Patent Abstract:
A level translator circuit for use between a lower voltage potential circuit and a higher voltage potential circuit is disclosed. The translator circuit comprises a first transistor coupled to the lower voltage potential circuit and a bootstrap mechanism coupled to the first transistor. The circuit includes a second transistor coupled to the first transistor, a higher voltage potential and the higher voltage potential circuit, and a third transistor coupled to the higher voltage potential circuit, the higher voltage potential and the second transistor. Finally, the circuit includes a fourth transistor coupled to the higher voltage potential circuit, the third transistor and the lower voltage potential circuit. The bootstrap mechanism allows for the dynamic modulation of the first transistor to maximize translation speed and to minimize power consumption. A level translator circuit in accordance with the present invention utilizes a bootstrap mechanism in the gate of the input transistor to allow translating between a low voltage potential to a high voltage potential to be performed more efficiently.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a level translator circuit and more particularly to a level translator circuit for use between circuits having distinct power supplies. 
     BACKGROUND OF THE INVENTION 
     Circuits for voltage level translation are utilized in a variety of applications. Level translator circuits are employed to allow circuits operating at different power supply potentials to communicate with one another. Typically, the area, power and performance of the translator circuit are critical to the operations of each of the different circuits. 
     FIG. 1 is a simple block diagram of a level translator system  10 . The system  10  includes a level translator circuit  12  coupled between circuits  14  and  16 . In this embodiment, Vddl circuit  14  is coupled to a lower voltage supply and Vddh circuit  16  is coupled to a higher voltage supply. Level translation is required only when a circuit on a lower voltage supply interfaces with one on a higher voltage supply. The level translates due to the voltage difference between Vddl circuit  14  and Vddh circuit  16 , causing a resulting leakage current. 
     It is important that a level translator circuit operate efficiently, utilize minimal power, and translate from one voltage supply potential to another as quickly as possible. The speed and performance of conventional translator circuits are typically adversely affected by contention between transistors within the circuit during the translation. For a more detailed description of this issue, refer now to the following discussion in conjunction with the accompanying figures. 
     FIG. 2 illustrates a first embodiment of a conventional level translator circuit  100  coupled between distinct power supplies. In this circuit, cross-coupled pfet transistors  102  and  106  connected to the Vddh circuit  16 ′ are used in conjunction with pull-down nfet transistors  104  and nfet transistor  108  and an inverter  110  which is connected to the Vddl supply. The circuit  100  operates as follows: For propagation of a logical ‘0’ from the Vddl circuit cloud  14 ′, transistor  104  is off, the inverter  110  produces a logical ‘1’ at node- 2  in the form of Vddl volts, which then turns on nfet transistor  108 , driving node-Z to a logical ‘0’, which in turn causes pfet transistor  102  to turn on, thereby raising node- 1  to Vddh volts, which in turn causes pfet transistor  106  to turn off. Since the gate of pfet transistor  106  is at Vddh and the source of pfet transistor  106  is also at Vddh, there is no leakage. This circuit is non-inverting. 
     For propagation of a logical ‘1’ from the Vddl circuit cloud  14 ′, nfet transistor  104  is on, resulting in node- 1  being drawn toward a logical ‘0’. The inverter  110  produces a logical ‘0’ at node- 2  in the form of 0 volts, which results in nfet transistor  108  turning off. Since node- 1  is being drawn to 0 volts, pfet transistor  106  is now on, driving node-Z to a logical ‘1’ in the form of Vddh volts, which in turn reinforces the node- 1  potential of ‘0’ by turning off pfet transistor  102 . 
