Abstract:
An embedded decoupling capacitor wearout monitor for power transmission line, which can be integrated and fabricated in any standard CMOS or BiCMOS circuits. The embedded noise monitor is employed to detect the degraded capacitor and disable it from further operation, which will extend the operation lifetime of the circuit system and prevent subsequent catastrophic failure as a result of hard-breakdown (or capacitor short). In one aspect, the monitor circuit and method detects early degradation signal before catastrophic decoupling capacitor failure and, further can pin-point a degraded decoupling capacitor and disable it, avoiding impact from decoupling capacitor breakdown failure. The monitor circuit and method provides for decoupling capacitor redundancy and includes an embedded and self-diagnostic circuit for functionality and reliability.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to semiconductor circuits generally, and specifically, a system and method for preventing circuit failures in integrated circuits. 
       BACKGROUND 
       [0002]    High-frequency noise in power transmission is detrimental to the operation of a semiconductor circuit. Unfortunately, it is unavoidable due to the external sources of radiation and the nature of semiconductor devices. Besides utilizing a radiation shield for isolating external noise sources, decoupling capacitors have been widely employed to reduce noise or noise transmission over circuit or system power line. By introducing a low impedance path between power transmission line and system ground, decoupling capacitor attenuates high frequency noise in power line. Not only as a discrete component, decoupling capacitor is also integrated into large semiconductor chips. Typically, in a large integrated circuit different function blocks have their own integrated decoupling capacitors to minimize the noise influence over power line. 
         [0003]    As decoupling capacitors are typically biased at full power supply voltage (Vdd) during circuit operation, their reliability or wearout has always been a concern. Particularly, with the introduction of deep-trench decoupling capacitor embedded in the silicon substrate, it is expected that its reliability becomes more critical due to the corners around the trench bottom as the weakest links for dielectric breakdown. 
         [0004]    The wearout of decoupling capacitors is due to the degradation or breakdown of its dielectric materials, including hard-breakdown and soft-breakdown. The hard-breakdown of the capacitor causes electric short and thus results in failure of the whole circuit. Before hard-breakdown, the capacitor dielectric material always has to go through the soft-breakdown regime, which results in gradual increase in leakage current and noise level even though the capacitor still remains functional. The extra noises generated in the soft-breakdown regime spread over a wide frequency range, from a few Hz up to hundred Hz range, for example, as shown in the graph of  FIG. 1  depicting an example plot  10  of l/f noise spectra of gate current  12  both before soft breakdown and gate current  15  after soft breakdown of a 2 nm oxide of the decoupling capacitor. As shown, the noise level increases by 10,000× after soft breakdown that is detectable before catastrophic “hard breakdown”. The increase of the noise caused by dielectric soft-breakdown has been shown in the reference entitled “Ultra-thin gate dielectrics: they break down, but do they fail?” by B. E. Weir et al. on International Electron Devices Meeting, 1997. Technical Digest., 7-10 Dec. 1997 pp: 73-76. 
         [0005]    As illustrated in  FIGS. 2A-2C , it is noted that a fresh decoupling capacitor  25 A effectively removes high-frequency noise signals  27  from the supplied power line  30  leading to semiconductor circuitry  50 ; and, slightly degraded decoupling capacitors  25 B in soft-breakdown regime are still functional in filtering high-frequency noise  27 ′, since the low-frequency noise  28  resulted from soft-breakdown does not impact the semiconductor circuitry  50  significantly (see  FIG. 2B ). However, failed decoupling capacitors (decap), such as decap  25 C that reach hard-breakdown regime cause catastrophic circuit failure of semiconductor circuitry  50  (see  FIG. 2C ) as power signals and high frequency noise  29  are shorted to ground  19  through the decap. 
         [0006]    By measuring power line low frequency noise caused by dielectric soft-breakdown, the decoupling capacitor wearout can be monitored. However, there is no current technique or solution available to accurately sense the noise level in soft-breakdown period of the decoupling capacitor. 
         [0007]    There are some teachings relating to power line noise sensing, such as described in U.S. Pat. No. 7,355,429 entitled “On-chip Power Supply Noise Detector,” U.S. Pat. No. 7,355,435 entitled “On-chip Detection of Power Supply Vulnerability,” U.S. Pat. No. 7,301,320 entitled “On-chip High Frequency Power Supply Noise Sensor,” and U.S. Pat. No. 6,605,929 entitled “Power Supply Noise Sensor.” However, all this prior art teaches measuring the voltage overshoots and/or undershoots, which do not represent the real noises of the power supply line. Hence, they are not suitable as representing wearout information of decoupling capacitors. 
         [0008]    In addition, there are some prior arts related to decoupling capacitors, such as U.S. Pat. No. 7,227,211 entitled “Decoupling Capacitors and Semiconductor Integrated Circuit,” and U.S. Pat. No. 6,011,419 entitled “Decoupling Scheme for Mixed Voltage Integrated Circuits.” Again, none of these references deal with decoupling capacitor reliability or wearout issues. 
