Abstract:
The present invention provides a body bias coordinator for use with a transistor employing a body region. In one embodiment, the body bias coordinator includes a control unit configured to control the transistor and make it operable to provide a virtual supply voltage from a source voltage during activation of the transistor. The body bias coordinator also includes a connection unit coupled to the control unit and configured to connect the body region to the virtual supply voltage during activation of the transistor. In an alternative embodiment, the connection unit is further configured to connect the body region to another voltage during non-activation of the transistor. These embodiments improve transistor active and passive performance, permit smaller transistor sizing and reduce leakage current.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     The present invention is directed, in general, to microelectronics and, more specifically, to a body bias coordinator, method of coordinating a body bias and a sub-circuit power supply employing the coordinator or the method.  
       BACKGROUND OF THE INVENTION  
       [0002]     Integrated circuit systems are rapidly increasing in device count and operating speed. Each of these attributes tends to increase power requirements directly while both together cause power requirements to increase exponentially. Therefore, dealing with power requirements associated with integrated circuit systems is becoming a much more critical design arena than before. These power requirements and their corresponding temperature effects have led to the need for additional power management considerations and techniques.  
         [0003]     One such management technique involves separating the integrated circuits that require full power all of the time to perform their intended tasks from those that may use reduced power to perform some of their intended tasks at least some of the time. Another power management technique further isolates blocks of circuits where the power may be fully removed during certain aspects of system operation. For example, these circuit blocks may have their operating power completely removed when they become operationally inactive for a period of time. Supplying and removing power, either partially or completely, from a block of circuitry may be controlled by a header or footer transistor.  
         [0004]     The header transistor forms a controllable switch between a positive power supply and a circuit block. Similarly, the footer transistor forms a controllable switch between a negative power supply and the circuit block. Activation of the header or footer transistor allows a virtual supply to be connected to the circuit block. Often, both header and footer transistors are employed to provide both positive and negative virtual supplies concurrently when the block of circuitry is active.  
         [0005]     Similarly, header and footer transistors are used to reduce current to blocks of circuitry during their inactive modes of operation. There is a potential advantage in changing the header or footer transistor body voltage to raise its threshold voltage and thereby reduce its leakage when in the inactive mode. Alternatively, lowering the threshold voltage during the active mode provides a reduced transistor voltage drop for the header or footer transistor. However, there is a capacitance associated with the body nodes of the header and footer transistors, which may be relatively large. This capacitance requires a dynamic switching power associated with switching a voltage on the body node that may provide too large a penalty to be used in some applications, especially if powering the circuitry on and off is required too frequently. Additionally, a forward body bias to lower threshold voltage in the active mode gives rise to forward biased diode current that is generally undesirable.  
         [0006]     Accordingly, what is needed in the art is an improved way to provide switchable power to a circuit block that is required on a more frequent basis and that will provide biasing for a lower threshold voltage in the active mode.  
       SUMMARY OF THE INVENTION  
       [0007]     To address the above-discussed deficiencies of the prior art, the present invention provides a body bias coordinator for use with a transistor employing a body region. In one embodiment, the body bias coordinator includes a control unit configured to control the transistor and make it operable to provide a virtual supply voltage from a source voltage during activation of the transistor. The body bias coordinator also includes a connection unit coupled to the control unit and configured to connect the body region to the virtual supply voltage during activation of the transistor. In an alternative embodiment, the connection unit is further configured to connect the body region to another voltage during non-activation of the transistor. These embodiments improve transistor active and passive performance, permit smaller transistor sizing and reduce leakage current.  
         [0008]     In another aspect, the present invention provides a method of coordinating a body bias for use with a transistor employing a body region. The method includes providing a virtual supply voltage from a source voltage during activation of the transistor and connecting the body region to the virtual supply voltage during activation of the transistor.  
         [0009]     The present invention also provides, in yet another aspect, a sub-circuit power supply. The sub-circuit power supply includes a source voltage and a body bias coordinator, coupled to the source voltage, for use with a transistor employing a body region. The body bias coordinator has a control unit that controls the transistor and makes it operable to provide a virtual supply voltage from the source voltage during activation of the transistor. The body bias coordinator also has a connection unit that is coupled to the control unit and connects the body region to the virtual supply voltage during activation of the transistor. The sub-circuit power supply also includes a power supply bus coupled to the virtual supply voltage for use by a sub-circuit.  
