Abstract:
A circuit that detects the power supply voltage requirement of each voltage domain in an IC includes 1) a ring oscillator in each voltage domain, and 2) a power module. Two different circuit implementations of the power module may provide a precise reference voltage to on-chip voltage regulators (LDO or DC-DC switching buck converter). The power module supports DVFS and can provide the desired power supply voltage for advanced CMOS technology nodes (45 nm and beyond) in less than 100 ns. The voltage detection circuit clamps the voltage to the desired level to address power supply voltage variations due to PVT and ageing. The proposed technique has minimal power and area overhead to compensate for the power supply voltage variation, thus reducing power supply voltage margins which yields higher power saving.

Description:
BACKGROUND 
       [0001]    Nanoscale technologies, similar to other technologies, face challenges in high power consumption and signal delay due to global interconnects, but due to their scope, addressing these challenges opens new areas of research. One research area is through silicon via (TSV) based 3D integrated chip (IC) technology, where each layer or stratum is fabricated separately and subsequently vertically integrated. With 3D ICs, the fabrication of disparate strata and the final system integration may be completed in separate manufacturing facilities, allowing for greater efficiency and the possibility of modular layers. The packaging manufacturer performing the final bonding, thus, may not necessarily need each layer&#39;s technology-dependent parameters such as voltage levels and frequency of operation to assemble the 3D IC. This transparency-to-technology information allows for off-the-shelf integration where dies from different foundries are bonded together by the packaging manufacturer to form a heterogeneous 3D IC. 
         [0002]    A semiconductor device scaling has exacerbated fundamental problems with CMOS technology like parametric variation and device aging. The most significant ill effect of these problems is seen through power supply voltage variation. Conventional microprocessor designs compensate for the worst case power supply voltage variation by introducing voltage guard bands which leads to a significant overhead on the total power consumption of the IC. In-situ aging sensors are deployed on microprocessors to automate the effects of circuit aging. However, a run-time aging detection and correction technique which can be used in tandem with on-chip voltage regulators is missing. 
       SUMMARY OF THE INVENTION 
       [0003]    A circuit that detects the power supply voltage requirement of each voltage domain in an IC includes 1) a ring oscillator in each voltage domain, and 2) a power module. Two different circuit implementations of the power module may provide a precise reference voltage to on-chip voltage regulators (LDO or DC-DC switching buck converter). The power module supports DVFS and can provide the desired power supply voltage for advanced CMOS technology nodes (45 nm and beyond) in less than 100 ns. The voltage detection circuit clamps the voltage to the desired level to address power supply voltage variations due to PVT and ageing. The proposed technique has minimal power and area overhead to compensate for the power supply voltage variation, thus reducing power supply voltage margins which yields higher power saving. 
         [0004]    The proposed circuit technique has another application for 3-D heterogeneous ICs. The 3-D IC may include RF, analog, micro/nano-electromechanical systems (MEMS/NEMS) as well as emerging technologies such as nano-FET and graphene-based device planes. The design and fabrication of these disparate device planes may take place at separate facilities. Unless technology specific information on each device plane is provided, the packaging facility carrying out the final 3-D integration of the device planes is unaware of the power supply voltage requirements of the different ICs. The proposed circuit detects the power supply voltage needs of each voltage domain on different device plans of the 3-D IC. This facilitates true plug-and-play integration for 3-D heterogeneous ICs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  shows the placement of components on the device and power planes. 
           [0006]      FIG. 2  shows a current starved RO with an output switching inverter. 
           [0007]      FIG. 3  shows the simulation results for detecting and clamping the power supply voltage for a voltage domain in a 22 nm device plane. 
           [0008]      FIGS. 4( a ), 4( b ), and 4( c )  are graphs that show the ring oscillator frequency variation with threshold voltage VTH, channel length, and MOSFET low-field mobility. 
           [0009]      FIG. 5  shows the circuit implementation of a Frequency to Voltage Converter (FVC). 
           [0010]      FIG. 6  shows a Voltage Controlled Current Source (VCVS) comprising a voltage comparator and a current source that charges a capacitor C. 
           [0011]      FIG. 7  shows the transient response of the 22 nm ring oscillator (Fout_22 nm), the FVC output voltage (Vfvc), and the control voltage generated by the VCVS block (Vctrl_22 nm). 