         [0009]    It would be highly desirable to provide a system, method and circuit with ability to detect early signals before catastrophic capacitor failure, to pin-point worn-out capacitor(s) and to disable it(them), and avoiding impact from capacitor breakdown failure. 
         [0010]    It would be further highly desirable to provide a system, method and circuit that provides for decoupling capacitor redundancy. 
       SUMMARY 
       [0011]    There is provided a system and method for detecting the soft-breakdown of a decoupling capacitor before catastrophic capacitor failure. The system and method enables pin-point determining of worn-out capacitor(s) and to disable it (them), and avoiding impact from decoupling capacitor breakdown failure. 
         [0012]    Thus, in one aspect, an embedded decoupling capacitor wearout monitor is provided for power transmission line of a semiconductor integrated circuit. The embedded noise monitor is employed to detect the degraded capacitor and disable it from further operation, which will extend the operation lifetime of the circuit system and prevent subsequent catastrophic failure as a result of hard-breakdown (or capacitor short). 
         [0013]    There is further provided an on-chip or embedded decoupling capacitor wearout monitor circuit that implements a self-diagnostic method, to find the degraded decoupling capacitor and prevent it from causing further catastrophic damages on the operating system or other circuitry. 
         [0014]    In one aspect, there is provided a decoupling capacitor (decap) wearout monitor for an integrated circuit (IC) device having a power transmission line supplying power to IC semiconductor circuits. The monitor comprises: a plurality of decoupling capacitors (decaps) embedded within the IC, each individual decap adapted to connect to the power transmission line in parallel with the circuits at a respective first terminal; a switch device responsive to a first control signal for selecting a target decap of the plurality for connection to the power transmission line and to couple noise signals present at the target decap to a noise monitor circuit embedded within the IC, the noise monitor circuit comprising: a noise sensor for generating from noise signals received from the target decap a corresponding constant voltage level signal; and, a comparator device for comparing the constant voltage level signal with a determined threshold voltage level, and generating an output signal when a noise signal level exceeds the determined threshold voltage level; and, a control device embedded within the IC, responsive to the output signal for generating a second control signal to disconnect the target decoupling capacitor from the parallel circuit connection; and, further generating a further first control signal to connect a second target decoupling capacitor of the plurality in parallel with the circuits. 
         [0015]    Further to aspect, there is provided a method for power line noise monitoring for an integrated circuit (IC) device having a power transmission line supplying power to IC semiconductor circuits. The method comprises: a) operably connecting, via a switch device responsive to a first control signal, a first target decoupling capacitor (decap) of a plurality of decoupling capacitors (decaps), embedded within the IC, to the power transmission line at a first terminal in a configuration parallel with the semiconductor circuits; b) continuously coupling noise signals present at the connected first target decap to a noise sensor embedded within the IC; c) generating, from noise signals coupled to the noise sensor, a corresponding constant voltage level signal; d) comparing, at a comparator device, the constant voltage level signal with a determined threshold voltage level; e) generating an output signal indicating a noise signal level exceeding the determined threshold voltage level; and, f) generating, at a control device embedded within the IC, responsive to the output signal, a second control signal for receipt by the switch device and operative to disconnect the first target decap from the parallel circuit configuration; and, further generating a first control signal to and switch device adapted to connect a second target decoupling capacitor of the plurality in a circuit configuration in parallel with the semiconductor circuits. 
         [0016]    Further to this aspect, the method for power line noise monitoring further includes successive repeating steps b)-f) for the second target decap and for each further target decaps of the plurality of decaps thereafter. 
         [0017]    In a further embodiment, there is provided a decoupling capacitor wearout monitor for an integrated circuit (IC) device having a power transmission line supplying power to one or more IC semiconductor circuit blocks. The monitor comprises: a decoupling capacitor(s) (decap(s)) embedded within the IC in association with a respective semiconductor circuit block(s), a respective decap having a first terminal for connection to the power transmission line in parallel with a respective semiconductor circuit block. That is, each CKT_i i  is in parallel with a respective decap. A switch device is associated with each respective decap and connected at a respective second decap terminal thereof, each switch device responsive to a first control signal to initially couple each respective decap in parallel with its the individual semiconductor circuit block for simultaneous parallel operation, and simultaneously couple low frequency noise signals present at the decap to a noise monitor circuit embedded within the IC, the noise monitor circuit comprising: a noise sensor for generating from noise signals received from the target decap a corresponding constant voltage level signal; and, a comparator device for comparing the constant voltage level signal with a determined threshold voltage level, and generating an output signal when a noise signal level exceeds the determined threshold voltage level; and, a control device embedded within the IC, responsive to the output signal for determining a first target decap providing a source of the noise signal that exceeds the determined threshold voltage level, and, generating a second control signal for receipt by the associated switch device of the first target decap, to disconnect the first target decoupling capacitor from its associated individual semiconductor circuit block, while remaining decaps remain connected to their the respective individual semiconductor circuit blocks for continued parallel operation. 
