Patent Description:
Connected portable devices require an amount of environmental awareness to fulfil their missions. The applications are too numerous to be exhausted here. There are for example known portable phones equipped with proximity detectors, temperature detectors, accelerometers, light level meters, hall sensor detectors, and many other. Environmental Information gathered from such sensors are used at many levels in portable devices. Proximity sensor may cause the phone to enter in a reduced-power mode. Hall sensor and light sensor can be used to determine whether the phone screen is exposed or covered and alter the user interface accordingly, and many others.

Known proximity sensors used in portable devices include capacitive sensors that determine whether (a part of) the user's body is close to the device. This information is important to determine whether the device is carried close to the body or is lying on a table or on a drawer. This information is used to comply with statutory SAR limits and to improve the use of the device. It is known for example to disable the touch screen during a call, if the capacitive proximity sensor in the telephone determines that the device is held close to the ear.

Capacitive proximity sensors are often proposed in the form of dedicated IC, with an analogue input connectable to a conductive pad, or to the RF antenna (via a decoupling circuit) whose capacitance is sensed, and digital output of various kind for communication with a processing unit.

Hall sensors are used, among other applications, as contactless switches to determine the presence, absence, or position of a part in which are installed magnets or ferromagnetic elements. They are used for example to determine whether the screen is covered or exposed, if an accessory is in a charging cradle, or else to tell the position of a determined accessory or part. Such sensors take also often the form of dedicated ICs, which include the Hall semiconductor device itself, an analogue front end to amplify the weak magnetic signal, discriminators and drivers providing a digital signal suitable for a microcontroller or a microprocessor.

Capacitive proximity sensors are described, among others, by patents <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and patent applications <CIT>, <CIT>, <CIT> assigned to the applicant. <CIT> discloses a laptop with a capacitive proximity sensor as well as a Hall sensor to determine a degree of aperture of the lid.

An aim of the present invention is the provision of an environmental integrated sensor circuit for a portable wireless device including both a capacitive proximity sensor configured for determining whether a user is in proximity with its body to the portable connected wireless device, by sensing variation in the capacitance of an electrode connectable with the environmental integrated sensor circuit, and a Hall-effect probe providing a signal proportional to a magnetic field strength. The environmental integrated sensor circuit also comprises an analogue/digital converter configured to produce proximity digital values representative of the capacitance of the electrode and magnetic field digital values representative of the magnetic field strength, and a digital processor configured for suppressing noise and drift components from the proximity digital values and from the magnetic field digital values.

Preferably, the inventive environmental integrated sensor circuit may comprise a magnetic field digital output, configured to switch from a logical state to an opposite logical state when the magnetic field sensed by the Hall-effect probe exceeds a predetermined threshold, and/or a digital bus output for communicating values of proximity and magnetic field to a host system, and/or an interrupt output for requesting the action of a host system when the values of proximity and/or magnetic field meet predetermined conditions.

The environmental integrated sensor circuit may be configured to wake up a host system when a predetermined combination of magnetic field and proximity status is detected.

The digital processor of the environmental integrated sensor circuit may comprise a nonlinear filter.

The digital processor of the environmental integrated sensor circuit may comprise a baseline and drift suppression unit configured to subtract a baseline component from an analogue signal presented at the input of the analogue/digital converter.

The environmental integrated sensor circuit may be configured to subtract at least a part of a baseline component from an analogue signal presented at the input of the analogue/digital converter.

A wireless portable connected device comprising the environmental integrated sensor circuit may be configured to reduce a RF power when the integrated circuit determine a proximity with the user and the sensitivity of the proximity sensor is variable dependent on the magnetic field strength.

The user interface of a wireless portable connected device including the environmental integrated sensor circuit may be programmed to change its behaviour dependent from the magnetic field strength.

<FIG> shows schematically an environmental integrated circuit <NUM> for detecting and processing proximity and magnetic field signals. Proximity signals arise from relative movements of the user in the environment of the portable device supporting the integrated circuit such as for example, the act of putting the portable device in a pocket or bringing it close to the head to make a phone call. Magnetic field signals may arise from a position change of an accessory, like a cover.

The environmental integrated circuit <NUM> illustrated in <FIG> comprises one or several capacitive proximity inputs that detects variations in the capacitance of conductors connected to the integrated circuit when, for example, a part of a user's body approaches the electrode or is taken away from it. The number of capacitive inputs is determined by the application and by the number of available pins in the integrated circuit.

