Abstract:
Self-triggered Multi-finger SCRs used in ESD protection circuitry capable of turning on all SCR fingers of the multi-finger SCRs include a first source, a second source, N SCR units, (N−1) diodes, and N resistors. Each of the N SCR units includes a first node, a second node coupled to the second source, and a trigger node. An nth diode of the (N−1) diodes is coupled between a first node of an nth SCR unit and a trigger node of an (n+1)th SCR unit. An nth resistor is coupled between the first node of the nth SCR unit and the first source, wherein n and N are integers. The (N−1) diodes can be replaced by directly coupled the first node of the nth SCR unit to the trigger node of the (n+1)th SCR unit when a trigger pulse is applied at the trigger node of a first SCR unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to ESD protection circuitry with multi-finger SCRs, especially to ESD protection circuitry which can turn on all of its multi-finger SCRs. 
     2. Description of the Prior Art 
     The electrostatic discharge (ESD) is a sudden and momentary electric current generated by friction or induction and then flows through circuitry. It may cause damage to electronic equipment. Some circuitry and devices are vulnerable to ESD, for example MOSFETs (Metal Oxide Semiconductor Field Effect Transistor). Therefore, ESD protection circuitry is often applied in IC designs. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention releases ESD protection circuitry with multi-finger SCRs, comprising a first source, a second source, N SCR units, (N−1) diodes, and N resistors. Each of the N SCR units includes a first node, a second node coupled to the second source, and a trigger node. An nth diode of the (N−1) diodes is coupled between a first node of an nth SCR unit and a trigger node of an (n+1)th SCR unit. An nth resistor is coupled between the first node of the nth SCR unit and the first source, wherein n and N are integers. 
     Another embodiment of the present invention releases ESD protection circuitry with multi-finger SCRs, comprising a first source, a second source, N SCR units, a first trigger input, and N resistors. Each of the N SCR units includes a first node, a second node coupled to the second source, and a trigger node, wherein a first node of an nth SCR unit of the N SCR units is coupled to a trigger node of an (n+1)th SCR unit of the N SCR units. The first trigger input is coupled to the trigger node of the first SCR unit of the N SCR units. An nth resistor is coupled between the first node of the nth SCR unit and the first source, wherein n and N are integers. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of multi-finger SCRs of the first embodiment according to the present invention. 
         FIG. 2  is a schematic diagram of multi-finger SCRs in  FIG. 1  with an external trigger input inputted at the base of each NPN BJT according to the second embodiment of the present invention. 
         FIG. 3  is a schematic diagram of multi-finger SCRs in  FIG. 1  with an external trigger input inputted at the base of each PNP BJT according to the third embodiment of the present invention. 
         FIG. 4  is a schematic diagram of multi-finger SCRs in  FIG. 1  with 2 external trigger inputs inputted at the base of each NPN BJT and the base of each PNP BJT according to the fourth embodiment of the present invention. 
         FIG. 5  is a schematic diagram of multi-finger SCRs in  FIG. 1  with an external trigger input inputted at the base of the NPN BJT of the first SCR finger according to the fifth embodiment of the present invention. 
         FIG. 6  is a schematic diagram of multi-finger SCRs in  FIG. 1  with an external trigger input inputted at the base of the PNP BJT of the first SCR finger according to the sixth embodiment of the present invention. 
         FIG. 7  is a schematic diagram of multi-finger SCRs in  FIG. 1  with 2 external trigger inputs inputted at the bases of the NPN BJT and the PNP BJT of the first SCR finger according to the seventh embodiment of the present invention. 
         FIG. 8  is a schematic diagram of multi-finger SCRs of the eighth embodiment according to the present invention. 
         FIG. 9  is a schematic diagram of multi-finger SCRs in  FIG. 8  with an external trigger input inputted at the base of each NPN BJT according to the ninth embodiment of the present invention. 
         FIG. 10  is a schematic diagram of multi-finger SCRs in  FIG. 8  with an external trigger input inputted at the base of each PNP BJT according to the tenth embodiment of the present invention. 
         FIG. 11  is a schematic diagram of multi-finger SCRs in  FIG. 8  with 2 external trigger inputs inputted at the base of each NPN BJT and the base of each PNP BJT according to the eleventh embodiment of the present invention. 
         FIG. 12  is a schematic diagram of multi-finger SCRs in  FIG. 8  with an external trigger input inputted at the base of the NPN BJT of the first SCR finger according to the twelfth embodiment of the present invention. 
