Patent Document

RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/327,040 filed Jun. 7, 1999 now U.S. Pat. No. 6,137,312, which is a continuation of U.S. application Ser. No. 08/803,343 filed Feb. 20, 1997 and issued as U.S. Pat. No. 5,910,734. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to electronic devices and, more specifically, to a voltage level translator circuit used in an electronic device. 
     BACKGROUND OF THE INVENTION 
     There are many instances involving integrated devices where voltage level translator circuits are needed to interface between operations circuits that function at different voltage levels. One operations circuit, for example, may transmit high signals based on a source voltage V CC . However, a second operations circuit receiving signals from the first might only recognize high signals at a greater voltage V CC ′. Therefore, a translator circuit is electrically interposed between the two operations circuits to receive a signal from the first and, if it is a high signal, to output a signal with an even higher voltage V CCP , that will properly register as a high signal in the second circuit. 
     One example of a translator in the prior art achieves this result in two distinct charging steps interrupted by a delay. As an input signal changes from low to high, this first prior art translator will begin to charge its output signal to V CC . A portion of the translator&#39;s circuitry, however, does not immediately register the change in the input signal due to a delaying element incorporated into the translator. Once the intermediate step of charging the output to V CC  is complete, the delaying element finally transmits the changed input to the remaining circuitry, which then completes the translation process by charging the output from V CC  to V CCP . 
     Such a translator, however, requires several transistors as well as logic devices, resulting in a relatively large circuit, which runs contrary to the desired goal of saving die space. Further, it should be noted that the proper delaying element must be chosen in advance of using the translator in non-test operations. If the delay is not long enough to allow the output signal to initially charge to V CC , a new delaying device must be chosen to accommodate the translator circuit. Conversely, too long of a delay runs contrary to the desired goal of quick circuit operations. Therefore, it would be desirable to have a translator that is not only smaller but is also capable of translating an input signal at a faster rate without having to pick-and-choose the proper delaying element. 
     A second translator in the prior art attempts to do just that by directly driving its output to V CCP , with no transition stage at V CC . While this second prior art translator is smaller and faster than the first, one of ordinary skill in the art can appreciate that the direct translation to V CCP  requires a larger charge pump than one used in the two stage translator. As a result, the larger charge pump uses more of the available operating current. Given the inefficiency in terms of a charge pump&#39;s ability to use operating current, a direct translation to V CCP  is not be desirable in certain applications. Therefore, it would be a major advance in the art to have a translator that is smaller and faster than the first prior art example, yet would allow charging to an intermediate voltage and then to V CCP  in order to avoid the inefficiency of the large charge pump used in the second prior art example. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention concerns a translator that provides an output signal having a generally consistent transition from an initial voltage to a secondary voltage and, eventually, to a final voltage, in response to a changing input signal. In one preferred embodiment, the translator is configured to sense when its output load is approaching a charge of magnitude V CC . This embodiment is further configured to automatically begin charging the output load to V CCP  at or around that time without the use of a delaying element. One advantage of this embodiment is that it is smaller and faster than prior art translators that operate using a discrete two-stage process to output a V CCP  signal. A further advantage of this embodiment is that it uses less current than prior art translators that directly charge an output load to V CCP . 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts an example of a translator as used in the prior art. 
     FIG. 2 is a cross-sectional view of a p-channel transistor which may be used in prior art as well as in an exemplary embodiment of the present invention. 
     FIG. 3 illustrates a second translator used in the prior art. 
     FIG. 4 is a schematic diagram of an exemplary embodiment in accordance with the present invention. 