Several arrangements of conductors can be used as proximity-sensing electrode in the frame of the invention, provided they are capable of coupling via electric induction with an approaching conductive or dielectric body. The circuit of the invention can have several terminals for connecting to a plurality of electrodes, that can be used to perform directional sensing, to provide screening electrodes, or to improve the overall sensitivity to approaching conductive or dielectric bodies. The proximity-sensing electrode may be a track or a conductive surface on a printed circuit board, possibly the same printed circuit board on which the integrated circuit of the invention is soldered. The capacitive electrode may have other functions besides the proximity sensing. For example, it may be a structural metallic element of the device, or a (part of a) radiofrequency antenna for example a Wi-Fi™ antenna, a Bluetooth® antenna, or an antenna for a cellular phone network.

In variants, one capacitive input of the circuit of the invention can be connected to a reference capacitance that is not influenced by conductive or dielectric bodies moving close or retreating but is still influenced by changes of temperature. This signal can be used as a sensitive thermometer for correcting a temperature drift and improve the detection of proximity.

In the figure, that must be taken as exemplificative rather than limitative, the integrated circuit <NUM> has four capacitive inputs: one used to read the capacitance of a radiofrequency antenna <NUM> (via a non-represented decoupling impedance), two more to read respectively a sense patch <NUM> and a shield patch <NUM> on a printed circuit board, and a fourth one connected to a reference capacitance107.

The capacitive inputs are connected to an analogue front-end section <NUM> of the integrated circuit <NUM>. The analog front-end comprises a capacitive readout and control circuit <NUM> that is configured to convert the self-capacitance seen at the inputs to an analog signal suitable for conversion into a digital value, for example a voltage level. Such a conversion can be obtained in several ways, as disclosed for example in the documents identified in the "related art" section. Preferably, the readout and control circuit <NUM> connects to the capacitive inputs one by one. The readout and control circuit <NUM> can be controlled such that, while it is connected to one input, the other inputs can be selectively set in a high-impedance state (floating), in a low-impedance state (grounded) or at the same potential as the input that is read in that moment (shield mode).

The integrated circuit further comprises a magnetic field transducer <NUM> that is configured to detect variations in a magnetic field in the proximity of the integrated circuit <NUM> caused for example by the movement of a magnet included in a smartphone or tablet case.

The magnetic field sensor may include any suitable transducer capable of generating an electric signal related to the local intensity of magnetic field. Hall-effect semiconductors are prevalent in the art, but other sensors are available and may be used in the frame of the invention. Specifically, the invention may use MEMS magnetometers, magnetoresistive sensors, fluxgate sensors, or pick-up coils. Some magnetic transducers, notably Hall-effect devices, can be advantageously integrated in the same die on which the integrated circuit of the invention is fabricated. The invention includes however variants in which the magnetic sensor and the environmental sensor circuit of the invention are fabricated on separate chips, in the same package or in separate interconnected packages.

The following description will refer to an embodiment with a Hall-effect semiconductor probe, which is a very popular implementation, but this should not be intended as a limitation of the invention.

The analog front-end section <NUM> comprises an offset correction unit <NUM> and an amplifier121 that are configured to bring the voltage signal generated by the Hall sensor <NUM> to a level matching the input range of the analog to digital converter <NUM>, as the output of the Hall sensor can be quite small.

The analogue proximity signals detected by the capacitive proximity sensor and by the Hall-effect probe are converted in a digital capacitive proximity signal and a digital magnetic signal by a shared analogue/digital converter (A/D converter) <NUM>. The measurements made by the capacitive proximity circuit <NUM> and the Hall-effect probe <NUM> are time-multiplexed.

In a particular embodiment illustrated in <FIG>, an A/D converter <NUM> is configured for having a recurrent scanning period <NUM> comprising.

This configuration of the A/D converter prevents interferences between the analogue capacitive signal and the analogue magnetic signal.

The inventive circuit also comprises a digital processor for processing the digital proximity and magnetic signals produced by the analogue/digital converter. The digital processor is configured for suppressing unwanted noise and/or drift components from the proximity digital values and from the magnetic field digital values. In the embodiment illustrated in <FIG>, the digital processor <NUM> follows the A/D converter <NUM>.

