Abstract:
Apparatus for configuring input/output signal levels of interfacing logic circuits operating at different voltage levels comprises: a logic circuit for operating at a first voltage level; a bank of input/output gates coupled to the logic circuit for interfacing input/output signals at a second voltage level, different from the first voltage level, to the logic circuit, the bank of gates including a port for setting the operational voltage level thereof; and a control circuit coupled to the port and governed by a control signal to configure the operational voltage level of the bank of gates to render the logic circuit and the interfacing input/output signals voltage level compatible.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/583,322, filed Oct. 19, 2006. 
     
    
     BACKGROUND 
       [0002]    Interfacing logic circuits with different I/O voltage levels is a problem that arises frequently, especially in the design of printed circuit boards (PCBs). Contemporary PCBs are designed with logic circuits in the form of fixed I/O integrated circuits, like application specific integrated circuits or chips (ASICs), for example. Because of rapidly changing integrated circuit technology, creating a design that is forwards compatible or backwards compatible with such fixed I/O devices presents a challenge. Often times, to achieve forwards and/or backwards compatibility, a new PCB design and/or added voltage translators are required. 
         [0003]    These solutions involve either redesigning a PCB or using a PCB that can be loaded with different circuit components to interface with the different logic circuits of different PCBs. Generally, each board redesign includes increased design time, cost, added product inventory and qualification. Using the same PCB loaded with different circuit components may reduce design time, but still requires added inventory and qualification, which will increase cost. 
       SUMMARY 
       [0004]    In accordance with one aspect of the present invention, apparatus for configuring input/output signal levels of interfacing logic circuits operating at different voltage levels comprises: a logic circuit for operating at a first voltage level; a bank of input/output gates coupled to the logic circuit for interfacing input/output signals at a second voltage level, different from the first voltage level, to the logic circuit, the bank of gates including a port for setting the operational voltage level thereof; and a control circuit coupled to the port and governed by a control signal to configure the operational voltage level of the bank of gates to render the logic circuit and the interfacing input/output signals voltage level compatible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a block diagram schematic of an exemplary embodiment of one aspect of the present invention. 
           [0006]      FIG. 2  is a block diagram schematic of an exemplary embodiment of another aspect of the present invention. 
           [0007]      FIG. 3  is a circuit schematic of an exemplary control circuit suitable for use in the embodiment of  FIG. 2 . 
           [0008]      FIG. 4  is a block diagram schematic of an alternate embodiment of the present invention. 
           [0009]      FIG. 5  is a block diagram schematic of another alternate embodiment of the present invention. 
           [0010]      FIG. 6  is a block diagram schematic of yet another alternate embodiment of the present invention. 
           [0011]      FIG. 7  is a block diagram schematic of yet another alternate embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    An exemplary embodiment of one aspect of the present invention is depicted in the block diagram schematic of  FIG. 1 . This exemplary embodiment provides a cross-board solution that allows a daughter board to interface to a variety of native signaling standards across a set of different mother boards. Referring to  FIG. 1 , fixed logic circuits of one printed circuit board (PCB)  10  which may be a mother board, for example, operate at a first voltage level which may be on the order of 2.5 to 2.8 volts, for example. In the present embodiment, the fixed logic circuits of board  10  are designed into an application specific integrated circuit (ASIC)  12  which is powered by a local power supply V S . In this embodiment, the voltage level of the signals of the ASIC  12  are set by the voltage VS. 
         [0013]    An interfacing PCB  14 , which may be considered a daughter board, is interfaced with the mother board  10 . The PCB  14  contains logic circuits that operate at a different voltage level. In this embodiment, some of the logic circuits of board  14  are programmed into a programmable gate array (PGA)  16  which may be of the field programmable type manufactured by Xilinx Corp. under the model no. XC3S100, for example. The PGA  16  may be powered by several power supply voltages. The core logic of PGA  16  is powered by a local power supply V c , which may be at 1.2 volts, for example. I/O signals of the PGA  16  are conducted through a bank of I/O gates  18  to a signal bus  20  which interconnects the I/O signals of the PGA  16  with I/O signals of the ASIC  12 . The bank of I/O gates  18  is powered by a voltage, supplied to a bank power supply port  22 , which may be set different from the core logic voltage level of the PGA  16 . Accordingly, the operational voltage level of the I/O gates  18  will be set by the voltage at the supply port  22 . 
         [0014]    In this embodiment, the I/O signals of the PGA  16  may be rendered compatible with the I/O signals of the ASIC  12  by setting an appropriate voltage at the bank power supply port  22 . Since the operational voltage levels of the I/O signals of the ASIC  12  are set by the power supply V S , one way of providing voltage level compatibility of the I/O signals over the bus  20  is by connecting the power supply V S  of board  10  to the supply port  22  as shown in the schematic of  FIG. 1 . In this configuration, the bank of I/O gates  18  of the PGA  16  will operate at a voltage level compatible with the I/O signal levels of the ASIC  12  notwithstanding the different operational signal levels of the logic circuits  12  and  16  of the interfacing PCBs  10  and  14 , respectively. In this manner, the I/O signals of logic circuits of one PCB may be interfaced with I/O signals of logic circuits of another PCB independent of the difference in operational voltage levels thereof. 
         [0015]    There may be occasions in which connecting the power supply of one board to another board is considered undesirable for whatever reason. The block diagram schematic of  FIG. 2  depicts a suitable alternative embodiment to that of  FIG. 1  for configuring the bank of I/O gates  18  to render the I/O signals of the interfacing board  14  compatible with the I/O signals of the board  10 . In the embodiment of  FIG. 2 , a voltage regulator (VR)  30  may be disposed on board  14  to power the bank of I/O gates  18  via port  22 . An exemplary voltage regulator  30  for the present embodiment may be of the type manufactured by Linear Technologies under the model no. LT1963, for example. The VR  30  may be powered by the local supply V c  and its output voltage level governed by an external signal over line  32  to set the operational voltage level of the bank of gates  18 . 
