Abstract:
The present invention relates to electronic driver circuits, and more particularly, to low power electronic driver circuits having low manufacturing costs. The present invention is a circuit design that utilizes two transistor types that can be manufactured together thereby reducing the number of processing steps and masks and resulting in lower cost.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/827,545, filed on Jun. 30, 2010, which claims priority to and the benefit of U.S. Provisional Patent Application No. 61/270,342, filed on Jul. 7, 2009, the entire disclosure of each of which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electronic driver circuits, and more particularly, to low power electronic driver circuits having low manufacturing costs. 
     SUMMARY OF THE INVENTION 
     Logic circuits have been constructed from many different transistor types. The preferred type at present for portable devices is CMOS. Bipolar circuits, such as TTL or RTL, are very fast but consume much power. This is because current is flowing continuously. TTL will typically utilize PNP and NPN type bipolar transistors. CMOS utilizes two transistor types: NMOS and PMOS. The advantage to CMOS is that only one of two transistors is switched on at a time resulting in a circuit in which current flows only when the logic state is switching. Certain capacitances in the circuit (e.g., the gate of the MOS devices) can result in slower operation, but power consumption is low. A disadvantage to these approaches is that of the multiple transistor types, each can require a large number of processing steps and photolithography masks to manufacture. Multiple types means multiple large sets of processing steps and expensive masks. 
     The present invention is a circuit design that utilizes two transistor types that can be manufactured together thereby reducing the number of processing steps and masks and resulting in lower cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a prior art driver circuit using CMOS logic. 
         FIG. 2  illustrates a prior art, RTL driver circuit using bipolar logic. 
         FIG. 3  illustrates a prior art driver circuit using NMOS logic. 
         FIG. 4  illustrates a driver circuit according to the present invention. 
         FIG. 5  illustrates a driver circuit according to the present invention with output amplification. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Logic circuits have been constructed from many different transistor types.  FIG. 1  depicts a prior art CMOS logic device (an inverter). The device is simple in design having just an NMOS  100  and a PMOS  101  transistor. When the input is high, the NMOS transistor  100  is switched on and the PMOS transistor  101  is switched off; with the NMOS transistor  100  switched on, the output is connected through the NMOS transistor  100  to ground. When the input is low, the PMOS transistor  101  is switched on and the NMOS transistor  100  is switched off; with the PMOS transistor  101  switched on, the output is connected through the PMOS transistor  101  to the positive supply. Since the NMOS  100  and PMOS transistor  101  are not on simultaneously (except for a moment during transition of the input from high to low or low to high), current does not flow in the circuit except during switching. Even at the output, given the typical case where the output is connected to the input of another similar device, current only flows through the switched on NMOS  100  or PMOS transistor  101  during transition so as to charge or discharge the MOS transistor gates of the subsequent stages. 
     With a bipolar circuit, as is depicted in  FIG. 2 , current typically flows from stage to stage as a function of the logic state. In  FIG. 2 , a RTL inverter will consume no power when the input is high as this will reverse bias the base junction of PNP transistor  110  resulting in that transistor being switched off. However, when the input is low, current flows from the positive supply through the emitter and base connections and to the low input source; current also flows from the positive supply through the transistor  110  and through resistor  111  to ground resulting in a high voltage at the output. In a typical case where the output is connected to the input of a similar circuit, when current is flowing through the first circuit resulting in a high output, the transistor of a subsequent circuit will be switched off. However, when the input is high to the first circuit and the current if not flowing, the output will be low and a subsequent circuit will have current flowing from the positive supply through the emitter-base junction and back into the resistor of the prior circuit. Current typically is flowing somewhere all the time. The same is generally true for RTL constructed from NPN transistors and for TTL logic. One advantage to RTL is that is can be made from a single transistor type (NPN or PNP). 