     FIG. 3 illustrates a second embodiment of a conventional level translator circuit  200  coupled between distinct power supplies. In this configuration, the inverter is eliminated and the source of nfet transistor  204  is connected to the gate input of the nfet transistor  208 , which is connected to the output of the Vddl circuit  14 ″. Also, the gate of nfet transistor  204  is connected directly to the Vddl supply. This circuit  200  operates as follows: For propagation of a logical ‘0’ from the Vddl circuit cloud  14 ″, nfet transistor  204  is on and nfet transistor  208  is off, thereby relinquishing control of node-Z. Since nfet transistor  204  is on, node- 1  is now at O-volts turning on pfet transistor  206 , raising node-Z to Vddh volts, which in turn shuts off pfet transistor  202 , which reinforces the node- 1  level of 0-volts. Also note that this circuit configuration is inverting. 
     For propagation of a logical ‘1’ from the Vddl circuit, nfet transistor  204  is on until the voltage at node- 1  can rise to Vddl-Vtn. This voltage rise begins to shut off pfet transistor  206 . Nfet transistor  208  is now active and pulling node-Z low, which in turn activates pfet transistor  202 , which raises the node- 1  potential to Vddh, which in turn shuts off the leakage from pfet transistor  206 . 
     In each of these embodiments, a basic problem is that there is a contention between nfet transistors  104  or  204  and pfet transistors  102  or  202  when translation takes place. When translation is initiated, these transistors are fighting each other for control of the output. In addition, due to sizing constraints, the nfet transistors  104  or  204  must be stronger than the pfet transistors  102  or  202 . In so doing, there is poor rising low-to-high performance in the output node. 
     Accordingly, the contention between nfet transistors  104  or  204  and pfet transistors  102  or  202  affects the speed and performance of the level translator  100  or  200 . Accordingly, what is desired is a level translator circuit that minimizes the time that these transistors are in contention so as to maximize the performance of the circuit and minimize its power dissipation. The circuit should be cost effective and have performance characteristics equal to or greater than conventional circuits. The circuits should also be easily implemented utilizing existing processes. The present invention addresses such a need. 
     SUMMARY OF THE INVENTION 
     A level translator circuit for use between a lower voltage potential circuit and a higher voltage potential circuit is disclosed. The translator circuit comprises a first transistor coupled to the lower voltage potential circuit and a bootstrap mechanism coupled to the first transistor. The circuit includes a second transistor coupled to the first transistor, a higher voltage potential and the higher voltage potential circuit, and a third transistor coupled to the higher voltage potential circuit, the higher voltage potential and the second transistor. Finally, the circuit includes a fourth transistor coupled to the higher voltage potential circuit, the third transistor and the lower voltage potential circuit. The bootstrap mechanism allows for the dynamic modulation of the first transistor to maximize translation speed and to minimize power consumption. A level translator circuit in accordance with the present invention utilizes a bootstrap mechanism in the gate of the input transistor to allow translating between a low voltage potential to a high voltage potential to be performed more efficiently. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simple block diagram of a level translator system. 
     FIG. 2 illustrates a first embodiment of a conventional level translator circuit coupled between distinct power supplies. 
     FIG. 3 illustrates a second embodiment of a conventional level translator circuit coupled between distinct power supplies. 
     FIG. 4 illustrates a first embodiment of a level translator circuit in accordance with the present invention. 
     FIG. 5 illustrates a second embodiment of a level translator circuit in accordance with the present invention. 
     FIG. 6 illustrates a third embodiment of a level translator circuit in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention relates generally to a level translator circuit and more particularly to a level translator circuit for use between circuits having distinct power supplies. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Thus, the present invention is not intended to be limited to the embodiment shown, but is to be accorded the widest scope consistent with the principles and features described herein. 
     What the applicant has determined is that, by providing a bootstrap mechanism on the input of the circuit, the output can respond more rapidly to the appropriate level while consuming lower power than when utilizing conventional level translator circuits. For a more detailed description of this feature, refer now to the following discussion in conjunction with the accompanying figures. 
