Modulator and method for producing a modulated signal

A modulator including a direct modulation synthesizer circuit, a reference frequency oscillator for providing an input reference signal to the direct modulation synthesizer circuit for locking a carrier frequency to a stable frequency and a pre-emphasis unit for data bits and for producing a modulating signal for direct modulation of the direct modulation synthesizer circuit, the modulating signal having data bit dependent voltage levels.

FIELD OF THE INVENTION

The present invention relates in general to the field of transmitting data from an in-vivo device. More specifically, the present invention relates to high bit rate transmission of a modulated signal from an in-vivo device.

BACKGROUND OF THE INVENTION

Devices and methods for in-vivo sensing of passages or cavities within a body, and for sensing and gathering information (e.g., image information, pH information, temperature information, electrical impedance information, pressure information, etc.), are known in the art.

In-vivo sensing devices such as capsules may include a sensing system and a transmission system, wherein the sensing system collects data and the transmission system transmits the collected data by Radio Frequency (RF) to an external receiver system, e.g., for further processing and display. One known method for transmitting information with an RF signal is by MSK (Minimum Shift Keying) direct modulation. However, the limited bandwidth of the modulator may limit the transmission rate.

SUMMARY OF THE INVENTION

In accordance with some embodiments of the present invention there is provided a modulator for producing a modulated signal, the modulator comprising:

a direct modulation synthesizer circuit;

a reference frequency oscillator for providing an input reference signal to the direct modulation synthesizer circuit for locking a carrier frequency to a stable frequency;

a pre-emphasis unit for receiving data bits and for producing a modulating signal for the direct modulation synthesizer circuit, the modulating signal having data bit dependent voltage levels.

In accordance with some embodiments, the modulator is located in an in-vivo sensing device.

There is also provided in accordance with the present invention an in-vivo sensing device comprising a modulator for producing a modulated signal, the modulator comprising:

a direct modulation synthesizer circuit;

a reference frequency oscillator for providing an input reference signal to the direct modulation synthesizer circuit for locking a carrier frequency to a stable frequency;

a pre-emphasis unit for receiving data bits and for producing a modulating signal for direct modulation of the direct modulation synthesizer circuit, the modulating signal having data bit dependent voltage levels.

In some embodiments, the in-vivo sensing device comprises an imager, one or more illumination sources and an optical system.

If desired, the in-vivo sensing device comprises a processor, a transmitter and an antenna.

There is also provided in accordance with some embodiments of the present invention, a method for producing a modulated signal, comprising:

providing a direct modulation synthesizer circuit;

inputting a reference signal to the direct modulation synthesizer circuit for locking a carrier frequency to a stable frequency;

inputting a modulating signal to the direct modulation synthesizer circuit, the modulating signal having data bit dependent voltage levels; and

outputting the modulated signal from the direct modulation synthesizer circuit.

If desired, the modulated signal is a CPFSK signal.

In accordance with some embodiments, the pre-emphasis unit is a digital-to-analog converter (D/A) and each voltage level of the modulating signal is a function of the bit values of a given data bit and of the data bit preceding the given data bit.

In accordance with some embodiments, the pre-emphasis unit is a digital-to-analog converter (D/A) and each voltage level of the modulating signal is a function of the bit values of a given data bit and of more than one data bit preceding the given data bit.

If desired, the modulating signal has at least four voltage levels.

In accordance with some embodiments, the at least four voltage levels are:

V0, if the given data bit is “0” and the preceding data bit is “0”;

V0−δV, if the given data bit is “0” and the preceding data bit is “1”,

V1, if the given data bit is “1” and the preceding data bit is “1”; and

V1+δV, if the given data bit is “1” and the preceding data bit is “0”;

where V1and V0are standard bit-voltage levels and V1is greater that V0, and δV is a positive voltage enhancement value by which the standard bit-voltage levels are altered by the pre-emphasis unit.

In accordance with some embodiments, the direct modulation synthesizer circuit comprises a voltage controlled oscillator, into which the modulating signal is inputted, a phase detector that produces a phase detector output signal by comparing the input reference signal with a local frequency signal outputted from a feedback frequency divider connected to the voltage controlled oscillator, a charge pump that receives the phase detector output signal and that has an output signal that is inputted into a loop filter that produces a filtered signal that is inputted into the voltage controlled oscillator together with the modulating signal.

