Abstract:
A surge protection circuit to reduce capacitance inherent of standard diode packaging and to improve voltage clamping reaction speeds under high surge conditions. The surge protection circuit has a coil having a first end and a second end and a diode cell having a top layer, a center diode junction, and a bottom layer. The top layer is directly connected to the second end of the coil and the bottom layer is directly connected to a ground. The diode cell has no wire leads.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application for patent claims priority from and the benefit of provisional application Ser. No. 61/054,410 entitled “DC PASS BROADBAND RF PROTECTOR,” filed on May 19, 2008, which is expressly incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The invention relates to surge protection. More particularly, the invention relates to a surge protection device for passing DC and RF signals. 
         [0004]    2. Related Art 
         [0005]    Surge protection devices protect electronic equipment from being damaged by large variations in the current and voltage across power and transmission lines resulting from lightning strikes, switching surges, transients, noise, incorrect connections, and other abnormal conditions or malfunctions. Large variations in the power and transmission line currents and voltages can change the operating frequency range of the electronic equipment and can severely damage and/or destroy the electronic equipment. For example, lightning is a complex electromagnetic energy source having potentials estimated from 5 million to 20 million volts and currents reaching thousands of amperes that can severely damage and/or destroy the electronic equipment. 
         [0006]    Surge protection devices typically found in the art and used in protecting electronic equipment include capacitors, diodes, gas tubes, inductors, and metal oxide varistors. A capacitor blocks the flow of direct current (DC) and permits the flow of alternating current (AC) depending on the capacitor&#39;s capacitance and the current frequency. At certain frequencies, the capacitor might attenuate the AC signal. For example, the larger the capacitance value, the greater the attenuation. Typically, the capacitor is placed in-line with the power or transmission line to block the dc signal and undesirable surge transients. 
         [0007]    Gas tubes contain hermetically sealed electrodes, which ionize gas during use. When the gas is ionized, the gas tube becomes conductive and the breakdown voltage is lowered. The breakdown voltage varies and is dependent upon the rise time of the surge. Therefore, depending on the surge, several microseconds may elapse before the gas tube becomes ionized, thus resulting in the leading portion of the surge passing to the capacitor. Gas tubes are attached at one end to the power or transmission line and at another end to the ground plane, diverting the surge current to ground. 
         [0008]    Inductors can be attached to the power or transmission line after the gas tube and before the capacitor to divert the leading portion of the surge to ground. An inductor is a device having one or more windings of a conductive material, around a core of air or a ferromagnetic material, for introducing inductance into an electric circuit. An inductor opposes changes in current, whereas a capacitor opposes changes in voltage. 
         [0009]    One drawback of conventional surge protection devices is the difficulty in impedance matching the surge protection device with the system. Another drawback of conventional surge protection devices is the elevated voltage at which they become conductive and the higher throughput energy levels. Still yet another drawback of conventional surge protection devices is poor bandwidth capabilities and poor RF performance at high power levels. 
       SUMMARY 
       [0010]    A surge protection circuit to reduce capacitance inherent of standard diode packaging and to improve voltage clamping reaction speeds under high surge conditions. The surge protection circuit has a coil having a first end and a second end and a diode cell having a top layer, a center diode junction, and a bottom layer. The top layer is directly connected to the second end of the coil and the bottom layer is directly connected to a ground. The diode cell has no wire leads. 
         [0011]    A surge protection device comprising a housing, a cavity defined by the housing, first and second connector pins positioned within the cavity, and a loop foil positioned within the cavity, the loop foil having a first end connected to the first connector pin and a second end connected to the second connector pin. The surge protection device may also include a coil positioned within the cavity, the coil having a first end connected to the first connector pin and a second end, and a diode cell connected to the housing, the diode cell having a top layer, a center diode junction, and a bottom layer, the top layer directly connected to the second end of the coil and the bottom layer directly connected to the housing. 
