TECHNICAL FIELD

The present invention relates to acoustic wave devices (AWDs) that are arranged to modulate or demodulate signals. The invention also relates to transceivers that comprise said AWD in accordance with the present invention. The invention equally relates to corresponding modulation/demodulation methods and to computer program products comprising instructions for implementing the steps of said methods.

BACKGROUND OF THE INVENTION

In wireless networks it is generally the aim to utilise transceivers that have a small form factor, i.e. physical size, and are inexpensive. Closely related to low-cost and small form factor is low-power, because in a wireless application a larger power source directly increases cost and form factor. Figure 1 illustrates in simplified block diagram form an exemplary state-of-the art transceiver for wireless sensor network. Transceivers can both receive and transmit radio signals depending on the operation mode. In Figure 1 there are shown seven major hardware units, namely an antenna 101 , an AWD 103 for operating as a band pass filter, a power amplifier/low noise amplifier 105, a high frequency analogue circuit 107, a low frequency analogue circuit 109, digital hardware + software 111 and a crystal 113 for providing a reference frequency. The high frequency analogue circuit 107 for instance performs most of the operations related to modulation/demodulation, but the low frequency analogue circuit 109 participates in modulation/demodulation when low frequency operations are needed. The high frequency analogue circuit 107 often contains an oscillator and/or a mixer. It is to be noted that the power amplifier is only used in the transmit mode, whereas the low noise amplifier is only used in the receive mode. However, both these units are optional. When operating as a transmitter, the high frequency analogue circuit 107, the low frequency analogue circuit 109 and the digital hardware + software 111 participate in transforming the desired signal into radio frequency, whereas when operating as a receiver, these units participate in transforming these signals into a baseband signal. State-of-the-art transceivers for wireless sensor networks commonly use both a crystal and an AWD. The crystal is used to generate a reference for a high frequency oscillator. On the transmit side the AWD suppresses out- of-band power that could interfere with transceivers operating in a different band. On the receive side it facilitates demodulation by suppressing out-of- band interferers. Depending on practical issues the AWD can be a bulk acoustic wave device (BAWD) or a surface acoustic wave device (SAWD).

The main disadvantages of a crystal are the relatively bulky form factor and the relatively high cost. It is widely recognised that the crystal is becoming a bottleneck in the further reduction of form factor and cost of wireless transceivers.

A disadvantage related to the common modulation and demodulation is the relatively high power consumption of various high frequency analogue building blocks, such as a high frequency oscillator and a mixer. This disadvantage is not so relevant for transmitters with a high transmit power or for receivers that are used in a system together with relatively high power components like a headphone. In upcoming applications like wireless sensor nodes high power consumption is acknowledged as a problem.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided an acoustic wave device arranged for modulating radio signals, the acoustic wave device comprising a substrate, at least one input transducer and at least one output transducer, the transducers being provided on the substrate, wherein the acoustic wave device is arranged to provide a modulated signal at the at least one output transducer in response to an electrical signal response provided at the at least one input transducer. Thus, the present invention provides a new application of an AWD. The AWD is directly used to modulate. When applied in a transceiver, further advantage is that the transceiver only uses an AWD instead of both an AWD and a crystal. Another advantage is reduced power consumption because fewer high frequency and high power analogue building blocks are required. The invention will result in lower power consumption, form factor and cost.

According to a second aspect of the invention, there is provided an acoustic wave system, wherein at least two acoustic wave devices according to the first aspect of the invention are combined. According to a third aspect of the present invention, there is provided an acoustic wave device arranged for demodulating radio signals, the acoustic wave device comprising a substrate, at least one input transducer and at least one output transducer, the transducers being provided on the substrate, wherein the acoustic wave device is arranged to provide a demodulated signal at the at least one output transducer in response to a radio frequency pulse provided at the at least one input transducer.

According to a fourth aspect of the present invention, there is provided a method for modulating a radio signal by use of an acoustic wave device comprising a substrate, at least one input transducer and at least one output transducer, the transducers being provided on the substrate, the method comprising:

- applying an electrical signal at the at least one input transducer;

- the electrical signal traversing the at least one output transducer; and

- the at least one output transducer generating a modulated RF pulse in response to the electrical signal.

According to a fifth aspect of the present invention, there is provided a method for demodulating a radio signal by use of an acoustic wave device comprising a substrate, at least one input transducer and at least one output transducer, the transducers being provided on the substrate, the method comprising:

- applying a modulated signal at the at least one input transducer; - the modulated signal traversing the at least one output transducer; and

- the at least one output transducer generating a demodulated signal in response to the modulated signal. According to sixth and seventh aspects of the present invention, there are provided computer program products comprising instructions for implementing the methods according to the fourth and fifth aspects of the invention when loaded and run on computer means of AWDs.

Other aspects of the invention are recited in the dependent claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent from the following description of non-limiting exemplary embodiments, with reference to the appended drawings, in which: - Figure 1 is a simplified block diagram of a state-of-the-art transceiver;

- Figures 2-4 show schematic representations of different AW configurations in accordance with embodiments of the present invention;

- Figure 5 is a simplified block diagram of a transceiver in accordance with an embodiment of the present invention; - Figure 6 is a flow chart illustrating the modulation method in accordance with an embodiment of the present invention; and

- Figure 7 is a flow chart illustrating the demodulation method in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION The present invention is based on an idea that an AWD can operate as a modulator or demodulator as will be explained later in more detail. When the AWD in accordance with the invention is applied to a transceiver as shown in Figure 1 , the crystal 1 13 can be omitted.