         [0010]     The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0012]      FIG. 1  illustrates a circuit diagram of an embodiment of a sub-circuit power supply constructed in accordance with the principles of the present invention; and  
         [0013]      FIG. 2  illustrates a flow diagram of an embodiment of a method of coordinating a body bias carried out in accordance with the principles of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0014]     Referring initially to  FIG. 1 , illustrated is a circuit diagram of an embodiment of a sub-circuit power supply, generally designated  100 , constructed in accordance with the principles of the present invention. The sub-circuit power supply  100  includes a header circuit  105 , a footer circuit  110  and a sub-circuit  135 . The header circuit  105  includes a header transistor Q 1  having a header body region  107  and a header body bias coordinator  115  having a header control unit  115   a  and a header connection unit  115   b . The header connection unit  115   b  includes first and second header body region switches Qa 1 , Qb 1 . The footer circuit  110  includes a footer transistor Q 2  having a footer body region  112  and a footer body bias coordinator  120  having a footer control unit  120   a  and a footer connection unit  120   b . The footer connection unit  120   b  includes first and second footer body region switches Qa 2 , Qb 2 . The sub-circuit power supply  100  also includes an optional state-maintaining header voltage circuit  125  and an optional state-maintaining footer voltage circuit  130 .  
         [0015]     In the illustrated embodiment, the sub-circuit power supply  100  further includes both a header power supply bus  106  that provides a header virtual supply voltage V HV  and a footer power supply bus  111  that provides a footer virtual supply voltage V FV  to the sub-circuit  135 . The header virtual supply voltage V HV  is provided from a header supply voltage V dd  when the header transistor Q 1  is conducting or activated. Correspondingly, the footer virtual supply voltage V FV  is provided from a footer supply voltage V ss  when the footer transistor Q 2  is conducting during activation. Activation of both the header and footer transistors Q 1 , Q 2  provides a high-power operating mode for the sub-circuit  135 . The high-power operating mode may be employed for conditions requiring higher frequency operations within the sub-circuit  135 .  
         [0016]     In the illustrated embodiment, the header circuit  105  employs p-channel MOSFET transistors and the footer circuit  110  employs n-channel MOSFET transistors. The first header and footer body region switches Qa 1 , Qa 2  are respectively coupled between the header and footer body regions  107 ,  112  and the header and footer power supply busses  106 ,  111 . When activated, the first header and footer body region switches Qa 1 , Qa 2  apply a forward body bias to the header and footer transistors Q 1 , Q 2  to lower their threshold voltages. Additionally, they respectively apply any header and footer body region charge that has accumulated during non-activation of the header and footer transistors Q 1 , Q 2  to the header and footer power supply busses  106 ,  111  thereby supplementing turn-on currents, as well.  
         [0017]     Generally, when the body regions  107 ,  112  are connected to the drains of the header and footer transistors Q 1 , Q 2 , as provided by the actions above, it forward-biases the source junctions so that a junction current or junction leakage is obtained, which would normally not be desirable. However, for our case, it may be recognized that this current originates from the respective drains and flows in parallel with the normal conduction current of the header and footer transistors Q 1 , Q 2  according to the principles of the present invention.  
         [0018]     When the header and footer transistors Q 1 , Q 2  are not activated (i.e., in their OFF state), the body regions are disconnected from the drains thereby eliminating the additional drain to body current that was afforded during their conducting or ON state. The second header and footer body region switches Qb 1 , Qb 2  provide separate header and footer body region biases to give a relatively high threshold voltage for the header and footer transistors Q 1 , Q 2  when in their non-activated or OFF state. This action results in a charge being placed on each of their respective body regions. These respective charges are then employed as discussed earlier in activation of the header and footer transistors Q 1 , Q 2 .  
         [0019]     Additionally, raising the body voltage of the header transistor Q 1 , when not conducting, to a higher voltage than the header supply voltage V dd  (such as a V dd  input/output supply voltage shown in  FIG. 1 ) raises the threshold voltage of the header transistor Q 1  and thereby reduces its transistor leakage current. If a bulk material is used for the embodiment of  FIG. 1 , the body voltage of the footer transistor Q 2 , when not conducting, is tied to a V SS  substrate supply. Alternatively, for SOI material with body bias (e.g., PDSOI) or with a bulk process employing an isolatable P-well (i.e., containing an N buried layer and deep N-well), the body voltage of the footer transistor Q 2 , when not conducting, is tied to a V SS  alternate supply, in the embodiment of  FIG. 1 .  
         [0020]     The V SS  substrate supply and the V SS  alternate supply are usually the same potential as the footer supply voltage V SS . Therefore, a benefit still exists when employing a body bias for the footer transistor Q 2  that is neither negative nor positive with respect to the footer supply voltage V SS . This is also true for the non-conducting header transistor Q 1  when the body bias is connected to the header supply voltage V dd . Each of these conditions reduces current and corresponding wasted power to the sub-circuit  135  when its activating power is fully removed.  
