PATENT DOCUMENT

Publication Number: US-8593777-B1
Application Number: US-201213470196-A
Country: US
Kind Code: B1

Title: User-actuated button ESD protection circuit with spark gap

Abstract:
A consumer electronic device including an electronic circuit designed to protect a user-actuated physical button from becoming degraded due to electrostatic discharges (ESD) strikes is described herein. The device includes a housing and the user-actuated physical button is exposed through the external surface of the housing. The device further includes a mechanical switch that is coupled to the physical button and a first resistor that is electrically coupled with a pair of terminals of the switch. The first resistor may be coupled either in series or in parallel with the terminals of the switch. To protect the first resistor from ESD strikes, a first spark gap is coupled in parallel with the first resistor. The device may also include a buffer circuit that is coupled to the switch. Other embodiments are also described.

Claims:
The invention claimed is: 
     
       1. A consumer electronic device comprising:
 a housing; 
 a user-actuated physical button exposed through an external surface of the housing; 
 a mechanical switch coupled to the physical button, the switch having a pair of terminals; 
 a first resistor being electrically coupled either in series or in parallel with the terminals of the switch; 
 a first spark gap coupled in parallel with the first resistor; and 
 a buffer circuit that is coupled to the switch, wherein the buffer circuit processes a signal that varies based on the switch being closed or open, and wherein the switch is closed when the user-actuated physical button is actuated and is open when the user-actuated physical button is not actuated. 
 
     
     
       2. The device of  claim 1 , further comprising:
 a DC power supply, wherein the first resistor is coupled to the power supply either in series between the power supply and the switch, or in parallel with the switch. 
 
     
     
       3. The device of  claim 1 , wherein
 the first resistor comprises a discrete surface mount resistor package soldered to a pair of pads in a top metal layer of a printed circuit board, and 
 the first spark gap includes a pair of conductive footprints patterned in the top metal layer and directly connected to the pair of pads in the top metal layer, respectively. 
 
     
     
       4. The device of  claim 1 , wherein the first spark gap passes signals having a high frequency and high voltage, and does not pass signals having a low frequency and low voltage. 
     
     
       5. The device of  claim 4 , wherein the signals having the high frequency and high voltage include an electrostatic discharge (ESD) strike and the signals having the low frequency and low voltage include signals from the switch. 
     
     
       6. The device of  claim 1 , wherein the first spark gap is directly connected to the first resistor. 
     
     
       7. The device of  claim 2 , wherein the first resistor is directly connected to at least one of the terminals of the switch. 
     
     
       8. The device of  claim 1 , wherein the buffer circuit further transmits the processed signal to a processor or a system on a chip (SOC) that detects whether the user-actuated physical button is actuated based on the processed signal. 
     
     
       9. A consumer electronic device comprising:
 a housing; 
 a user-actuated physical button exposed through an external surface of the housing; 
 a mechanical switch coupled to the physical button, the switch having a pair of terminals; 
 a first resistor being electrically coupled either in series or in parallel with the terminals of the switch; 
 a first spark gap coupled in parallel with the first resistor; 
 a DC power supply, wherein the first resistor is coupled to the power supply either in series between the power supply and the switch, or in parallel with the switch; 
 a second resistor being electrically coupled in series between the terminals of the switch and ground, wherein the first resistor is coupled in series between the power supply and the switch; and 
 a second spark gap coupled in parallel with the second resistor. 
 
     
     
       10. A electronic circuit comprising
 a mechanical switch coupled to a physical button, the switch having a pair of terminals; 
 a first resistor being electrically coupled either in series or in parallel with the terminals of the switch; 
 a first spark gap coupled in parallel with the first resistor; and 
 a buffer circuit that is coupled to the switch, wherein the buffer circuit processes a signal that varies based on the switch being closed or open. 
 
     
     
       11. The electronic circuit of  claim 10 , further comprising:
 a DC power supply, wherein the first resistor is coupled to the power supply either in series between the power supply and the switch, or in parallel with the switch. 
 
     
     
       12. The electronic circuit of  claim 10 , wherein
 the first resistor comprises a discrete surface mount resistor package soldered to a pair of pads in a top metal layer of a printed circuit board, and 
 the first spark gap includes a pair of conductive footprints patterned in the top metal layer and directly connected to the pair of pads in the top metal layer, respectively. 
 