     FIG. 5 is a graph illustrating output voltage over time of the prior art translator of FIG. 1 as compared to an exemplary embodiment in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates the two-stage translator found in the prior art. An input signal IN enters a first inverter  10  and the output is connected to three separate paths. First, the inverted signal passes through a second inverter  12 . The output of this second inverter  12  is coupled to the first input of a first NAND gate  14 . The output of the second inverter  12  also couples to a delaying element  16 , which outputs to a third inverter  18 . The third inverter  18 , in turn, has an output coupled to a second input of the first NAND gate  14 . The output of the first NAND gate  14  serves as the input for a first circuit portion  20 . The first circuit portion  20  is comprised of a p-channel transistor Q 101  with a source coupled to V CCP  and a drain coupled to the drain of an n-channel transistor Q 102 . The source of transistor Q 102 , in turn, couples to ground. The two coupled drains serve as an output for the first circuit portion  20  and are also connected to the gate of another p-channel transistor Q 103 , which also has a source connected to V CCP . Further, the transistor Q 103  has a drain attached to the drain of another n-channel transistor Q 104  having a grounded source. The coupled drains of Q 103  and Q 104  attach to the gate of Q 101 . The output of the first NAND gate  14  drives the gate of transistor Q 102 . The first circuit portion  20  is further comprised of a fourth inverter  22 , which also receives the output of the first NAND gate  14  and inverts that signal before it reaches the gate of transistor Q 104 . The output of the first circuit portion  20  drives the gate of an n-channel transistor Q 105 , which has a drain coupled to V CC  and a source coupled to the main output node  24 . 
     The output of first inverter  10  also couples to a first input of a NOR gate  26 . The NOR gate  26  receives a second input from the third inverter  18 . The output of the NOR gate  26  enters a second circuit portion  28 . This second circuit portion is comprised of an n-channel transistor Q 106  that is driven by the output of NOR gate  26 . Transistor Q 106  also has a source coupled to ground and a drain coupled to a node A. The output of NOR gate  26  also couples to the source of an n-channel transistor Q 107 , which is driven by V CC  and has a drain coupled to the source of another n-channel transistor Q 108  at node B. Transistor Q 108  is driven by V CCP  and has a drain that couples at node C to the drain of a p-channel transistor Q 109 . The source of transistor Q 109  is attached to V CCP . The coupled drains of Q 109  and Q 108  are connected to the gate of another p-channel transistor Q 110 , which also has a source attached to V CCP . By way of node D, the drain of transistor Q 110  is coupled to the gate of transistor Q 109 , as well as to node A. Node A represents the output of the second circuit portion  28 , and connects to the gate of a p-channel transistor Q 111 . The source of transistor Q 111  connects to V CCP  and the drain of Q 111  connects to the main output node  24 . Node A also connects to a first input of a second NAND gate  30 . 
     Finally, the output of first inverter  10  acts as a second input for the second NAND gate  30 . The output of this second NAND gate  30  passes through a fifth inverter  32  and drives an n-channel transistor Q 112 . Transistor Q 112  has a source coupled to ground and a drain coupled to the main output node  24 . Output node  24  is also coupled to a path configured to carry an output signal OUT. A final matter of coupling this prior art translator is illustrated in FIG.  2 . For every p-channel transistor, an n-well  34  within a p-region  36  is coupled to V CCP  at node  38  to provide the proper back bias. 
     The discrete two-step operation of this translator is best illustrated by examining its functions as IN changes from a low to high signal. The initial low signal from IN results in a high signal output from the first inverter  10 . This high signal is again changed at the second inverter  12  to a low signal, which is input to the first NAND gate  14  and the delaying element  16 . At this point, the signal IN has remained low long enough for the delay element  16  to transmit the low signal to the third inverter  18 , which outputs a high signal. This high signal combines with the low signal from the second inverter  12  in the NAND gate  14 . The resulting high signal enters the first circuit portion  20  and turns on transistor Q 102 . Further, the high signal is inverted by the fourth inverter  22 , and the low signal output turns off transistor Q 104 . With transistor Q 102  on, the gate of transistor Q 103  is grounded, thereby turning on Q 103 . Because Q 104 &#39;s off state prevents Q 103 &#39;s signal from grounding, Q 103  instead transmits a high signal to Q 101 &#39;s gate, turning Q 101  off. In addition, Q 101 &#39;s off state and Q 102 &#39;s on state result in a low signal output from the first circuit portion  20 . This low signal turns off transistor Q 105 , isolating V CC  from the main output node  24 . 
