Abstract:
The invention discloses a power gating for in-rush current mitigation. Firstly the circuit uses small power switch cells at first stage, such that those power switch cells run in saturation region. Secondly a delay unit delays a switch signal to control the dwell time of current to reduce the peak value of the current. Thirdly large power switch cells are used at the rest, such that those power switch cells operate in linear region.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a circuit for stabilizing current, and more particularly to a power gating apparatus for in-rush current mitigation. 
     2. Description of the Prior Art 
     Currently, the system-on-a-chip (SOC) applied in telecommunication products or in computers is developing in the trend of high performance and portability, and thus its power consumption has become an important consideration in design. The most effective way to reduce the power consumption of a circuit is to reduce the operating voltage of the circuit. However, if the operating voltage is lowered, the overall performance of the circuit will be lowered accordingly. Therefore, in order to maintain the overall performance of the circuit, threshold voltages of transistors must be lowered, which will lead to an indexed growth of the sub-threshold leakage current. 
     Due to the nanoscale nature of semiconductor development processing, power consumption sharply increases due to leakage current. In order to reduce the leakage current, a technique referred to as power gating is used to cut off power supplied to a circuit block that is not currently used in a chip. 
     It is known to provide integrated circuits with one or more virtual power rails and one or more virtual ground rails. These virtual rails are selectively connected or disconnected to the main power rails and the main ground rails respectively by header transistors and footer transistors. This technique is useful in reducing power consumption when a block/domain within an integrated circuit is not required to be active and accordingly can be powered down and isolated from the power supply and the ground by the use of these header and/or footer transistors. These header and/or footer devices are selected such that when they are switched off they have a high resistance and thus, a low leakage current. This is generally done by selecting devices with a high threshold voltage. 
     Accordingly, those skilled in the art seek methods and apparatus that are capable of controlling integrated circuits incorporating power gating technology in such a manner that reacts to the dynamic conditions being experienced by the power gating circuitry. 
       FIG. 1  shows a circuit for in-rush current mitigation according to the prior art. Small switch cells  11  receive power and “Sleep” signal, and after a Schmitt trigger  13  detects voltage signal, a logic unit  14  enable/disable big switch cells  12 . The extra Schmitt trigger compromises the IC design in some applications. 
       FIG. 2  shows a circuit for in-rush current mitigation according to another prior art. The methodology to mitigate in-rush current is to utilize so-called “Mother/Daughter” switch cell, which has two switches of different size inside (one small switch is named “Daughter” and another bigger one is named “Mother”). When all switch cells are turn-on, the Daughter&#39;s input  211  in switch cell  21  receives SleepEn signal and the Daughter&#39;s output  212  transmits it to the next switch cell  22  having a corresponding Daughter&#39;s input  221  and Daughter&#39;s output  222  which is then transmitted to switch cell  23  having a corresponding Daughter&#39;s input  231  and Daughter&#39;s output  232  and so on. As going on the last switch cell&#39;s  29  Daughter&#39;s input  291  receives SleepEn signal and the Daughter&#39;s output  292  transmits it back to the Mother&#39;s input  293  in same switch cell  29 . From the Mother&#39;s output  294  the SleepEn signal is transferred to the Mother&#39;s input  213  in switch cell  21  via switch cells  28 - 22  and corresponding Mother&#39;s inputs  283 ,  273 ,  264 ,  254 ,  244 ,  233 , and  223  and Mother&#39;s outputs  284 ,  274 ,  263 ,  253 ,  243 ,  234 , and  224  and goes out an ACK signal from the Mother&#39;s output  214 .  FIG. 3A  indicates the I-V curve at Daughter&#39;s input  291  when switching on Daughter switches only.  FIG. 3B  indicates the I-V curve at the Mother&#39;s input  293  as switching on Mother switches only. 
     In order to fit nowadays&#39; specification, switch cells should be used in design. However, there is large in-rush current while maintaining ramp-up time. “In-rush current” could compromise the power network integrity. It needs to reduce in-rush current to acceptable one, such that this design could meet specifications. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is to provide a power gating apparatus for in-rush current mitigation, which adopts a delay unit to delay a switch signal, such that the dwell time of the current is controlled for reducing the peak value of the current. 