           [0012]      FIG. 8  shows a block diagram of the various components of the 3-D IC supply voltage detection and clamping circuit. 
           [0013]      FIGS. 9( a )-9( c )  show various circuit details described herein. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Introduction 
       [0014]    The plug-and-play approach described above may be driven in several ways. First, organizations may develop, and the industry adopts, guidelines to standardize the interface circuit properties (location and electrical characteristics of IO ports and ESD protection) for each device plane. Second, the 3D IC stack&#39;s global power and clock-generation circuits must be met for each stratum. 
         [0015]    The power supply voltage detection and power delivery circuit described herein provides the global power generation and distribution through a power delivery system that senses the power supply voltage needed by each voltage domain (VDD_DP) in each device plane at run time. A dedicated power plane detects each domain&#39;s power supply voltage requirement, and delivers power to all voltage domains in the 3D stack accordingly. The power plane generates a range of voltages (ideally from 0.5 V to 5 V) to meet the power supply voltage requirements of the various technology nodes. Further, device planes may have significantly varying power budgets, requiring single or multiple power planes interspersed between device planes, depending upon the 3D IC stack configuration. 
         [0016]    The design described herein provides power to a heterogeneous device configuration that may include CMOS, MEMS, or RFICs operating on disparate substrates not limited to Silicon or III-V technologies (GaAs, GaN, InP, etc.). 
         [0017]    II. Run Time Voltage Detection and Power Delivery 
         [0018]    Each voltage domain within each device plane includes a ring oscillator capable of generating an output frequency F out  of 1 GHz when a control voltage equal to the power supply voltage V DD   _   DP  of the domain is applied. A 1 GHz frequency is an arbitrarily chosen value for the proposed circuit and may be adjusted based on set standards, and reflects one value that serves as a common frequency of operation for all ring oscillators placed on different device planes in a given 3-D IC stack. As proposed, the only required overhead for each voltage domain is the ring oscillator. The remaining components of the voltage sense circuit are part of the power module placed on the dedicated power plane. 
         [0019]      FIG. 1  shows the placement of the components on the device and power planes. The 3-D stack  100  includes device planes  110 ,  120  containing multiple voltage domains  112 ,  114  and  122 ,  124  served by a power plane  130  with multiple power modules  132 ,  134 . Each power module  132 , 134  includes a voltage-controlled voltage source (VCVS)  136  controlled by voltage generated from a frequency to voltage converter (FVC)  138 . A ring oscillator  116  placed in each voltage domain provides a controlling frequency to the FVC  138 . 
         [0020]    The Fout generated by the ring oscillator  116  propagates through TSVs  150  to the power plane  130 . The FVC  138  generates a voltage Vfvc inversely proportional to Fout. Vfvc is equal to 690 mV when an input frequency of 1 GHz is applied to the FVC  138 . The ring oscillator frequency  116  increases until 1 GHz is reached, which is determined by comparing the FVC  138  output voltage to a reference voltage source Vref set to 690 mV. The VCVS  136  supplies the control voltage to the ring oscillator  116 . The VCVS  136  is controlled by a voltage comparator that compares the Vfvc with Vref. Dedicated power modules  132 ,  134  comprising the FVC  138  and the VCVS  136  facilitate point of load power delivery that: 1) reduces noises due to a reduction of the parasitic impedance of the power distribution network as the voltage source is closer to the load circuit, 2) supplies different voltages to heterogeneous circuits, and 3) provides finer granularity for voltage control. 
         [0021]    The circuit structure and operation of components included in the voltage sense and power delivery circuit are described below. Circuits may be designed with 45 nm and 22 nm PTM models for, respectively, the power plane and device plane, but circuits designed and fabricated in any technology node are plausible. 
         [0022]    A. Ring Oscillator Circuit for Individual Voltage Domains 
         [0023]    Ring oscillators (RO) may be used as voltage controlled oscillators (VCO) in high performance integrated circuits as the fundamental block for frequency synthesizers, clock recovery circuits, and clock distribution networks. The application of ring oscillators is not limited to VCOs, as ROs may be used for on-chip thermal sensors and test structures to measure process variability. The RO&#39;s flexibility may be attributed to a simple CMOS implementation with no passive components, which reduces the occupied silicon area. The output frequency may be stable in the presence of process, voltage, and temperature variation (PVT) and the applied control voltage. 