     Meanwhile, the high signal from the third inverter  18  combines with the high signal from the first inverter  10  at the NOR gate  26 , which outputs a low signal to the second circuit portion  28 . This low signal turns off transistor Q 106 . In doing so, node A is isolated from ground. Moreover, the low signal induces a corresponding low voltage at node C, which consequently turns on transistor Q 110 . As a result, transistor Q 110  transmits a high signal to transistor Q 109 , turning Q 109  off. This high signal also reaches node A and is output from the second circuit portion  28 . The high signal turns off transistor Q 111 , isolating V CCP  from the main output node  24 . 
     The high signal from node A combines with the high signal from the first inverter  10  at the second NAND gate  30 . The low signal from the NAND gate  30  is changed by the fifth inverter  32 , and the high signal from the fifth inverter  32  turns on Q 112 , grounding any signals that reach the main output node  24 . Thus, the low signal IN causes a low signal OUT. 
     As the IN signal changes from a low to a high signal, the first inverter  10  outputs a low signal and, hence, the second inverter  12  outputs a high signal. The first NAND gate  14  receives this high signal as a first input. However, the new high signal is held up by the delaying element  16  and, as a result, the third inverter  18  temporarily continues to output a high signal to the second input of the first NAND gate  14 . Receiving two high signals, the first NAND gate  14  transmits a low signal to the first circuit portion  20 . This low signal turns off transistor Q 102 . Further, the low signal passes through the fourth inverter  22  and the resulting high signal turns on transistor Q 104 , which provides a path to ground. This grounding turns on transistor Q 101 , which provides a path from V CCP . With transistor Q 102  off, the V CCP  signal from Q 101  has no path to ground and is therefore diverted to the gate of transistor Q 103 , turning off Q 103 . The V CCP  signal is also transmitted to the gate of Q 105 , thereby turning on Q 105 . With transistor Q 105  on, the V CC  signal coupled to the drain of transistor Q 105  is able to reach the main output node  24 . It should be noted that this configuration allows a full V CC  signal to be transmitted. If transistor Q 105  were driven by a mere V CC  signal, only a signal of magnitude V CC −V t  could pass through transistor Q 105 , where V t  is the voltage threshold of transistor Q 105 . 
     Because of the high signal that is temporarily transmitted from the third inverter  18 , the NOR gate  26 , receiving this high signal as well as the low signal from the first inverter  10 , continues to send out a low signal to the second circuit portion  28 . As a result, the state of the second circuit portion  28  does not change: a high signal at node A (1) turns off transistor Q 111 , thereby isolating V CCP  from the main output node; and (2) acts as one input for the second NAND gate  30 . The other input for the second NAND gate  30  is the low signal from the first inverter  10 . The resulting high signal is inverted by the fifth inverter  32  so that the final low signal turns off transistor Q 112 , preventing any output signals from grounding at that point. Therefore, during this transition phase, while the delaying element  16  is postponing the change of signals, the translator&#39;s output signal OUT increases to V CC . 
     After a time determined by the configuration of the delay element  16 , the high signal output from the second inverter  12  reaches the third inverter  18 , thereby triggering the second stage of translation. The first NAND gate  14  accepts the low signal from the third inverter  18  and the high signal from the second inverter  12 . The resulting high signal from the first NAND gate  14  returns the first circuit portion  20  to the state originally described, with transistors Q 102  and Q 103  on, transistors Q 101  and Q 104  off, and a low signal output from the first circuit portion  20  that turns off transistor Q 105 . With transistor Q 105  off, V CC  can no longer reach the main output node  24 . 
     At the same time, however, the newly generated low signal from the third inverter  18 , in combination with the low signal from the first inverter  10 , results in a high signal output from the NOR gate  26 . This allows transistor Q 107  to push node B to V CC −V t . Node C is also pushed to this level, which partially turns off transistor Q 110 . Because a full V CC  signal is not applied to transistor Q 110 , Q 110  continues to pass some current. However, the high signal from the NOR gate  26  also turns on transistor Q 106 , which is configured to be large enough to overdrive Q 110 . With transistor Q 106  on, a path to ground is provided for nodes A and D. Node D&#39;s connection to ground turns on Q 109 , which in turn allows a V CCP  signal to reach the gate of transistor Q 110  through node C, turning off transistor Q 110  completely. Node A&#39;s connection to ground turns on Q 111 , allowing a V CCP  signal to reach the main output node  24 . 