         [0018]    According to this further embodiment, there is provided a method for power line noise monitoring for an integrated circuit (IC) device having a power transmission line supplying power to IC semiconductor circuits. The method comprises: a) operably connecting, via a switch device responsive to a first control signal, a respective decoupling capacitor (decap) embedded within the IC to a respective one or more the semiconductor circuits at a first decap terminal for simultaneous parallel circuit operation; b) continuously coupling noise signals present at a second terminal of each respective the connected decap to a noise sensor embedded within the IC; c) generating, from noise signals coupled to the noise sensor, a corresponding constant voltage level signal; d) comparing, at a comparator device, the constant voltage level signal with a determined threshold voltage level; e) generating an output signal indicating a noise signal level exceeding the determined threshold voltage level; and, f) determining, at a controller device embedded within the IC, in response to a generated output signal, a target decap of the plurality that provides a source of the noise signal that exceeds the determined threshold voltage level; and, g) generating a second control signal for receipt at the switch and operative to decouple the target decap from the parallel circuit configuration while remaining decaps remain connected to their the respective individual semiconductor circuit blocks for continued parallel operation. 
         [0019]    Further to this aspect, the method for power line noise monitoring includes successively iterating steps b)-g) to determine, at each iteration, a target decap to disconnect from its corresponding semiconductor circuit block, while remaining circuit blocks connected in circuit to its respective corresponding decap for continued parallel operation. 
         [0020]    Advantageously, embedded semiconductor circuits sensitive to noisy power source can be disabled early on at the occurrence of degradation in the corresponding decoupling capacitors. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0021]    Other aspects, features and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which similar elements are given similar reference numerals. 
           [0022]      FIG. 1  illustrates an example plot  10  of l/f noise spectra of gate current  12  both before soft breakdown and after soft breakdown of a 2 nm oxide of the decoupling capacitor according to prior art; 
           [0023]      FIGS. 2A-2C  illustrate example plots depicting conceptually operation of decoupling capacitor (decap) when fresh ( FIG. 2A ), when slightly degraded ( FIG. 2B ) and when failed ( FIG. 2C ) in accordance with one embodiment; 
           [0024]      FIG. 3  illustrates the de-cap noise monitor  100  that is functionally situated in parallel with circuits  50  and a decap  101  to be monitored in accordance with one embodiment; 
           [0025]      FIG. 4  illustrates a circuit schematic of an FET-device based active resistor implementation of band pass filter in accordance with one embodiment; 
           [0026]      FIG. 5  depicts a block diagram schematic of the Noise Sensing Unit, wherein the noise from the decoupling capacitor  101  is coupled to from band pass filter element according to one embodiment; 
           [0027]      FIG. 6  illustrates an example circuit schematic of the Noise Effective Detector (NED) according to one embodiment that receives the amplified noise signals from op amp according to one embodiment; 
           [0028]      FIG. 7  depicts an embedded wearout monitor  100 ′ for power line decoupling capacitors including noise monitor and diagnostic circuits according to one embodiment; 
           [0029]      FIG. 8  depicts a flowchart illustrating an exemplary control method  300  implementing, in one embodiment, a diagnostic method for: (1) sensing of decoupling capacitor degradation; and (2) extending circuit lifetime by decoupling capacitor redundancy for the embodiment illustrated in  FIG. 7 ; 
           [0030]      FIG. 9  depicts an embedded wearout monitor  100 ″ for power line decoupling capacitors including noise monitor and diagnostic circuits according to a further embodiment; and, 
           [0031]      FIG. 10  depicts a flowchart illustrating an exemplary control method  300 ′ implementing, in one embodiment, a diagnostic method for extending circuit lifetime by decoupling capacitor redundancy for the embodiment illustrated in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIG. 3  illustrates the general circuit block diagram of the invention comprising an embedded wearout monitor  100  for power line decoupling capacitors (“de-cap”), such as the de-cap  101  connecting a power transmission line  104 , e.g., having a voltage Vdd power source, for instance, to ground and utilized for protecting circuits  50  receiving power via said power transmission line. According to one aspect, as shown in  FIG. 3 , the de-cap noise monitor  100  is integrated and fabricated using any standard CMOS or BiCMOS circuitry using conventional lithography and semiconductor processing steps, and, is functionally situated in parallel with circuits  50  and the de-cap  101  to be monitored. In one embodiment, de-cap noise monitor  100  includes a band pass filter element or circuit element  105  and, a Noise Sensing Unit (NSU)  115 , situated in parallel. 
         [0033]    The Band pass Filter  105  is configured to pass a low frequency noise signal of interest and filter out the high frequency noise which is not generated by  101 , and noise sensing unit  115  accurately monitors low-frequency noise in the transmission line  104  due to the aging of decoupling capacitor  101 . 
