US-12618694-B2 - Proximity sensor and antenna

US12618694B2US 12618694 B2US12618694 B2US 12618694B2US-12618694-B2

Abstract

A capacitive proximity sensor with a stacked electrode structure where an inner electrode is partially screened by an upper one. The self-capacitances of selected electrodes is measured while other electrodes are held to ground or to a shield potential. In this manner, the proximity sensor estimates a value of the dielectric permittivity of the approaching body.

Inventors

Sébastien Grisot

Assignees

SEMTECH CORPORATION

Dates

Publication Date: 20260505
Application Date: 20230607
Priority Date: 20220617

Claims (9)

1 . A capacitive proximity sensor for detecting the presence of a conductive or dielectric body in a detection region adjacent to a portable device, the sensor comprising a stacked structure having on a first layer a first electrode facing the detection region and, on a second layer an internal electrode, wherein the first electrode has a plurality of openings that allow a partial capacitive coupling between the internal electrode and conductive and/or dielectric bodies in the detection region, such that the first electrode screens partially the internal electrode, the capacitive proximity sensor comprising one or more than one capacitance reading units configured to determine a capacitance of one electrode and a shield control unit configured to generate a shield potential following that of an electrode whose capacitance is measured by a capacitance reading unit, the capacitive proximity sensor comprising a readout circuit configured to determine a first capacitance of either the first electrode or the internal electrode by applying the shield potential to the other electrode and a second capacitance of either the first electrode or the internal electrode while keeping the other electrode at a fixed potential, and to determine a permittivity of a body in the detection region based on said first capacitance and second capacitance, the capacitive proximity sensor comprising a data transmission interface for the communication with a host system, the data transmission interface being configured to transmit a permittivity value encoding the permittivity of the body in the detection region as a binary variable.
2 . The capacitive proximity sensor of claim 1 , wherein the readout circuit is configured to determine a distance between the capacitive proximity sensor and the body in the detection region based on said first capacitance and second capacitance.
3 . The capacitive proximity sensor of claim 1 , wherein the openings are arranged in a regular lattice of holes or stripes.
4 . The capacitive proximity sensor of claim 1 , wherein the fixed potential is the ground potential.
5 . The capacitive proximity sensor of claim 1 , the data transmission interface being configured to transmit one or more than one of: a logic proximity signal indicating that a body is in the detection region, a proximity value encoding a distance between the capacitive proximity sensor and the body in the detection region as a binary variable, the distance being determined from first capacitance and second capacitance.
6 . The capacitive proximity sensor of the claim 1 , wherein the data transmission interface is a serial bus, for example a I2C bus.
7 . The capacitive proximity sensor of claim 1 , comprising an interrupt request output that is asserted when a body is detected in the detection region.
8 . The capacitive proximity sensor of claim 1 , wherein the first electrode and the internal electrode are etched in the conductive layer of a multilayer printed circuit board.
9 . The capacitive proximity sensor of claim 8 , wherein the first electrode and/or the inner electrode are capacitively coupled to a radio circuit and provide an antenna for the radio circuit.

Description

REFERENCE DATA The present application claims priority from China patent application 202210686233-6 of Jun. 17, 2022, the content whereof are hereby incorporated in their entirety. TECHNICAL DOMAIN The present disclosure concerns a proximity sensor for detecting closeness to a body part of a user, rejecting the unwanted influence of water drops or other similar contaminations. Embodiments of this invention concern connected portable devices like cell phones tablets or laptops that, being equipped with the proximity sensor of the invention, can detect reliably when a user is close. A special but not exclusive embodiment is a portable connected device whose power of radio emission is adapted in consideration of the user's proximity, to limit the exposition to RF energy. Another special application of the present invention is in wearable devices, such as smart watches, sport watches, earplugs and so on, where the proximity sensor is advantageously used as input device. RELATED ART In many applications it is important to detect whether a body portion is at short distance of an apparatus. In the special case of connected portable devices such as cell phones tablets and laptops, this information is instrumental in several important functions like, limiting the absorbed dose of RF energy, or limiting the power consumption by shutting down the display when the phone is brought to the ear, or activating special functions. Another important function of proximity sensors is, in a portable phone, disabling the tactile screen when the user brings the phone to the ear. Without this, the user could inadvertently cut a call or trigger unwanted actions by touching the screen with his/her cheek or fingers. There is an ever-increasing need for miniaturizing proximity sensors in wearable devices such as smart watches, sport watches and wireless earphones and so on. Space in wearables is very limited and conventional switch buttons are undesirable. Proximity sensors are used as described above as well as input devices, for example for increasing or decreasing the reproduction volume, rejecting or accepting a call, start a Bluetooth® pairing or any other useful function. The device of the invention can be used as genuine proximity sensor in wearables too, for example to detect whether an earplug is inserted in the ear of a user or not. Avoiding false detections is as important as the ability to sense proximity. Many proximity sensors used in portable phone exploit the changes in the capacity of an electrode in response to the approach of a body part. This technique is appealing because the sensor is a simple conductive electrode, easy to integrate on a printed circuit board. It can give rise to false detections, however, because conventional capacitive systems are incapable of discriminating between a large object at a certain distance, and a small one at closer distance. They are also unable to distinguish between the approach of a part of a human body such as a hand or the head of a user and an inanimate object, like a tabletop. Other proximity detection techniques are available, for example based on optical detection. Drawbacks of these systems are however the power consumption, the cost of the needed components and of their integration in the mobile device and the inability to discriminate between different objects. European patent EP2876407 B1, in the name of the applicant describes capacitive sensors that are read by means of charge amplifiers connected to a floating variable voltage reference. The same document describes the use of such sensors in touch-sensitive displays. Capacitive proximity sensors determine the presence of both conductive and dielectric bodies in the detection region. The effect of a dielectric body on the measured capacitances will change according to his size, distance from the sensor and to the polarizability of the material, the latter being measured by the material's relative dielectric permittivity εr (also simply called the permittivity or dielectric constant of the material). For the purposes of this disclosure, conductive bodies can be regarded as dielectric bodies with a very high permittivity. In the art, proximity sensor decide that a body is approaching when the measured capacitance exceeds some given threshold. This however can happen at different distances according to size and permittivity of the approaching body, and conventional sensors cannot discriminate between these factors. SHORT DISCLOSURE The present disclosure proposes a proximity detector with the ability to discriminate between objects of different permittivity. In this way, approaching bodies of different nature can trigger different actions, and the proximity threshold can be corrected to be less dependent from the permittivity. According to the invention, these aims are attained by the object of the attached claims, and especially by a capacitive proximity sensor for detecting the presence of a conductive or dielectric b