         [0012]    A surge protection device having a housing, a cavity defined by the housing, a diode positioned within the cavity, and first and second connector pins positioned within the cavity. The surge protection device may also include a loop foil positioned within the cavity, the loop foil having a first plate connected to the first connector pin, a second plate connected to the second connector pin, and a third curved plate connecting the first plate to the second plate, and an inductor positioned within the cavity, the inductor having a first end connected to the first connector pin and a second end connected to the diode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The features, objects, and advantages of the invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, wherein: 
           [0014]      FIG. 1  is a schematic diagram of a surge protection circuit according to an embodiment of the invention; 
           [0015]      FIGS. 2A-2D  are schematic diagrams showing different diode and capacitor configurations that can be implemented with the surge protection circuit of  FIG. 1  according to various embodiments of the invention; 
           [0016]      FIG. 3  is a top view of a surge protection device having the surge protection circuit of  FIG. 1  according to an embodiment of the invention; 
           [0017]      FIG. 4  is a side view of the surge protection device of  FIG. 3  according to an embodiment of the invention; 
           [0018]      FIG. 5  is a perspective view of a diode of the surge protection device of  FIG. 4  according to an embodiment of the invention; 
           [0019]      FIG. 6  is a top view of a diode of the surge protection device of  FIG. 4  according to an embodiment of the invention; 
           [0020]      FIG. 7  is a side view of a diode of the surge protection device of  FIG. 4  according to an embodiment of the invention; 
           [0021]      FIG. 8  is a side view of a loop foil according to an embodiment of the invention; 
           [0022]      FIG. 9  is a top view of a loop foil according to an embodiment of the invention; 
           [0023]      FIG. 10  is a front view of a loop foil according to an embodiment of the invention; 
           [0024]      FIG. 11  is a side view of a loop foil according to another embodiment of the invention; 
           [0025]      FIG. 12  is a top view of a loop foil according to another embodiment of the invention; 
           [0026]      FIG. 13  is a front view of a loop foil according to another embodiment of the invention; and 
           [0027]      FIG. 14  shows a graph of the average RF power handling capabilities of a number of different connectors according to various embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Apparatus, systems and methods that implement the embodiments of the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate some embodiments of the invention and not to limit the scope of the invention. Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements. In addition, the first digit of each reference number indicates the figure in which the element first appears. 
         [0029]      FIG. 1  is a schematic diagram of a surge protection circuit  100  according to an embodiment of the invention. The surge protection circuit  100  may include a first port  105 , a second port  110 , a loop foil  115 , a coil  120 , a diode  125 , and a ground  130 . Optionally, the surge protection circuit  100  may include a capacitor  135 . The surge protection circuit  100  provides improved RF coupling between the first port  105  and the second port  110 , improved voltage clamping using the coil  120  and the diode  125 , improved surge current performance by the diode  125 , improved RF performance and grounding at higher RF power levels (e.g., greater than 750 Watts), and greater bandwidth capabilities. The surge protection circuit  100  may operate in a bi-directional manner. 
         [0030]    The first connector or port  105  and the second connector or port  110  may include center connector pins  106  and  111  of a coaxial cable or line. The first port  105  and the second port  110  maintain the system RF impedance between the device and the connected termination (e.g., 50 ohm, 75 ohm, etc.). The first connector  105  and the second connector  110  may be selected from one of the following connectors: 7/16 connector, N-Type connector, BNC connector, TNC connector, SMA connector, and SMB connector. The first connector  105  and the second connector  110  may be press-fit connectors, flange-mount connectors, or any other type of connectors. 
         [0031]      FIG. 14  shows a graph of the average RF power handling capabilities of a number of different connectors. The combined RF plus DC power handling capabilities of the surge protection device  100  are generally limited by the type of connectors used. In one embodiment, the first connector  105  may be a N-type connector and the second connector  110  may be a SMA connector. In this example, the RF power handling capabilities may be limited to approximately 350 Watts (i.e., the power handling capabilities of the SMA connector). 