         [0034]    More particularly, the RC Band pass Filter  105  is designed to: (1) filter out DC component from the power line  104 ; (2) allow low frequency noise generated by a slightly degraded decoupling capacitor to enter Noise Sensing Unit ( 115 ); and (3) to filter out the high-frequency ripple from operating circuitry (such as switching circuits). Therefore, signals of only a range of frequency (e.g., from 100 Hz to 10K Hz) is allowed to pass through the Band pass Filter ( 105 ) into the Noise Sensing Unit ( 115 ). In order to implement such band pass filter into the integrated circuit, the associated resistance should be large, e.g., as high as about 100 Mohms, making it not feasible to use passive resistor. Therefore, FET-based active resistors are implemented in this filter to ensure such large resistance. 
         [0035]      FIG. 4  depicts a circuit schematic of an FET-device based active resistor implementation of band pass filter  105 . In  FIG. 4 , FET device  201  (e.g., NFET N 0 ) is a primary magnifying NFET device which is configured to operate under saturation mode for large gain. C 1  and C 2  are the capacitors in the filter, and in one embodiment, are at about 10 pF capacitance each. FET device  205  (e.g., PFET P 1 ) and FET device  207  (e.g., NFET N 1 ) form a gate bias voltage for FET N 0    201 . The input resistance of N 0 , the source-drain resistances of PFET P 1   205  and NFET N 1   207  are all in parallel which together form the high pass filter with capacitor C 1 . The gate leakage current of N o  is in the order of pA (picoampere), so that the filters equivalent resistance is on the order of 10 Gohms (10 giga ohms). The resistors R 1 , R 2  and R 3  in band pass filter  105  provide the gate voltages for FETs P 1   205  and N 1   207 , and the resistances of the three resistors (R 1 , R 2  and R 3 ) are tuned to make both P 1   205  and N 1   207  operate under accumulation mode. In such situation, the drain currents of P 1  and N 1  are in the order of nano amperes (nA), and the equivalent resistances are on the order of 1 Gohms (1 giga ohms). Therefore the total resistance of the high pass filter can reach as high as about 100 Mohms. For the low pass filter, the resistor is a FET  210  (e.g., NFET N 2 ) which has the drain and gate connected together so that it operates under saturation mode, e.g., with an equivalent resistance of about 1 Mohms. 
         [0036]    Referring back to  FIG. 3 , the Band pass Filter element  105  situated in parallel between the power signal transmission line  104  and Noise Sensing Unit  115  screens out the unwanted signals and allows the filtered signal (low-frequency noise) component  150 , representing the flicker noise of the decoupling capacitor, to pass through to the input of the Noise Sensing Unit  115 . 
         [0037]      FIG. 5  depicts a block diagram schematic of the Noise Sensing Unit  115 , wherein the noise from the decoupling capacitor  101  shown in  FIG. 3  is coupled to band pass filter element  105 . The Noise Sensing Unit  115  particularly monitors low-frequency noise signals (e.g., at frequency ranging from 100 Hz-10K Hz). That is, in one embodiment, referring to  FIG. 5 , Noise Sensing Unit  115  includes an operational amplifier (op amp) element  127  having a single terminal for receiving input filtered noise from the Band pass Filter element  105 , and, having a second terminal for receiving a reference voltage through resistor  123 . In one embodiment, this resistor  123  receives a reference voltage Vb, that in one embodiment, is about Vdd/2 (where Vdd is the power source voltage that ranges, as an example but not limited to, between 0.5V and 5V), which makes the voltage across output coupling capacitor C 2  (from band pass filter  105 ) much less than Vdd for longer operation. In one embodiment, the Bandgap Voltage reference Vb  131  is a stable voltage source to the OP Amp ( 107 ) and there are various other ways to supply a stable voltage to the circuit. 
         [0038]    The output of the op amp element  127  is input to a Noise Effective Detector  130  which detects a noise level. The detector output signal  135  of Noise Effective Detector  130  is input to a first terminal of a comparator device  139  (which may be an operational amplifier configured as a comparator). A determined threshold voltage V th    141  is generated and applied to a second terminal of comparator device  139 . The output signal  145  of comparator device  139  is a logic signal, either logic “1” of logic “0” dependent upon the noise level detected by the Noise Effective Detector  130  as compared to the reference voltage V th . This logic level output signal  145  is input to a noise monitor controller device  146  and is associated with the monitored decap C i . 
         [0039]    More particularly, in view of  FIG. 5 , after coupling the filtered noise to the Noise Sensing Unit  115 , the operational amplifier (op amp)  127  amplifies the noise to a certain voltage level for the Noise Effective Detector (NED)  130 . NED  130  senses the amplified noise and outputs a range of DC voltages  135  for comparison with the Vth signal  141 . In one embodiment, the Vth signal  141  is a pre-defined threshold voltage level, which, in one embodiment, represents the threshold noise level. This could be supplied by various ways, such as a regular voltage source which can be tuned in circuit to meet the exact application requirement. The preferred range of values are few hundreds milli-volts to half (½×) of the supply voltage for the Comparator  139 . 