         [0024]    Several ring oscillator circuit topologies may provide a steady frequency reference for the detection of the targeted VDD_DP of a given voltage domain. The selected ring oscillator circuit topology should provide a large frequency range when the applied control voltage varies from VDD_DP/2 to VDD_DP and a minimum variation in frequency due to sensitivity to PVT. A current starved RO with an output switching inverter (shown in  FIG. 2 ) provides frequency stability in terms of temperature variation (less than 2%), a low phase noise of 0.06 radians, and frequency sensitivity to power supply variation of less than 10%. 
         [0025]    The current-starved topology with an output switching inverter is a building block to implement the ring oscillator. The control voltage Vctrl  202  is applied to both the control transistor M 1   204  and VDD_DP as shown in  FIG. 2 . The RO circuit  200  may be implemented using a 22 nm high-performance (HP) PTM model with a VDD_DP of 0.8 V. An output frequency of 1 GHz is achieved with three current starved inverting stages ( 210 ,  212 ,  214 ) each with transistor W/L ratios ranging between 8 to 10. None of the transistors are minimum-sized to reduce the impact of line-edge roughness and random dopant fluctuations that cause significant variation in the VTH in the subnanometer technology nodes. 
         [0026]    The VTH, low-field mobility, and effective channel length are three parameters impacted by lithographic variation, stress, and doping concentration in strained silicon technology. The impact of process variation on the output frequency of the ring oscillator is evaluated with Monte Carlo analysis. A typical corner is simulated for statistical variation of VTH, channel length, and mobility considering both process variation and device mismatch. The ring oscillator frequency variation with VTH , channel length, and MOSFET low-field mobility is shown, respectively, in  FIGS. 4( a ), 4( b ), and 4( c ) . 
         [0027]    The corresponding ratio of the variance to the mean for VTH, the effective channel length, and the low-field mobility as a percentage are, respectively, 11.9%, 5.64%, and 6.12%. The ring oscillator therefore exhibits moderate deviation in output frequency with process variation. The power module on the power plane that detects the ring oscillator frequency is designed to compensate for deviation from the 1 GHz target frequency due to PVT variation to ensure reliable detection and setting of the power supply voltage. 
         [0028]    B. Frequency to Voltage Converter Circuit 
         [0029]    The output from the ring oscillator  116  on the device planes  110 ,  120  is connected to an FVC circuit  138  placed on the dedicated power plane  130 . The connection between the ring oscillator  116  and the FVC  138  is through TSVs  150 . With careful floor planning and the development of 3-D IC interface circuit standards, the vertical alignment of the ring oscillators  116  and the FVC circuits  138  on the respective device and power planes ensures minimum electrical degradation of the frequency signal in terms of induced jitter and propagation delay. The FVC  138  operates based on charge redistribution between two switching capacitors. The generated output voltage is linearly related to the input frequency and does not require filtering to remove AC ripples, which is a common limitation with other FVC implementations using low pass filtering techniques or digital counters. The circuit implementation is area efficient, as a limited number of components are required. The FVC circuit  138  is implemented using a 45 nm low-performance (LP) PTM model with the power supply voltage VDD_PP set to 1 V. 
         [0030]      FIG. 5  shows a circuit implementation of the FVC  138  with transistors M 1 -M 5 . The current source may be set to 20 μA. The capacitors C 1   550  and C 2   552  may be each 10 fF and implemented as MOSCAPS to reduce the occupied silicon area. The voltage across the capacitors  550 ,  552  is inversely proportional to the frequency of the input signal and corresponds to a voltage of 690 mV when the input frequency is 1 GHz. 