         [0016]    In the present embodiment, the governing signal  32  may be generated by a signal generator circuit  34  disposed on the mother board  10 . If the operational voltage level of the logic circuits  12  of board  10  are set by the supply V S , then the signal generator  34  may be governed thereby to generate the signal over line  32  to control the VR  30  as illustrated by the line  36 . In the alternative, the signal generator  34  may be governed by a signal generated by the logic circuits  12  as shown by the dashed line  38 . The intent is to set the operational voltage level of the bank of gates  18  by the VR  30  to render the I/O signals of the interfacing board  14  compatible with the I/O signals of the motherboard  10 . 
         [0017]    For example, if the daughter board  14  is installed on a different mother board which is powered by a different voltage level than V S , then the operational voltage level of the I/O signals of the ASIC of the different mother board will also change. In the embodiment of  FIG. 2 , the signal generator  34  may detect this change by either monitoring the voltage level of its power supply via line  36  or monitoring the operational voltage of the logic of the new ASIC via line  38 . In either case, the signal generator  34  may adjust the governing signal  32  accordingly to control the VR  30  to render the appropriate supply voltage to the bank of I/O gates  18  via port  22 . In this manner, the signal generator  34  may render the I/O signals of the PGA  16  on the daughter board  14  compatible with the I/O signals of any mother board and ASIC interfaced thereto. 
         [0018]    In one case as depicted in  FIG. 3 , the governing signal  32  may be an analog signal which is input to a voltage reference port of the VR  30  to adjust its output voltage V o  commensurate therewith. The output V o  powers the bank of gates  18  via port  22 . In this example, the signal generator  34  is connected via line  32  to the VR  30  to adjust the output voltage thereof to render the I/O signals of the logic circuits  16  compatible with the logic circuits  12 . In one embodiment as depicted in  FIG. 4 , a governing analog signal  32  of the VR  30  may be set by a resistance network comprising resistors R 1  and R 2  powered by a voltage V D  which may be the same as V S  or different therefrom. In this embodiment, the voltage of signal  32  may be set commensurate to the supply voltage powering the ASIC  12  or by adjusting the resistance of the resistance network R 1 /R 2  accordingly. 
         [0019]    In another embodiment as depicted in  FIG. 5 , the governing signal  32  of the VR  30  may be digitally set by a plurality of resistance networks  40 ,  42  and  44  configured in parallel and powered by the voltage V D  which may be the same as V S  or different therefrom. Each resistance network may include a pull-up resistor and a pull-down resistor. The voltage at each connecting node of the pull-up and pull-down resistors of the resistance networks  40 ,  42  and  44  may be considered a digital one or zero to provide the digital code  32  to the VR  30 . In this embodiment, the digital code of signal  32  may be set commensurate to the supply voltage powering the ASIC  12  by adjusting the resistance of the resistance networks  40 ,  42  and  44 . For example, when the ASIC  12  is replaced with a new ASIC with a different operational voltage, the resistance of the networks  40 ,  42  and  44  may be set to provide the appropriate digital code for signal  32  to reflect the new operational voltage. 
         [0020]    The resistance of each network  40 ,  42  and  44  may be adjusted or set by installing or removing a pull-up or pull-down resistor thereof. For instance, for a ‘1,1,1’ digital code may be implemented by installing a predetermined ohm pull-up resistor and removing the pull-down resistor in each of the networks  40 ,  42  and  44 . Another implementation to adjust the resistance of the networks  40 ,  42  and  44  for the same code may be to install a 100 ohm resistor for each pull-up resistance and install a 1K ohm resistor for each pull-down resistance. 
         [0021]    In yet another embodiment as depicted in  FIG. 6 , a microcontroller  50  may be included on the PCB  10  to control a digital-to-analog (D/A) converter  52  to render the appropriate voltage of the governing signal  32 . In this embodiment, the microcontroller  50  may be operative to monitor the voltage of the power supply V S  of the ASIC  12  via line  54  or to monitor the operational voltage of the logic of the ASIC  12  via line  56  and control the output voltage of the D/A converter  52  accordingly. 
         [0022]    In yet another alternate embodiment of the present invention as illustrated in the block diagram schematic of  FIG. 7 , the voltage regulator  30  may be replaced with a programmable power module  60  which may be of the type manufactured by Linear Technology bearing model no. LTC7510, for example. In this example, the power module  60  may be governed by the governing signal  32  to produce the desired voltage output to power the bank of gates  18  via port  22 . The power module  60  may either accept an analog or digital signal  32  to adjust or trim its output voltage to the desired level to render the I/O signal levels between the logic circuits  12  and  16  compatible with one another. 
         [0023]    In summary, the present invention allows I/O signals of logic circuits on an interfacing PCB to interface compatibly with I/O signals of fixed logic circuits having different operational signal levels. Accordingly, the invention increases design flexibility on future systems by allowing for I/O signal level adjustments to achieve interface compatibility as chip technology changes the operational voltage level of fixed logic circuits. 
         [0024]    While the present invention has been described herein above in connection with one or more embodiments, it is understood that such presentations were made merely by way of example. For example, some of the embodiments depict control circuits on the PCB  10  and the voltage regulation circuits on PCB  14 , but this need not be the case. These circuits may be embodied on either PCB  10  or PCB  14  or in a different location altogether. Therefore, the present invention should not be limited in any way to any such described embodiments, but rather construed in breadth and broad scope in accordance with the recitation of the claims appended hereto.