In accordance with some embodiments, the pre-emphasis unit comprises a digital-to-analog converter (D/A) and a low pass filter of at least order two with damping factor having a value of less than one, the low pass filter being located between the digital-to-analog converter and the direct modulation synthesizer circuit.

Further in accordance with some embodiments, the modulating signal outputted from the low pass filter to the direct modulation synthesizer circuit has two voltage levels.

Yet further in accordance with some embodiments, the modulating signal has an overshoot if a given data bit is1and the data bit preceding the given data bit is0; and has undershoot if the given data bit is0and the data bit preceding the given data bit is1.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, various aspects of the invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the invention. However, it will also be apparent to a person skilled in the art that the invention may be practiced without the specific details presented herein. Furthermore, well-known features may be omitted or simplified in order not to obscure the invention.

It should be noted that although a portion of the discussion may relate to in-vivo imaging devices, systems, and methods, the present invention is not limited in this regard, and embodiments of the present invention may be used in conjunction with various other in-vivo sensing devices, systems, and methods. For example, some embodiments of the invention may be used, for example, in conjunction with in-vivo sensing of pH, in-vivo sensing of temperature, in-vivo sensing of pressure, in-vivo sensing of electrical impedance, in-vivo detection of a substance or a material, in-vivo detection of a medical condition or a pathology, in-vivo acquisition or analysis of data, and/or various other in-vivo sensing devices, systems, and methods.

It is noted that discussions herein utilizing terms such as “processing”, “computing”, “calculating”, “determining”, or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device or platform, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices.

Embodiments of the present invention may include apparatuses for performing the operations herein. Such apparatus may be specially constructed for the desired purposes, or it may comprise a general purpose computer selectively activated, adapted, operated, configured or re-configured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but not limited to, a disk, a hard disk drive, a floppy disk, an optical disk, a CD-ROM, a DVD, a magnetic-optical disk, Read-Only Memory (ROM), Random Access Memory (RAM), Electrically Programmable ROM (EPROM), Electrically Erasable and Programmable ROM (EEPROM), Flash memory, volatile memory, non-volatile memory, magnetic or optical cards, or any other type of storage media or storage unit suitable for storing electronic instructions and capable of being operatively connected to a computer system bus or a computing platform.

Some embodiments of the present invention are directed to a typically swallowable in-vivo sensing device, e.g., a typically swallowable in-vivo imaging device. Devices according to embodiments of the present invention may be similar to embodiments described in U.S. Pat. No. 7,009,634 and/or in U.S. Pat. No. 5,604,531, each of which is assigned to the common assignee of the present invention and each of which is hereby fully incorporated by reference. Furthermore, a receiving and/or display system which may be suitable for use with embodiments of the present invention may also be similar to embodiments described in U.S. Pat. No. 7,009,634 and/or in U.S. Pat. No. 5,604,531. Of course, devices and systems as described herein may have other configurations and/or other sets of components. For example, the present invention may be practiced using an endoscope, needle, stent, catheter, etc.

Reference is now made toFIG. 1showing a block diagram of a CPFSK (Continuous Phase Frequency Shift Keying) direct modulator10according to an embodiment of the present invention. The modulator10includes a direct modulation synthesizer circuit12, similar to a constant wave (CW) synthesizer, that sets the carrier frequency. The direct modulation synthesizer circuit12has a voltage controlled oscillator (VCO)14, into which a modulating signal16, having a modulation voltage, is inputted; a phase detector18that produces a phase detector output signal20by comparing an input reference signal22with a local frequency signal24outputted from a feedback frequency divider26connected to the VCO14; a charge pump28that receives the phase detector output signal20and that has a charge pump output signal30that is inputted into a loop filter32that produces a filtered signal34that is inputted into the VCO14together with the modulating signal16. The VCO input may be the combined sum of the modulating signal16and the filtered signal34. The input reference signal22may be produced by a reference frequency oscillator36, such as crystal oscillator, followed by a reference frequency divider38. The modulating signal16may be obtained from data bits40that have undergone pre-emphasis by a pre-emphasis unit, such as a digital-to-analog converter (D/A)42. The data bits40(also referred to in the drawings as, “transmitted bits”) may be transmitted internally in an in-vivo sensing device from a sensor, such as an imager (see description below with respect toFIG. 7), to the digital-to-analog converter42. The output signal44may be inputted to a transmitter inside the in-vivo sensing device for transmitting to an external receiver system, e.g., for further processing and display. The voltage controlled oscillator14may include a transmitting antenna, in which case a separate transmitter is not required.