         [0040]    For each decap C i  if the detected noise level is higher than the Vth value, the comparator  139  outputs a logic level “1” signal, in one embodiment, to the Noise Monitor Controller circuit  146  which indicates a defective de-cap and instructs removal of the targeted decoupling capacitor(s)  101  shown in  FIG. 3  from the circuit. In one embodiment, as will be described in greater detail below, removal of the targeted decoupling capacitor(s)  101  from the circuit is accomplished by a switch, such as MOSFET, e-fuse, MEMS switches, etc., in order to reduce the noise generated by this decoupling capacitor. If the sensed noise level is lower than the Vth, the comparator device  139  outputs “0” so that the targeted decoupling capacitor(s) C i  stays on (i.e., is (are) not removed). 
         [0041]      FIG. 6  illustrates an example circuit schematic of the Noise Effective Detector (NED)  130  according to one embodiment that receives the amplified noise signals from op amp  127 . NED  130  includes an amplifier, e.g., a transistor. In one embodiment, the amplifier is embodied as a Bipolar Junction Transistor  160 ; however, other high impedance, high gain amplifier configurations could be used, e.g., a MOSFET transistor. In one embodiment, Bipolar Junction Transistor  160  is configured as a common-emitter amplifier, and having added resistors Rb (base resistor) and Re (emitter resistor). Collector terminal of BJT transistor  160  is tied to another power voltage source, Vcc in the embodiment shown, although it is understood that this may be Vdd (same voltage source). 
         [0042]    In one aspect, the Noise Effective Detector ( 130 ) of  FIGS. 5 and 6  is based on the concept of “pseudo-peak detector” that translates an AC noise signal to a DC voltage level. In one embodiment, the corresponding output DC voltage level is a fraction of the peak of the input AC signal. In one embodiment, the corresponding DC voltage level is about three quarters (¾) of the peak value of the AC noise when monitoring the noise level. 
         [0043]    Operating in a common-emitter amplifier configuration, transistor  160  receives the input from the output of the op amp ( 127 ) and rectifies the signal and passes the signal as an output of a filter  170 , shown in  FIG. 6  that includes filter elements C 1 -R 1 -C 2 . In one embodiment, the resistors Rb and Re set the bipolar transistor Q in a non linear mode for the rectification, the C 1 -R 1 -C 2  filter are of values designed to sense certain levels of voltages, such as three quarters (¾) and a quarter (¼) of the normal (e.g., peak) output of the common-emitter amplifier when configured without filter device. 
         [0044]    A further embodiment of the embedded wearout monitor  100 ′ for power line decoupling capacitors including noise monitor and diagnostic circuits is shown in  FIG. 7 . In the embodiment of  FIG. 7 , each decoupling capacitor (de-caps)  101   1 ,  101   2 ,  101   3 , . . . ,  101   i  is shown connected at one terminal to the power supply transmission line  104  and in parallel with a respective individual semiconductor circuit, e.g.  50   1 ,  50   2 ,  50   3 , . . . ,  50   i  intended to be protected. That is, each of the several decoupling capacitors  101   1 ,  101   2 ,  101   3 , . . . ,  101   i  are coupled, at one end, to the power transmission line  104  in parallel with a respective corresponding individual semiconductor circuit, e.g.  50   1 ,  50   2 ,  50   3 , . . . ,  50   i . At the other end of each de-cap  101   1 ,  101   2 ,  101   3 , . . . ,  101   i  there is connected a respective switch device, e.g., devices  108   1 ,  108   2 ,  108   3 , . . . ,  108   i , that is programmed, in response to control signals, to either couple the respective de-cap in or out of circuit, i.e., switch a decap  101 , to/from the power transmission line  104 , thereby configuring the decap either in parallel with its respective circuit  50   i  or, decouple the respective de-cap  101   i  from the power transmission line  104 , thereby eliminating the decap from its parallel circuit connection with its respective circuit  50   i . That is, the path to each decoupling capacitor  101   1 ,  101   2 ,  101   3 , . . .  101   i  is controlled by a respective switching devices  108   1 ,  108   2 ,  108   3 , . . . ,  108   i , such as large size pMOSFET device, a MEMS switch device (i.e., a “Micro-Electro-Mechanical System” that includes one or more miniaturized mechanical switch structures integrated in the semiconductor chip), or e-fuse devices, and the like. 
         [0045]    In one embodiment, a large size pMOSFET provides smaller turn-on impedance, compared with the impedance of the corresponding decoupling capacitors  101 , so the turn-on impedance of pMOSFET can be ignored in the circuit. Therefore, the size of pMOSFET is determined by the impedance of the corresponding decoupling capacitor. It is understood that an nMOSFET may also be used for this purpose. 
         [0046]    In the example embodiment depicted in  FIG. 7 , using pMOSFET devices as respective switches  108   1 ,  108   2 ,  108   3 , . . . , ,  108   i , for example, each decap is connected or disconnected to an electrical ground  19  by appropriately biasing a gate  119  of the switch, e.g., a pMOSFET device, with a voltage appropriate to turn on or turn off switching devices  108   1 ,  108   2 ,  108   3 , . . . ,  108   i . For example, decoupling capacitor is coupled to the system  100  by biasing the gate of the pMOSFET device to ground (GND) voltage  19 , and is decoupled by biasing the gate to power line voltage (Vdd) to switch off pMOSFET device. As shown in  FIG. 7 , each respective switch  108   1 ,  108   2 ,  108   3 , . . . ,  108   i  is controlled by a respective gate control signal  119   1 ,  119   2 ,  119   3 , . . . ,  119   i  that is provided by address selector circuit  225  in accordance with control signals generated as a result of executing logic in Noise Monitor Controller circuit  146 . 