     FIG. 4 illustrates a first embodiment of a level translator circuit  300  in accordance with the present invention. In this level translator configuration, node-Y is isolated from the input node via an nfet pass transistor  306 , whose gate is bootstrapped coupled through nfet transistor  304 . Pfet transistor  302  provides a Vddl potential to node-X when the input is a “0” allowing nfet transistor  306  to conduct, thereby propagating the “0” to node-Y. A “0” on node-Y deactivates nfet transistor  312  and allows pfet transistor  310  to conduct raising the output to a Vddh potential. The Vddh potential on node-Z deactivates pfet transistor  308  and ensures no leakage between Vddh and the input. When the input transitions from “0” to high (Vddl), pfet transistor  302  stops conducting, allowing node-X to be bootstrapped above the Vddl supply through the capacitor configured nfet transistor  304 . 
     Node-X can achieve the lower of (Vddl+Vtn) or (Vddl+Vtp) potential before pfet transistor  302  begins to conduct and limits the bootstrapped potential from going any higher. Since node-X is now at Vddl+Vtn, the full input voltage Vddl is transferred to node-Y. This causes nfet transistor  312  to begin conducting more vigorously and reduces the conduction of pfet transistor  310 , allowing the output node-Z to begin to fall towards “0”, which in turn causes pfet transistor  308  to begin to conduct raising the node-Y potential to Vddh. 
     When node-Y reaches Vddh, device pfet transistor  310  is completely off, eliminating any short-circuit current through nfet transistor  312 . Nfet transistor  306  isolates node-Y from the input. Now, should the voltage on node-X be close to or higher than the Vddl (the input bias) plus Vt of nfet transistor  306 , some conduction between node-Y will take place. A means to eliminate this possible conduction will be disclosed later. There are two possible connection configurations for the gate of nfet transistor  312 . One connects the gate of nfet transistor  312  to the input, while the other connects the gate of nfet transistor  312  to the gate of pfet transistor  310 . Either one of these connections will result in a level translation, but only one connection can be made. That is, they are mutually exclusive. 
     The advantage of connecting the gate of nfet transistor  312  to the input lies in the fact that the output stage begins to switch both on and off sooner. For the case when the input is “0” and is rising to a “1”, nfet transistor  312  activates immediately, which results in the output beginning to fall sooner. This advantage results in higher short-circuit current in the output stage since the pfet transistor  310  is still active, but the duration of the current spike is reduced. The maximum voltage that the gate of the nfet transistor will attain is Vddl. Hence, the power associated with charging and discharging the nfet transistor  312  gate node is less than if the other connection were made, since the maximum gate voltage would be Vddl rather than Vddh. 
     For the other transition, input falling from a “I” to a “0”, the nfet transistor  312  of the output stack would discharge more rapidly, and before the pfet transistor  310  could  7 ′ activate, thereby eliminating any short-circuit current resulting in lower power and higher performance. 
     FIG. 5 illustrates a second embodiment of a level translator circuit  400  in accordance with the present invention. Components common to circuit  300  have the same reference numerals. Transistor  402  is used to ensure Vt tracking of transistor  306 ′ and as such may be deemed optional. In addition, a very, very small pfet transistor and nfet transistor stack (pfet transistor  404  and nfet transistor  406 ) can be added between node-X and ground whose gates are connected to Node-Z, and the input, respectively, will remove any excess charge on Node-X and ensure isolation. The stack is used to clamp node-X to |Vtp| when Vin is a “1” and the output has reached a steady state value of “0”. This will completely eliminate any unwanted leakage power. 
     The drawback of this configuration is that active power will be dissipated transiently as the node-X potential is reduced from Vddl or Vddl+|Vtp| down to |Vtp| and the performance of the circuit when the input is transitioning from “1” to “0” will also be compromised, as we must wait for node-X to rise. This configuration results in an inverting level translation like that of the circuit illustrated in FIG.  3 . 
     The optional devices (nfet transistor  402 , pfet transistor  404  and nfet transistor  406 ) can be eliminated if the voltage on node-X is held in check by the threshold voltage of pfet transistor  302 ′. The threshold voltage of pass nfet transistor  306 ′ should be higher than that of optional nfet transistor  406 , due to the body effect on nfet transistor  306 ′. A superior solution is illustrated in FIG.  6 . 