     Grounded node A further provides a low signal for the second NAND gate  30 , which also accepts the low signal from the first inverter  10 . The high signal output from the second NAND gate  30  is inverted by the fifth inverter  32  so that a low signal maintains transistor Q 112 &#39;s off-state. Thus, the V CCP  signal originating at transistor Q 111  is transmitted as the translator&#39;s output signal OUT. In this way, a high input signal is translated into a signal of magnitude V CCP . 
     In translating an IN signal changing from high to low, the translator circuit is initially at the state described immediately above: the V CC  signal is isolated because transistor Q 105  is off; a direct path to ground is not available because transistor Q 112  is off; and with transistor Q 111  on, V CCP  is output as the translator&#39;s OUT signal. As IN transmits a low signal, the first inverter  10  sends a high signal to the second inverter  12 . The second inverter  12  transmits a low signal to the first NAND gate  14 . However, because the low signal from the second inverter  12  has not yet cleared the delaying element  16 , the third inverter  18  still outputs a low signal for the first NAND gate  14 . Given these two low signals, the first NAND gate  14  continues to send a high signal to the first circuit portion  20 . It follows that the first circuit portion  20  continues to send a low signal to Q 105  and isolate V CC  from the main output node  24 . 
     Nevertheless, the high signal from the first inverter  10  does change the output from the NOR gate  26 . The high signal from the first inverter  10  plus the remaining low output from the third inverter  18  causes the NOR gate  26  to send a low signal to the second circuit portion  28 . This turns off transistor Q 106 , isolating the drain of Q 110  and the gate of Q 109  from ground. Further, a low signal is then transmitted through node C to transistor Q 110 , turning on that transistor. A V CCP  signal then passes through transistor Q 110  and node D to transistor Q 109 , turning it off. Further, this V CCP  signal transmits to node A, turning off transistor Q 111  and isolating V CCP  from the main output node  24 . 
     The high signal from node A also enters the second NAND gate  30 , which also receives the high signal from the second inverter  12 . The result from the second NAND gate  30  is a low signal, which is inverted by the fifth inverter  32 . The output high signal turns on transistor Q 112 , which grounds the main output node  24  and, thus, the signal OUT. 
     Moreover, the transition of OUT to a low signal is not affected by the function of the delaying element  16 . Even after the third inverter  18  receives the low signal from the second inverter  12 , the resulting high signal does not change the input to the first circuit portion  20 . Having received a low signal from the second inverter  12  in addition to the new high signal from the third inverter  18 , the first NAND gate  14  continues to send a high signal to the first circuit portion  20 . Similarly, the NOR gate continues to send a low signal to the second circuit portion  28 . Thus the V CC  and V CCP  signals continue to be isolated and the signal OUT continues to be pulled to ground through transistor Q 112 . 
     In FIG. 5, line P graphically demonstrates the operation of this prior art translator. The right portion of line P represents the translation of an IN signal going from high to low voltage. The relatively smooth transition indicates that OUT is not affected by the delaying element in a high to low operation. 
     The left side of the graph, however, clearly illustrates the two stage process required to translate a signal IN going from a low to high voltage. Line P demonstrates one transition from ground to V CC . The leveling slope of line P occurs as OUT approaches V CC  but the delaying element  16  has not yet allowed V CCP  to couple to the main output node  24 . Once the delay is over, the signal OUT then once again begins to increase in voltage until V CCP  is reached. 
     FIG. 3 illustrates the smaller, faster circuit that translates a low-to-high signal directly to V CCP , without the use of a transitory V CC  source. This translator is essentially a paired-down version of the first translator, with only the second circuit portion  28  and the first inverter  10  remaining. As a result, this translator operates in a manner similar to that second circuit portion  28 . Given a low signal IN, the first inverter  10  sends out a high signal. This high signal allows transistor Q 107  to push node B to V CC −V t . Node C is also pushed to that level, thereby partially turning off transistor Q 110 . The high signal from the first inverter  10  also turns on transistor Q 106 . Having been configured to be able to overdrive transistor Q 110 , transistor Q 106  grounds any signal passing through transistor Q 110 . This creates a low voltage at node D, which turns on transistor Q 109 . The resulting V CCP  signal completely turns off transistor Q 110 . With node A also coupled to ground via transistor Q 106 , this translator&#39;s output signal OUT is a low signal. 