For transmitting information, it is required that AWDs can generate an appropriately modulated signal in response to, for instance, a step or impulse. For receiving information, it is required that AWDs allow simple low-power analogue processing in response to the intended modulated signal. An example of an AWD that can be used for both transmitting and receiving is shown in Figure 2. There is shown one (interdigital) transducer with a large coupling at the electrical input and there are many transducers at the electrical output. The transducers are provided on a substrate, such as piezoelectric substrate.

In this example, an electrical step at the input will generate an acoustic wave front in the AWD that will pass the transducers of the output one by one. The output transducers will pick this up as an RF pulse. Such an RF pulse is a properly modulated signal for amplitude shift keying, on off keying or pulse position modulation. If the AWD is driven by a train of impulses, this will result in a train of RF pulses and not in a continuous signal, i.e. the periodicity of the impulse train is not taken into account in the AWD design.

Applying a step function to the AWD results in an RF pulse, which carries one bit (or two bits) of information (depending on the modulation used). To send more than one (or two) bits of information the step function has to be repeated after a bit period (as often as needed); a straight-forward implementation of this would result in a stair-like signal, but a more practical implementation would use a step function changing from level 0 to level 1 and after a short while returning to level 0 and repeating this for every bit, i.e. a square wave or a train of impulses. Thus, a step function is enough to communicate limited data, i.e. one or two bits, with the present invention, whereas it is not sufficient with the existing solutions. To communicate unlimited data by using the present invention, the step function needs to be repeated and this might mean in practice using a square wave or a train of pulses as an input.

The functions of output and input can also be interchanged. A step at the output will induce an acoustic sine wave in the AWD. The wave pattern will propagate to the input and will be picked up as an RF pulse. The same AWD can also be used in the receiver. The response to an RF pulse of the right frequency can be detected with a peak detector.

An AWD with one input and one output can be used for amplitude shift keying, on off keying or pulse position modulation. By combining several AWDs more robust modulation methods can be used. For instance, the AWD in Figure 3 can generate RF pulses of two different frequencies. It can be used for frequency shift keying.

Several AWDs can be integrated into one AWD with multiple inputs. An example of such a device is shown in Figure 4. In this example the output can be connected to the antenna and the inputs to a peak detector.

In theory AWDs are not the only devices that can be used for direct modulation and demodulation. AWDs are especially suitable for it though, because the propagation speed is such that the device has practical dimensions. Figure 5 illustrates a transceiver where the above-described AWD 103 is employed. When compared to the solution described in Figure 1 , it can be realised that the crystal is missing. Indeed, the AWD 103 in accordance with the present invention makes the crystal useless in transceivers. Furthermore, the high frequency analogue circuit 107 is also omitted. The high frequency analogue circuit 107 can be omitted since the AWD 103 in accordance with the present invention performs the frequency translation into higher frequencies. When the transceiver operates as a modulator, the AWD 103 creates a radio frequency modulated signal in response to a low frequency analogue signal. Depending on the AWD 103 the low frequency analogue signal can for instance be a step or an impulse. Especially a circuit that generates a step, which contains high frequency components, can be implemented easily and by using very low power. Compared to the solution shown in Figure 1 , the order of the AWD 103 and the optional power amplifier/low noise amplifier 105 is reversed. The purpose of the optional power amplifier 105 is to increase the operational range. As explained earlier, the power amplifier is only applied in the transmit mode, whereas the low noise amplifier is only applied in the receive mode.

There is a clear difference between the present invention's transmitter and a transmitter that uses the AWD as a resonator (thereby replacing the crystal) for a radio frequency oscillator. In such a transmitter the AWD needs to have similar properties as a crystal. Such a transmitter also has the disadvantage of the relatively high power consumption of various high frequency analogue building blocks like a high frequency oscillator and a mixer. The AWD of the present invention does not need to be a resonator. When operating as a receiver, the AWD 103 is selective to the intended modulated signal. The low frequency analogue circuit 109 can for instance be a simple and low power peak detector. Again there is a clear difference between the present invention's receiver and a receiver that uses the AWD as a resonator for a radio frequency oscillator, like for instance a super-regenerative receiver. In such a receiver the AWD needs to have similar properties as a crystal. Such a receiver also has the disadvantage of the relatively high power consumption of various high frequency analogue building blocks like a high frequency oscillator and a mixer. The AWD in accordance with the present invention does not need to be a resonator. The teachings of the present invention can be applied basically in any of the numerous wireless (sensor) network transceivers where it is desirable to reduce power, form factor and/or cost. There are for instance many wireless sensor network applications within Consumer Lifestyle Solutions where these teachings invention can be applied. There are also activities within research exploring patient tracking and monitoring, both within hospitals and at patients' houses. These activities are relevant for the healthcare business sector and can use the teachings of the present invention.

The present invention equally relates to modulation and demodulation methods by using the above described AWD. With reference to the flow chart of Figure 6, in step 601 an electrical function, such as a step function, is applied at the input of the AWD 103. In step 603 the electrical function traverses the output transducers one by one. Finally in step 605 the output transducers generate a modulated RF pulse in response to the electrical function.

With reference to the flow chart of Figure 7, in step 701 a modulated radio signal is received by the input transducer(s). In step 703 the modulated

RF pulse traverses the output transducers one by one. Finally in step 705 the output transducers generate a demodulated signal in response to the modulated RF signal.

The present invention also relates to a computer program product that is able to implement any of the method steps as described above when loaded and run on computer means of the AWD 103. The computer program may be stored/distributed on a suitable medium supplied together with or as a part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. The invention also relates to an integrated circuit that is arranged to perform any of the method steps in accordance with the embodiments of the invention.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, the invention being not restricted to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope of the invention.