     
     
       13. The electronic circuit of  claim 10 , wherein the first spark gap passes signals having a high frequency and high voltage, and does not pass signals having a low frequency and low voltage. 
     
     
       14. The electronic circuit of  claim 13 , wherein the signals having the high frequency and high voltage include an electrostatic discharge (ESD) strike and the signals having the low frequency and low voltage include signals from the switch. 
     
     
       15. The electronic circuit of  claim 10 , wherein the first spark gap is directly connected to the first resistor. 
     
     
       16. The electronic circuit of  claim 11 , wherein the first resistor is directly connected to at least one of the terminals of the switch. 
     
     
       17. The electronic circuit of  claim 10 , wherein the buffer circuit further transmits the processed signal to a processor or a system on a chip (SOC) that detects whether the switch is open or closed based on the processed signal. 
     
     
       18. An electronic circuit comprising:
 a mechanical switch coupled to a physical button, the switch having a pair of terminals; 
 a first resistor being electrically coupled either in series or in parallel with the terminals of the switch; 
 a first spark gap coupled in parallel with the first resistor; 
 a DC power supply, wherein the first resistor is coupled to the power supply either in series between the power supply and the switch, or in parallel with the switch; 
 a second resistor being electrically coupled in series between the terminals of the switch and ground, wherein the first resistor is coupled in series between the power supply and the switch; and 
 a second spark gap coupled in parallel with the second resistor.