     As the signal IN increases to a high signal, the first inverter  10  transmits a low signal that turns off transistor Q 106 . At this stage, node C carries a low signal to transistor Q 110 , which turns on accordingly. With no path to ground through transistor Q 106 , a V CCP  signal travels through transistor Q 110  and node D to the gate of transistor Q 109 . This V CCP  signal turns off Q 109 . Further, this V CCP  signal travels to node A and ultimately serves as the output signal OUT. Thus, as a high signal is input, the translator drives its load directly to V CCP , with no transition stage involving V CC . Should signal IN make the transition from a high signal back to a low signal, the translator would return to the state originally described above. 
     FIG. 4 illustrates a preferred embodiment of the current invention. An input signal IN leads to a primary inverter  40 . The output of the primary inverter couples to the gate of a p-channel transistor Q 201  and the gate of an n-channel transistor Q 202 . In addition to having coupled gates, the drains of transistors Q 201  and Q 202  are coupled to each other. The coupled drains are in turn connected to a node E. The source of transistor Q 202  is coupled to ground and the source of transistor Q 201  is coupled at a node F to the drain of another p-channel transistor Q 203 . Transistor Q 203  has a source coupled to a source voltage V CC . Further, as described earlier and illustrated in FIG. 2, transistor Q 203 , as well as every other p-channel transistor in this exemplary embodiment, has an n-well  34  within a p-region  36  is coupled to V CCP , at node  38  to provide the proper back bias. 
     It should also be noted that the values of V CC  and V CCP  in this exemplary embodiment may not necessarily have the same values as discussed in the prior art translators. Further, it should be noted that, while this invention can be coupled to various voltage sources, no voltage source is claimed as part of the invention. 
     Returning to the primary inverter  40 , its output drives the coupled gates of another pair of transistors: p-channel transistor Q 204  and n-channel transistor Q 205 . The drains of transistors Q 204  and  205  join at a node G. The source of transistor Q 205  is coupled to ground and the source of transistor Q 204  is coupled to node E. In addition, node G is coupled to the gate of transistor Q 203 . The output of primary inverter  40  also serves as input for a secondary inverter  42 . 
     This exemplary embodiment also contains three transistors, Q 206 , Q 207 , and Q 208 , coupled in series. Transistor Q 206  is a p-channel transistor with a source coupled to V CCP  and a drain coupled to the drain of n-channel transistor Q 207 . The source of transistor Q 207  is coupled to the drain of n-channel transistor Q 208 , whose source couples to ground. The gate of transistor Q 206  is connected to node G; the gate of transistor Q 207  is connected to the output of the secondary inverter  42 ; and the gate of transistor Q 208  is connected to node E. Finally, the coupled drains of transistors Q 206  and Q 207  drive a p-channel transistor Q 209 . The source of transistor Q 209  is coupled to V CCP  and the drain of Q 209  is coupled to an output node H. Output node H is also connected to node E and carries the translator&#39;s output signal OUT. 
     Once again, the operation of this exemplary circuit is best demonstrated by examining its function as IN changes from a low to a high signal. The initial low signal IN is inverted by the by the primary inverter  40 . The resulting high signal turns on transistor Q 202  but turns off transistor Q 201 . Further, with Q 202  providing a path to ground for output node H, OUT is a low signal. Additionally, Q 202 &#39;s activation results in a low voltage signal passing through node E to transistor Q 208 , turning that transistor off as well. 
     The high signal output from the primary inverter  40  also turns off transistor Q 204  even as it turns on transistor Q 205 . As Q 205  provides a path to ground, the resulting low voltage at node G turns on Q 203 . As a result, node F is pushed to V CC . With Q 201  in an off state, however, the V CC  charge is isolated from the rest of the circuit. The low voltage at node G also turns on transistor Q 206 . 
