Abstract:
A device to sense changes in current level almost instantaneously and convert those current levels, almost instantaneously, into voltage levels that may be used by a microprocessor for logical and mathematical operations. This device employs a current conveyer to receive two inputs representing current levels. Once a sufficient difference in current levels is detected by the current conveyer, the current from each input is passed to a P-sense amplifier that converts the current to an equivalent voltage level and amplifies that voltage level. Thereafter, two outputs are generated reflecting an amplified voltage of the current input

Description:
FIELD  
         [0001]    The invention relates to a device for current sensing in an amplifier with PMOS (Positive channel Metal Oxide Semiconductor) voltage conversion. More specifically, the invention relates to a device that may quickly convert a current detected to a voltage that may be used for processing purposes in a microprocessor.  
         BACKGROUND  
         [0002]    In the rapid development of computers many advancements have been seen in the areas of processor speed, throughput, communications, and fault tolerance. Microprocessor speed is measured in cycles per second or hertz. Today&#39;s high-end 32-bit microprocessors operate well in excess of 1 Ghz (gigahertz), one billion cycles per second, and in the near future this is expected to go substantially higher. At this sort of cycle speed a clock would have to generate a pulse or cycle at least once each billionth of a second and usually several orders of magnitude faster. It is during this clock cycle that the processor executes programmed functions. These functions would include everything from a portion of a read function to some mathematical operation. Further, complexity of the operation performed by a microprocessor has increased exponentially. Today, a microprocessor is expected to perform mathematical operations on 32, 64, and a 128 bit words. Further, in microprocessor chips not only are mathematical as well as logical functions performed but memory related functions take place such as the management of cache memory. With the increase in the complexity of the functions performed the lengths in data paths and logic paths required has also increased. This increase in data and logic paths length has served to slow processor execution. This is because the fundamental mechanism used to communicate between components is through resistance/capacitance (RC) networks which are inherently slow. The longer the distance of the logic path the more R/C networks involved and the slower the processor. Thus, the need to increase speed is at odds with the need to increase complexity.  
           [0003]    The reason for this conflict lies within the fundamental mechanism by which components in a processor on a single chip exchange information. The fundamental mechanism by which data processors operate is through the representation of logical states in data as binary values (either zero or one). At the hardware level a binary value of one may be represented by high or positive voltage or current, while a binary value of zero may be represented by a low or negative voltage or current. Presently a transmitting circuit would set a voltage high and that would be transmitted to a receiving circuit. The receiving circuit would determine or sense the signal, referred to as voltage sensing, and take the appropriate action.  
           [0004]    An alternative approach would utilize current sensing rather than voltage sensing and this is often called a differential current system and the receiving or detecting circuit would be called a current conveyer. This current conveyer has almost zero input resistance at the leading end and thus the current conveyer can detect, almost instantaneously, the presence of current. However, all computations and logic in the microprocessor are still based on voltage rather than current. Therefore, current must then be converted back to voltage and the current mechanisms, prior to the present invention, used to convert from current to voltage are relatively slow because it was more complex requiring more devices, that took up more space on the chip and used more power which required more cooling. Thus, a potential limit, block or envelop exists that may prevent the further increase in microprocessor speed and complexity to one, two, three, or more gigahertz per second.  
           [0005]    Therefore, what is needed is a device that will take advantage of the near instantaneous detection of a change in current realized by a current conveyer but will almost as quickly be able to convert this detected current back to a voltage. This device should be simple to implement and thereby be able to operate quickly. Further, it must take up as little space on the microprocessor chip so that the space may be utilized for logic, mathematical functions as well as expanded cache memory. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The foregoing and a better understanding of the present invention will become apparent from the following detailed description of exemplary embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the foregoing and following written and illustrated disclosure focuses on disclosing example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and the invention is not limited thereto. The spirit and scope of the present invention are limited only by the terms of the appended claims.  
         [0007]    The following represents brief descriptions of the drawings, wherein:  
         [0008]    [0008]FIG. 1 is an example embodiment of the circuit used to convert current detected back to voltage in the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0009]    Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference numerals and characters may be used to designate identical, corresponding or similar components in differing figure drawings. Further, in the detailed description to follow, exemplary sizes/models/values/ranges may be given, although the present invention is not limited to the same. As a final note, well-known components of computer networks may not be shown within the FIGS. for simplicity of illustration and discussion, and so as not to obscure the invention.  
         [0010]    [0010]FIG. 1 is an example embodiment of the device/circuit used to convert differential current detected back to voltage in the present invention. The circuit show in FIG. 1 of this example embodiment of the present invention is divided into two major components. The first component is a current conveyer  10  and the second is a P-sense amplifier  20 .  
         [0011]    Still referring to FIG. 1, the current conveyer  10  serves the functions of providing the circuits with zero input resistance so that a current input at input  30  (also labeled “in”) and its complement second input  40  (also labeled “in#”) may be sensed as a change in current almost instantaneously. Further, the current conveyer  10  will output a relatively small differential voltage at first differential link  50  (also labeled “d”) and at second differential link  60  (also labeled “d#”). The current conveyer  10  is enabled using enable signal  80 . It is important that a first NMOS (Negative channel Metal Oxide Semiconductor) transistor  130  and second NMOS transistor  140  be tuned or sized to maintain the first differential link  50  (also labeled “d”) and the second differential link  60  (also labeled “d#”) close to ground to insure P-sense amplifier  20  functions effectively.  
