Patent Publication Number: US-7719344-B1

Title: Stabilization component for a substrate potential regulation circuit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application is a Continuation of commonly-owned patent application Ser. No. 10/747,022, filed on Dec. 23, 2003, now U.S. Pat. No. 7,012,461 entitled “A STABILIZATION COMPONENT FOR A SUBSTRATE POTENTIAL REGULATION CIRCUIT”, by Chen et al., which is incorporated herein by reference. 
     This case is related to commonly assigned U.S. patent application “A PRECISE CONTROL COMPONENT FOR A SUBSTRATE POTENTIAL REGULATION CIRCUIT”, by T. Chen, Ser. No. 10/746,539, which is incorporated herein in its entirety. 
     This case is related to commonly assigned U.S. patent application “FEEDBACK-CONTROLLED BODY-BIAS VOLTAGE SOURCE”, by T. Chen, U.S. patent application Ser. No. 10/747,016, filed on Dec. 23, 2003, which is incorporated herein in its entirety. 
     This case is related to commonly assigned U.S. patent application “SERVO-LOOP FOR WELL-BIAS VOLTAGE SOURCE”, by Chen, et al., U.S. patent application Ser. No. 10/747,015, filed on Dec. 23, 2003, which is incorporated herein in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate to body biasing circuits for providing operational voltages in integrated circuit devices. 
     BACKGROUND ART 
     As the operating voltages for CMOS transistor circuits have decreased, variations in the threshold voltages for the transistors have become more significant. Although low operating voltages offer the potential for reduced power consumption and higher operating speeds, threshold voltage variations due to process and environmental variables often prevent optimum efficiency and performance from being achieved. Body-biasing is a prior art mechanism for compensating for threshold voltage variations. Body-biasing introduces a reverse bias potential between the bulk and the source of the transistor, allowing the threshold voltage of the transistor to be adjusted electrically. It is important that the circuits that implement and regulate the substrate body biasing function effectively and precisely. Inefficient, or otherwise substandard, body bias control can cause a number of problems with the operation of the integrated circuit, such as, for example, improper bias voltage at the junctions, excessive current flow, and the like. 
     DISCLOSURE OF THE INVENTION 
     Embodiments of the present invention provide a stabilization component for substrate potential regulation for an integrated circuit device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention: 
         FIG. 1  shows an exemplary integrated circuit device in accordance with one embodiment of the present invention. 
         FIG. 2  shows a diagram depicting the internal components of the regulation circuit in accordance with one embodiment of the present invention. 
         FIG. 3  shows a diagram of a resistor chain in accordance with one embodiment of the present invention. 
         FIG. 4  shows a diagram of a current source in accordance with one embodiment of the present invention. 
         FIG. 5  shows a diagram of a stabilization component in accordance with one embodiment of the present invention. 
         FIG. 6  shows a diagram of a positive charge pump regulation circuit in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of embodiments of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the embodiments of the present invention. 
       FIG. 1  shows an exemplary integrated circuit device  100  in accordance with one embodiment of the present invention. As depicted in  FIG. 1 , the integrated circuit device  100  shows an inverter having connections to a body-biasing substrate potential regulation circuit  110  (e.g., hereafter regulation circuit  110 ). The regulation circuit  110  is coupled to provide body bias currents to a PFET  102  through a direct bias contact  121 , or by a buried n-well  126  using contact  122 . In the  FIG. 1  diagram, a p-type substrate  105  supports an NFET  101  and the PFET  102  resides within an n-well  115 . Similarly, body-bias may be provided to the NFET  101  by a surface contact  121 , or by a backside contact  123 . An aperture  125  may be provided in the buried n-well  126  so that the bias potential reaches the NFET  110 . In general, the PFET  120  or the NFET  110  may be biased by the regulation circuit  110  through one of the alternative contacts shown. The integrated circuit device  100  employs body-biasing via the regulation circuit  110  to compensate for any threshold voltage variations. 
