Dynamic voltage scaling scheme for an on-die voltage differentiator design

[0001] Contained herein is material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction of the patent disclosure by any person as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all rights to the copyright whatsoever.

[0002] The present invention relates to integrated circuits; more particularly, the present invention relates to generating multiple power supply voltages on an integrated circuit.

[0003] Recently, power consumption has become an important concern for high performance computer systems. Consequently, low power designs have become significant for present-day very large scale integration (VLSI) systems. The most effective way to reduce power dissipation in an integrated circuit (IC) is by decreasing the power supply voltage (V_CC) at the IC.

[0004] In order to simultaneously achieve high performance and low power, multi-V_CC design, various techniques have been developed. However, due to the high cost of packaging and routing, it is typically difficult to generate multi-V_CC designs using traditional off-chip voltage regulators.

[0011] A mechanism to dynamically scale voltage at one or more circuit blocks on an integrated circuit (IC) using on-die voltage differentiators is described. In the following description, numerous details are set forth. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention.

[0012] Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

[0013] FIG. 1 is a block diagram of one embodiment of an IC 100. According to one embodiment, IC 100 is partitioned into twenty-five circuit blocks 110. In a further embodiment, each circuit block 110 includes a voltage differentiator 120. Each voltage differentiator 120 generates a local power supply (V_CC—local) from an external power supply (V_CC—global).

[0014] In one embodiment, differentiator 120 dynamically changes V_CC—local based upon the operation status of the particular circuit block 110 in which the differentiator 120 is included. One of ordinary skill in the art will appreciate that other quantities of circuit blocks 110 may be implemented within IC 100.

[0015] FIG. 2 is a block diagram of one embodiment of a circuit block 110. Circuit block 110 includes voltage differentiator 120, a functional unit block (FUB) 230 and a control module 250. FUB 230 is coupled to voltage differentiator 120. In one embodiment, FUB 230 is logic circuitry that may encompass various components within IC 100 (e.g., microprocessor logic, microcontroller logic, memory logic, etc.). FUB 230 is powered by V_CC—local received from voltage differentiator 120.

[0016] Control module 250 is coupled to voltage differentiator 120 and FUB 230. According to one embodiment, control module 250 transmits a binary encoded signal to voltage differentiator 120 that is used to scale the local operating voltage generated at voltage differentiator 120. In a further embodiment, control module 250 transmits either a local control signal or a global control signal. In yet another embodiment, the global control signal overrides the local control signal.

[0017] FIG. 3 illustrates one embodiment of voltage differentiator 120 coupled to control module 250. Voltage differentiator 120 includes bandgap reference circuit 310, reference voltage selector 320 and linear voltage regulator 330. Bandgap reference circuit 310 generates a bandgap reference voltage V_BG. In one embodiment, V_BG is a stable voltage source that is insensitive to temperature and process variations.

[0018] Reference voltage selector 320 is coupled to bandgap reference circuit 310 and control module 250. Reference voltage selector 320 generates a reference voltage (V_REF) for linear voltage regulator 330. FIG. 4 illustrates one embodiment of reference voltage selector 320. Reference voltage selector 320 includes PMOS voltage divider transistors P1–Pn, PMOS pass transistors P11–Pn−1 and a NMOS transistor N. According to one embodiment, up to n−1 voltage levels can be selected. For instance, if four voltage levels are needed, four PMOS pass transistors P11–P14 are used.

[0019] In one embodiment, voltage divider transistors P1–Pn are series connected transistors that provide a variable resistance to V_BG received from bandgap reference circuit 310 in order to generate V_REF. For instance, if the number of transistors in the voltage divider is n, the granularity of V_REF is V_BG/n.