     Another purpose of this invention is to provide a power gating apparatus for in-rush current mitigation, which controls a front-end switch circuit assembly and a back-end switch circuit assembly to be opened and closed for reducing the rise time of current. 
     Another purpose of this invention is to provide a power gating apparatus for in-rush current mitigation. The controller controls effectively the switch circuit element be opened and closed for stabilizing current. If one of the switch circuit element is broken down, other switch circuit element still keep working. Thus, this invention provides high reliability. 
     To achieved the above-mentioned objective, one embodiment of the present invention provides a power gating apparatus for in-rush current mitigation, including a controller receiving an input power and a switch signal, at least one front-end switch circuit assembly receiving an input current and the switch signal, wherein the input current of the input power passes through the front-end switch circuit assembly, and the switch signal is outputted; wherein a current is inputted into at least one of the front-end switch circuit assembly by the controller according to a target value of an in-rush current of the input power for in-rush current mitigation; a delay unit electrically connected to the front-end switch circuit assembly and receiving the switch signal, wherein the delay unit delays the switch signal to reduce the peak value of the current and outputs the switch signal; and at least a back-end switch circuit assembly electrically connected to the delay unit and receiving the switch signal, wherein the back-end switch circuit assembly maintains a linear relationship between the current and a voltage for outputting the stable current. The invention adopts the delay unit delays the switch signal to control the dwell time of the current and reduce the peak value of the current. However, the quantity of electricity is not be changed. 
     To achieved the above-mentioned objective, one embodiment of the present invention provides a power gating apparatus for in-rush current mitigation, including: a controller receiving an input power and a switch signal; a plurality of switch circuit assemblies, wherein each switch circuit assembly receives an input current and the switch signal, wherein the input current of the input power passes through the switch circuit assembly and the switch signal is outputted; wherein a current is inputted into at least one of the switch circuit assembly by the controller according to a target value of an in-rush current of the input power for in-rush current mitigation; and a delay unit electrically connected to the switch circuit assembly and receiving the switch signal, wherein the delay unit delays the switch signal to reduce the peak value of the current and outputs the switch signal. 
     Other advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, which are set forth by way of illustration and example, to certainly embody the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a diagram showing a circuit for in-rush current mitigation according to the prior art; 
         FIG. 2  is a diagram showing a circuit with Mother/Daughter switch cell according to the prior art; 
         FIGS. 3   a  and  3   b  show an I-V curve according to the prior art; 
         FIG. 4  is a schematic diagram illustrating a power gating apparatus for in-rush current mitigation according to one embodiment of the present invention; 
         FIG. 5  is a schematic diagram illustrating a power gating apparatus for in-rush current mitigation according to one embodiment of the present invention; 
         FIG. 6  is a schematic diagram illustrating a power gating apparatus for in-rush current mitigation according to another embodiment of the present invention; 
         FIG. 7  shows an I-T curve according to one embodiment of the present invention; and 
         FIG. 8  shows an I-T curve according to another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The detailed explanation of the present invention is described as following. The described preferred embodiments are presented for purposes of illustrations and description, and they are not intended to limit the scope of the present invention. 
     The invention discloses a circuit for in-rush current mitigation and reliability enhancement, which minimizes in-rush current while prevent the damage of circuit. 
       FIG. 4  is a schematic diagram illustrating a power gating apparatus for in-rush current mitigation according to one embodiment of the present invention. The front-end switch circuit assembly  41  receives an input power (VDDT) and a switch signal (SleepEn). When the input power inputs the front-end switch circuit assembly  41 , the current of input power goes to the virtual voltage (VDDV) through the front-end switch circuit assembly  41 . Because the front-end switch circuit assembly  41  includes a plurality of switch circuit elements  411 ,  412 , and  413  serially connected, the voltage can be raised to reduce the voltage difference between the input power (VDDT) and the virtual voltage (VDDV). 
     The delay unit  43  is electrically coupled to the front-end switch circuit assembly  41  and receives the switch signal (SleepEn). The delay unit  43  delays the switch signal to reduce the peak value of the current. 
     The back-end switch circuit assembly  42  is electrically coupled to the delay unit  43  and receives the switch signal (SleepEn). The back-end switch circuit assembly  42  maintains a linear relationship between the current and a voltage for outputting the stable current. 