         FIG. 13  is a schematic diagram of multi-finger SCRs in  FIG. 8  with 2 external trigger inputs inputted at the bases of the NPN BJT and the PNP BJT of the first SCR finger according to the thirteenth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a domino-like, self-triggered design capable of turning on all SCR fingers in multi-finger SCRs used as ESD protection circuitry. Once an SCR finger in the multi-finger SCRs is turned on first, the present invention utilizes a diode or a trigger pulse to force some ESD current flowing through the first turned-on SCR finger to flow through an SCR next to it to turn on the next SCR finger. After the next SCR finger is turned on, some current flowing through it is forced by another diode, a trigger pulse inputted at the first SCR finger or at the present SCR finger itself to turn on an SCR finger next to it again. As a domino effect, all the SCR fingers in the multi-finger SCRs are turned on one after another. Thus, at least one SCR finger is turned on first, other SCR fingers in the multi-finger SCRs are triggered to be turned on subsequently. Even though all SCR fingers in the multi-finger SCRs can not be turned on at the same time, all SCR fingers can be turned on before any SCR finger is damaged. This is the self-triggered principle of the present invention. 
     Please refer to  FIG. 1 .  FIG. 1  is a schematic diagram of multi-finger SCRs  100  of the first embodiment according to the present invention. The multi-finger SCRs  100  include an I/O pad line  101 , a ground line  103 , 3 SCR fingers, SCR 1 , SCR 2 , and SCR 3 , 3 diodes, D 1 , D 2 , and D 3 , and 3 resistors, Rc 1 , Rc 2 , and Rc 3 . The SCR 1  includes a first node  111  coupled to the I/O pad line  101 , and a second node  113  coupled to a positive node of the diode D 1 . The SCR 1  further includes a PNP BJT  115 , an NPN BJT  117 , and 2 resistors  118  and  119 . The PNP BJT  115  includes an emitter coupled to the first node  111  and the resistor  119 , a base coupled to the resistor  119 , and a collector coupled to the resistor  118 . The NPN BJT  117  includes an emitter coupled to the second node  113  and the resistor  118 , a base coupled to the resistor  118  and the collector of the PNP BJT  115 , and a collector coupled to the base of the PNP BJT  115  and the resistor  119 . The resistor Rc 1  is coupled between the ground line  103  and the second node  113  of the SCR finger SCR 1 . The diode D 3  includes a negative node coupled to the base of the NPN BJT  117 . The SCR 2  includes a first node  121  coupled to the I/O pad line  101 , and a second node  123  coupled to a positive node of the diode D 2 . The SCR 2  further includes a PNP BJT  125 , an NPN BJT  127 , and 2 resistors  128  and  129 . The PNP BJT  125  includes an emitter coupled to the first node  121  and the resistor  129 , a base coupled to the resistor  129 , and a collector coupled to the resistor  128 . The NPN BJT  127  includes an emitter coupled to the second node  123  and the resistor  128 , a base coupled to the resistor  128 , and the collector of the PNP BJT  125 , and a collector coupled to the base of the PNP BJT  125  and the resistor  129 . The resistor Rc 2  is coupled between the ground line  103  and the second node  123  of the SCR finger SCR 2 . The diode D 1  includes a negative node coupled to the base of the NPN BJT  127 . The SCR 3  includes a first node  131  coupled to the I/O pad line  101 , and a second node  133  coupled to a positive node of the diode D 3 . The SCR 3  further includes a PNP BJT  135 , an NPN BJT  137 , and 2 resistors  138  and  139 . The PNP BJT  135  includes an emitter coupled to the first node  131  and the resistor  139 , a base coupled to the resistor  139 , and a collector coupled to the resistor  138 . The NPN BJT  137  includes an emitter coupled to the second node  133  and the resistor  138 , a base coupled to the resistor  138  and the collector of the PNP BJT  135 , and a collector coupled to the base of the PNP BJT  135  and the resistor  139 . The resistor Rc 3  is coupled between the ground line  103  and the second node  133  of the SCR finger SCR 3 . The diode D 2  includes a negative node coupled to the base of the NPN BJT  137 . Please note that the number of the SCR fingers  3  given in the first embodiment is not meant to limit to the number of SCR fingers of the present invention, any integer number of the SCR fingers greater than 1 can be applied as well in the present embodiment. 
