A method of encoding an analog signal into a digital signal and corresponding device.

Abstract

A method of encoding an analog signal into a digital signal, the method comprising the steps of: determining an envelope of a received analog signal thereby producing an enveloped signal, applying a non-linear transformation to the enveloped signal thereby obtaining a non-linearly transformed enveloped signal, Analog-to-Digital converting, by an Analog-to-Digital converter, ADC, the non-linearly transformed enveloped signal, to produce the digital signal, wherein the ADC is a delta modulator.

Description

[0001] Title

[0002] A method of encoding an analog signal into a digital signal and corresponding device.

[0003] Technical Field

[0004] The present disclosure relates to methods of encoding analog signals into digital signals, using the envelope of a signal a non-linear transformation of the signal and a delta modulation of the signal.

[0005] Background

[0006] Ultrasound, US, imaging is an important branch in both non-destructive testing, NDT, and medical diagnostics, offering a safe, non-invasive way to visualize internal structures. With advances in technology, the demand for higher resolution and more detailed imaging has driven an increase in both the number of transducer elements and the frequency of the ultrasound signals used. Higher ultrasound frequencies provide better spatial resolution, allowing for finer detail in imaging. However, these improvements come at a cost: they significantly increase the amount of data generated during the scanning process, which directly impacts both storage and transmission requirements.

[0007] In B-mode (brightness mode) imaging, which is one of the most commonly used ultrasound modes for visualizing tissue structures, each transducer element captures a large amount of raw data. These data must be processed to generate a clear image of the target area. However, the transmission and handling of these raw data may dominate the power consumption of the ultrasound system, especially in portable devices such as handheld medical scanners. This may be problematic, as reducing power consumption may be important for improving the battery life and performance of mobile ultrasound devices. To address this challenge, one approach is to reduce the amount of data that needs to be transmitted and processed without sacrificing image quality.

[0008] In ultrasound (US) imaging, digital data compression methods like JPEG, MPEG, or compressive sensing are sometimes used to reduce data size. While effective, these approaches require significant computational power, which can increase overall power consumption. This presents a challenge in applications where US imagers lack high- performance digital signal processors (DSPs) or powerful onboard computing resources.

[0009] Emerging applications, such as wearable ultrasound patches and in-catheter ultrasound systems, face strict space and power constraints. In such cases, implementing computation-heavy data compression methods may be impractical, as they could quickly drain battery life or exceed processing capabilities.

[0010] Summary

[0011] Therefore, it would be beneficial to find an encoding technique which reduces the amount of data needed to be transmitted, while keeping a similar level of image quality.

[0012] In a first aspect of the disclosure, there is provided a method of encoding an analog signal into a digital signal, the method comprising the steps of: determining an envelope of a received analog signal thereby producing an enveloped signal; applying a non-linear transformation to the enveloped signal thereby obtaining a non-linearly transformed enveloped signal;

[0013] Analog-to-Digital converting, by an Analog-to-Digital converter, ADC, the non-linearly transformed enveloped signal, to produce the digital signal, wherein the ADC is a delta modulator.

[0014] The inventors have found that it may be beneficial to utilize envelope determination of an analog signal prior to the transmission of the digital signal.

[0015] Envelope determination is a signal processing technique used in ultrasound imaging to extract the amplitude or envelope of frequency signals. It removes the carrier frequency - if applicable - preserving only the low-frequency modulated signal, which represents useful imaging data, reducing data size and simplifying further processing. This method reduces the input signal variation, which reduces the data needed to be transmitted.

[0016] After this step, the signal may be transformed using a non-linear transformation, which allows for fine quantization of small reflections, and a coarse quantization of strong reflections, improving on the trade-off typically present for delta encoding. Delta encoding utilizes bits to represent an increase or decrease of an amplitude level. When the delta decoding utilizes synchronous encoding schemes, it may be inaccurate for large changes in the signal amplitude. When the delta decoding utilizes non-synchronous encoding schemes, the data needed to be transferred may be increased. Both are unwanted.

[0017] Therefore, obtaining an envelope before delta encoding decreases both unwanted effects and furthermore transforming the signal into a non-linearly transformed signal further decreases the unwanted effects.

[0018] This is because the non-linear transform effectively decreases the number of bits needed to accurately portray large changes in amplitude, due to its nonlinear behavior. This may decrease the error, because larger “steps” may be made, more accurately following the signal, and it may decrease the number of bits needed to follow the signal accurately, due to the same advantage.

[0019] Hereafter, the data may be transmitted, with an effective reduction of the total amount of data that is transmitted compared to that of the prior art.

[0020] In an example of the disclosure, quantization levels of the ADC are spaced according to a non-linear scale for implementing the step of applying the nonlinear transformation.

[0021] In this example the non-linear scale transformation is performed by the ADC, wherein the scale of the signal is transformed to create non-linear transformation levels. This allows the aforementioned advantages of decreasing the number of to-be sent bits. This example may further be beneficial as it negates the need of any nonlinear power amplifier, PA.

[0022] In an example of the disclosure, the method comprises the steps of: outputting, by the ADC, a polarity signal representative of a polarity of the received analog signal such that the digital signal is associated with a polarity.

[0023] It may be beneficial to add a sign detection into the method according to the disclosure, as it may provide a more accurate result. The envelope is indeed an estimation of the outline of the signal, but it does not incorporate the fact that a signal may have a positive and negative sign. This may be provided by using an additional bit, which tells when the signal is positive or negative. This does increase the number of bits to be sent per sample by one bit but may provide for a more accurate representation of the signal, which may be desired. This therefore provides a tradeoff between a more accurate result with a slightly increased datastream, a less accurate result with a reduced datastream.

[0024] In an example of the disclosure, the ADC is a Level-Crossing, LC, ADC.

[0025] Herein a LC ADC may be incorporated as a non-synchronous ADC. A level-crossing ADC is a type of non-synchronous ADC that samples the input signal when it crosses predefined thresholds, rather than at fixed time intervals, making it event-driven rather than clock-driven. This approach dynamically adjusts the sampling rate based on signal activity — more samples are taken during rapid signal changes, and fewer samples are taken when the signal is stable. The level-crossing ADC is the most common type of non-synchronous ADC due to its simplicity and efficiency in handling signals with varying dynamics.

[0026] While level-crossing ADCs are the primary example, all other types of non-synchronous ADCs are fundamentally based on similar event-driven sampling methods. These include variations that may use different criteria for triggering a sample, such as changes in the slope of the input signal, but they all share the principle of recording samples only when significant signal changes occur. This reduces unnecessary data and reduces power consumption across a wide range of non- synchronous ADC implementations, making the level-crossing ADC representative of non-synchronous ADCs in general.

[0027] In an example of the disclosure, the received analog signal is a received ultrasound analog signal.

[0028] An ultrasound image is created by sending a sound wave and listening for the reflections. The amplitude of the reflection provides information, and therefore the envelope of the signal can be used, instead of the original US one. Ultrasound imaging is an important branch of non-destructive testing and medical diagnostics.

[0029] Therefore, the inventors have found that it may be beneficial to utilize the present disclosure for ultrasound imaging, as it may benefit from the advantages presented thus far.

[0030] In an example of the disclosure, the non-linear scale is a logarithmic scale.

[0031] A typical example of a non-linear scale to be implemented is the logarithmic scale. This has some distinct advantages, such as a constant multiplicative step size. For example, 10, 100, 1000 may be depicted, which may be advantageous as it provides an ease to read and to use in calculations. Furthermore, exponential differences may also be captured by using a logarithmic scale. In short, the logarithmic scale is a typical scale to use in such a scenario.

[0032] In an example of the disclosure, the delta modulator is a 1-bit delta modulator.