     Accordingly, in one embodiment the front-end switch circuit assembly  41  includes N switch circuit elements  411 ,  412 , and  413  serially connected. The switch circuit elements  411 ,  412 , and  413  are semiconductor devices, and have the characteristics of semiconductor. In addition, the front-end switch circuit assembly  41  has higher resistance with higher input power, and lower resistance with lower input power. 
     The delay unit  43  is a programmable delay unit for controlling dwell time of the current. The back-end switch circuit assembly  42  includes N switch circuit elements  411 ,  412 , and  413  serially connected. The switch circuit elements are semiconductor devices, and have the characteristics of semiconductor. The delay unit  43  controls the time for the switch signal (SleepEn) entering into the semiconductor switch cell and lets the back-end switch circuit assembly  42  run in linear region. When the back-end switch circuit assembly  42  is turned on, the I-V relation of the back-end switch circuit assembly  42  will be located at linear operation region due to low voltage difference between the input power (VDDT) and the virtual voltage (VDDV). 
     Accordingly, the smaller semiconductor switch cell in the back-end switch circuit assembly  42  shunts the current to prevent the damage of circuit by large current and mitigate the impact of the integrated circuit by in-rush current. The delay unit  43  also controls the time for current passing through the front-end switch circuit assembly  41  and the time for opening the back-end switch circuit assembly  42 . 
     In one embodiment, the front-end switch circuit assembly  41 , the delay unit  43  and the back-end switch circuit assembly  42  are metal oxide semiconductor field effect transistors integrated in one chip, or embedded in a system-on-chip. 
     In addition,  FIG. 7  shows an I-T curve according to one embodiment of the present invention. At the same Q value, the delayed current I 1 ′ will be lower than the original current I (difference in X). Therefore the in-rush current can be mitigated. 
       FIG. 5  is a schematic diagram illustrating a power gating apparatus for in-rush current mitigation according to one embodiment of the present invention. A first stage of circuit includes a controller  50  and switch circuit assemblies  511 ,  512 ,  513 . The switch circuit assemblies  511 ,  512 ,  513  are composed by several switch circuit elements  5111 ,  5112 , and  5113 ,  5121 ,  5122 , and  5123 , and  5131 ,  5132 , and  5133  in serial connection electrically. The controller  50  adapts the power supplied to each of the switch circuit assembly in response to the input power according to a target value of an in-rush current of the input power, in order to mitigate in-rush current entering into the switch circuit assembly. Each of switch circuit assembly  511 ,  512 ,  513  receives an input current and the switch signal (SleepEn), so that the current of input power can pass through. 
     Each of switch circuit assembly  511 ,  512 ,  513  has a plurality of switch circuit elements made of PMOS transistors and connected serially electrically. Although 3 switch circuit assemblies are used in this embodiment, in the real life situation they may have more than 3 switch circuit assemblies to solve problem, such that more switch circuit elements in one cell group could happen reasonably. The controller  50  may have more selections with more switch circuit assemblies randomly, which may give higher stability to the present invention. 
     The controller  50  controls the on/off of switch circuit assembly  511 ,  512 ,  513  by receiving the switch signal (SleepEn). When the target current is large, more switch circuit assemblies are turned on to reduce the current entering into the switch circuit assemblies. On the contrary, when the current is low, less switch circuit assemblies are turned on for keeping the stable current. In addition, when 3 switch circuit assemblies  511 ,  512 ,  513  are turned on simultaneously, the current can be raised to a prescribed value quickly, in order to reduce the ramp-up time. In another embodiment, when the switch circuit assembly cannot work properly, the controller  50  will not select the subject switch circuit assembly, in order to keep stable current. 
     The delay unit  53  is coupled to the switch circuit assemblies  511 ,  512 ,  513  and input the switch signal (SleepEn). The delay unit  53  is a programmable delay unit for controlling dwell time of the current. The delay unit  53  delays the switch signal to reduce the peak value of the current by receiving signal  501  transmitted by the controller  50 . 