         [0031]    C. Voltage-Controlled Voltage Source Implementation 
         [0032]    As shown in  FIG. 6 , the control voltage (Vctrl) and power supply voltage (VDD_DP) of the RO in the device plane are provided by a voltage controlled voltage source (VCVS  136 ) that is part of the power module in the power plane  130 . The VCVS  136  includes a voltage comparator and a current source that charges a capacitor C. The charging of the capacitor through the current source is controlled by the output of the voltage comparator. The VCVS  136  is implemented using the 45 nm thick oxide PTM model available through the NCSU 45 nm PDK. The current source is designed to generate stable output voltages up to 3 V, which is sufficient to serve analog and IO devices implemented in subnanometer technologies. It is possible to generate output voltages up to 5 V by selecting an older technology node (greater than 65 nm) to implement the current source on the dedicated power plane  130 . By supplying voltages from 0.5 V to 5 V, a wide range of disparate technologies are integrated to form a 3-D system. 
         [0033]    The ring oscillator  116  generates distinct frequencies when the input control voltage lies between VDD_DP/2 and VDD_DP. The FVC  138  responds to these frequencies by generating an output voltage inversely proportional to the input frequencies. The varying output voltage from the FVC  138  is constantly compared to Vref. When Vfvc is equal to or less than Vref, the comparator output becomes active low and stops the charging of the capacitor C through the current source, as shown in  FIG. 6 . 
         [0034]    III. Simulation Results 
         [0035]    The three circuit blocks, which include the  22  nm three stage current starved output switching ring oscillator circuit on the device plane (power supply voltage VDD_DP of 0.8 V), the 45 nm FVC circuit (power supply voltage VDD_PP of 1 V), and the 45 nm VCVS, are simulated together. The simulation also includes the impedance of the TSVs. The connectivity of the circuit blocks is shown in  FIG. 6  and the transient response is shown in  FIG. 7 . Assuming a vertical alignment between the power module on the power plane and the ring oscillator on the device plane, the interconnect length is negligible and is not considered in the simulation. 
         [0036]    The control voltage from the VCVS and the output signal of the ring oscillator propagate through TSVs. The impact of the TSVs is incorporated by using an equivalent RC pi-model. The values of the DC resistance (505.8 mΩ), 1 GHz resistance (570.72 mΩ), and capacitance (8.7 fF) of a single 
         [0037]    TSV are computed from closed form expressions. The pi-model represents a Tungsten filled TSV with a length of 16 μm, diameter of 1.5 μm, and dielectric thickness of 0.25 μm. Each RC pi-model shown in  FIG. 6  represents two TSVs in parallel. 
         [0038]      FIG. 7  shows the transient response of the 22 nm ring oscillator (Fout_22 nm), the FVC output voltage (Vfvc), and the control voltage generated by the VCVS block (Vctrl_22 nm). The ring oscillator is the only load element served by the power module for the transient simulation. The VCVS transient simulation therefore excludes the impact of load transients and resistive losses due to the power delivery network and additional load circuits. The desired power supply voltage of 0.8 V is reached in less than 80 ns. The proposed voltage detection and power delivery circuit is further tested to provide the power supply voltage to a 45 nm device plane. A three-stage current starved ring oscillator is designed using a 45 nm LP PTM model (VDD_DP of 1 V). The VCVS is able to reliably generate a control voltage of 1 V (Vctrl_45 nm) in less than 100 ns, as shown in  FIG. 7( c ) . 
         [0039]    IV. Universal Power Plane 
         [0040]    Through silicon via (TSV) based 3D integrated circuits (IC) permit the integration of heterogeneous technologies with CMOS. The integrated system may include RF, analog, micro-nano-electromechanical systems (MEMS/NEMS) as well as emerging technologies such as nano-FET and graphene-based device planes. The design and fabrication of these disparate device planes may take place at separate facilities. Unless technology specific information on each device plane is provided, the packaging facility carrying out the final 3D integration of the device planes may be unaware of the power supply voltage requirements of the different ICs. 
         [0041]    A universal power plane comprises circuits capable of detecting the power supply voltage requirement of each device plane in the 3-D IC stack. The universal power plane may have multiple on-chip voltage regulators serving the power needs of each voltage domain in each device plane of the 3D stack. This arrangement facilitates point-of-load power delivery through the use of TSVs. The shorter path between the power source and load leads to both lower IR drop and parasitic impedance of the power distribution network. Each dedicated voltage regulator for a given voltage domain facilitates dynamic voltage and frequency scaling (DVFS). 3D IC interface guidelines would help to successfully implement this circuit, and would include specifications for the location of ports for power, clock, and signal delivery for each device plane of the 3D IC stack. 
