Abstract:
A method and a device, the device has ground voltage elevation compensation capabilities and includes: multiple current consuming components; a positive voltage supply input; a negative voltage supply input; and a compensation circuit, coupled to the negative voltage supply input and to a grounding element; wherein the compensation circuit is adapted to detect a ground voltage elevation resulting from a flow of excess consumption current through the grounding element, and in response couple the negative voltage supply input to the grounding element; wherein the excess current flows through the grounding element due to an increment in a current consumption of a current consuming element of the device.

Description:
FIELD OF THE INVENTION 
     The present invention relates to devices and methods for compensating for ground voltage elevations within an integrated circuit. 
     BACKGROUND OF THE INVENTION 
     Modern integrated circuits are required to operate at very high frequencies while consuming a relatively low supply voltage which has dramatically decreased during the last decade. 
     This supply voltage reduction has some drawbacks such as an increased sensitivity to ground voltage elevations that are proportional to a current (I) consumed by components of the integrated circuit and to the resistance (R) of grounding elements through which the current flows. 
     A ground voltage elevation can reduce the voltage that is provided to internal components of the integrated circuit, increase the noise level within the integrated circuit and thus can temporarily prevent the integrated circuit from operating in a proper manner. 
     There is a need to provide a device and method for efficiently compensating for ground voltage elevations. 
     SUMMARY OF THE PRESENT INVENTION 
     A device and a method for compensating for ground voltage elevations, as described in the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: 
         FIG. 1  illustrates a device and voltage supply units according to an embodiment of the invention; 
         FIG. 2  illustrates various portions of an integrated circuit, according to an embodiment of the invention; 
         FIG. 3  is a schematic electric diagram of a compensation circuit as well as various equivalent components according to an embodiment of the invention; and 
         FIG. 4  is a flow chart of a method for compensating for a ground voltage elevation according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following figures illustrate exemplary embodiments of the invention. They are not intended to limit the scope of the invention but rather assist in understanding some of the embodiments of the invention. It is further noted that all the figures are out of scale. 
     According to various embodiments of the invention a method and device for compensating for ground voltage elevations are provided. The compensation can involve comparing the voltage at a sensing point to a voltage at a reference point and providing a source path to a negative voltage supply unit when a ground voltage elevation (especially of above a certain value) is detected. Conveniently, the compensation process is relatively fast, in comparison to the development of the ground voltage elevation. 
       FIG. 1  illustrates device  10 , and voltage supply units  44  and  48  according to an embodiment of the invention. 
     Device  10  can include one or more integrated circuits, can be connected to multiple voltage supply units, and can be a mobile device such as but not limited to a cellular phone, a laptop computer, a personal data accessory and the like. 
     For convenience of explanation only  FIG. 1  illustrates device  10  as including integrated circuit  20  that is connected to positive voltage supply unit  44  and negative voltage supply unit  48 . It is noted that device  10  can include one or more of these voltage supply units, but this is not necessarily so. 
     According to an embodiment of the invention negative voltage supplied by negative voltage supply unit  48  is used by integrated circuit  20  only for ground voltage elevation compensation purposes, but this is not necessarily so. For example, the negative voltage can be used for additional purposes. 
     Positive voltage supply unit  44  provides a positive supply voltage Vcc  45  while the negative voltage supply unit  48  provides a negative supply voltage Vc  49 . Conveniently Vc  49  is supplied to one or more negative voltage supply inputs of integrated circuit  20  and Vcc  45  is supplied to one or more positive voltage supply inputs of integrated circuit  20 . 
     The value of Vcc  45  can substantially equal the absolute value of Vc  49 , but this is not necessarily so. For example, Vc  49  can be substantially lower than Vcc  45 . 
     Integrated circuit  20  includes multiple current consuming components (such as cores, cache memory units, DMA controllers) that can rapidly increase their current consumption thus causing ground voltage elevations. 
     Conveniently, multiple compensation circuits are located near current consuming elements that are connected to the ground grid through grounding elements which are expected to experience ground voltage elevations, and provide local compensation for local ground voltage elevations. The grounding elements can form one or more ground grids, as illustrated in  FIG. 2 . 
     The provision of local compensation circuits that are relatively small and can be connected to one or more negative voltage supply inputs via relatively narrow (and hence relatively highly resistive) conductors reduces a die area penalty associated with the ground voltage elevation compensation scheme. 
       FIG. 2  illustrates various portions of an integrated circuit  20 , according to an embodiment of the invention. 
     Integrated circuit  20  includes multiple grounding elements that can form one or more ground grids.  FIG. 2  illustrates a single ground grid  22  that includes multiple grounding elements that are represented by portions of the vertical and horizontal lines that represent a single ground grid. An ellipse surrounds grounding element  29  that connects reference point  33 ′ and sensing point  32 ′. It is noted that reference point  33 ′ is not necessarily connected to ground through pin  61 . Integrated circuit  20  also includes one or more power supply grids that are not shown for convenience of explanation. Ideally, the voltage level across the whole power grid is the same but in reality, due to the resistance of grounding elements that form ground grid  22 , the voltage level can differ from one grounding element to another, and thus local compensation circuits can be very effective. 
     Integrated circuit  20  also includes current consuming components such as cores  24  and  24 ′, peripherals (I/O pads etc.)  26  and memory units  28  and  28 ′. 
     Ground grid  22  is connected to one or more pins  61  that also can serve as a ground voltage reference point  33 . 
     Ground grid  22  is connected to core  24 , core  24 ′, memory unit  28 , memory unit  28 ′, and to peripherals  26 . 