         [0012]    Still referring to FIG. 1, the current conveyer  10  also has a first PMOS transistor  90 , a second PMOS transistor  100 , a third PMOS transistor  110  and a fourth PMOS transistor  120 . In addition, first PMOS transistor  90  is cross linked to second input link  40  via link  200  and second PMOS transistor  100  is cross linked to input link  30  via link  210 .  
         [0013]    Still referring to FIG. 1, the second major component of the present invention is the P-sense amplifier  20 . The P-sense amplifier has a second supply voltage  180  connected to fifth PMOS transistor  190  which is in turn connected to a clock  220 . The P-sense amplifier  20  has a sixth PMOS transistor  240  and a seventh PMOS transistor  230 . Sixth PMOS transistor  240  receives input from first differential link  50  and seventh PMOS transistor  230  receives its input from current conveyer  10  from second differential link  60 . In addition, the sixth PMOS transistor  240  and seventh PMOS transistor  230  are connected to an addition four NMOS transistors in the P-sense amplifier  20 . The NMOS transistors in the P-sense amplifier  20  are third NMOS transistor  250 , fourth NMOS transistor  260 , fifth NMOS transistor  270 , and sixth NMOS transistor  280 . Third NMOS transistor  250  and sixth NMOS  280  are also connected to second clock  350  and third clock  360 . Further, third NMOS transistor  250  is connected to ground  290 , fourth NMOS transistor  260  is connected to ground  300 , fifth NMOS transistor  270  is connected to ground  310 , and sixth NMOS transistor  280  is connected to ground  320 . The P-sense amplifier  20  generates voltage outputs via first output  370  (also labeled “out#”) and second output  380  (also labeled “out”). It should be noted that fifth NMOS transistor  270  is cross connected to output  370  via link  330  while fourth NMOS transistor  260  is cross connected to output  380  via link  340 , thereby grounding output  370  and  380  during precharge phase, discussed ahead.  
         [0014]    Still referring to FIG. 1, the device having the current conveyer  10  and the P-Sense amplifier  20  operates in two phases. The first phase is a precharge phase in which the enable signal  80  is set to high and the current conveyer  10  is disabled. However, the first NMOS transistor  130  and second NMOS transistor  140  are on because of being connected to the first supply voltage  70  which is providing them with power. Since first NMOS transistor  130  and second NMOS transistor  140  are connected to ground  160  and ground  170 , respectively, this maintains first differential link  50  and second differential link  60  at ground also during this precharge phase. Further, second and third clocks  350  and  360  are held high and all the third through sixth NMOS transistors  250 - 280  are forced to low or to grounds  290  through  320 . In addition, first clock  220  is also set high which automatically turns off fifth PMOS transistor  190  by the nature of how PMOS transistors operate. Of course, as would be appreciated by one of ordinary skill in the art, first clock  220 , second clock  350 , and third clock  360  may be the same clock. This completes the precharge phase which serves to set the device to a ground state including output  370  and  380 .  
         [0015]    The second phase that the device operates in is an evaluation phase. The evaluation phase serves to activate the device and allows it to detect current and convert it to voltage in a simple and almost instantaneous manner. This begins by the enable signal  80  being set low in order to activate or enable third PMOS transistor  110  and the four the PMOS transistor  120 . This is opposite to that of the precharge phase where the enable signal  80  is set high and current from input  30  and input  40  are prevented from moving through the current conveyer  10  to the P-sense amplifier  20 . Since input  30  and input  40  have differential current being supplied a delta exists between the two inputs. Once sufficient differential voltage is obtained between first differential link  50  and second differential link  60  then clock  220  is set low. As would be appreciated by one of ordinary skill in the art, a differential voltage value of between approximately 100 and 150 millivolts would be adequate to set clock  220  low and thus activate the P-sense amplifier  20  by activating fifth PMOS transistor  190  and enabling supply voltage  180 . Current would now be following to sixth PMOS transistor  230  and seventh PMOS transistor  240 . However, since the first PMOS transistor  10  and second PMOS transistor  120  have been enabled, a differential voltage now is sensed by sixth PMOS transistor  240  and seventh PMOS transistor  230 . Sixth PMOS transistor  240  and seventh PMOS transistor  230  may also be referred to as differential input pairs since they are receiving differential input voltage.  
         [0016]    Still referring to FIG. 1, it should also be noted that fourth NMOS transistor  260  is cross connected to output  380  and fifth NMOS transistor  270  is cross connected to output  370 . The NMOS transistors in P-sense amplifier  20  include third NMOS transistor  250 , fourth NMOS transistor  260 , fifth NMOS transistor  270 , and sixth NMOS transistor  280 . Since fourth NMOS transistor  260  and fifth NMOS transistor  270  are no longer ground they act as feedback devices via links  330  and  340 . Further, since a small differential voltage is being applied to P-sense amplifier  20  via current conveyer  10 , a large differential voltage would be output from output  370  and output  380  in a positive feedback loop. Thus, either output  370  may be forced high because of a higher differential current and output  380  is forced low or vice versa. Both output  370  and output  380  cannot be high or low at the same time.  
         [0017]    For example, if input  30  has a higher current level than input  40 , then first differential link  50  would have a higher voltage level than second differential link  60  and as a result the voltage output from output  380  would also be higher than that of output  370 .  
         [0018]    The benefit resulting from the present invention is that a simple, reliable, fast device is used to convert current representing binary values to voltage representing binary values. Using this device a significant obstacle to more complex and faster microprocessors has been removed. Further, since the design is simpler it requires less space on the microprocessor and uses less energy and thus generate less heat.  
         [0019]    While we have shown and described only a few examples herein, it is understood that numerous changes and modifications as known to those skilled in the art could be made to the example embodiment of the present invention. Therefore, we do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.