using "nested" FM transmission could be used, as described for example in J.F.M. Gerrits, J.R. Farserotu and J.R. Long, "UWB Considerations for "My Personal Global Adaptive Network" (MAGNET) Systems", ESSCIRC 2004.

An alternative more "digital- friendly" approach is to use spread spectrum techniques (including frequency hopping) which can spread a low- frequency tone over a much larger bandwidth. So, for instance a 100 kHz tone can be spread over a bandwidth of 100 MHz. Due to the spreading the transmission power is also spread over the larger bandwidth, resulting in lower power-per-MHz thus easier fulfilling the radiation requirements of the standardization bodies. It is noted however that the redundancy in the wideband transmission should not have a too-low frequency, as it may take a very long time to detect low-frequency signals. For instance a 1 kHz modulation will require at least 1 ms for proper detection.

In principle, the above scenarios assume a crystal as frequency reference in the master. However, this is not mandatory. The bandwidth for the transmission can be widened to also cover the frequency uncertainty in the master. In an alternative example, the master could get its reference from other systems, like the global positioning system (GPS).

This invention can be used for ultra-low-power radio devices or wireless consumer devices or any other receivers, transmitters or transceivers.

To summarize, an apparatus and a system having at least one of a transmitter portion or apparatus for transmitting a transmission signal and receiver portion or apparatus for receiving a transmission signal, and a method of operating such an apparatus and system have been described. A reference frequency is generated at an oscillator circuit which is used for frequency conversion in at least one of the transmitter and receiver portion, and the transmission signal is filtered at a filter circuit before it is input to the transmitter portion or after it is output from the receiver portion. At least one of a physical or electronic coupling of at least one bandwidth parameter at the filter circuit to the oscillator circuit is provided to thereby relax accuracy requirements at said oscillator circuit. Thereby, the oscillator circuit can be configured without crystal resonator element(s) and the size of the apparatus and system can be reduced.

The present invention is not restricted to the above specific examples of physical or electronic coupling arrangements. Rather, and any kind of physical or electronic coupling could be used, which serves to couple a bandwidth parameter of or at the concerned filter circuit to the oscillator circuit. The preferred embodiments may thus vary within the scope of the attached claims.

Finally but yet importantly, it is noted that the term "comprises" or

"comprising" when used in the specification including the claims is intended to specify the presence of stated features, means, steps or components, but does not exclude the presence or addition of one or more other features, means, steps, components or group thereof. Further, the word "a" or "an" preceding an element in a claim does not exclude the presence of a plurality of such elements. Moreover, any reference sign does not limit the scope of the claims.

Claims

CLAIMS:

1. An apparatus having at least one of a transmitter portion for transmitting a transmission signal and receiver portion for receiving a transmission signal, said apparatus comprising: a) an oscillator circuit (82; 162) for generating a reference frequency for frequency conversion in at least one of said transmitter and receiver portions; b) a filter circuit (10) for filtering said transmission signal before it is input to said transmitter portion or after it is output from said receiver portion; and c) a coupling arrangement (160; 72, 74; 77) for providing at least one of a physical or electronic coupling of at least one bandwidth and/or centre frequency parameter at said filter circuit (10) to said oscillator circuit (82; 162) to thereby relax accuracy requirements at said oscillator circuit.

2. An apparatus according to claim 1, wherein said coupling arrangement comprises a common substrate (160) on which said oscillator circuit (82) and said filter circuit (10) are jointly integrated.

3. An apparatus according to claim 2, wherein said oscillator circuit (82) and said filter circuit (10) are implemented based on surface or bulk acoustic wave technology.

4. An apparatus according to claim 2, wherein said oscillator circuit (82) and said filter circuit (10) are implemented based on a film bulk acoustic resonator technology or a micro-electro-mechanical system technology.

5. An apparatus according to any one of claims 2 to 4, wherein said oscillator circuit (82) is operated at twice the frequency of said filter circuit (10).

6. An apparatus according to any one of claims 2 to 4, wherein said oscillator circuit (82) and said filter circuit (10) are operated at substantially the same frequency.