         [0047]    For example, in one embodiment, each pMOSFET gate represented by elements  108   1 ,  108   2 ,  108   3 , . . . ,  108   i  is controlled by the Noise Monitor Controller  146  through the address Selector  225 . The power line noise is measured by the Noise Sensing Unit  115  through Band pass Filter  105 , and its output value is sent to the Noise Monitor Controller  146  for switching control. In particular, referring to  FIG. 5 , the logic value signal “0” or “1” output of the comparator element  139  is received by Noise Monitor Controller  146  for controlling the switching of a respective gate of an element  108   1 ,  108   2 ,  108   3 , . . . ,  108   i  to de-couple or remove the corresponding decap C i . That is, for a respective de-cap  101   1 ,  101   2 ,  101   3 , . . . ,  101   i , as a result of the processing in band pass filter and noise sensing units, either a logic value signal “0” or “1” is output of the comparator. Responsive to the receipt of comparator output signal logic value signal “0” or “1” Noise Monitor Controller  146  implements logic for triggering generation of a respective switch signal  119   1 ,  119   2 ,  119   3 , . . . ,  119   i  for respectively controlling the gate of a respective switch element  108   1 ,  108   2 ,  108   3 , . . . ,  108   i  to either bias the de-cap off or let it remain functioning in the chip. 
         [0048]    In particular, Noise Monitor Controller  146  (such as a configured shift register, decoder or micro-controller element) implements a control method for respectively controlling the respective switch element  108   1 ,  108   2 ,  108   3 , . . . ,  108   i . The selector  225  knows what switch to disable based on the index C i , or simply the address corresponding to each capacitor stored in the controller. 
         [0049]      FIG. 8  depicts a flowchart illustrating an exemplary method of self-diagnosis and a control method  300 , implemented by the noise measurement circuit and effected by decoupling capacitors switches. That is,  FIG. 8  depicts, in one embodiment, a diagnostic method for: (1) sensing of decoupling capacitor degradation; and (2) extending circuit lifetime by decoupling capacitor redundancy for the embodiment illustrated in  FIG. 7 . 
         [0050]    The diagnostic method  300  to determine and de-couple worn-out decoupling capacitors is now shown in  FIG. 8 . In this method, every circuit (CKT) block “i” on the chip has its own corresponding decoupling capacitor (C i ). In the embodiment shown in  FIG. 7 , all C i &#39;s are initially connected to their corresponding CKT block by default for simultaneous parallel operation. When the low frequency noise detected exceeds the threshold, every C i  is sequentially monitored by the disclosed circuit and method for early sign of degradation in each C i . Once early degradation is detected, the C i  is disabled (by opening the corresponding switch) and a warning signal sent before catastrophic failure. 
         [0051]    In  FIG. 8 , at  301 , the embedded wearout monitor circuit and system  100 ′ is turned on. Initially, each of the respective switch element  108   1 ,  108   2 ,  108   3 , . . . ,  108   i  are activated or turned “on” to respectively simultaneously connect each decap/circuit combination to the noise monitoring circuitry of the embedded wearout monitor system  100 ′. As the method includes continuously monitoring a power line noise level, Q_noise, then, at  305 , a first noise level of power transmission line  104  is measured and the value is stored as a noise level Q_criteria. That is, Q_criteria is obtained as the initial noise level of a fresh circuit (or system) when the circuit (or system) is powered on for the first time. Then, at  307 , the Q_noise is constantly monitored (measured) by filter  105 /noise sensing unit  115  statically once the system is powered on. Programmed logic initializes an index i, corresponding to monitored decap C i , where initially, index i=1. Then, at  310 , the monitored Q_noise level of transmission line is compared against the stored threshold value, Q_criteria, representing the maximum noise level that can be permitted during normal operation of the system. If, at  310 , it is determined that the measured Q_noise is less than or equal to the Q_criteria, no action is needed, and the method returns to  307  where the noise monitor continues monitoring the power line noise level and performs the threshold comparison made at  310 . In one aspect, the monitored noise level (Q_noise) is integrated over a preset time. 
         [0052]    If at  310 , it is determined that the measured Q_noise is greater than the Q_criteria, then at  312 , the decoupling capacitor C i  is disconnected from the system  100 ′. That is, if, at  310 , the measured noise Q_noise value is greater than the criteria noise level Q_criteria, the decoupling diagnostic operation is triggered and starts to function. 