[0020] In one embodiment, V_REF is determined by the encoded control signal received at transistors P11–P14 from control module 250. The received signal is determined by the operation status of FUB 230. For example, if a relatively high V_REF is needed, the binary control signal 01110 is received at transistors P11–P14 and transistor N, respectively. As a result, only transistor P11 is activated and V_REF is equal to V_BG*(1-1/n), where n is the number of transistors in the voltage divider. Similarly, V_REF is equal to V_BG*(1-2/n), V_BG*(1-3/n) and V_BG*(1-4/n) when the control signal is 10110, 11010, 11100, respectively.

[0021] According to one embodiment, the value of V_CC—local changes dynamically based upon the activity of the corresponding FUB 230. For instance, if a FUB 230 requires a relatively high voltage, a higher V_REF is generated by reference voltage selector 320. Consequently, a higher V_CC—local is generated by line voltage regulator 330. Conversely, if a FUB 230 requires a relatively low voltage, lower V_REF and V_CC—local voltages are generated.

[0022] In a further embodiment, a higher V_REF may be needed to satisfy performance requirements for circuit blocks 110 that are in a critical path. However, for other circuit blocks 110 that are not in a critical path, a lower V_REF can be selected to reduce power dissipation. In a further embodiment, control module 250 may cause circuit block 110 to enter a standby mode by transmitting 11111 as the control signal. In such an instance, only transistor N is activated, and a V_REF of 0V is transmitted to linear voltage regulator 330.

[0023] Referring back to FIG. 3, linear voltage regulator 330 generates V_CC—local for circuit block 110. FIG. 5 illustrates one embodiment of linear voltage regulator 330. Linear voltage regulator 330 includes a comparator 530, a PMOS transistor (P), resistors R1 and R2 and a capacitor. Comparator compares the V_REF received from reference voltage selector 320 with a feedback voltage (V_FB) received from transistor P through resistors R1 and R2.

[0024] If V_FB falls below V_REF, the output of comparator 530 is activated at a low logic level (e.g., logic 0). Otherwise, the output of comparator 530 remains at high logic level (e.g., logic 1). According to one embodiment, comparator 530 is an operational amplifier. However, one of ordinary skill in the art will recognize that other comparison logic circuitry may be used to implement comparator 530.

[0025] The output of comparator 530 is coupled to the gate of transistor P. The source of transistor P is coupled to V_CC—global, while the drain is coupled to resistor R1, the capacitor and FUB 230 through V_CC—local. Transistor P is activated whenever comparator 530 is activated to logic 0.

[0026] Resistor R1 is coupled to resistor R2 and comparator 530. Resistors R1 and R2 are used to generate V_FB for comparator 530. Resistors R1 and R2, and the generation of V_FB, help to control the output of linear voltage regulator 330 by providing a larger voltage range. However, one of ordinary skill in the art will appreciate that resistors R1 and R2 are not necessary to implement linear voltage regulator 330.

[0027] As described above, the value of V_CC—local changes dynamically based upon the activity of the corresponding FUB 230. During the active mode, transistor P is activated whenever V_FB falls below V_REF. In particular, comparator 530 senses such a condition and is activated to logic 0. Consequently, the gate of transistor P is activated to logic 0. Transistor P charges the decouple capacitor, thus increasing V_CC—local. In the active mode, linear voltage regulator 330 generates V_CC—local=V_REF*(1+R1/R2).

[0028] During the standby mode, V_REF is 0. Accordingly, V_FB is always greater than or equal to V_REF, and the output of the comparator is logic 1 and transistor P is turned off. As a result, V_CC—local is floating to reduce the leakage power at circuit block 110.

[0029] The use of on-die voltage differentiators enables the generation of a local power supply voltage for each circuit block within an IC. The local power supply voltage changes dynamically based on the activity of the corresponding circuit block. This reduces the power dissipation while maintaining performance. Moreover, the dynamic voltage scaling mechanism using on-die voltage differentiator has a standby control capability, which can drastically reduce leakage power during idle time for a circuit block.

[0030] Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular embodiment shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various embodiments are not intended to limit the scope of the claims which in themselves recite only those features regarded as the invention.