7. An apparatus according to any one of the preceding claims, wherein said coupling arrangement comprises a measuring unit (74) for measuring a band-pass characteristic of said filter circuit (10), and a control unit (72) for adjusting the frequency of said oscillator circuit (162) in response to an output of said measuring unit (74).

8. An apparatus according to claim 7, wherein said coupling arrangement comprises a connecting arrangement (14, 170) for injecting a signal derived from said oscillator circuit (162) to an input of said filter circuit (10).

9. An apparatus according to claim 7 or 8, wherein said connecting arrangement

(14, 170) comprises a switching element (14) which is only closed in a calibration mode of said apparatus.

10. An apparatus according to any one of claims 7 to 9, wherein said measuring unit (74) is adapted to measure a DC voltage generated at a receiving mixer circuit (42, 44).

11. An apparatus according to any one of the preceding claims, wherein said coupling arrangement comprises a detection unit (66) for detecting a temporarily increased bandwidth of a transmission signal received through said filter circuit (10), and a frequency control unit (77) for controlling said oscillator circuit (162) in accordance with the detection result during a locking operation for capturing a transmission frequency.

12. An apparatus according to claim 11, wherein said frequency control unit (77) is adapted to detect a frequency error of said receiver portion and to control the frequency of said oscillator circuit (162) based on the detected frequency error.

13. An apparatus according to claim 12, further comprising a memory unit (78) for storing on said detected frequency error.

14. An apparatus according to any one of claims 11 to 13, wherein said frequency control unit (77) is adapted to transmit an acknowledgment to a transmission end of said transmission signal, if the detected frequency error indicates a frequency locking state of said receiver portion.

15. A method of operating at least one of a transmitter portion for transmitting a transmission signal and receiver portion for receiving a transmission signal, said method comprising the steps of: a) generating at an oscillator circuit (82; 162) a reference frequency for frequency conversion in at least one of said transmitter and receiver portions; b) filtering said transmission signal at a filter circuit (10) before it is input to said transmitter portion or after it is output from said receiver portion; and c) providing at least one of a physical or electronic coupling of at least one bandwidth and/or centre frequency parameter at said filter circuit (10) to said oscillator circuit (82; 162) to thereby relax accuracy requirements at said oscillator circuit.

16. A method according to claim 15, wherein said physical coupling is achieved by jointly integrating said oscillator circuit (82) and said filter circuit (10) on a common substrate (160).

17. A method according to claim 16 or 17, wherein said electronic coupling is achieved by measuring a band-pass characteristic of said filter circuit (10), and a adjusting the frequency of said oscillator circuit (162) in response to a result of said measuring.

18. A method according to claim 17, further comprising injecting a signal derived from said oscillator circuit (162) to an input of said filter circuit (10).

19. A method according to any one of claims 15 to 18, wherein said electronic coupling is achieved by detecting a temporarily increased bandwidth of a transmission signal received through said filter circuit (10), and by controlling said oscillator circuit (162) in accordance with the detection result during a locking operation for capturing a transmission frequency.

20. A method according to any one of claims 15 to 19, further comprising transmitting an acknowledgment to a transmission end of said transmission signal, if the detected frequency error indicates a frequency locking state of said receiver portion.

21. A system for operating at least one of a transmitter apparatus for transmitting a transmission signal and a receiver apparatus for receiving said transmission signal, said system comprising: a) a detection unit (66) for detecting a temporarily increased bandwidth of said transmission signal, said increased bandwidth being set by said transmitter apparatus; and b) a frequency control unit (77) for controlling an oscillator circuit (162), which is provided for frequency conversion in said receiver apparatus, in accordance with the detection result during a locking operation for capturing a transmission frequency; c) wherein said frequency control unit (77) is adapted to transmit an acknowledgment to a transmission end of said transmission signal, if a detected frequency error indicates a frequency locking state of said receiver portion; d) wherein said transmitter apparatus is adapted to reduce the bandwidth of said transmission signal in response to a receipt of said acknowledgement.

22. A system according to claim 21, wherein said transmitter apparatus is adapted to increase the bandwidth of said transmission signal at regular intervals, in order to trigger said locking operation.