Abstract:
An apparatus comprising a first stage and a second stage. The first stage may be configured to generate an intermediate signal having a first voltage in response to an input signal having a second voltage received from a pad. The second stage may be configured to generate a core voltage in response to the first voltage. The voltage received from the pad may operate at a voltage compliant with one or more published interface specifications.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to I/O devices generally and, more particularly, to a method and/or apparatus for implementing a low power receiver for a high voltage interface implemented with low voltage devices. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional circuits use thin gate oxide IO devices to operate reliably on a 1.8V supply. Conventional circuits sometimes implement a comparator-based architecture for a receiver used in high voltage interfaces implemented with low voltage devices. Since such a comparator consumes DC power, this solution has the drawback of having constant power consumption. 
         [0003]    It would be desirable to implement a receiver architecture that operates reliably under normal operation where I/O devices operating at one voltage (e.g., in the range of 2.5V/3.3V) may be used to interface with core devices operating at a second voltage (e.g., in the range of 1.8V) to meet LVCMOS JEDEC specifications. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention concerns an apparatus comprising a first stage and a second stage. The first stage may be configured to generate an intermediate signal having a first voltage in response to an input signal having a second voltage received from a pad. The second stage may be configured to generate a core voltage in response to the first voltage. The voltage received from the pad may operate at a voltage compliant with one or more published interface specifications. 
         [0005]    The objects, features and advantages of the present invention include providing an I/O device that may (i) reduce DC power consumption, (ii) be implemented using 1.8v I/O devices, (iii) interface with 2.5v/3.5v core supplies, (iv) meet LVCMOS JDEC Specifications, and/or (v) provide a high voltage interface to protect one or more circuits on an Integrated Circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other objects, features and advantages of the present invention will be apparent from the following detailed description and the appended claims and drawings in which: 
           [0007]      FIG. 1  is a diagram of a context of an embodiment of the invention; 
           [0008]      FIG. 2  is a diagram of a receiver in accordance with an embodiment of the invention; 
           [0009]      FIG. 3  is an alternate embodiment of a receiver; 
           [0010]      FIG. 4  is a plot of the circuit of  FIG. 2 ; 
           [0011]      FIG. 5  is a transient plot of circuit of  FIG. 1 ; 
           [0012]      FIG. 6  is a DC plot of the circuit of  FIG. 3 ; and 
           [0013]      FIG. 7  is a transient plot of the circuit of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    Referring to  FIG. 1 , a block diagram of a circuit  50  is shown illustrating a context of an embodiment of the invention. The circuit  50  generally comprises a plurality of devices (or circuits)  60   a - 60   n,  a plurality of devices (or circuits)  70   a - 70   n , a block (or circuit)  80 , and a plurality of devices (or circuits)  100   a - 100   n.  In one example, the devices  60   a - 60   n  may be implemented as pins connected to a package of an integrated circuit (IC). The devices  70   a - 70   n  may be implemented as bond pads. The bond pads  70   a - 70   n  may be connected to the pins  60   a - 60   n  through a lead frame. The pads  70   a - 70   n  may be connected to the circuits  100   a - 100   n  through a plurality of bond wires. The circuit  80  may be implemented as a core circuit. The circuits  100   a - 100   n  may be implemented as a number of interface circuits. Each of the circuits  100   a - 100   n  may be configured to interface with supply voltages higher than the devices used to implement the circuits  100   a - 100   n.    
         [0015]    Referring to  FIG. 2 , a diagram of a circuit  100  is shown illustrating an embodiment of the invention. The circuit  100  generally comprises a block (or circuit)  110 , a block (or circuit)  112 , a block (or circuit)  114  and a block (or circuit)  116 . The device  110  may be implemented as a transistor. The device  110  may be implemented as a first stage. The device  110  may have a gate that may receive a signal (e.g., BIAS). The device  110  may present a signal (e.g., PAD_MOD) received from the pad  70   a.  The device  112  may be implemented as a second stage. The device  114  (e.g., IPAD) may be implemented as a current source. The device  116  may be implemented as an inverter. The first stage  116  is generally designed to trip at around 50% of an 10 supply voltage (e.g., VDDIO) in order to meet JEDEC Specifications. For example, the first stage  116  may be implemented as a 2.5V LVCMOS device that may trip at 1.25V. The inverter  116  may be implemented as a balanced inverter. In one example, the device  116  may be implemented as a 1.8V IO device that may be designed to trip at 0.9V. For the inverter to trip at 1.25V without the circuit  100 , a skew of the ratio between PMOS to NMOS occurs, which degrades transient performance of inverter across PVT corners. The skewing without the circuit  100  also limits the frequency of operation. The circuit  100  may be configured to reduce and/or eliminate such skewing. The circuit  100  may be configured to increase transient performance. 