     What is needed is a logic design in which only one transistor type is used and current generally does not continuously flow. One such design is shown in  FIG. 3 . In this MOS design, only NMOS transistors are used. The output is controlled by NMOS transistor  120 . A problem presented here is that in order to pass the voltage level of the supply to the output, the voltage on the gate of NMOS transistor  120  must exceed the voltage to be provided to the output by the threshold voltage (V th ) of the NMOS transistor  120 . To achieve this, assuming that the highest available voltage is the supply voltage, the gate voltage must be generated by the circuit. In this case, the voltage on the gate of NMOS transistor  120  is generated in stages. First, the largest available voltage (the supply voltage) is applied to the precharge (PRCH) input through diode  121  while the boost (BOOST) and reset (RST) inputs are held low. Then, the boost input is raised and the rising edge is capacitively coupled through NMOS transistor  122  which is wire up as a capacitor. The capacitively coupled boost voltage will raise the voltage on the gate resulting from the precharge input up to a new higher voltage that will enable the output NMOS transistor  120  to pass the desired voltage to the output. To switch off the output, the precharge input must first be lowered and then the reset input (RST) raised; this will dump the charge from the gate of NMOS transistor  120  through reset NMOS transistor  123  to ground, thereby switching off the output NMOS transistor  120 . The disadvantage is that the series of steps to switch on and off the various inputs results in slower operation. (Similar circuits can be constructed using opposite voltage polarities and PMOS transistors.) 
     The present invention is a combination of bipolar logic and MOS logic.  FIG. 4  depicts a bipolar-MOS type circuit. In this circuit, output PNP transistor  131  will provide a voltage pulse to the output that can be within the emitter-collector saturation voltage (V CESAT ) of the positive supply. This is accomplished by connecting the base of PNP transistor  131  through enable NMOS transistor  132  to NMOS transistor  133  which is wired up as a capacitor; the current will flow from the positive supply through the emitter-base junction of PNP transistor  131  and into capacitor  133  until that capacitor is fully charged. The size of capacitor  133  determines the duration of this current pulse. While this current pulse is flowing, current will flow to the output in an amplified amount as a function of the gain (i.e., the transistor Beta, β) of PNP transistor  131 . When capacitor  133  is charged, the current through PNP transistor  131  stops flowing. The enable NMOS transistor  132  is turned on by raising the voltage on the enable input (EN). The circuit is reset by lowering the voltage on the enable input (EN) and then raising the voltage on reset input (RST) which will cause the charge on reset NMOS transistor  134  to be dumped to ground. Because PNP transistor  131  is switched on by lowering the voltage on its base, no boost voltage level is required and the two steps of precharging and then boosting as is required for the circuit depicted in  FIG. 3  is replaced by the single step of raising the enable input in the circuit depicted in  FIG. 4 . This results in greater speed in operation. Furthermore, since the current only flows when the enable input (EN) is first raised (i.e., until capacitor  133  is charged), the power consumed is similar to that of a CMOS circuit (i.e., current only flows during switching while the gate of a MOS transistor is being charged). Also, the output voltage pulse can come to within V CESAT  of the supply voltage without boost circuitry. (Similar circuits can be constructed using opposite voltage polarities and PMOS and NPN transistors.) 
     A variation on the circuit of  FIG. 4 , would be to eliminate the capacitor (transistor  133 ) and connect enable NMOS transistor  132  directly between the base of PNP transistor  131  and ground (eliminating the capacitor  133  also eliminates the requirement for a reset transistor  134  as well). While this variation will consume more power for the static current path from the supply voltage through PNP transistor  131  and enable NMOS transistor  132  to ground, it is a simpler circuit that can be operated for longer than just the time to charge the capacitor (transistor  133 ). Alternatively, reset NMOS transistor  134  could be switched on while enable input (EN) is high thereby bypassing capacitor transistor  133  to accomplish the same effect. 
       FIG. 5  depicts an identical circuit to that depicted in  FIG. 4  except that the output has increased gain. In this instance, the current to the output is increased by an additional β multiplier (of secondary output NPN transistor  135 ) in a darlington-like configuration. The tradeoff is that the maximum output voltage is an additional V f  lower than that of the circuit of  FIG. 4  due to the forward voltage drop (V f ) of the base-emitter junction of NPN transistor  135 . 