         [0053]    For the embodiment of  FIG. 7 , where the integrated circuit is manufactured with more than one (plural) decoupling capacitors  101   1 ,  101   2 ,  101   3 , . . . ,  101   i  protecting circuitry coupled to the power transmission line in parallel, the diagnostic circuit turns off the decoupling capacitors C i  one by one while continually monitoring the power line noise sequentially. That is, in one aspect, for the decap C i  being diagnosed, in response to the measured Q_noise being greater than the Q_criteria, the system turns off the individual decoupling capacitor C i  by controlling a gate of the corresponding switch element  108 , by selector  225  operating under control of noise controller circuit  146 . In one embodiment, the first C 1  is turned off. 
         [0054]    Then, with C i  decap decoupled from the system, at  315 , a determination is again made whether the measured noise level Q_noise is greater than the determined threshold noise level Q_criteria. If at  315  the measured Q_noise level is determined not greater than the determined threshold noise level Q_criteria, the method returns to step  307  where the remaining decap noise level as passed through the bandpass filter element is again continuously monitored. That is, when Q_noise&lt;Q_criteria, there is no need to repeat “power on”, as the system keeps monitoring the noise level. 
         [0055]    Otherwise, if at  315 , after disconnecting decoupling capacitor C i , it is determined that the measured Q_noise level is now greater than the determined threshold noise level Q_criteria, the process proceeds to step  320  where the decoupling capacitor C i  is connected back in circuit. That is, after switching off decap C i  at  312 , if, at  315 , it is determined that the Q_noise is now less than the Q_criteria, it is determined that the extra noise is from C i . Consequently, the control circuit then disables C i  and generates a warning signal. If, at  315 , it is determined that Q_noise remains the same (i.e., greater than Q_criteria) after C i  is disconnected, then at  320 , C i  will be turned back on and the diagnostic procedure will continue to  325 , where a determination is made as to whether the C i  is the last decap being processed. If it is determined that the C i  is not the last decap in the chip, the decap index “i” is incremented (e.g., i=i+1) and the next decap C i+1  is monitored by returning to step  307 . Furthermore, in one embodiment, if at  315 , Q_noise increases slightly after C i  is switched off but still stays lower than Q_criteria, C i  will be kept off and the diagnostic procedure will proceed to the next capacitor where logic implemented at steps  307 ,  310 ,  312 ,  315 ,  320   325  are repeated for all C i . If all the decoupling capacitors have been checked and the noise level is still higher than the noise criteria level, the diagnostic procedure will generate an external signal for warning circuit (or system) failure at  329 . 
         [0056]    Thus, in methodology  300  shown in  FIG. 8 , steps  307  to  325  are performed continuously throughout the lifetime of the chip, under control of the noise monitor controller  146  until such time as the last decap is processed, where, in response to the last decap being processed, the noise control monitor will generate an external warning signal indicating which decap(s) C i  have been the cause of the noise exceeding the determined threshold noise level Q_criteria. 
         [0057]    A further embodiment of the embedded wearout monitor  100 ″ for power line decoupling capacitors including noise monitor and diagnostic circuits is shown in  FIG. 9 . In this embodiment, there is configured multiple decaps for at least one CKT block for redundancy. Only one decap C i  is initially connected via a respective switch to the CKT block by default. The connected C i  is continuously monitored by the disclosed circuit and method for early sign of degradation. Once early degradation is detected, the degraded C i  is disconnected and the next C i  is connected for redundancy. 
         [0058]    As shown in the embodiment of  FIG. 9 , decoupling capacitors de-caps  101   1 ,  101   2 ,  101   3 , . . . ,  101   i  are shown connected to power transmission line  104  in parallel with semiconductor circuitry  50  intended to be protected. Each of the several decoupling capacitors  101   1 ,  101   2 ,  101   3 , . . . ,  101   i  are coupled, at one end, to voltage power source Vdd at power transmission line  104 . At the other end of each de-cap  101   1 ,  101   2 ,  101   3 , . . . ,  101   i  there is connected a respective switch device, e.g., devices  108   1 ,  108   2 ,  108   3 , . . . ,  108   i , that connects or disconnects the respective de-cap to electrical ground  19 . Using pMOSFET devices as respective switches  108   1 ,  108   2 ,  108   3 , . . . ,  108   i , for example, a decoupling capacitor is turned on (i.e., coupled) by biasing the gate of the pMOSFET switch element to ground (GND) voltage  19 , and is switched off (i.e., decoupled) by biasing the gate of the pMOSFET switch element to power line voltage (Vdd). 
         [0059]      FIG. 10  depicts a flowchart illustrating a further method of self-diagnosis and a control method  300 ′, implemented by the noise measurement circuit and effected by decoupling capacitors switches. That is,  FIG. 10  depicts, in an alternate embodiment, a diagnostic method for: (1) sensing of decoupling capacitor degradation; and (2) extending circuit lifetime by decoupling capacitor redundancy for the embodiment illustrated in  FIG. 9 . 