     FIG. 6 illustrates a third embodiment  500  of a level translator circuit in accordance with the present invention. In FIG. 6, a stacked device configuration of pfet transistor  502  and nfet transistor  504  are connected between the Vddl supply and node-X. The gate of nfet transistor  504  is connected to the input, and the gate of pfet transistor  502  is connected to the output Z. The stack is very similar to that which was illustrated in FIG. 4, in that, the gates of the devices are controlled in the same manner. The difference is that the stack is now connected between Vddl and node-X, rather than between ground and node-X. Also, the order of the devices in the stack has been swapped with nfet transistor  504  now connected to node-X. The operation is as follows: For an input at “0”, pfet transistor  302 ″ is active, which forces node-X to Vddl volts. This allows nfet transistor  306 ″ to conduct and propagate the input “0” to node-Y. Node-Y at “0” deactivates nfet transistor  312 ″ and activates pfet transistor  310 ″ allowing the output to attain a “1”. The “1” on the output keeps pfet transistor  308 ″ and pfet transistor  502  off. The input at “0” keeps nfet transistor  504  off as well. There are two possible connection configurations for the gate of nfet transistor  312 ″. One connects the gate of nfet transistor  312 ″ to the input, while the other connects the gate of nfet transistor  312 ″ to the gate of pfet transistor  310 ″. Either one of these connections will result in a level translation, but only one connection can be made. 
     That is, they are mutually exclusive. 
     Now as the input transitions from a “0” to a “1”, pfet transistor  302 ″ is deactivated while nfet transistor  504  activates. Node-X is essentially in a dynamic mode, initially allowing nfet transistor  304 ″ to capacitively couple the input to node-X, effectively bootstrapping the node above Vddl. The maximum voltage that node-X can achieve in steady state is Vddl+|Vtp| due to the presence of pfet  302 ″. Nfet transistor  306 ″ conducts more vigorously when the higher bias is applied to node-X, allowing node-Y to achieve Vddl potential more rapidly, thereby reducing the conduction of pfet transistor  310 ″. Nfet transistor  312 ″ will respond to the input rising to Vddl regardless of which connection is made, but for the purposes of this discussion it is assumed that the gate of nfet transistor  312 ″ is connected to the input. Since nfet transistor  312 ″ is on the output, Z will be moving toward ground. 
     As the output falls from Vddh toward ground, pfet transistor  308 ″ begins to conduct and causes node-Y to rise to Vddh, which in turn causes pfet transistor  310 ″ to stop conducting and allows the output to achieve a full ground potential. As node-Z is falling toward ground, it causes pfet transistor  502  to conduct, thereby clamping node-X to Vddl−|Vtn|. This potential will ensure that there is no leakage across nfet transistor  306 ″. Steady state has been achieved. From this steady state condition, if the input were to change from a “1” to a “0”, node-X, which was held at Vddl−|Vtn|, would rise to Vddl through the conduction of pfet transistor  302 ″. 
     The bootstrap capacitor will now attempt to couple node-X downward, but pfet transistor  302 ″ will resist the action. With pfet transistor&#39;s  306 ″ gate at a sufficiently high potential, node-Y will begin to discharge to ground. Nfet transistor  312 ″ would have shut off upon arrival of the input signal, thereby allowing node-Z to ‘float’. Pfet transistor  308 ″ is still active as the node-Z potential has not risen yet until node-Y forces conduction of pfet  310 ″. Pfet transistor  308 ″ continues to resist node-Y from falling to “0” until the output has reached a sufficiently high voltage, and as such, its size must be very small. As the system stabilizes, the output attains a “1”. Node-X is held at Vddl volts. This configuration of devices yields very good overall performance, very low power, and eliminates any steady state dynamic nodes in the translator circuit  500 . 
     A level translator circuit in accordance with the present invention utilizes a bootstrap mechanism in the gate of the input transistor to allow translating between a low voltage potential to a high voltage potential to be performed more efficiently. 
     Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.

Technology Classification (CPC): 7