     Two exemplary, non-limiting and out of scale sensing points  32  and  32 ′ are also illustrated. Sensing point  32  is positioned within the area of core  24  while sensing point  32 ′ is located within core  24 ′. It is noted that much more than a pair of sensing points can be defined within integrated circuit  20 . It is further noted that sensing points can be located within other components of the integrated circuit  20  as well as between components of the integrated circuit  20 . Each compensation circuit can detect the voltage potential between such a sensing point and a reference point that is expected to be less affected or not affected at all by the ground voltage elevation. The reference points can be located near pins  61 , especially between pins  61  and a decoupling capacitor (not shown). 
     Ground voltage elevations are formed when the current consumption of one or more of these components increases, and especially when the consumed currents are relatively high. Such an increase in current consumption is usually associated with complex computational tasks, memory transfer bursts and the like. 
     The multiple sensing points are selected such as to detect these ground voltage elevations. The selection is usually based upon a simulation of the integrated circuit. Designers are usually well aware of the possible current consuming components. Typically, more than one local compensation circuit is positioned such as to take care of a single core. In addition, the local compensation circuits can be placed at any distance from pins  61 . 
       FIG. 3  is a schematic electric diagram of a compensation circuit  90  as well as various grid components  71 ,  72 ,  73 ,  74 ,  76 , according to an embodiment of the invention. 
     Grid components include equivalent resistors  71 ,  74  and  76 , equivalent capacitor  72  and current sink  73  that represent the resistances, capacitance and current consumption of various components of integrated circuit  20 . 
     Resistor  71  represents the (parasitic) resistance of a positive voltage supply element  44  that connects positive voltage supply input  62  to a certain internal point of integrated circuit  20 . Resistor  74  represents the resistance of grounding element  29  that is located between pin  61  (and reference point  33 ′) and sensing point  32 ′. Resistor  76  represents the resistance of a relatively highly resistive conductor that connects negative voltage supply input  63  to switch  89  of compensation circuit  90 . Capacitor  72  represents the equivalent capacitance of the integrated circuit as viewed between pin  61  and positive voltage supply input  62 . Current sink  73  represents the current consumption of one or more components of integrated circuit  20 , as viewed between pin  61  and positive voltage supply input  62 . 
     Capacitor  72  can represent a decoupling capacitor that is drained by excessive current that flows through grounding element  29  once the current consumption experiences a transient. 
     Compensation circuit  90  includes comparator  80 , switch  89  and a conductor that connects switch  89  to negative voltage supply input  63 . A non-inverting input  81  of comparator  80  is connected to sensing point  32 ′ (sensing point  32 ′ is graphically illustrated as being connected to the grounding element  29  adjacent to one end of capacitor  72  and one end of current sink  73 ). The other ends of capacitor  72  and current sink  73  are connected to the certain internal point of integrated circuit  20 . That certain internal point is connected to resistor  71 . 
     An inverting input  83  of comparator  80  is connected to ground voltage reference point (also referred to as reference point)  33 ′ that represents ground potential, which is not affected by the voltage elevation. Comparator  80  is connected in parallel to grounding element  29  thus is capable of detecting ground voltage elevation. It is noted that the detection can involve detecting a ground voltage elevation that exceeds a predefined value. A certain amount of current can flow through the grounding element  29  while causing ground voltage elevation, lower than the predefined level once a ground voltage elevation is detected, comparator  80  outputs a control signal via output  85  and opens switch  89  which is a MOSFET transistor. When switch  89  is opened, it connects the grounding element  29  to the negative voltage supply unit  48  (via negative voltage supply input  63 ) and allows input  63  to drain the excessive current. When switch  89  is opened it stops the discharge of capacitor  72  by providing the excess current drain path. 
     Conveniently, compensation circuit  90  is characterized by a response time that is relatively short in comparison to a development time of a substantially ground voltage elevation. 
       FIG. 4  is a flow chart of method  200  for compensating for a ground voltage elevation according to an embodiment of the invention. 
     Method  200  starts by optional stage  210  of defining or receiving a detection policy. The detection policy can mandate that the detection is performed in a continuous manner, according to a predefined detection pattern, in response to a reception of an alert that can represent expected current raise, and the like. 
     Each detection session can occur within a predefined measurement period, as well as within a dynamically changing measurement period. It is noted that the detecting can involve sampling the voltage developed over the grounding element. 
     Stage  210  is followed by stage  230  of detecting a ground voltage elevation resulting from a flow of excess current through a grounding element. Conveniently, the excess current flows through the grounding element due to an increment in a current consumption of a current consuming element of the device. Conveniently, the excess current is discharged through a decoupling capacitor. 
     Stage  230  is followed by stage  250  of connecting a negative voltage supply input to the grounding element in response to the detection. 
     Conveniently, stage  250  enables sinking of at least a portion of the excess current. 
     Conveniently, stage  250  includes connecting the negative voltage supply input via a relatively highly resistive conductor. The level of the negative supply voltage provided to the negative voltage supply input and a resistance of the relatively highly resistive conductor are designed to be matched such as to provide successful compensation and optimal overall circuit performance. 
     Conveniently, stage  250  of coupling includes closing a switch. Conveniently, the switch can be pulse width modulated. Conveniently, the switch is a transistor. 
     Conveniently, stage  250  at least partially reduces a discharge of a decoupling capacitor by the excess current. 
     Conveniently, various stages of method  200  can be executed concurrently by multiple compensation circuits that are mutually independent. 
     Stage  250  is followed by stage  270  of disconnecting the negative voltage supply from the grounding element. Stage  270  can be followed by stage  230 . Stage  250  can be followed by stage  270  once the compensation is completed. The compensation can be completed once a completion criterion is fulfilled. The completion criterion can relate to a reduction in the ground voltage elevation to an acceptable level. 
     Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the invention is to be defined not by the preceding illustrative description but instead by the spirit and scope of the following claims.