[0033] A 1-bit delta modulator uses only one bit per sample, making the design and implementation simpler. This simplicity often translates to lower cost in both hardware and software.

[0034] In an example of the disclosure, the step of determining the envelope of the received analog signal comprises: rectifying and filtering, using a low pass filter, the received analog signal.

[0035] This may be beneficial, as the low-pass filter filters out the high frequency variations, resulting in merely the low frequency variations. This may be used in constructing or determining or approximating the envelope of the received analog signal. Again, this is advantageous as unwanted data is filtered out using this low-pass filter, reducing the data to be transmitted. This in turn reduces the power needed to transmit such a signal.

[0036] In an example of the disclosure, the step of determining the envelope of the received analog signal is line with:

[0037] E(t) = max(|r(t)|, |rH(t)|) + min(|r(t)|, |rH(t)|) / 2 where r(t) is the received analog signal, m(t) is the received analog signal with a 90 degree phase shift relative to a signal centre frequency and E(t) is the envelope of the received analog signal over time (t).

[0038] The inventors have found that an approximation of the envelope E could be implemented more efficiently, by not using any minimum signal in the analog domain, it therefore leaves out such a term. This would more efficiently lead to an envelope without compromising image quality.

[0039] In a second aspect of the disclosure, there is provided a device arranged for encoding an analog signal into a digital signal, the device comprising: process equipment arranged for determining an envelope of a received analog signal thereby producing an enveloped signal; transform equipment for applying a non-linear transformation to the enveloped signal thereby obtaining a non-linearly transformed enveloped signal

[0040] An Analog-to-Digital converter, ADC, arranged for converting the non-linearly transformed enveloped signal, to produce the digital signal, wherein the ADC is a delta modulator.

[0041] As mentioned in the first aspect of the disclosure, the inventors have found that it may be beneficial to provide an encoding prior to the transmission of the signal, therefore they also have found that it may be beneficial to provide a device, which is arranged to perform the encoding, so that the amount of data needed to be transmitted being reduced. Such a device, therefore, referring to the first aspect of the disclosure, needs to be able to perform the envelope detection, non-linear transform and ADC conversion of the signal.

[0042] In an example of the disclosure, the transform equipment is embodied in the ADC by the ADC having quantization levels spaced according to a non-linear scale.

[0043] It should be noted that the following explanation follows the explanation above and may refer to the entire disclosure but is further explained here. The nonlinear transform is at least performed prior to the transmission of the data. This nonlinear transform is further performed prior to the usage of the delta encoder. This delta encoder may namely utilize the non-linearly transformed enveloped signal. The nonlinear transform allows the delta encoder to more efficiently track the enveloped signal, both in synchronous and in non-synchronous scenarios. Therefore, it may not be important for a delta encoding side when the non-linear transformation is taking place, prior to or during the analog to digital conversion, as long as it is done prior to the delta decoding.

[0044] The spacing of the quantization levels may therefore suffice for transforming the signal into a non-linear signal. This is because the non-linear quantization levels may be used in the delta decoding step.

[0045] In an example of the disclosure, the ADC is further arranged for outputting a polarity signal representative of a polarity of the received analog signal such that the digital signal is associated with a polarity.

[0046] The polarity represents the sign of the signal at a given point. Because the absolute value of the signal is utilized to construct the envelope of the signal, it may be beneficial to provide, after the envelope detection, the polarity of the signal at a given point. This may more accurately represent the signal.

[0047] In an example of the disclosure, the ADC is a Level-Crossing, LC, ADC. Level-crossing implemented in an ADC is a term used to indicate that an ADC sets a “measurement” each time a level is crossed. To do this, a grid may be used which every time that a certain value is exceeded or that the signal value decreases that certain value a discrete measurement is taken. This is done to track the signal discretely. The opposite of level-crossing, which may alternatively be used, is using time dependent measurements.

[0048] Coupling level-crossing with a non-linear scale allows for the tracking of small changes in the regime where small changes are of importance and it allows for the tracking of large changes in the regime where those dominate the signal. This increases the accuracy of the obtained discrete signal and / or decreases the number of measurements to be taken.

[0049] In an example of the disclosure, the received analog signal is a received ultrasound analog signal.

[0050] From the measurement tools an analog signal is obtained, this is to be converted into a digital signal for use later. An ultrasound signal may arise from a measurement of a heart. This is a medical operation that may be performed.

[0051] In an example of the disclosure, the non-linear scale is a logarithmic scale.

[0052] As mentioned before, any non-linear scale may be used, though the logarithmic scale may be easiest to use and conceptually to understand.

[0053] In an example of the disclosure, the delta modulator is a 1-bit delta modulator.

[0054] Using a 1-bit delta modulator allows for a sharp decrease in the number of bits that are used in the data transmission. This is advantageous as less power may be consumed.

[0055] In an example of the disclosure, the process equipment comprises a low pass filter arranged for filtering the rectified received analog signal.

[0056] In the appended figures, similar components and / or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

[0057] The above and other aspects of the disclosure will be apparent from and elucidated with reference to the examples described hereinafter.

[0058] Brief description of the figures

[0059] Fig. 1 depicts a flowchart of the method of the present disclosure;

[0060] Fig. 2 depicts a signal with its envelope;

[0061] Fig. 3 depicts an enveloped signal with logarithmic quantization levels.

[0062] Detailed description

[0063] It is noted that in the description of the figures, same reference numerals refer to the same of similar components performing a same of essentially similar function.

[0064] A more detailed description is made with reference to particular examples, some of which are illustrated in the appended drawings, such that the features of the present disclosure may be understood in more detail. It is noted that the drawings only illustrate typical examples and are therefore not to be considered to limit the scope of the subject matter of the claims. The drawings are incorporated for facilitating an understanding of the disclosure and are thus not necessarily drawn to scale. Advantages of the subject matter as claimed will become apparent to those skilled in the art upon reading the description in conjunction with the accompanying drawings.

[0065] The ensuing description above provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the disclosure, it being understood that various changes may be made in the function and arrangement of elements, including combinations of features from different embodiments, without departing from the scope of the disclosure.

[0066] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof. Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or" in reference to a list of two or more items, covers all the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0067] These and other changes can be made to the technology considering the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein.

[0068] In figure 1 , a flowchart 100 of the method according to the disclosure is depicted. Herein the analog (ultrasound) signal 101 is first provided. This analog signal 101 is first processed by an analog envelope detection 102. Herein the envelope of the analog signal 101 is acquired. Then this enveloped signal 1011 is processed by a log-compression 103. This may alternatively be a different non-linear transformation. This may be performed prior to or during an analog-to-digital conversion, or as part of the analog-to-digital conversion, of the signal. The analog signal could for example be multiplied by a power amplifier, the digital signal could be processed using a non-linear scale. After the digital log- compressed enveloped signal 1012 is provided, the delta encoding 104 is performed. After this, the digital data 105 may be transmitted. An optional step of sign detection, i.e. providing the polarity of the signal accompanying every bit, may be performed.

[0069] The order at which the steps are to be performed may be shuffled. It is not required to have the determination of the envelope before the non-linear transformation, this may also occur in a different order.

[0070] In figure 2, a depiction 200 of the envelope 201 of the signal 202 is provided. The envelope of the signal may be thought of as an outline of the signal. It also considers the negative values of the signal. Therefore, also mentioned in the previous figure, it may be more accurate to provide a description of the polarity of the signal in time. In this figure, the y axis presents the amplitude 203 of the signal, wherein the magnitude is unitless. The x axis provides the time 204 in microseconds. The ultrasound signal may have a frequency in the megahertz range.