Reference is now made toFIG. 2which shows four graphs. The graph labeled “transmitted bits” shows an example for data bits40given by an MSK1bit/symbol signal. The graph labeled “Modulation voltage” shows the modulation voltage of the modulating signal16outputted by the digital-to-analog converter42to the VCO14. The two lower graphs show the output frequency and output phase of the output signal44, outputted by the modulator10for the case of ideal modulation in which there is no distortion of the signal modulated by the modulator10. In this ideal case, the VCO14changes the output frequency instantly during transitions between binary bit0and binary bit1.

The output phase is calculated as an integral over the output frequency. Since this example is for MSK modulation, each symbol causes a phase difference of ±π/2 [rad] according to the modulated bits. Binary bit1corresponds to +π/2 [rad] while binary bit0corresponds to −π/2 [rad]. Throughout the specification and claims, the terms ‘binary bit0’ and ‘binary bit1’ will also be denoted simply by “0” and “1”, respectively. In this example, there are only 4 possible values to phase at the end of each symbol: Φ0, Φ0±π/2, Φ0-π. In the phase calculation it is assumed, for simplicity, that the carrier frequency is zero. Other phase differences and modulated bits may be used.

In practice, the VCO14has a finite bandwidth, and a finite time is required for the frequency to reach its steady state value. The wider the VCO bandwidth, the less time is required for frequency change.FIG. 3shows an example for direct MSK modulation for a case in which the VCO14has a narrow-bandwidth, according to one embodiment of the present invention. While the modulation voltage inFIG. 3is identical to that ofFIG. 1, the output frequency of the VCO14inFIG. 3is different from that ofFIG. 1. Whenever there is a frequency change between two adjacent symbols, the output frequency reaches the desired steady state frequency only after some finite time interval (marked as Δ inFIG. 3). On the other hand, if the frequency does not change between two adjacent symbols, this problem does not exist. Another way of describing this situation is by saying that the finite convergence time of the output frequency to reach its steady state value, appears only when there are “1”→“0” or “0”→“1” transitions in the data bits. The existence of the finite time interval, Δ, required for frequency convergence may cause, for example, the following problems:1. The phase difference corresponding to a symbol following a transition does not reach the ±π/2 phase deviation. As a result:a. The Bit Error Rate (BER) performance of the receiver is deteriorated since the minimal distance between signal points decreases according to sin2(phase difference).b. The phases of the subsequent symbols do not have the four possible values as in the case of ideal modulation namely, Φ0, Φ0±π/2, Φ0-π. This makes it difficult for the receiver to track the phase.2. The phase change for symbols which are substantially identical to the preceding symbols is still ±/2.

In other words, the phase of a given symbol depends not only on the given symbol but also on the preceding symbol. Of course, when Δ is small relative to the symbol length (for example, if Δ is smaller than 10% of the symbol time), the above observations may be practically ignored.

In cases in which Δ cannot be ignored, the modulating signal may be pre-emphasized (or, pre-distorted) so that the modulated signal may have the desired properties. According to one embodiment of the present invention, this is done by controlling the D/A output voltage (i.e., the modulation voltage) so that it is a function of both a given data bit and the bit preceding given data bit. This is in contrast to the ideal case (FIG. 2) in which the D/A output is only a function of each given data bit.

According to an embodiment of the present invention, the modulating signal has four voltage levels. Each voltage level is a function of the binary bit value of a given data bit and of the binary bit value of the data bit preceding the given data bit. The four voltage level may be given by:

V0, if the given data bit is “0” and the preceding data bit is “0”;

V0-δV, if the given data bit is “0” and the preceding data bit is “1”;

V1, if the given data bit is “1” and the preceding data bit is “1”; and

V1+δV, if the given data bit is “1” and the preceding data bit is “0”;

where V1and V0are standard bit voltage levels, V1is greater that V0, and δV is a positive voltage enhancement value by which the standard bit voltage levels are altered by the digital-to-analog converter42.

According to some embodiments, each voltage level may be a function of the binary bit value of a given data bit and of the binary bit value of more than one data bit preceding the given data bit.

According to some embodiments of, the modulating signal may have more than four voltage levels.