         [0021]     Other embodiments of the present invention may employ different values of the header and footer supply voltages V DD , V SS , or may employ only a header circuit or a footer circuit. For example, raising and lowering the header and footer supply voltages V DD , V SS  separately may affect transistors in the sub-circuit  135  differently due to the effect of the back bias voltages. Raising the magnitudes of the back bias voltages will generally raise the threshold voltage, but doing so will also increase junction leakage thereby providing a trade-off. Additionally, there may be a balance where lowering one of the header and footer supply voltages V dd , V ss  while raising the other provides a lower overall power requirement.  
         [0022]     In the illustrated embodiment of  FIG. 1 , an optional low-power operating mode is also provided by the optional state-maintaining header voltage circuit  125  and the optional state-maintaining footer voltage circuit  130 , which allow state in the sub-circuit  135  to be maintained as may be required for latches or memory arrays when the header or footer transistors Q 1 , Q 2  are not conducting during non-activation. This low-power operating mode may also be employed for conditions that allow lower frequency operation within the sub-circuit block  135 . The state-maintaining header and footer voltage circuits  125 ,  130  may employ a diode, a diode-connected transistor, a resistor or a regulator circuit to provide reduced values or differing values of header and footer virtual supply voltages V HV , V FV .  
         [0023]     In the embodiment of  FIG. 1 , the header and footer control units  115   a ,  120   a  provide the same activation signal or its complement for controlling the operation of the rest of the header and footer circuits  105 ,  110 , as shown. Optionally, different signals may be used to apply different timing. For example, when the header transistor Q 1  is turned OFF and the header virtual supply voltage V HV  is maintained by the state-maintaining header voltage circuit  125 , it is not essential to raise the threshold voltage of the header transistor Q 1 . Thus, the second header body region switch Qb 1  may remain non-activated and the first header body switch Qa 1  optionally left ON or OFF when the header transistor Q 1  is turned OFF, while the header virtual supply voltage V HV  is maintained at a reduced value. The second header body region switch Qb 1  may be turned ON when transitioning to a full power-off for the sub-circuit  135 . If the system does not use a full power-off mode, the second header body region switch Qb 1  may be omitted. Of course, the foregoing discussion may be analogously applied to the footer circuit  110 , as well.  
         [0024]     Turning now to  FIG. 2 , illustrated is a flow diagram of an embodiment of a method of coordinating a body bias, generally designate  200 , carried out in accordance with the principles of the present invention. The method  200  is for use with a transistor employing a body region and starts in a step  205 . Then, a virtual supply voltage is provided from a source voltage during activation of the transistor, in a step  210 .  
         [0025]     In one embodiment of the present invention, the transistor is a MOSFET and the source voltage is a supply voltage for the transistor. Additionally, the source of the MOSFET is connected to the source or supply voltage and the drain of the MOSFET is connected to a bus of the virtual supply voltage during activation of the MOSFET. The virtual supply voltage may be a header virtual supply voltage or a footer virtual supply voltage as appropriate to a particular application. Then, in a step  215 , the body region of the transistor is connected to the virtual supply voltage during activation of the transistor.  
         [0026]     During non-activation of the transistor in a step  220 , the body region of the transistor is connected to another voltage. In one embodiment, this voltage employs a same polarity voltage having a greater magnitude than the virtual supply voltage. That is, if the virtual supply voltage is positive, the body region of the transistor is connected to a voltage that is more positive than the virtual supply voltage, such as a positive input/output supply voltage. Correspondingly, if the virtual supply voltage is negative, the body region is connected to a voltage that is more negative, such as a negative input/output supply voltage. Alternatively, the body region may be connected to the source voltage during non-activation of the transistor. The method  200  ends in a step  225 .  
         [0027]     While the method disclosed herein has been described and shown with reference to particular steps performed in a particular order, it will be understood that these steps may be combined, subdivided, or reordered to form an equivalent method without departing from the teachings of the present invention. Accordingly, unless specifically indicated herein, the order or the grouping of the steps is not a limitation of the present invention.  
         [0028]     In summary, embodiments of the present invention employing a body bias coordinator, a method of coordinating a body bias and a sub-circuit power supply employing the coordinator or the method have been presented. Advantages include a reduction in power required, particularly for frequent switching into and out of the fully-powered or active mode, while allowing a fast restoration of the virtual supply voltage produced by a header or footer circuit, for example. Also, there is an inherent forward body bias of the header or footer transistor when it is conducting, which allows a reduction of the voltage across it thereby providing both a lower power loss and a virtual supply voltage that more closely approximates the source or supply voltage.  
         [0029]     Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.