     Please referring  FIG. 6  is a schematic diagram illustrating a power gating apparatus for in-rush current mitigation according to one embodiment of the present invention. The front-end switch cell includes a controller  60  and front-end switch circuit assemblies  611 ,  612 ,  613 . The switch circuit assemblies  611 ,  612 ,  613  are composed by several switch circuit elements  6111 ,  6112 , and  6113 ,  6121 ,  6122 , and  6123 , and  6131 ,  6132 , and  6133  in serial connection electrically. The controller  60  adapts the power supplied to each of the switch circuit assembly in response to the input power according to a target value of an in-rush current of the input power, in order to mitigate in-rush current entering into the switch circuit assembly. Each of switch circuit assembly  611 ,  612 ,  613  receives an input current, so that the current of input power can pass through. 
     Each of switch circuit assembly  611 ,  612 ,  613  has a plurality of switch circuit elements made of PMOS transistors in serial connection electrically. Although 3 sets of switch circuit assemblies  611 ,  612 ,  613  are used in this embodiment, in the real life situation they may have more switch circuit assemblies or every set has more switch circuit elements. 
     The controller  60  can control the on/off of switch circuit assembly. When the target current is large, more switch circuit assemblies are turned on to reduce the current entering into the switch circuit assemblies. On the contrary, when the current is low, less switch circuit assemblies are turned on for keeping the stable current. 
     The delay unit  63  is coupled to the switch circuit assemblies  611 ,  612 ,  613  and input the current. The delay unit  63  is a programmable delay unit for controlling dwell time of the current to reduce the peak value of the current. The delay unit  63  receives the signal  601  transmitted by the control unit  60  to control the time interval of current passing through. 
     The back-end switch circuit assembly  62  has several switch circuit assemblies  621 ,  622 ,  623  electrically connected to the delay unit  63  for inputting the current. The back-end switch circuit assembly  62  maintains a linear relationship between the current and a voltage for reducing the ramp-up time and outputting the stable current. The back-end switch circuit assembly  62  outputs an ACK signal (confirmed signal)  602  back to the control unit  60 . 
     Each of back-end switch circuit assembly  621 ,  622 ,  623  has a plurality of switch circuit elements made of PMOS transistors in serial connection electrically, and the back-end switch circuit assemblies  621 ,  622 ,  623  are electrically connected in parallel. Although 3 sets of switch circuit assemblies  621 ,  622 ,  623  are used in this embodiment, in the real life situation they may have more switch circuit assemblies or every set has more switch circuit elements. 
     Accordingly, in one embodiment the each of back-end switch circuit assembly  621 ,  622 ,  623  includes N switch circuit elements  6211  to  621 N,  6221  to  622 N,  6231  to  623 N serially connected. The switch circuit elements are semiconductor devices, and have the characteristics of semiconductor. 
     The delay unit  63  is a programmable delay unit for controlling dwell time of the current, in order to control the time interval of current passing through. 
     Accordingly, the front-end switch circuit assembly  611 ,  612 ,  613  and the back-end switch circuit assembly  621 ,  622 ,  623  would turn-on simultaneously to receive the switch signal (SleepEn) for reducing the ramp-up time of the present invention. 
     Please referring  FIG. 8  shows an I-T curve according to one embodiment of the present invention. At the same Q value, the delayed current I 2 ′ will be lower than the original current I (difference in X). Therefore the in-rush current can be mitigated by the present invention. Because 3 sets of front-end switch circuit assemblies  611 ,  612 ,  613  are used in this embodiment, the current can reach the prescribed value quickly. 
     The front-end switch circuit assembly is run in saturation region in the present invention. The delay cell is used to delay the switch signal to control the passing time of current, in order to reduce the peak value of current. Finally, the back-end switch circuit assembly maintains a linear relationship between the current and a voltage for reducing the ramp-up time. They may be integrated in an integrated circuit and finished in a same process. 
     In addition, the control unit controls effectively the switch circuit element been opened and closed for stabilizing current. The quantity of switch circuit assembly should be able to be increased or decreased in accordance with the design of switch circuit element. Thus the best current buffer circuit can be made in accordance with the present invention. If one of the switch circuit assemblies is broken down, other switch circuit assemblies still keep working. Thus, this invention provides high reliability. 
     It is understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of this invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but rather that the claims be construed as encompassing all the features of patentable novelty that reside in the present invention, including all features that would be treated as equivalents thereof by those skilled in the art to which this invention pertains.