According to an embodiment of the present invention, each of the above voltages is chosen such that the phase difference for all symbols is ±π/2. This can be achieved using a calibration procedure for V0, V1, δV.FIG. 4shows the four voltage levels of the modulation voltage as well as the resulting output frequency and phase of the output signal44. Note that the final steady state frequency corresponding to enhanced level for bit ‘1’ is greater than the steady state frequency for bit ‘1’. However, the accumulated phase for both cases is +π/2. Similarly the final steady state frequency corresponding to the enhanced level binary bit0is less than the steady state frequency for the non-enhanced level binary bit0while the accumulated phase for both cases is −π/2.

According to an embodiment of the present invention, the output phase of the output signal produced by the pre-emphasized modulating signal is not the same as the output phase of the output signal44for the output phase for the ideal modulation case shown inFIG. 2. However, the phases at the end of each symbol are located at four points, namely Φ0, Φ0±π/2, Φ0−π. This improves the BER performance as well as the receiver tracking of the output phase of the output signal44. Although the present invention has been illustrated inFIGS. 2 to 4for MSK modulation, it will be apparent to the skilled person that it may easily extended to CPFSK modulation for any number of bits/symbol.

Attention is now drawn toFIGS. 5 and 6.FIG. 5shows a block diagram of a second CPFSK modulator110according to another embodiment of the present invention. The second modulator110is similar in structure to the modulator10shown inFIG. 1, except that the digital-to-analog converter142is a two-level D/A and there is a high order Low Pass Filter (LPF)132′ between the digital-to-analog converter142and the voltage controlled oscillator114. The low pass filter132′ is of at least second order, with damping factor ζ<1. The modulating signal116does not undergo pre-emphasis, so that the voltage level of a given data bit depends only on the value of the given data bit (V0for binary bit0and V1for binary bit1, seeFIG. 6).

The modulating signal116is passed through the low pass filter132′ and the low damping factor causes overshoot and undershoot of the frequency of the modulating signal116as shown inFIG. 6(see “Output frequency”). In accordance with some embodiments, the output frequency of the modulating signal has overshoot if a given data bit is “1” and the data bit preceding the given data bit is “0” (i.e., a “0”→“1” transition); and has undershoot if the given data bit is “0” and the data bit preceding the given data bit is “1” (i.e., a “1”→“0” transition). If the given data bit and the data bit preceding the given data bit are equal, then the low pass filter132′ does not alter the modulating signal116. The amount of overshoot or undershoot can be controlled through the value of the damping factor ζ. As the damping factor ζ decreases the overshoot and undershoot deviations from steady state value increase. The value of ζ may be calibrated in order to reach a phase difference of ±π/2 for every symbol. Although the embodiment of present invention shown inFIGS. 5 and 6has been illustrated for MSK modulation, it will be apparent to the skilled person that it may easily extended to CPFSK modulation for any number of bits/symbol.

Reference is made toFIG. 7, showing a schematic diagram of an in-vivo sensing device100according to embodiments of the present invention. In some embodiments, the in-vivo sensing device100may be a wireless device. In some embodiment, the in-vivo sensing device100may be autonomous. In some embodiments, the in-vivo sensing device100may be a swallowable capsule for sensing the gastrointestinal tract of a patient. However, other body lumens or cavities may be sensed or examined with the in-vivo sensing device100. The in-vivo sensing device100has a housing112having an external surface114and an inner chamber115that may include at least one sensor such as an imager118for capturing image frames of images of the gastrointestinal tract or other body lumens or cavities, a viewing window120, one or more illumination sources122, an optical system124, a transmitter126, a processor128, the modulator10,110according to embodiments of the invention, and a power supply such as a battery131. The modulator10,110may be part of the transmitter126. An antenna134may be connected to the transmitter126. According to some embodiments, the processor128may include a memory.

The illumination sources122may project light through the viewing window120to illuminate portions of the body lumens or cavities, in which the in-vivo sensing device100is located, and images of the illuminated portions are captured by the imager118via the optical system124. Captured image data in the form of data bits40may be inputted to the modulator10, as described hereinabove. As described with respect toFIG. 1, the output signal44may be inputted to the transmitter126for transmission to an external receiver system, e.g., for further processing and display. As mentioned above, the voltage controlled oscillator14may include a transmitting antenna, in which case the separate transmitter126and antenna34may not be required. While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents may occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.