[0071] In figure 3, the enveloped signal 201 is depicted. Herein again the y axis presents the amplitude 203 of the (enveloped) signal and the x axis presents the time 204 in microseconds. The enveloped signal is further compressed using log compression. This can be observed by the periodic in and decrease of the signal 301. This is provided using a 1-bit delta encoder. A bit 0 describes that the signal decreases to a lower boundary of the level, wherein these boundaries 302 of the level are also depicted. A bit 1 describes that the signal increases to a higher boundary. If a signal stays within a level, the bits give an oscillatory behaviour, as can be observed by the periodic up and down trajectory within a same level. This therefore is described by the signal 1010101010 etc. If two bit 1s are provided consecutively, the signal is crossing a level. Because this is a logarithmic scale, it allows for the tracking of small changes in the lower levels, and the tracking of large changes in the higher levels.

[0072] As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms.

[0073] Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

Claims

CLAIMS1. A method of encoding an analog signal into a digital signal, the method comprising the steps of: determining an envelope of a received analog signal thereby producing an enveloped signal; applying a non-linear transformation to the enveloped signal thereby obtaining a non-linearly transformed enveloped signal;Analog-to-Digital converting, by an Analog-to-Digital converter, ADC, the non-linearly transformed enveloped signal, to produce the digital signal, wherein the ADC is a delta modulator.

2. A method in accordance with claim 1 , wherein quantization levels of the ADC are spaced according to a non-linear scale for implementing the step of applying the non-linear transformation.

3. A method in accordance with any of the previous claims, wherein the method comprises the steps of: outputting, by the ADC, a polarity signal representative of a polarity of the received analog signal such that the digital signal is associated with a polarity.A method in accordance with any of the previous claims, wherein theADC is a Level-Crossing, LC, ADC.

5. A method in accordance with any of the previous claims, wherein the received analog signal is a received ultrasound analog signal.

6. A method in accordance with any of the previous claims, wherein the non-linear scale is a logarithmic scale.

7. A method in accordance with any of the previous claims, wherein the delta modulator is a 1 -bit delta modulator.

8. A method in accordance with any of the previous claims, wherein the step of determining the envelope of the received analog signal comprises: filtering, using a low pass filter, the received analog signal.

9. A method in accordance with any of the previous claims, wherein the step of determining the envelope of the received analog signal is line with:E(t) = max(|r(t)|, |rH(t)|) where r(t) is the received analog signal, m(t) is the received analog signal with a 90 degree phase shift relative to a signal centre frequency and E(t) is the envelope of the received analog signal over time (t).

10. A device arranged for encoding an analog signal into a digital signal, the device comprising: process equipment arranged for determining an envelope of a received analog signal thereby producing an enveloped signal; transform equipment for applying a non-linear transformation to the enveloped signal thereby obtaining a non-linearly transformed enveloped signal An Analog-to-Digital converter, ADC, arranged for converting the non-linearly transformed enveloped signal, to produce the digital signal, wherein the ADC is a delta modulator.

11. A device in accordance with claim 10, wherein the transform equipment is embodied in the ADC by the ADC having quantization levels spaced according to a non-linear scale.

12. A device in accordance with any of the previous claims 10 -11 , wherein the ADC is further arranged for outputting a polarity signal representative of a polarity of the received analog signal such that the digital signal is associated with a polarity.

13. A device in accordance with any of the claims 10 - 12, wherein the ADC is a Level-Crossing, LC, ADC.

14. A device in accordance with any of the claims 10 - 13, wherein the received analog signal is a received ultrasound analog signal.

15. A device in accordance with any of the claims 10 - 14, wherein the non- linear scale is a logarithmic scale.

16. A device in accordance with any of the claims 10 - 15, wherein the delta modulator is a 1 -bit delta modulator.

17. A device in accordance with any of the claims 10 - 16, wherein the process equipment comprises a low pass filter arranged for filtering the received analog signal.

Images