         [0032]    Referring back to  FIG. 1 , the loop foil  115  allows DC currents and RF signals to pass from the first port  105  to the second port  110  and vice versa. The loop foil  115  is a curved copper foil material formed in the shape of a “U” or backwards “U”. The loop foil  115  is a single integral piece of copper material but for illustrative purposes, the loop foil  115  will be referred to as having a first plate  115   a , a second plate  115   b , and a third curved plate  115   c . The copper material of the loop foil  115  is about 0.016 inches in thickness. In one embodiment, the first plate  115   a  is positioned about 0.2 inches apart from the second plate  115   b . The first plate  115   a  is positioned substantially parallel to the second plate  115   b . The third curved plate  115   c  connects the first plate  115   a  to the second plate  115   b.    
         [0033]    The inductance, the mutual impedance, and the positioning of the loop foil  115  within the cavity  310  is used for impedance matching to compensate for internal RF mis-match impedances of the coil  120 , the diode  125 , and the cavity  310 . The capacitance of the device can be increased by positioning the loop foil  115  closer to the walls of the cavity  310 . The inductance of the device can be increased by using a thinner material for the loop foil  115 . The mutual impedance of the device can be increased by moving the first plate  115   a  and the second plate  115   b  closer together. By increasing the inductance and the mutual impedance of the loop foil  115 , the size and number of turns required in the coil  120  can be reduced resulting in further simplification of design and cost. 
         [0034]    The coil  120  may be an inductor having one or more loops. The coil  120  has a first end  120   a  directly attached to the center connector pin  106  and a second end  120   b  directly attached to the diode  125 . The coil  120  may have a 14AWG, 16AWG, 18AWG, or larger AWG. In one embodiment, the coil  120  has an inductance of about 0.5 uH. The coil  120  isolates the diode  125  from the RF transmission path. Also, the coil  120  adds isolation between the center connector pins and the diode  125  to achieve better passive intermodulation (PIM) performance compared to that of the diode  125  without isolation. When a surge event occurs (or a high DC surge voltage), the coil  120  effectively becomes a short circuit and the diode  125  operates to pass the surge event. 
         [0035]    The diode  125  is connected to the coil  120  and the ground  130 . That is, a first end of the diode  125  is connected to the coil  120  and a second end of the diode  125  is connected to the ground  130 . The diode  125  can be oriented for a positive polarity or negative polarity DC clamping. In addition, the diodes  125  can be stacked to obtain higher voltage clamping while maintaining the equivalent current carrying capabilities. 
         [0036]    The capacitor  135  is positioned in parallel with the diode  125 . In one embodiment, the capacitor  135  has a capacitance of about 1,000 pF or higher. The capacitor  135  allows the energy to be shunted to ground  130  and prevents the diode  125  from prematurely being turned on. The size of the capacitor  135  is dependent on the frequency of operation and generally allows for broadband applications. The capacitor  135  provides better RF grounding for the surge protection circuit  100  at higher power levels. The surge path generally includes the coil  120 , the diode  125 , and the capacitor  135 . 
         [0037]      FIGS. 2A-2D  are schematic diagrams showing different diode and capacitor configurations that can be implemented with the surge protection circuit of  FIG. 1  according to various embodiments of the invention. The capacitor  135  may or may not be implemented in the surge protection circuit  100 . The diodes  125  have superior voltage clamping characteristics.  FIG. 2A  shows a uni-directional diode,  FIG. 2B  shows a bi-directional diode,  FIG. 2C  shows multiple uni-directional diodes stacked in a series configuration, and  FIG. 2D  shows a uni-directional diode. 
         [0038]    In one embodiment, the diode  125  can be a low voltage, bi-directional diode that is capable of handling 10 kA 8×20 micro-second surge currents with excellent voltage let-thru characteristics. In one embodiment, the diode  125  can be a bi-directional, high current transient voltage suppressor (TVS) diode having a breakdown voltage of between about 5.0-150.0 volts (e.g., 6, 12, 18 or 24 volts) and a high peak pulse power rating (e.g., 5,000, 20,000 or 30,000 watts). By isolating the diode  125  from the RF transmission path using the coil  120 , the negative RF affects (e.g., capacitance) of the diode  125  are mitigated. The high frequency (RF) isolation characteristics of the coil  120  increases the impedance looking into the coil  120  and the diode  125  but the low frequency (DC and surge) components have a low impedance path to the diode  125 . 