     Moreover, a first trigger pulse can be inputted selectively at the bases of the PNP BJTs  115 ,  125 , and  135 , or only at the base of the PNP BJT  115  to give an external trigger pulse for turning on the SCR fingers more rapidly and effectively in the first embodiment. Or a second trigger can be inputted selectively at the bases of the NPN BJTs  117 , 127 , and  137 , or only at the base of the NPN BJT  117  for the same cause. Or both the first and second trigger pulses can be inputted together at the base of each PNP BJT and the base of each NPN BJT, or only at the bases of the PNP BJT  115  and NPN BJT  117 . When a trigger, or two triggers are applied to the SCR finger SCR 1 , or each SCR finger respectively, the diode (in the first embodiment, it refers to the diode D 3 ) coupled between the last SCR finger (in the first embodiment, the last SCR finger refers to the SCR finger SCR 3 ) and the first SCR finger (in the first embodiment, the first SCR finger refers to the SCR finger SCR 1 ) can be omitted for the first SCR finger has already been triggered by the trigger pulse, and is definitely to be turned on. Please refer to  FIGS. 2 ,  3 ,  4 ,  5 ,  6 , and  7  together.  FIG. 2  shows a schematic diagram of multi-finger SCRs  140  in  FIG. 1  with an external second trigger input inputted at the base of each NPN BJT according to the second embodiment of the present invention.  FIG. 3  shows a schematic diagram of multi-finger SCRs  150  in  FIG. 1  with an external first trigger input inputted at the base of each PNP BJT according to the third embodiment of the present invention.  FIG. 4  shows a schematic diagram of multi-finger SCRs  160  in  FIG. 1  with external first and second trigger inputs inputted at the base of each NPN BJT and the base of each PNP BJT according to the fourth embodiment of the present invention.  FIG. 5  shows a schematic diagram of multi-finger SCRs  170  in  FIG. 1  with an external second trigger input inputted at the base of the NPN BJT  117  of the first SCR finger SCR 1  according to the fifth embodiment of the present invention.  FIG. 6  shows a schematic diagram of multi-finger SCRs  180  in  FIG. 1  with an external first trigger input inputted at the base of the PNP BJT  115  of the first SCR finger SCR 1  according to the sixth embodiment of the present invention.  FIG. 7  shows a schematic diagram of multi-finger SCRs  190  in  FIG. 1  with external first and second trigger inputs inputted at the bases of the NPN BJT  117  and the PNP BJT  115  of the first SCR finger SCR 1  according to the seventh embodiment of the present invention. 
     In the above embodiments, the diode of the present invention has a negative node coupled to a base of an NPN BJT of an SCR finger, and a positive node coupled to an emitter of an NPN BJT of a former SCR finger connected to the SCR finger in parallel. However, the present invention is not confined to this connection only. The diode of the present invention may have the positive node coupled to a base of a PNP BJT of an SCR finger, and the negative node coupled to an emitter of a PNP BJT of a former SCR finger connected to the SCR finger in parallel. In this case, the resistor connected to the SCR finger in series is coupled between the I/O pad line  101  and the first node of the SCR finger. Of course, in this case, a first trigger pulse can be inputted selectively at the bases of all the PNP BJTs, or only at the base of the first PNP BJT to give an external trigger pulse for turning on the SCR fingers more rapidly and effectively. Or a second trigger can be inputted selectively at the bases of all the NPN BJTs, or only at the base of the first NPN BJT for the same cause. Or both the first and second trigger pulses can be inputted together at the base of each PNP BJT and the base of each NPN BJT, or only at the bases of the first PNP BJT and NPN BJT. When a trigger, or two triggers are applied to the first SCR finger, or each SCR finger respectively, the diode coupled between the last SCR finger and the first SCR finger can be omitted for the first SCR finger has already been triggered by the trigger pulse, and is definitely to be turned on. 
     Moreover, the diode of the present invention may have the positive node coupled to a base of a PNP BJT of an SCR finger, and the negative node coupled to an emitter of a PNP BJT of a former SCR finger connected to the SCR finger in parallel, and the resistor connected to the former SCR finger in series is coupled between the I/O pad line  101  and the first node of the former SCR finger; the latter diode may have a negative node coupled to a base of an NPN BJT of a latter SCR finger connected to the SCR finger in parallel, and a positive node coupled to an emitter of the NPN BJT of the SCR finger, and the resistor connected to the SCR finger in series is coupled between the ground line  103  and the second node of the SCR finger. In this case, a first trigger pulse also can be inputted selectively at the bases of all the PNP BJTs, or only at the base of the first PNP BJT to give an external trigger pulse for turning on the SCR fingers more rapidly and effectively. Or a second trigger can be inputted selectively at the bases of all the NPN BJTs, or only at the base of the first NPN BJT for the same cause. Or both the first and second trigger pulses can be inputted together at the base of each PNP BJT and the base of each NPN BJT, or only at the bases of the first PNP BJT and NPN BJT. When a trigger, or two triggers are applied to the first SCR finger, or each SCR finger respectively, the diode coupled between the last SCR finger and the first SCR finger can be omitted for the first SCR finger has already been triggered by the trigger pulse, and is definitely to be turned on. 