     Additional description of the operation of a regulation circuit in accordance with embodiments of the present invention can be found in commonly assigned “FEEDBACK-CONTROLLED BODY-BIAS VOLTAGE SOURCE”, by T. Chen, U.S. patent application Ser. No. 10/747,016, filed on Dec. 23, 2003, which is incorporated herein in its entirety. 
       FIG. 2  shows a diagram depicting the internal components of the regulation circuit  200  in accordance with one embodiment of the present invention. The regulation circuit  200  shows one exemplary component configuration suited for the implementation of the regulation circuit  110  shown in  FIG. 1  above. 
     In the regulation circuit  200  embodiment, a current source  201  and a variable resistor  202  are coupled to generate a reference voltage at a node  220  (e.g., hereafter reference voltage  220 ) as shown. The reference voltage  220  is coupled as an input for a comparator  205 . The output of the comparator  205  is coupled to a charge pump  210  and a stabilization component  215 . The output of the regulation circuit  200  is generated at an output node  230 . The output node  230  can be coupled to one or more body bias contacts of an integrated circuit device (e.g., the contacts  121 - 123  shown in  FIG. 1 ). 
     In the regulation circuit  200  embodiment, the current source  201  and the variable resistor  202  form a control circuit, or control component, that determines the operating point of the regulation circuit  200 . The current source  201  and the variable resistor  202  determine the reference voltage  220 . The comparator  205  examines the reference voltage  220  and the ground voltage  221  and switches on if the reference voltage  220  is higher than the ground voltage  221 . The comparator output  206  turns on the charge pump  210 , which actively drives the output node  230  to a lower (e.g., negative) voltage. The effect of turning on the charge pump  210  is to actively drive the body bias of a coupled integrated circuit to a lower voltage. This lower voltage will eventually be seen at the reference voltage node  220  of the comparator  205 . Once the reference voltage  220  and the ground voltage  221  are equalized, the comparator will switch off, thereby turning off the charge pump  210 . With the constant reference current from the current source  201 , the body bias of the integrated circuit device will thus be equal to the voltage drop across the variable resistor  202 . 
     Once the charge pump  210  is turned off, the body bias of the integrated circuit device will rise over time as the numerous components of the integrated circuit device sink current to ground. When the reference voltage  220  rises above the ground voltage  221 , the comparator  205  will switch on the charge pump  210  to re-establish the desired body bias. A typical value for the integrated circuit device is 2.5 volts. 
     As described above, the current source  201  and the variable resistor  202  determine the reference voltage  220 , and thus, the operating point of the regulation circuit  200 . The reference voltage  220  is generated by a reference current flowing from the current source  201  through the variable resistor  202 . Accordingly, the reference voltage  220  is adjusted by either adjusting the reference current or adjusting the resistance value of the variable resistor  202 . 
     In one embodiment, the reference current is designed for stability and is controlled by a band gap voltage source of the integrated circuit device. Thus, as the temperature of the device changes, the reference current should be stable. Additionally, the reference current should be stable across normal process variation. A typical value for the reference current is 10 microamps. In such an embodiment, the reference voltage  220  is adjusted by changing the variable resistance  202 . 
     In the present embodiment, the stabilization component  215  functions as a stabilizing shunt that prevents over charging of the body bias. As described above, once the charge pump  210  is turned off, the body bias of the integrated circuit device will rise over time as the integrated circuit device sinks current to ground. The stabilization component  215  functions in those cases when the charge pump  210  overcharges the body bias. 
       FIG. 3  shows a diagram of a resistor chain  300  in accordance with one embodiment of the present invention. The resistor chain  300  shows one configuration suited for the implementation of the variable resistor  202  shown in  FIG. 2  above. The resistor chain  300  comprises a chain of resistor elements  301 - 308  arranged in series. In the present embodiment, a resistance value for the resistor chain  300  is selected by tapping a selected one of the resistor elements  301 - 308 . This is accomplished by turning on one of the coupled transistors  311 - 318 . For example, increasing the resistance value is accomplished by tapping a resister earlier in the chain (e.g., resistor  301 )  300  as opposed to later in the chain (e.g., resistor  307 ). The resistance value is selected by writing to a configuration register  310  coupled to control the transistors  311 - 318 . 