Description:
FIELD 
     An embodiment of the invention relate generally to a consumer electronic device having an electronic circuit with a spark gap to protect the device&#39;s user-actuated physical button from degradation caused by electrostatic discharges (ESD). 
     BACKGROUND 
     One form of electrostatic discharge (ESD) is the ESD spark. The ESD spark occurs when a heavy electric field creates an ionized conductive channel in the air. For example, such ESD sparks may be created when handling electronic equipment. While the ESD sparks only causes mild discomfort to a person receiving the discharge, the ESD sparks may cause damage to integrated circuits within the electronic equipment. When subjected to repeated ESD strikes, circuit elements may significantly degrade over time and eventually suffer permanent damage. For instance, the resistance of a resistor element greatly increases with every ESD strike. Accordingly, the electronic circuits may not function as intended when the properties of the elements included in the circuit vary over time. Thus, ESD strikes are a threat to the reliability and performance of electronic devices. 
     SUMMARY 
     In one embodiment of the invention, a consumer electronic device includes an electronic circuit designed to protect a user-actuated physical button from becoming degraded due to an electrostatic discharge (ESD). The consumer electronics device may include a housing that has a user-actuated physical button exposed through an external surface of the housing. The device further includes a mechanical switch that is coupled to the physical button, a first resistor that is electrically coupled with a pair of terminals of the switch, and a buffer circuit that is coupled to the switch. The first resistor may be coupled either in series or in parallel with the terminals of the switch. To protect the first resistor from ESD strikes, a first spark gap that allows the signals having a high frequency and high voltage (e.g., ESD strikes) to pass and does not allow signals having a low frequency and low voltage (e.g., signals from the mechanical switch) to pass may be coupled in parallel to the first resistor. In this configuration, the first spark gap may protect the first resistor from degrading by preventing the ESD strikes from passing through the first resistor. In some embodiments, the first spark gap may be directly connected to the first resistor and the first resistor may be directly connected to at least one of the terminals of the switch. In some embodiments, the buffer circuit processes a signal that varies based on the switch being closed or open. The switch may be closed when the user-actuated physical button is actuated and may be open when the user-actuated physical button is not actuated. The buffer circuit may also transmit the processed signal to a processor or a system on a chip (SOC) that detects whether the switch is open or closed based on the processed signal received from the buffer circuit. 
     In another embodiment of the invention, an electronic circuit is designed to protect a physical button from becoming degraded due to an electrostatic discharge (ESD). The electronic circuit comprises a mechanical switch that is coupled to a physical button and that includes a pair of terminals, a first resistor that is electrically coupled either in series or in parallel with the terminals of the switch, and a buffer circuit electrically coupled to the switch. The first resistor may include a discrete surface mount resistor package that is soldered to a pair of pads in a top metal layer of a printed circuit board. The circuit may also include a first spark gap that is coupled in parallel with the first resistor to protect the first resistor from ESD strikes. The first spark gap may include a pair of conductive footprints patterned in the top metal layer and directly connected to the pair of pads in the top metal layer, respectively. The circuit may also include a DC power supply that is coupled to the first resistor and that provides less than 2 volt output voltage. In some embodiments, the circuit may further include a second resistor that is electrically coupled in series between the switch and ground, and a second spark gap that is coupled in parallel with the second resistor to protect the second resistor from ESD strikes. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems, apparatuses and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations may have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment of the invention in this disclosure are not necessarily to the same embodiment, and they mean at least one. In the drawings: 
         FIG. 1  illustrates one example of a consumer electronic device in which an embodiment of the invention may be implemented. 
         FIG. 2  shows an electronic circuit included in a consumer electronic device according to one embodiment of the invention. 
         FIG. 3  illustrates exemplary spark gap footprint patterns included in an electronic circuit according to one embodiment of the invention. 
         FIG. 4  shows a graph that illustrates the voltage (V) of an electrostatic discharge (ESD) over time (t). 
         FIG. 5  shows a graph that illustrates the effects of repeated ESD strikes on the resistance of resistors R 1  and R 2 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown to avoid obscuring the understanding of this description. 
       FIG. 1  illustrates one instance of a portable consumer electronic device (or “mobile device”) in which an embodiment of the invention may be implemented. As shown in  FIG. 1 , the mobile device  1  may be a mobile telephone communications device or a smartphone such as an iPhone™ device, from Apple Inc. of Cupertino, Calif. The mobile device  1  may also be a tablet computer such as an iPad™ device, or a personal digital media player such an iPod™ device, which are all from Apple Inc. of Cupertino, Calif. While  FIG. 1  illustrates a mobile device  1 , it is understood that embodiments of the invention may also be implemented in a non-mobile device such as a compact desktop computer such as an iMac™, from Apple Inc. of Cupertino, Calif. The device housing  2  (also referred to as the external housing) encloses a plurality of electronic components of the device  1 . For example, the device  1  may include electronic components such as a processor, a data storage containing an operating system and application software for execution by the processor, and input-output devices such as a display screen which may be a touch screen, and physical buttons. As shown in  FIG. 1 , physical buttons of the mobile device  1  may include a user-actuated physical button  3  that is a movable button member that is exposed through an external surface of the housing  2 . A user of the mobile device  1  may supply input commands by actuating the button  3 . For example, the button  3  may be a menu button. 
     In one embodiment, the button  3  may be coupled to a mechanical switch that is used to provide electronic switching capabilities. Referring to  FIG. 2 , the mechanical switch S 1  is illustrated in an electronic circuit included in the consumer electronic device  1  according to one embodiment of the invention. For example, when the button  3  is actuated by a user (i.e., actuated position), the mechanical switch S 1  is closed and when the button  3  is not actuated by a user (i.e., unactuated position), the mechanical switch S 1  remains open. The mechanical switch S 1  may include at least two contacts that are electrically connected when the switch S 1  is closed, and are electrically disconnected when the switch S 1  is open. In some embodiments, the switch S 1  may include an inverted dome with a base and a conductive underside. The base of the inverted dome may be attached to the button  3  that includes electrical contacts facing the conductive underside of the inverted dome. The electrical contacts may include an inner contact and an outer contact. When the button  3  is in an actuated position, the inverted dome may be compressed such that the conductive underside of the inverted dome comes into contact with the electrical contacts. In an actuated position, the inner contact and the outer contact are electrically connected such that the switch S 1  is closed to form a closed path between inductors L 1  and L 2  via the switch S 1 . When the button  3  is in the unactuated position, the conductive underside of the inverted dome does not come into contact with the electrical contacts such that the inner and outer contacts are electrically disconnected from one another. In this unactuated position, the switch S 1  is open and an open circuit is formed between inductors L 1  and L 2  via the switch S 1 . 
     The electronic circuit included in the consumer electronic device  1  as shown in  FIG. 2  provides a signal to a processor or a system on a chip (SOC) that detects whether the button  3  has been actuated based on the signal. The processor may be a computer processing unit (CPU). In some embodiments, the processor or the SOC may be executing button actuation detection software. Since the user interacts with the mobile device  1  via the button  3 , the button  3  is a site where ESD strikes may likely occur. Repeated exposure to ESD strikes may cause the degradation of the internal components that affect the function of button  3 . Accordingly,  FIG. 2  illustrates one embodiment of a circuit that protects electronic components therein from ESD strikes that originate from the button  3 . 
     As shown in  FIG. 2 , the electronic circuit comprises the mechanical switch S 1  that is coupled the physical button  3 , resistors R 1 , R 2 , and R 3 , spark gaps SG 1  and SG 2 , inductors L 1  and L 2 , a diode D 1 , a buffer circuit B 1  and a power supply V. In the embodiment shown in  FIG. 2 , the terminals T 1 , T 2  of the switch S 1  are coupled to resistor R 1  and resistor R 2 , respectively. While  FIG. 2  illustrates an embodiment where the resistors R 1  and R 2  are electrically coupled in series with the terminals of the switch S 1 , it is contemplated that the resistors R 1 , R 2  may also be electrically coupled in parallel with the terminals of the switch S 1 . 
     In one embodiment, the resistors R 1  and R 2  may have resistance values that are relatively low (e.g., 6 k ohms) while the resistor R 3  may be a relatively higher resistance value (e.g., 300 k ohms). In this embodiment, the resistors R 1  and R 2  may be used primarily for antenna isolation purposes. As shown in  FIG. 2 , the resistor R 1  may be connected in series with the inductor L 1  and ground, and the resistor R 2  may be connected in series to inductor L 2 , resistor R 3 , and the power supply V. In this embodiment, the resistor R 1  is coupled in series between the switch S 1  and ground while the resistor R 2  is coupled in series between the switch S 1  and the power supply V. The power supply V may be, for example, a DC power supply that provides less than a 2 volt output voltage. In some embodiments, the power supply V may also be electrically coupled to a memory (e.g. SDRAM). 
     The buffer circuit B 1  may be a digital buffer that processes the signal from the switch S 1  and transmits the processed signal to the processor or the SOC. In some embodiments, processing by the digital buffer includes cleaning and reproducing the received signal (e.g., non-inverting buffer). In other embodiments, the buffer circuit B 1  may be a low-power dual buffer with open-drain output that is configured to provide two non-inverting buffers with open-drain output. The buffer circuit B 1  may process (or clean) the received signal to ensure that the processed signal output can clearly be detected by the processor or the SOC as being logic “high” or “low.” In  FIG. 2 , when the button  3  is unactuated, the circuit is open at the switch S 1  and the signal being output from the buffer circuit B 1  may be logic high because the power supply V pulls the signal inputted to the buffer circuit B 1  “up.” Further, as illustrated in  FIG. 2 , the input of buffer circuit B 1  is coupled to the diode D 1  and a node between resistor R 3  and inductor L 2 . In this configuration, when the button  3  is in the unactuated position, the diode D 1  may be configured to prevent the current from travelling from the node between resistor R 3  and the inductor L 2  to ground such that the input of buffer circuit B 1  reads as logic “high.” In  FIG. 2 , when button  3  is actuated, the circuit is closed at switch S 1  and the signal being output from the buffer circuit B 1  may be logic “low” because the signal inputted to the buffer circuit B 1  is being pulled “down” to ground. 