In a particular embodiment illustrated in <FIG>, the digital processor <NUM> includes a drift filter <NUM> and a noise filter <NUM>. The drift filter is used to discriminate a legitimate variation of the measured capacitance, such as the approach of a user, from drifts that may arise for example from a variation of temperature around the capacitive proximity sensor. The noise filter is used to suppress the unwanted white noise arising from the natural electric and magnetic activity around the sensors.

The drift filter <NUM> may comprise a baseline and drift suppression unit <NUM>. The baseline is a spurious value that is constant or slowly drifting. This baseline may be due the background capacitance of the electrode and as the change in the capacitance due to the approach of a user body part may be several times small than this background capacitance, it may be crucial to filter the baseline to identify proximity signals. The baseline and drift suppression unit can be configured for subtracting a baseline component from an analogue signal presented at the input of the A/D converter. The amount of baseline subtraction is individually adjustable for the capacitive channels and the magnetic readout channel. The desired level of subtraction may be adjusted digitally by writing into registers of the inventive device, for example via a digital device interconnection bus, such as I2C, I3C, or SPI, adjusted autonomously by the circuit of the invention, or adapted in any suitable way. Advantageously, the drift suppression unit is configured to suppress or limit the drifts arising for example from a thermal variation.

As illustrated in <FIG>, the digital processor <NUM> may comprise.

The environmental integrated circuit may comprise a two-value digital output configured to switch from a logical state to an opposite logical state when the magnetic field sensed by the Hall-effect probe exceeds a predetermined threshold. In the aforementioned example of the smartphone case, the threshold may be determined so that a magnetic field exceeding the threshold corresponds to a closed case as a magnet included in the case is brought near the Hall-effect probe, and a magnetic field below the threshold corresponds to an open smartphone case as the magnet is far from the Hall-effect probe. In the embodiment of the integrated circuit illustrated in <FIG>, the two-value digital output <NUM> is in electric connection with the digital processor <NUM>.

The environmental integrated circuit may also comprise a digital bus output for communicating values of proximity and magnetic field to a host system. The digital bus output may be an inter-integrated circuit (I2C) or any suitable type of digital bus output. In the embodiment illustrated in <FIG>, a digital bus output <NUM> is in electric connection with the digital processor <NUM>.

The environmental integrated circuit may also comprise an interrupt output for requesting the action of a host system when the values of proximity and/or magnetic field meet predetermined conditions.

In an embodiment illustrated in <FIG>, the environmental integrated circuit <NUM> comprises a I2C digital bus output <NUM> connected to a host system <NUM> and a shared interrupt output <NUM>. If a variation in the proximity and/or magnetic field value is detected, then the interrupt output <NUM> goes low and the host system <NUM> is communicated the proximity and magnetic field value to identify which value has changed. In this embodiment, the electrode <NUM> connected to the proximity sensor <NUM> is included in the integrated circuit.

In another embodiment illustrated in <FIG> the environmental integrated circuit <NUM> comprise a I2C digital bus output <NUM> connected to a host system <NUM>, an interrupt output <NUM> and a binary digital output two-value digital output <NUM>. While the interrupt output <NUM> is dedicated to send a signal to the host system <NUM> if a variation in the proximity signal is sensed, the binary digital output <NUM> switches from a logical state to the opposite, i.e. from <NUM> to <NUM> or from <NUM> to <NUM>, if a variation of the magnetic field exceeds a given threshold. In this embodiment, the electrode <NUM> is external to the circuit and connected to the capacitive proximity sensor <NUM>.

The environmental integrated circuit may be configured to wake up a host system when a predetermined combination of magnetic field and proximity status is detected. This functionality can be used for example to lock the screen of a smartphone when a user is approaching his head from the smartphone to give a call, or to activate the screen when a smartphone case is opened. However, these are not the only examples of applications.

In a particular embodiment, a wireless portable connected device is configured for reducing a RF power when the integrated circuit determines a proximity with the user. This allows for example to comply with daily body dose limits. The sensitivity of the proximity sensor can be configured to depend upon the magnetic field strength.