       FIG. 4  shows a diagram of a current source  400  in accordance with one embodiment of the present invention. The current source  400  shows one configuration suited for the implementation of the current source  201  shown in  FIG. 2 . The current source  400  includes a band gap voltage reference  410  coupled to an amplifier  415 . The amplifier  415  controls the transistor  403 , which in turn controls the current flowing through the transistor  401  and the resistor  404 . This current is mirrored by the transistor  402 , and is the reference current generated by the current source  400  (e.g., depicted as the reference current  420 ). 
     In this embodiment, the use of a band gap voltage reference  410  results in a stable reference current  420  across different operating temperatures and across different process corners. The reference voltage  220  is governed by the expression K*Vbg, where K is the ratio of the variable resistor  202  and the resistance within the band gap reference  410  and Vbg is the band gap voltage. 
       FIG. 5  shows a diagram of a stabilization component  500  in accordance with one embodiment of the present invention. The stabilization component  500  shows one configuration suited for the implementation of the stabilization component  215  shown in  FIG. 2 . In the present embodiment, the stabilization component  500  functions as a stabilizing shunt that prevents over charging of the body bias. 
     As described above, once the charge pump  210  is turned off, the body bias of the integrated circuit device, and thus the ground voltage  221 , will rise over time as the integrated circuit device sinks current to ground. The stabilization component  215  functions in those cases when the charge pump  210  overcharges the body bias. For example, there may be circumstances where the charge pump  210  remains on for an excessive amount of time. This can cause an excessive negative charge in the body of the integrated circuit device. The stabilization component  215  can detect an excessive charging action of the charge pump  210 . 
     When excessive charging is detected (e.g., the charge pump  210  being on too long), the stabilization component  215  can shunt current directly between ground and the body bias (e.g., Vpw), thereby more rapidly returning the body bias voltage to its desired level. When the reference voltage  220  rises to the ground voltage  221 , the comparator  205  will switch on the charge pump  210  to maintain the desired body bias. 
     In the stabilization component  500  embodiment, the output of the comparator  205  is coupled as an input to three flip-flops  511 - 513 . The flip-flops  511 - 513  receive a common clock signal  501 . The flip-flops  511  and  512  are coupled in series as shown. The outputs of the flip-flops  512  and  513  are inputs to the AND gate  515 . The AND gate  515  controls the enable input of a shunt switch  520 . 
     In normal operation, the comparator output  206  will cycle between logic one and logic zero as the comparator  205  turns on and turns off the charge pump  210  to maintain the voltage reference  220  in equilibrium with ground  221 . Thus, the output  206  will oscillate at some mean frequency (e.g., typically 40 MHz). The clock signal  501  is typically chosen to match this frequency. If the comparator output  206  remains high for two consecutive clock cycles, the shunt switch  520  will be enabled, and current will be shunted between, in a negative charge pump case, between Vpw and ground, as depicted. In a positive charge pump case (e.g.,  FIG. 6 ) current will be shunted between Vnw and Vdd. 
       FIG. 6  shows a diagram of a positive charge pump regulation circuit  600  in accordance with one embodiment of the present invention. The regulation circuit  600  shows one exemplary component configuration suited for the implementation of a positive charge pump (e.g., Vnw) version of the regulation circuit  110  above. 
     The regulation circuit  600  embodiment functions in substantially the same manner as the circuit  200  embodiment. A current source  601  and a variable resistor  602  are coupled to generate a reference voltage at a node  620  as shown. The reference voltage  620  is coupled as an input for a comparator  605 . The output of the comparator  605  controls a charge pump  610  and a stabilization component  615 . The output of the regulation circuit  600  is generated at an output node  630  and is for coupling to the Vnw body bias contacts of an integrated circuit device. 
     As with the circuit  200  embodiment, the current source  601  and the variable resistor  602  form a control circuit that determines the operating point. The comparator  605  and the charge pump  610  actively drive the output node  630  to force the reference voltage  620  and Vdd  621  into equilibrium. With the constant reference current from the current source  601 , the Vnw body bias of the integrated circuit device will thus be equal to the voltage drop across the variable resistor  602 . 
     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.