         [0060]    The diagnostic method  300 ′ to determine and de-couple worn-out decoupling capacitors shown in  FIG. 10  include steps  302 ,  306 ,  308  and  311  that correspond exactly to the steps  301 ,  305 ,  307  and  310  of the methodology depicted in  FIG. 8 . The only difference is that, in this embodiment, a single decap C i  at a time is coupled in circuit at a time to provide protection for circuit  50 . Thus, at  302 , the embedded wearout monitor  100 ″ circuit and system is turned on. Initially, only one of the respective switch elements  108   1 ,  108   2 ,  108   3 , . . . ,  108   i  are activated or turned “on” to couple a single de-cap C i  (e.g.,  101   1 ,  101   2 ,  101   3 , . . . ,  101   i ) being diagnosed, to the noise monitoring circuitry of the embedded wearout monitor  100 ″ system. For example, in  FIG. 9 , switch  108   1  has coupled a first decap, e.g., decap  101   1 , to the noise monitor. As the method includes continuously monitoring a power line noise level, Q_noise, then, at  306 , a first noise level of power transmission line  104  is measured and the value is stored as a noise level Q_criteria. That is, Q_criteria is obtained as the initial noise level of a fresh circuit (or system) when the circuit (or system) is powered on for the first time. Then, at  308 , the Q_noise is continuously monitored (measured) by filter  105 /noise sensing unit  115  statically once the system is powered on. Programmed logic implemented the method of  FIG. 10 , has set an index i=1, where index i=1 represents the initial coupled decap C 1 . At  311 , the monitored Q_noise level is compared against the obtained threshold value, Q_criteria, representing the maximum noise level than can be permitted during normal operation of the system. If, at  311 , it is determined that the measured Q_noise is less than the Q_criteria, no action is needed, and the method returns to  308  where the noise monitor continues monitoring the power line noise level and performs the threshold level comparison at  311 . In one aspect, the monitored noise level (Q_noise) is integrated over a preset time. 
         [0061]    If at  311 , it is determined that the measured Q_noise is greater than the Q_criteria, then at  313 , this indicates that the first decap C i  (e.g., i=1) being diagnosed is the potential source of the noise (indicating potential decap wear) and, at  313 , the decoupling capacitor C i  is disconnected from the system  100 ″ at  313 . Thus, for the actual de-cap C i  being diagnosed, in response to the measured Q_noise being greater than the Q_criteria, in one embodiment, the system turns off the individual decoupling capacitor C i  by controlling a gate of the corresponding switch element  108   i  (e.g., i=1) by selector  225  operating under control of noise controller circuit  146  receiving indication for the monitored C i . 
         [0062]    Continuing, in the embodiment of  FIG. 10 , where the integrated circuit is manufactured with more than one (plural) embedded decoupling capacitors  101   1 ,  101   2 ,  101   3 , . . . ,  101   i  protecting semiconductor circuitry  50 , in addition to decoupling the diagnosed decoupling capacitor C i  (i=1) at  313  when the measured Q_noise is greater than the Q_criteria, the system further initiates coupling a next second decap C i  (i=i+1), e.g., C 2 , to the system  100 ″. Then the process continues to  316  where again the level of monitored power line noise is compared to the Q_criteria threshold. At  316 , if the measured Q_noise is not greater than the Q_criteria, the process returns to  308  and  311  where the Q_noise is continually monitored until such time as the measured Q_noise again becomes greater than the Q_criteria, when, at  313 , the next redundant actual de-cap C i  (e.g., i=2) being diagnosed is turned off by controlling a gate of the corresponding switch element  108 , by selector  225  operating under control of noise controller circuit  146 . In addition to decoupling the diagnosed decoupling capacitor C i  (i=2) at  313  when the measured Q_noise is greater than the Q_criteria, the system initiates coupling a next decap C i  (i=1+1), e.g., decap C 3 , to the system  100 ″ before proceeding to  316  where again the level of monitored power line noise is compared to the Q_criteria threshold. 
         [0063]    At  316 , after decap C i  is switched off and next redundant decap C i+1  is switched on, if it is determined that Q_noise is less than Q_criteria, the diagnostic procedure will repeat steps  308 ,  311 ,  313  and continue monitoring the noise level of the next coupled decap C i+1  until such time as Q_noise is greater than Q_criteria. Otherwise, at  316 , if determined that Q_noise is greater than Q_criteria, the process proceeds to  326  where a determination is made as to whether the last decap has been processed. If the last decap has not been processed, the process proceeds back to  308  where the decap noise level is again continuously monitored at steps  308 ,  311 ,  313 . 
         [0064]    Thus, in methodology  300 ′ shown in  FIG. 10 , steps  308  to  326  are performed continuously throughout the lifetime of the chip, under control of the noise monitor controller  146  until such time as the last decap is processed, where, at  330 , in response to the last decap being processed, the noise control monitor will generate an external warning signal indicating which or all decap(s) C_i have been the cause of the noise exceeding the determined threshold noise level Q_criteria. For example, if all the decoupling capacitors have been checked and the noise level is still higher than the criteria level, the diagnostic procedure will generate at  330  an external signal for warning circuit (or system) failure. 
         [0065]    Although a few examples of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes might be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.