If the environmental integrated circuit is included in a wireless portable connected device comprising a user interface, such as for example a smartphone screen, the user interface may be programmed to modify its behaviour according to the strength of the magnetic field. This is typically the case when a smartphone or a tablet is protected by a foldable case covering the screen. Magnets included in the part of the case covering the screen induce a variation of the magnetic field as the cover is approached or brought away from the Hall-effect probe in the integrated circuit. According to the situation, the user interface may be programmed to allow an interaction with a user or alternatively to prevent any such interaction.

The embodiments of the invention disclosed so far use a magnetic field transducer that is responsive to a single component of the environmental magnetic field, in other words, a projection of the magnetic field vector B on a given direction. This is not an essential feature, however, and the invention is not limited to those realizations. Indeed, the magnetic field transducer could be a multi-axis sensor capable of determining two or three independent components of the magnetic vector, whereby the magnetic field can be reconstructed in a <NUM>-dimensional plane or in a <NUM>-dimensional space. In such cases, the environmental sensor circuit is configured to provide two or three magnetic field digital values, each representative of an independent component of the magnetic field strength.

The multi-axis magnetic field measurement can be used advantageously to determine an angle between two mutually pivotable elements, one equipped with the inventive sensor and the other carrying a permanent magnet. <FIG> shows an example: a portable device has two elements <NUM> and <NUM> connected by a hinge <NUM>, such that they can be open (folding angle ϑ=<NUM>°) or closed together (ϑ=<NUM>°). This arrangement is found in folding smartphones, for example. The first folding element <NUM> has a multi-axis Hall sensor <NUM>, or another equivalent sensor for measuring the magnetic field, that is capable of measuring a horizontal component By of the local magnetic field, a vertical component Bz of the local magnetic field and, preferably, the second horizontal component Bx that s orthogonal to By and Bz and is not visible in the drawing because it is orthogonal to the drawing plane. The other folding element has a permanent dipole magnet <NUM>.

When the folding elements are open or closed, such that the angle ϑ changes, this reflects in a change of the intensity and the direction of the magnetic field B seen by the sensor <NUM>. The plot of <FIG> shows how the components By and Bz depend on the fold angle ϑ. The informed reader will appreciate that the shape of the curves is a result of a choice of the positions of the sensor <NUM> and of the magnet <NUM> and of the orientation of the latter in the element <NUM>, and that other shapes could be obtained by changing these geometry parameters, without leaving the invention. Importantly, these geometry parameters can be chosen such that each possible value of the fold angle ϑ corresponds to a unique combination of By and Bz, such that the circuit of the invention can be configured to compute the folding angle ϑ, or an approximate representation thereof, from By and Bz. This can be obtained in many ways, for example by trigonometric calculation or through a double entry look-up table.

In many situations, a precise knowledge of the folding angle ϑ is not necessary and it is sufficient to know when the angle ϑ is within a stated interval. In such cases, the circuit of the invention can be configured to compare the values of By and Bz with two threshold values Yth and Zth and raising a detection flag when both comparisons succeed. <FIG> shows in a plot the values of By and Bz in relation with the threshold values Yth and Zth. The values Yth and Zth are chosen such that By>Yth and Bz>Zth when the representative point is in the region <NUM>, that is to say, ϑ is approximatively between <NUM>° and <NUM>°. This method allows to determine when the folding angle is in the determined interval with a minimum of computations. Different angle intervals can be chosen by changing the threshold values, the sign of the comparison, or else rotating or changing the position of the magnet <NUM>.

In variants of the above embodiment, the circuit of the invention may compare a combination of two components, for example Bz+BY or Bz-BY with fixed thresholds. This is equivalent to cutting the plot of <FIG> along lines at <NUM>° to the axis.

Claim 1:
An environmental integrated sensor circuit (<NUM>) for a portable connected wireless device, the circuit comprising (a) a capacitive proximity sensor (<NUM>) configured to determine whether a user is in proximity with its body to the portable connected wireless device, by sensing variation in the capacitance of an electrode (<NUM>) connectable to the environmental integrated sensor circuit, (b) a magnetic field probe (<NUM>), providing a signal proportional to a magnetic field strength,
the environmental integrated sensor circuit further comprising an analogue/digital converter (<NUM>) configured to produce proximity digital values representative of the capacitance of the electrode (<NUM>) and magnetic field digital values representative of the magnetic field strength, and further comprising a digital processor (<NUM>) configured for suppressing noise and drift components from the proximity digital values and from the magnetic field digital values.