     The high signal from the primary inverter  40  is inverted by the secondary inverter  42 , thereby turning off transistor Q 207 . Thus, with transistor Q 206  on and transistors Q 207  and Q 208  off, a V CCP  signal drives transistor Q 209 , turning off Q 209  as well. Therefore, with IN transmitting a low signal, OUT also transmits a low signal, as it is coupled to ground through output node H and transistor Q 202 . Moreover, V CCP  is isolated from the circuit, but a V CC  charge is stored within the circuit in anticipation of future changes in the IN signal. 
     As the signal IN increases to high, the V CC  signal from node F reaches output node H. The manner in which this takes place begins as the high IN signal is inverted to a low signal by the primary inverter  40 . This low signal turns off transistor Q 202  and turns on transistor Q 201 . Thus, the V CC  signal at node F is diverted through nodes E and H as the OUT signal. 
     However, even as OUT approaches a potential of V CC , the translator is operating to isolate the V CC  source. The low signal from the primary inverter  40  turns on transistor Q 204  and turns off transistor Q 205 . Thus, the high signal from node E is transmitted by way of the source of transistor Q 204  and through node G to the gate of transistor Q 203 , turning off transistor Q 203 . As a result, V CC  is eventually no longer able to transmit through transistor Q 203 . 
     Nevertheless, the same operations that isolate V CC  simultaneously function to couple V CCP  to output node H. The high signal at node G turns off transistor Q 206 . The low signal from the primary inverter  40  is inverted by the secondary inverter  42  and the resulting high signal turns on transistor Q 207 . Subsequently, the high signal from node E turns on transistor Q 208 . The states of these three transistors cause the coupled drains of transistors Q 206  and Q 207  to send a low signal to transistor Q 209 . This turns on Q 209  and allow V CCP  to charge output node H. 
     Thus, while the input signal IN is low, the translator prepares to transmit a V CC  signal. As IN increases, the ability of V CC  to reach output node H increases. As the potential of OUT approaches the V CC  level, the translator automatically operates to gradually shut off V CC  while coupling V CCP  to output node H. The result is a smooth transition of OUT from a low signal of 0 volts to a V CC  signal and, finally, to a high signal of magnitude V CCP . The smooth transition allowed by this invention can be seen in line I of FIG.  5 . The advantage of this embodiment over the first prior art example is particularly evident on the left part of the graph, denoting the output signal OUT in the event of a low to high IN signal. Specifically, line I demonstrates that the speed of this invention is not limited by the presence of a delaying element. Rather, this exemplary embodiment is configured to automatically provide additional charging when the output approaches the desired intermediate voltage. Further, because this embodiment allows for an intermediate boost to V CC , there is no need for the inefficiently large charge pump that must be used in the second prior art translator. As a result, this embodiment uses less operating current that does the second prior art translator. 
     If the signal IN transitions from high to low, then the circuit for this embodiment returns to the state first described: transistor Q 202  turns on, grounding the output signal; transistor Q 209  turns off, isolating V CCP ; transistor Q 201  turns off, isolating V CC  at node F; and transistor Q 203  turns on to charge node F to V CC  in anticipation of the next low-to-high signal. As shown by the right side of the graph in FIG. 5, although the first prior art translator is not encumbered by the delaying element in the high-to-low transition, this embodiment of the current invention operates faster because it is a smaller circuit. 
     Finally, one of ordinary skill in the art can appreciate that, although a specific embodiment of this invention has been described above for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. As demonstrated in U.S. Pat. No. 5,136,190, by Chern et al., for example, the proper number of inverters would allow the translator to output a V CCP  signal in response to a high-to-low input signal change rather than a low-to-high change. As another example, an additional n-channel transistor could be interposed between transistor Q 203  and V CC . Driving this additional transistor at V CCP  would ensure that a signal of magnitude V CC  would not be transmitted through transistor Q 203  until V CCP  exceeded V CC . Moreover, a circuit similar to the embodiments disclosed above could be configured to translate an input signal having a low voltage into an output signal having even a lower voltage Accordingly, the invention is not limited except as stated in the claims.

Technology Category: 5