         [0039]      FIGS. 3 and 4  are top and side views of a surge protection device  300  having the surge protection circuit of  FIG. 1  according to an embodiment of the invention. Referring to  FIGS. 3 and 4 , the surge protection device  300  has a housing  305  and a cavity  310  defined by the housing  305 . The cavity  310  may be formed in the shape of a circle (as shown), oval, ellipse, square, and rectangle. The loop foil  115  is positioned within the cavity  310 . The loop foil  115  does not come into direct contact with the housing  305  but rather is connected between the center connector pins  106  and  111 . The coil  120  is also positioned within the cavity  310  and is connected to the center connector pin  106  and the diode  125 . In one embodiment, the diode  125  is connected to a base plate  315  or a base of the cavity  310 . 
         [0040]    The surge protection device  300  has various frequency characteristic bands within the range of approximately 300 Hz to 5 GHz. Return losses of greater than or equal to 20 dB and insertion losses of less than or equal to 0.1 dB, for example, are from approximately 700 MHz to 2,400 MHz. A return loss of greater than 50 dB may be realized within a narrow band, for example, between approximately 1,400 MHz and 1,600 MHz. 
         [0041]      FIGS. 5 ,  6  and  7  are perspective, top and side views of a diode of the surge protection device of  FIG. 4  according to an embodiment of the invention. In one embodiment, the diode  125  may be a diode cell  500  having three layers  505 ,  510 , and  515 . The center diode junction or layer  510  may be sandwiched between top and bottom metal layers  505  and  515 . The diode cell  500  does not have any wire leads, thus reducing the inductance and improving voltage clamping under high surge conditions. The second end  120   b  of the coil  120  is directly attached to the top metal layer  505  of the diode cell  500 . The bottom metal layer  515  of the diode cell  500  is directly attached to the ground  130 . No wire leads are used to connect the diode cell  500  to the coil  120  or the ground  130 . 
         [0042]    In one embodiment, the diode cell  500  may have a length L 1  of about 9.40 mm, a width W 1  of about 9.40 mm, and a thickness T 1  of about 1.29 mm. The diode  125  may be two or more diodes in parallel circuit configuration. The diode cell  500  may include a hole  520  for mounting to the housing  305 . If the hole  520  is not present, the diode cell  500  may be mounted or soldered to the base plate  315  to facilitate grounding of the diode  125  to the housing  305 . 
         [0043]      FIGS. 8 ,  9  and  10  are side, top and front views of a loop foil  115  according to an embodiment of the invention. In this embodiment, H 2  is about 15.875 mm, L 2  is about 22.36 mm, W 2  is about 8.89 mm, and T 2  is about 0.41 mm. The loop foil  115  is symmetrical when the end connectors are the same. That is, L 3  and L 4  have the same length of about 11.18 mm. 
         [0044]      FIGS. 11 ,  12  and  13  are side, top and front views of a loop foil  115  according to another embodiment of the invention. In this embodiment, H 2  is about 15.875 mm, L 2  is about 22.36 mm, W 2  is about 8.89 mm, and T 2  is about 0.41 mm. Since one connector is a SMA connector and one connector is a N-Type connector, L 3  and L 4  have different lengths. That is, L 3  is about 11.53 mm and L 4  is about 10.06 mm. Each series of connectors (N or SMA, etc.) are manufactured for a fixed impedance (e.g., 50 Ohms) generally to the formula for coaxial lines which is a relationship including pin diameter, connector shell inside diameter and the supporting medium dielectric coefficient. The physical size of the two connectors is obviously different while maintaining the same impedance. Because of this physical difference, L 3  and L 4  must vary to impedance match to the cavity. There is actually some difference when using connectors of the same series but different gender, because actual center pin length varies. The variance is less dramatic than that of non similar series connectors in which case L 3  and L 4  generally are the same. 
         [0045]    The previous description of the disclosed examples is provided to enable any person of ordinary skill in the art to make or use the disclosed methods and apparatus. Various modifications to these examples will be readily apparent to those skilled in the art, and the principles defined herein may be applied to other examples without departing from the spirit or scope of the disclosed method and apparatus. The described embodiments are to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.