     A eighth embodiment is given in  FIG. 8  to further illustrate the purpose of the present invention. Please refer to  FIG. 8 .  FIG. 8  is a schematic diagram of multi-finger SCRs  500  of the eighth embodiment according to the present invention. The multi-finger SCRs  500  include an I/O pad line  101 , a ground line  103 , 3 SCR fingers, SCR 1 , SCR 2 , and SCR 3 , 3 resistors, Rc 1 , Rc 2 , and Rc 3 , and a first trigger input. The SCR 1  includes a PNP BJT  115 , an NPN BJT  117 , and 2 resistors  118  and  119 . The connections of the PNP BJT  115 , the NPN BJT  117 , and the 2 resistors  118  and  119  are substantially similar to the connections in the first embodiment, therefore the description is omitted here for the sake of brevity. The resistor Rc 1  is coupled between the ground line  103  and a second node  113  of the SCR finger SCR 1 . The first trigger input is coupled to the base of the PNP BJT  115  of the first SCR finger SCR 1 . The SCR 2  includes a PNP BJT  125 , an NPN BJT  127 , and 2 resistors  128  and  129 . The connections of the PNP BJT  125 , the NPN BJT  127 , and the 2 resistors  128  and  129  are substantially similar to the connections in the first embodiment, therefore the description is omitted here for the sake of brevity. The resistor Rc 2  is coupled between the ground line  103  and a second node  123  of the SCR finger SCR 2 . The SCR 3  includes a first node  131  coupled to the I/O pad line  101 . The SCR 3  further includes a PNP BJT  135 , an NPN BJT  137 , and 2 resistors  138  and  139 . The connections of the PNP BJT  135 , the NPN BJT  137 , and the 2 resistors  138  and  139  are substantially similar to the connections in the first embodiment, therefore the description is omitted here for the sake of brevity. The resistor Rc 3  is coupled between the ground line  103  and a second node  133  of the SCR finger SCR 3 . The SCR 1  further includes a first node  111  coupled to the I/O pad line  101 , and a second node  113  coupled to a base node of the NPN BJT  127 . The SCR 2  further includes a first node  121  coupled to the I/O pad line  101 , and a second node  123  coupled to a base node of the NPN BJT  137 . Please note that the number of the SCR fingers  3  given in the eighth embodiment is not meant to limit to the number of SCR fingers of the present invention, any integer number of the SCR fingers greater than 1 can be applied as well in the present embodiment. 
     Moreover, a first trigger pulse can be inputted selectively at the bases of the PNP BJTs  115 ,  125 , and  135  to give an external trigger pulse for turning on the SCR fingers more rapidly and effectively in the eighth embodiment. Or a second trigger can be inputted selectively at the bases of the NPN BJTs  117 ,  127 , and  137 , or only at the base of the NPN BJT  117  for the same cause. Or both the first and second trigger pulses can be inputted together at the base of each PNP BJT and the base of each NPN BJT, or only at the bases of the PNP BJT  115  and NPN BJT  117 . When a trigger, or two triggers are applied to the SCR finger SCR 1 , or each SCR finger respectively, the second node of the last SCR finger (in the eighth embodiment, the last SCR finger refers to the SCR finger SCR 3 , and the second node of the last SCR finger refers to the second node  133 ) doesn&#39;t need to be coupled to the base of the NPN BJT of the first SCR finger (in the eighth embodiment, the first SCR finger refers to the SCR finger SCR 1 , and the NPN BJT of the first SCR finger refers to the NPN BJT  117 ) for the first SCR finger has already been triggered by the trigger pulse, and is definitely to be turned on. Please refer to  FIGS. 9 ,  10 ,  11 ,  12 , and  13  together.  FIG. 9  shows a schematic diagram of multi-finger SCRs  540  in  FIG. 8  with an external second trigger input inputted at the base of each NPN BJT according to the ninth embodiment of the present invention.  FIG. 10  shows a schematic diagram of multi-finger SCRs  550  in  FIG. 8  with an external first trigger input inputted at the base of each PNP BJT according to the tenth embodiment of the present invention.  FIG. 11  shows a schematic diagram of multi-finger SCRs  560  in  FIG. 8  with external first and second trigger inputs inputted at the base of each NPN BJT and the base of each PNP BJT according to the eleventh embodiment of the present invention.  FIG. 12  shows a schematic diagram of multi-finger SCRs  570  in  FIG. 8  with an external second trigger input inputted at the base of the NPN BJT  117  of the first SCR finger SCR 1  according to the twelfth embodiment of the present invention.  FIG. 13  shows a schematic diagram of multi-finger SCRs  590  in  FIG. 8  with external first and second trigger inputs inputted at the bases of the NPN BJT  117  and the PNP BJT  115  of the first SCR finger SCR 1  according to the thirteenth embodiment of the present invention. 