         [0016]    Referring to  FIG. 3 , a diagram of a circuit  100 ′ is shown. The circuit  100 ′ illustrates an alternate implementation of the circuit  100 . The circuit  100 ′ is shown including a transistor M 1 , and a device  120 . The transistor M 1  may be connected between the source and drain of the transistor  112 . The inverter  120  may present the voltage PAD MOD to a gate of the transistor M 1 . 
         [0017]    The circuit  100  (or  100 ′) may provide an architecture to implement a receiver that may avoid skewing of the inverter  116 . A signal from the PAD  70   a  may be passed through pass gate  110  as the signal PAD_MOD. The pass gate  110  may have a gate that may be connected to the signal BIAS. The signal BIAS may be implemented as a voltage that is generally designed to be less than 2 Volts across process, voltage and temperature (PVT) variations. 2 Volts may be the approximate reliability limit for a 1.8V IO device. While a 2 volt target for the signal BIAS is provided as an example, the particular voltage for the signal BIAS may be varied to meet the design criteria of a particular implementation. 
         [0018]    The pass gate  110  may be implemented as a native device. The pass gate  110  may limit the voltage on the signal PAD_MOD to the value of the voltage of the signal BIAS. The devices in the stages following the circuit  100  may be protected from voltage stress (e.g., voltages that are larger than an operating voltage of the other devices). The signal PAD_MOD may be passed through a diode connected device  112 . The device MDIO ( 112 ) may present a signal (e.g., PAD-VT) that may operate at the voltage received from the PAD minus Vt, where Vt is a threshold drop from the device MDIO. The voltage threshold Vt may be adjusted by around 0.3 to 0.4V by adjusting the current source IPAD. The signal PAD-VT presented to the inverter  116  may be designed to lag by the voltage threshold Vt from the pad  70   a.    
         [0019]    Referring to  FIG. 4  and  FIG. 5 , DC and transient plots are shown of the circuit  100 . Current consumption for the pad  70   a  (e.g., shown as PAD) is in the range of 40 uA during a nominal condition. The signal PAD-VT shows a drop from the voltage PAD. A shift of the switching threshold towards a JEDEC range for high voltage applications is normally implemented. 
         [0020]    Referring to  FIG. 6  and  FIG. 7 , DC and transient plots are shown of the circuit  100 . Current consumption of the signal PAD is shown in the range of 4 uA during a nominal condition. Similarly, the signal PAD-Vt shows a drop from the voltage PAD. A shift of the switching threshold towards a JEDEC range for high voltage applications is normally implemented. 
         [0021]    The circuit  100  may be used to clamp a signal received from one of the pads  70   a - 70   n  to known voltage if the signal received is floating. The signals received from the pads  70   a - 70   n  may be processed to operate as a core level signal to meet JEDEC specifications. The circuit  100  may generate the signal PAD-Vt to help achieve a JEDEC compliant signal. The device  110  may be implemented as a native device. The device may be used to clamp the signal PAD_MOD to be the same as gate voltage (e.g., BIAS) even if input voltage (e.g., PAD) is higher than the gate voltage. The output of the native device  110  will normally be limited to voltage of the signal BIAS. 
         [0022]    The various signals of the present invention are generally “on” (e.g., a digital HIGH, or 1) or “off” (e.g., a digital LOW, or 0). However, the particular polarities of the on (e.g., asserted) and off (e.g., de-asserted) states of the signals may be adjusted (e.g., reversed) accordingly to meet the design criteria of a particular implementation. 
         [0023]    The terms “may” and “generally” when used herein in conjunction with “is(are)” and verbs are meant to communicate the intention that the description is exemplary and believed to be broad enough to encompass both the specific examples presented in the disclosure as well as alternative examples that could be derived based on the disclosure. The terms “may” and “generally” as used herein should not be construed to necessarily imply the desirability or possibility of omitting a corresponding element. 
         [0024]    The present invention may also be implemented by the preparation of ASICs (application specific integrated circuits), Platform ASICs, FPGAs (field programmable gate arrays), PLDs (programmable logic devices), CPLDs (complex programmable logic device), sea-of-gates, RFICs (radio frequency integrated circuits), ASSPs (application specific standard products), one or more integrated circuits, one or more chips or die arranged as flip-chip modules and/or multi-chip modules or by interconnecting an appropriate network of conventional component circuits, as is described herein, modifications of which will be readily apparent to those skilled in the art(s). 
         [0025]    While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention.