Patent Document

FIELD OF THE INVENTION 
     The present invention relates generally to protecting electronic devices in electronic systems from electrostatic discharge (ESD) and electromagnetic interference (EMI). 
     BACKGROUND OF THE INVENTION 
     This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Many modern electronic devices, including television sets, have inputs that are sensitive to ESD and/or EMI. Known protection circuits that have been effective for ESD protection in analog systems are less effective for digital applications. This is in part because of the larger bandwidth required by digital television signals compared to analog signals. Additionally, known protection circuits do not effectively prevent the entry of EMI generated by an external device. Another disadvantage of known ESD protection circuits is that they require significant duplication of components to protect multiple devices connected to a given input. A system and method for protecting electronic devices from effects attributable to ESD and/or EMI in digital signal processing applications is desirable. 
     SUMMARY OF THE INVENTION 
     Certain aspects commensurate in scope with the disclosed embodiments are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below. 
     An exemplary embodiment of the present invention relates to an electrostatic discharge/electromagnetic interference (ESD/EMI) protection circuit for an integrated circuit. The ESD/EMI protection circuit comprises an input that is adapted to receive a communication signal, a Zener diode pair connected between the input and a ground that is shared with the input, a resistor coupled to the input, and a capacitor coupled in series with the resistor between the input and the integrated circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the invention may become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a schematic diagram of a known ESD protection circuit useful in illustrating an example of a problem addressed by an exemplary embodiment of the present invention; 
         FIG. 2  is a block diagram of an electronic device in accordance with an exemplary embodiment of the present invention; and 
         FIG. 3  is a schematic diagram of an ESD/EMI protection circuit in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
       FIG. 1  is a schematic diagram of a known ESD protection circuit useful in illustrating an example of a problem addressed by an exemplary embodiment of the present invention. The ESD protection circuit is generally referred to by the reference number  100 . The ESD protection circuit  100  comprises a video input  102 , which may be adapted to receive an input signal such as a television signal. An input resistor  104  is connected across the video input  102  to system ground. A capacitor C Clamp    106  and a resistor R ESD    108  are connected in series between the video input  102  and a target integrated circuit (IC) device  112 . The target IC  112 , which may comprise a video switch, is the device being protected from ESD by the ESD protection circuit  100 . A Zener diode D ESD    110  is connected to system ground from a junction between the resistor R ESD    108  and the target IC  112 . 
     The value of the capacitor C Clamp    106  depends on the voltage level needed to protect the target IC  112  from damage. The value of the resistor R ESD    108  is chosen to limit current generated by ESD. The Zener diode D ESD    110  dissipates and limits the actual ESD event, and the Zener breakdown voltage is usually chosen to be higher than the pin voltage of the target IC  112 , but close to a supply voltage of the target IC  112 . 
     Although the ESD protection circuit  100  works relatively well for protecting inputs that receive analog video signals, it is not as effective for protecting inputs that are adapted to receive digital video signals such as high definition television signals. One problem is that the low pass roll-off of the ESD protection circuit  100  typically limits the bandwidth of the input with respect to its ability to receive digital video signals. For example, a typical value of the resistor R ESD    108  is about 68 ohms and a typical value of the capacitor C Clamp    106  is about 100 picofarads (pf) for a bandwidth of 23 Megahertz (MHz). 
     Another problem with the ESD protection circuit  100  is that it does not effectively prevent EMI from being coupled out of the video input  102 . Digital noise from internal sources such as leaking clock circuits creates undesirable EMI that may interfere with external RF processes. 
     Yet another problem with the ESD protection circuit  100  is that it requires significant duplication of components if multiple devices such as the target IC  112  are in need of ESD protection or if multiple pins of the target IC  112  are connected to the video input  102 . For example, each device or pin needing ESD protection could require additional capacitors, resistors and Zener diodes corresponding to the capacitor C Clamp    106 , the resistor R ESD    108  and the Zener diode D ESD    110 . In addition to the added expense associated with component replication, circuit board layout could be made more difficult as well. 
       FIG. 2  is a block diagram of an electronic device in accordance with an exemplary embodiment of the present invention. The electronic device, which may comprise a television set, a projector, a set top box, a computer system or the like, is generally referred to by the reference number  200 . The electronic device  200  comprises a video input  202 , an ESD/EMI protection circuit  204 , a processor  208 , a memory  210 , and a display  212 . The memory  210  may be adapted to hold machine-readable computer code that allows the processor  208  to control the operation of the electronic device  200 . 