         [0042]    V. Alternate Power Supply Detection and Clamping Circuit 
         [0043]      FIG. 8  shows a block diagram of the various components of a 3-D IC supply voltage detection and clamping circuit  800 . Each voltage domain in the device plane  810  comprises a ring oscillator  816  with a current-starved output switching stage. The ring oscillator  816  operates at a frequency of  1  GHz when the applied control voltage equals the power supply voltage of the given domain. The oscillation frequency of 1 GHz is selected and achievable with minimum current starved inverter stages in a deep sub-micron CMOS technology as well as in GaAs based RF circuits. The power module  830  that serves a voltage domain consists of a clock divider  860 , frequency detector  870 , voltage ramp generator  880 , voltage peak detector  890 , and a voltage regulator  850 . 
         [0044]    The ring oscillator  816  output frequency may be down-converted by a factor of 40 by the clock divider  860  comprising a divide-by-8 cascaded together with a divide-by-5 circuit block. The frequency comparator compares the output of the clock divider  860  with a 25 MHz clock source (off-chip crystal oscillator)  865 . The frequency comparator  900  may be implemented using four D-FFs  910  as shown in  FIG. 9( a ) . The frequency comparator may be preferable over a phase frequency detector (PFD) as the PFD generates UP and DOWN signals (due to D-FF clock-to-Qdelay) even when the inputs are phase locked. In addition, the voltage detection circuit does not require that the down converted ring oscillator frequency is matched in phase with the 25 MHz reference signal. 
         [0045]    A voltage ramp generator circuit (RGC)  920  includes a constant current source charging a capacitor C 1  and a switch S 1  that controls the duration of the ramp voltage, as shown in  FIG. 9( b ) . The UP and inverted DOWN signal are logically ANDed together (UPDOWN) to generate the control signal for S 1 . When the 3-D IC is first powered on, the ramp generator provides an initial voltage to the ring oscillator, and the UP signal from the frequency detector is high as the down converted frequency from the ring oscillator is less than 25 MHz. The frequency increases as the ramp generator output voltage increases. When the ring oscillator reaches the 1 GHz frequency, the UP signal may be de-asserted and any further increase in frequency asserts the DOWN signal. The switch S 1  is in the open state, preventing any further increase of charge (and therefore voltage) on C 1 . The voltage VRGC on C 1  corresponds to the power supply voltage of the voltage domain (VDD_VI) in which the ring oscillator is placed. The discharging of the capacitor C 1  through the load circuit causes the ring oscillator frequency to drop below 1 GHz, which re-asserts the UP signal and places Si in the closed state. The UP signal continues to periodically toggle ensuring that the voltage VRGC is maintained at the desired level. 
         [0046]    The variations in VRGC due to discharging of the capacitor C 1  are filtered using a voltage peak detector circuit  930  (shown in  FIG. 9( c ) . The peak detector circuit consists of a PMOS M 1  that controls the current charging the capacitor C 2 . A voltage comparator compares the output voltage VRef across the capacitor C 2  with VRGC. The output voltage from the comparator biases M 1 . VRef follows the positive transition of VRGC and at steady state equals the maximum value of VRGC. The peak detector circuit therefore provides a steady voltage reference with less than 1% ripple voltage variation from the targeted power supply voltage of the device plane (VDD_VI). VRef is used as the reference voltage for the voltage regulator serving the load circuit in the device plane. On-chip voltage regulator topologies like the LDO and buck converter are suitable for integration with the proposed voltage detection and clamping circuit. The stable reference voltage provided by the proposed circuit ensures superior line regulation offered by the voltage regulator. 
         [0047]    VI. Simulated Circuit Results 
         [0048]    Two device planes may be simulated using the 45 nm low-performance (LP) (VDD_VI of 1 V) and 22 nm high-performance (HP) (VDD_VI of 0.8 V) PTM models [6]. The designed ring oscillators for each device plane include three inverter stages in a current starved output-switching configuration. The design is robust against threshold voltage variation, channel length variation, and low-field mobility variation. 