     In the above embodiments, a base of an NPN BJT of an SCR finger is coupled to an emitter of an NPN BJT of a former SCR finger connected to the SCR finger in parallel. However, the present invention is not confined to this connection only. A base of a PNP BJT of an SCR finger may be coupled to an emitter of a PNP BJT of a former SCR finger connected to the SCR finger in parallel. In this case, the resistor connected to the SCR finger in series is coupled between the I/O pad line  101  and the first node of the SCR finger. Of course, in this case, a first trigger pulse can be inputted selectively at the bases of all the PNP BJTs, or only at the base of the first PNP BJT to give an external trigger pulse for turning on the SCR fingers more rapidly and effectively. Or a second trigger can be inputted selectively at the bases of all the NPN BJTs, or only at the base of the first NPN BJT for the same cause. Or both the first and second trigger pulses can be inputted together at the base of each PNP BJT and the base of each NPN BJT, or only at the bases of the first PNP BJT and NPN BJT. When a trigger, or two triggers are applied to the first SCR finger, or each SCR finger respectively, the last SCR finger doesn&#39;t need to be connected back to the first SCR finger for the first SCR finger has already been triggered by the trigger pulse, and is definitely to be turned on. 
     Moreover, a base of a PNP BJT of an SCR finger of the present invention may be coupled to an emitter of a PNP BJT of a former SCR finger connected to the SCR finger in parallel, and the resistor connected to the former SCR finger in series is coupled between the I/O pad line  101  and the first node of the former SCR finger; a base of an NPN BJT of a latter SCR finger connected to the SCR finger in parallel may be coupled to an emitter of the NPN BJT of the SCR finger, and the resistor connected to the SCR finger in series is coupled between the ground line  103  and the second node of the SCR finger. In this case, a first trigger pulse also can be inputted selectively at the bases of all the PNP BJTs, or only at the base of the first PNP BJT to give an external trigger pulse for turning on the SCR fingers more rapidly and effectively. Or a second trigger can be inputted selectively at the bases of all the NPN BJTs, or only at the base of the first NPN BJT for the same cause. Or both the first and second trigger pulses can be inputted together at the base of each PNP BJT and the base of each NPN BJT, or only at the bases of the first PNP BJT and NPN BJT. When a trigger, or two triggers are applied to the first SCR finger, or each SCR finger respectively, the last SCR finger doesn&#39;t need to be connected back to the first SCR finger for the first SCR finger has already been triggered by the trigger pulse, and is definitely to be turned on. 
     The present invention utilizes multi-finger SCRs instead of multi-finger MOSFETs because the SCRs have the following advantages: 
     a smaller area: the holding voltage of a MOSFET is around 4˜5V, however, although an SCR needs a trigger to turn it on, the holding voltage of an SCR is only around 1V. Therefore, with the same ESD current, an SCR needs a smaller size to discharge it than a MOSFET does. 
     2. without a gate: a gate part of a MOSFET is the easiest part to be punched through by currents, and an SCR doesn&#39;t include a gate part. Hence, an SCR is more difficult to be punched through by ESD currents when compared with a MOSFET. 
     3. a higher withstanding voltage: an SCR can stand a higher ESD voltage when compared with a MOSFET. 
     The present invention utilizes a domino-like, self-triggered design capable of turning on all SCR fingers in multi-finger SCRs used as ESD protection circuitry. The SCR is superior to the MOSFET due to its smaller area, a higher withstanding voltage, and no gate structure as used in ESD protection circuitry. As a result, the present invention can provide an effective, lasting ESD protection circuitry by using the domino-like, self-triggered multi-finger SCRs. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.