     When the button  3  is actuated by the user and an ESD strike occurs, the ESD strike may pass through the resistors R 1  and R 2 , causing the resistors R 1  and R 2  to degrade over time. Repeated ESD strikes may cause the resistance of the resistors R 1  and R 2  to increase over time and permanently damage the resistors R 1  and R 2 . If, for example, the resistance of resistor R 2  is greatly increased, the voltage of the signal being received by the buffer circuit B 1  cannot be pulled down when the button  3  is actuated. In other words, the resistance of the path via the damaged resistor R 2  and closed switch S 1  to ground remains too high. Accordingly, the damaged resistor R 2  will cause the actuation of the button  3  not to be detected by the processor or SOC because the processed signal outputted from buffer circuit B 1  will be read as logic “high” despite the button  3  being actuated to close the path at switch S 1 . 
     In order to protect the resistors R 1  and R 2  from degrading due to ESD strikes, spark gaps SG 1  and SG 2  may be coupled in parallel to the resistors R 1  and R 2 , respectively. The spark gaps SG 1  and SG 2 , respectively, may also be directly connected in parallel to the resistors R 1  and R 2  (See  FIG. 2 ). In one embodiment, spark gaps SG 1  and SG 2  may comprise a pair of conducting electrodes or pads separated by a space. Spark gaps SG 1  and SG 2  may be configured to pass signals having a high frequency and high voltage, and not to pass signals having a low frequency and low voltage. As shown in  FIG. 4 , which illustrates the voltage of an ESD over time in a graph, the ESD strike is a signal that has a high frequency and high voltage. In contrast, the signals having low frequency and low voltage include signals from the mechanical switch S 1 . In the configuration illustrated in  FIG. 2 , the spark gaps SG 1  and SG 2  provide an additional channel for the ESD strikes such that the ESD strikes are passed through the spark gaps SG 1  and SG 2  instead of the resistors R 1  and R 2 , respectively. Thus, the addition of the spark gaps SG 1  and SG 2  protect the resistors R 1  and R 2  from the damage caused by ESD strikes. Additionally, since the spark gaps SG 1  and SG 2  may be configured to not pass signals that have a low frequency and low voltage (e.g., signals from the switch S 1 ), the resistors R 1  and R 2  are not shorted out of the circuit in  FIG. 2 . Instead, the resistors R 1  and R 2  are still able to pass signals from the switch S 1  and thus, the circuit in  FIG. 2  may be used to provide a processed signal to a processor or SOC that detects whether the button  3  has been actuated based on the processed signal. 
     As shown in  FIG. 2 , when an ESD strike occurs at button  3 , the inductors L 1  and L 2 , which are used for antenna isolation, receive the ESD strikes that pass through the spark gaps SP 1  and SP 2 , respectively. In some embodiments, the inductors L 1  and L 2  may be a larger sized surface mount (e.g., 0603 package) in relation to the surface mount size of the resistors R 1  and R 2  (e.g., 0201 package). Accordingly, the inductors L 1  and L 2 , as a larger size package, may not be damaged by the high energy of the ESD strike. Further, since the inductor L 2  is coupled in series between the switch S 1  and the resistor R 3 , the inductor L 2  may also protect the resistor R 3  from being damaged by the ESD strike originating from the switch S 1 . 
     In one embodiment, each of the resistors R 1  and R 2  may include a discrete surface mount resistor package soldered to a pair of pads in a top metal layer of a printed circuit board. The discrete surface mount resistor package may be a small sized surface mount, low voltage resistor (e.g., 0201 package). In this embodiment, each of the spark gaps SG 1  and SG 2  may include a pair of conductive footprints that is patterned in the top metal layer of the printed circuit board and are directly connected to the pair of pads in the top metal layer, respectively. The pair of conductive footprints of the spark gaps SG 1  and SG 2  may be wired in parallel with the discrete surface mount resistor package.  FIG. 3  illustrates exemplary spark gap footprint patterns for spark gap SG 1  and SG 2  included in the electronic circuit according to one embodiment of the invention. 
       FIG. 5  shows a graph that illustrates the effects of repeated ESD strikes on the resistance of resistors R 1  and R 2 . Specifically, the resistance of resistors R 1  and R 2  in a circuit without the spark gaps SP 1  and SP 2  and the resistance of resistors R 1  and R 2  in a circuit including the spark gaps SP 1  and SP 2  (See  FIG. 2 ) are contrasted in  FIG. 5 . The resistors R 1  and R 2  in  FIG. 5  are initially 6 k ohm resistors. As clearly shown, the resistance of resistors R 1  and R 2  is greatly increased after only two ESD strikes to about 105 k ohms. In contrast, with the addition of the spark gaps SP 1  and SP 2  coupled in parallel with the resistors R 1  and R 2 , the resistance of resistors R 1  and R 2  after two ESD strikes appears to remain between 6 k ohms and 9 k ohms. 
     While the invention has been described in terms of several embodiments, those of ordinary skill in the art will recognize that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting. There are numerous other variations to different aspects of the invention described above, which in the interest of conciseness have not been provided in detail. Accordingly, other embodiments are within the scope of the claims.

Metadata:
Filing Date: 20120511
Publication Date: 20131126
Grant Date: 20131126
Priority Date: 20120511
Inventors: LI XINGQUN
Assignee: APPLE INC
CPC Classifications: [{"code": "H10D89/911", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10D89/911", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01T4/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01H9/42", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/026", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01H9/42", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01H2239/008", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01T4/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01H2239/008", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/026", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K3/3442", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01T4/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02H9/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01T4/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01H13/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01H13/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/3442", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02H9/06", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 49548420