     The video input  202  is adapted to receive a video signal such as a high definition (or other digital) television signal. The operation of the ESD/EMI protection circuit  204  is explained in detail below with respect to  FIG. 3 . The processor  208  is adapted to received the tuned signal and create a display signal corresponding to the tuned signal. The display  212  is adapted to receive the display signal and to display an image corresponding thereto. 
       FIG. 3  is a schematic diagram of an ESD/EMI protection circuit in accordance with an exemplary embodiment of the present invention. The ESD/EMI protection circuit is generally referred to by the reference number  300 . The ESD/EMI protection circuit  300  comprises a video input  302 , which may be adapted to receive a wide bandwidth input signal such as a digital television signal. The specific construction of the video input  302  is not an essential feature of an exemplary embodiment of the present invention. An RCA jack or connector is one example of a suitable configuration for the video input  302 . An input resistor  304  is connected across the video input  302  to system ground. 
     The ESD/EMI protection circuit  300  comprises a back-to-back Zener diode pair D ESD    306 , referred to hereinbelow as the Zener diode pair D ESD    306 . The Zener diode pair D ESD    306 , which is connected between the video input  302  and system ground, is shown in dashed lines in  FIG. 3 . In an exemplary embodiment of the present invention, the Zener diode pair D ESD    306  comprises a first Zener diode  308  and a second Zener diode  310 . 
     A resistor R ESD    312  and a capacitor C Clamp    314  are connected in series between the video input  302  and a target IC device  316 . The target IC  316 , which may comprise a video switch, is the device being protected from ESD and/or EMI by the ESD/EMI protection circuit  300 . 
     In the exemplary embodiment of the present invention illustrated in  FIG. 3 , the resistor R ESD    312  and the Zener diode pair D ESD    306  perform the dual functions of ESD protection and EMI protection. With respect to ESD protection, the Zener diode pair D ESD    306  clamps an incoming ESD pulse to a known voltage, such as approximately six volts. In an exemplary embodiment of the present invention, the first Zener diode  308  and the second Zener diode  310  each have a value of about five volts in the reverse direction and about 0.7 volts in the forward direction. The resistor R ESD    312  limits the residual voltage to a low current that is unlikely to harm the target IC  316 . In an exemplary embodiment of the present invention, the value of the resistor R ESD    312  is about 33 ohms, which is less than half the value of the resistor R ESD    108  in a typical known ESD protection circuit such as the circuit  100  shown in  FIG. 1 . 
     Those of ordinary skill in the art will appreciate that the effect of RC roll-off is reduced in an exemplary ESD/EMI protection circuit  300  with respect to the known circuit  100  shown in  FIG. 1  because the value of the resistor R ESD    312  ( FIG. 3 ) is significantly lower than the value of the resistor R ESD    108  ( FIG. 1 ). Additionally, those of ordinary skill in the art will appreciate that the contribution of capacitance to RC roll-off is significantly reduced in the ESD/EMI protection circuit  300  relative to the known ESD protection circuit  100  shown in  FIG. 1  because there is no capacitance corresponding to the diode D ESD    110  after the series R ESD    108  ( FIG. 1 ) in the ESD/EMI protection circuit  300 . 
     With respect to EMI protection, the ESD/EMI protection circuit  300  provides RC roll-off in the opposite direction (i.e., from the perspective of the target IC  316 ). This RC roll-off is provided by the resistor R ESD    312  and capacitance of the Zener diode pair D ESD    306 , which may have a value of about 20 picofarads (pf). 
     A benefit of an exemplary embodiment of the ESD/EMI protection circuit  300  is that it allows protection of multiple pins on a target IC or even pins on multiple target ICs with only minimal additional circuitry. For example, a capacitor C Clamp    318  (shown in dashed lines in  FIG. 3 ) is the only additional circuitry needed to provide ESD and EMI protection to a second target IC  320  (also shown in dashed lines). 
     Those of ordinary skill in the art will appreciate that an exemplary embodiment of the present invention provides numerous benefits. Among those benefits is reduced part count with respect to known ESD protection circuits, which contributes to reduced system cost. In addition, protection against EMI is added and circuit board layout is simplified with respect to known ESD protection circuits. 
     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.

Technology Category: h