     The present invention can be manufactured using standard processes. In the course of manufacturing the MOS transistors, polysilicon gate material is deposited and this is then patterned and etched and then dopants are implanted. With the present invention, some of the polysilicon material deposited to form the MOS gates can be patterned and etched to remain above areas that are just field oxide or the like. Then, when implanting the MOS transistors, this poly can be implanted to form the PNP transistors at the same time. When contacts to the MOS gates are formed, contacts to the base, emitter and collectors of the PNP transistors can also be formed at the same time. 
     Furthermore, the present invention can be used in a variety of circuits. In particular, embodiments of the present invention can be used in the design of devices such as memory products, and in particular non-volatile memory products, for portable devices wherein low power is desirable as well as other devices wherein low power may not be as necessary. The present invention can be implemented with cross point memory arrays wherein the memory arrays&#39; surrounding circuitry is also implemented with embodiments of the present invention; these arrays may be one of many tiles or sub-arrays in a larger device or an array within a 3-D arrangement of arrays or tiles. In such a memory device, the storage cells can incorporate field-emitters, diodes or other non-linear conductor devices that conduct current better in one direction than the other for a given applied voltage. The storage element can be a fuse, an antifuse, a phase-change material such as a Chalcogenide (including a Chalcogenide in which the programmed resistivity can be one of two resistance values and, in the case of more than one bit per cell storage cells, in which the programmed resistivity can be one of three or more resistance values), a resistance that can be electrically altered, or a field-emitter element programming mechanism including an element for which the resistance or the volume is changeable and programmable. 
     The bipolar-MOS driver of the present invention will find applications in array circuits such as a memory array, display array, and the like. In such array applications, the mechanism to control the voltage on the enable input (EN) can be implemented as is done in U.S. patent application Ser. No. 11/926,778 and this Allowed patent application Ser. No. 11/926,778 is hereby included herein by reference in its entirety. In that allowed patent application Ser. No. 11/926,778, the gates of the MOS drivers on a plurality of row lines (said plurality comprising either all of the rows or a subset of the rows) of the array are all charged by a precharge mechanism and then all but one driver is discharged by means of a binary diode decoder/selector array (using diodes or some other non-linear current steering devices) thereby leaving one driver enabled. In the present invention, a plurality of driver bipolar transistor  131 /enable MOS transistor  133  pairs associated with a plurality of row lines of the array (said plurality comprising either all of the rows or a subset of the rows of the array) could be activated by charging the base of every enable MOS transistor  133  of the plurality (but, typically while the supply voltage is switched off by a switching means, said means not shown in  FIG. 4 , but that is well understood by those skilled in the art) and then all but one enable MOS transistor  133  is discharged by means of a binary diode decoder/selector array (using diodes or some other non-linear current steering devices or other decoding selection means) thereby leaving only one driver enabled. After such a precharge and then all-but-one disabling of drivers, the supply voltage could be switched on. (Of course, the row lines could be column lines if the array were rotated 90 degrees.) 
     Memory devices incorporating embodiments of the present invention may be applied to memory devices and systems for storing digital text, digital books, digital music (such as MP3 players and cellular telephones), digital audio, digital photographs (wherein one or more digital still images can be stored including sequences of digital images), digital video (such as personal entertainment devices), digital cartography (wherein one or more digital maps can be stored, such as GPS devices), and any other digital or digitized information as well as any combinations thereof. Devices incorporating embodiments of the present invention may be embedded or removable, and may be interchangeable among other devices that can access the data therein. Embodiments of the invention may be packaged in any variety of industry-standard form factor, including Compact Flash, Secure Digital, MultiMedia Cards, PCMCIA Cards, Memory Stick, any of a large variety of integrated circuit packages including Ball Grid Arrays, Dual In-Line Packages (DIP&#39;s), SOIC&#39;s, PLCC, TQFP&#39;s and the like, as well as in proprietary form factors and custom designed packages. These packages can contain just the memory chip, multiple memory chips, one or more memory chips along with other logic devices or other storage devices such as PLD&#39;s, PLA&#39;s, micro-controllers, microprocessors, controller chips or chip-sets or other custom or standard circuitry. 
     Many variations come to mind in light of the present teaching. These include using any combination of switch devices that can be manufactured in parallel, or mostly or generally in parallel, in a semiconductor fabrication facility (fab). 
     The foregoing description of and examples of the preferred embodiment of the invention and the variations thereon have been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description.