         [0049]    The components of the power module may be implemented with the 45 nm PTM models. The divide-by-40 clock divider and frequency detector circuits are simulated using the 45 nm LP PTM model (VDD_PP of 1 V). The voltage ramp generator and peak detector circuits are implemented using the 45 nm thick oxide (VDD_Ramp of 3 V) PTM model. A DC-DC level shifter is used to convert the UP and DOWN signals from a VDD_PP of 1 V to a VDD_Ramp of 3 V. The slope of the voltage ramp signal is deliberately kept low (0 V to 3 V in 2 μs) to ensure stable operation. The minimum voltage detected reliably by the power module is 0.7 V. The maximum voltage provided by the ramp generator is 2.5 V. SPICE circuit simulations indicate a maximum variation of 1% in the reference voltage VRef provided to the on-chip voltage regulator for VDD_VI of less than 1 V. This is comparable to the stability of reference voltages used by off-chip buck converters, where approximately 1% variation is currently achieved. 
         [0050]    The simulation results for detecting and clamping the power supply voltage for a voltage domain in a 22 nm device plane are shown in  FIG. 3 . VRef reaches VDD_VI of 0.8 V in 370 ns. The detection and clamping circuits on the 45 nm device plane require 420 ns for VRef to reach the target voltage VDD_VI of 1 V. The proposed circuit therefore offers a fast transition to the desired power supply voltage level at startup and is suitable for integration with on-chip voltage regulators. 
         [0051]    VII. Other Applications 
         [0052]    Other applications of the circuits described herein may be as a way to maintain consistent voltage over time to overcome degradation. The power supply power detection and power delivery unit could, through its detection ability, detect any degradation and maintain consistent voltage through the circuit. 
         [0053]    The power supply detection and power delivery unit may auto compensate for the drift in power supply voltage with time due to the aging of devices in each voltage domain served by a ring oscillator. 
         [0054]    Further, the units may be fabricated in a 2-D or 3-D IC. The units may provide run-time aging or process, voltage, and temperature (PVT) variation detection and correction used in conjunction with on-chip voltage regulators. 
         [0055]    The power supply detection and power delivery unit may be part of a power conditioning circuit of a battery charged portable electronic device and the power delivery unit is integrated into a portable charger. The run-time voltage detection mechanism eliminates the need to down convert the voltage from 5V as obtained through standard USB based battery chargers. 
         [0056]    VIII. Conclusions 
         [0057]    A mechanism to detect the power supply voltage of a given voltage domain in a 3-D IC is implemented by placing a ring oscillator in each domain located on disparate device planes. The chosen circuit topology for the ring oscillator exhibits acceptable response to deviations due to PVT variations in a 22 nm technology. A u/p ratio (as a percentage) of 11.9%, 5.64%, and 6.12% is determined for, respectively, threshold voltage variation, channel length variation, and low-field mobility. The power requirement of each voltage domain is served by a single power plane that includes multiple point of load power modules, with each module consisting of a voltage controlled voltage source regulated by a frequency to voltage converter. The power supply voltage detection and delivery mechanism is demonstrated by simulating the device plane and power plane in two different technology nodes. The targeted power supply voltage for both the 22 nm and 45 nm device planes is detected and set in less than 100 ns, as shown through simulation. 
         [0058]    A circuit to detect and reliably set the power supply voltage of a given voltage domain in a 3-D IC is also described. All components except for a ring oscillator are part of the power module located in a separate and dedicated 45 nm power plane. Multiple power modules serve as point of load voltage delivery circuits to the different device planes. Correct power supply voltage detection and clamping is demonstrated through circuit simulation for two device planes, one in 22 nm and the other in 45 nm technologies. The power module is capable of setting the power supply voltage of a device plane ranging from 0.7 V to 2.5 V. The precise voltage generated from the power module acts as a reference voltage for an on-chip LDO or buck converter. The reference voltage is within 1% of the targeted power supply voltage, as indicated by simulated results. 
         [0059]    The power regulation described herein has been made in reference to ICs and in particular IC manufacture with layers produced separately. Other uses of the device described herein, however, are possible, including the use of the device as a universal power converter that could be used to allow for power differences between electric devices and power delivery systems. 
         [0060]    While the invention has been described with reference to the embodiments above, a person of ordinary skill in the art would understand that various changes or modifications may be made thereto without departing from the scope of the claims.