CMOS voltage translator circuit

Abstract: The circuit (300) is for translating a switching signal (Ldrive) disposed between the earth level (0V) and Vdd to a translated switching signal (hdrive) disposed between Vhsrc and Vhstrap. The circuit (300) comprises a bistable circuit formed by two branches which include two nMOS transistors (315, 320) the sources of which are connected to earth and which are controlled, respectively, by a switching-on signal (on) and by a switching-off signal (off) derived from the switching signal (Ldrive) by means of a buffer (305) and an inverter (310), respectively. Two pMOS transistors (325, 330) having their sources at the voltage Vhstrap and the drain of one connected to the gate of the other output the translated switching signal (hdrive) at one of their drains. Two further pMOS transistors (335, 340) having gates at the voltage Vhsrc are interposed between the two nMOS transistors (315, 320) and the two pMOS transistors (325, 330).

Description: The present invention relates to a voltage translator circuit according to the preamble to Claim 1, usable in particular in a switching system. In some switching systems (or controlled-switching systems), for example in "step-down" switching regulators such as that shown in Figure 1, there is an electronic switch which requires a driver device having a supply terminal connected to a terminal of the switch. As shown in Figure 1, the switching system 100 comprises an N-channel MOS transistor (nMOS) 105 as an electronic switch; the transistor 105 is connected in the circuit shown by means of two terminals thereof, that is, its source and drain terminals, so as alternately to open and to close the connection between two branches of the circuit connected to these terminals. The transistor 105 is connected, by means of its drain, to a voltage supply indicated as the input voltage Vin (relative to earth). If this switch is opened and closed alternately, that is, if the transistor 105 is cut off and made conductive alternately, a series of voltage pulses of amplitude Vin, having a mean voltage value depending upon the duration of the intervals in which it is switched on and off is produced at the source of the transistor 105. A voltage Vout (relative to earth) is applied to a load 125 by means of a diode 110 and a filter constituted by an inductance 115 and a capacitor 120 (used to reduce the residual alternating component of the voltage at the source of the transistor 105). If the switching frequency of the transistor 105 is high enough, the load 125 is supplied with a direct-current voltage of a value equal to the mean value of the voltage at the source of the transistor 105. The transistor 105 is controlled by a driving device (or driver 130) supplied by a suitable voltage supply produced, in the example shown, by means of a "bootstrap" circuit which uses a capacitor 135 connected by means of a diode 140 to a supply terminal Vcc. The supply terminals of the driver 130 which are connected to the terminals of the capacitor 135, are indicated Vhstrap and Vhsrc. The terminal Vhsrc is also connected to the source of the transistor 105. The switching system 100 receives a logic switching input signal (Ldrive) which can assume two levels, one being a high or on level and the other a low or off level; the logic switching signal (Ldrive) is applied to the system 100 by means of a driver 145 supplied by a further voltage supply Vdd. For example, the switching-on signal is equal to the value Vdd of the supply voltage, and the switching-off signal is equal to a zero voltage (0V), that is, to the earth potential level. A translator circuit 150 is interposed between the driver 145 (supplied between Vdd and earth) and the driver 130 (supplied between Vhstrap and Vhsrc). This circuit 150 enables the logic switching signal to be translated from a value between 0 and Vdd (for example 5V) to a value between Vhsrc and Vhstrap, where Vhstrap-Vhsrc is constant (for example 5V or 12V) but Vhsrc is variable with time. In the example shown in the drawing, Vhsrc varies from a value of 0V when the switch 105 is open to a value of Vin when the switch 105 is closed; it should be noted that, in certain cases, the voltage Vhsrc may even assume very high values of the order of some tens or hundreds of volts. Some switching systems comprising various voltage translator devices known in the art are shown in Figure 2. With reference, in particular, to Figure 2a, a simple voltage translator circuit which uses a Zener diode 205 connected between the supply terminal Vhstrap and the input of the driver 130 is shown. A resistor 210 which does not have a high value, is connected in parallel with the Zener diode 205 to prevent the switch from switching off too slowly. This translator circuit has a high consumption since, in the switching-on stage, the currents are quite high (of the order of a few hundreds of µA up to a few mA). To prevent this problem, as shown in Figure 2b, it has been proposed to replace the resistor in parallel with the Zener diode 205 with a current generator 215 which is switched off during the switching-on stage. The switching-on current (Ion) and the switching-off current (Ioff) can thus be reduced to a few tens of µA when switching has taken place without the logic state of the switch being lost. This circuit nevertheless also has a consumption in the switching-off stage since the switching-off current (Ioff) cannot be zero. A different known solution which has a static consumption theoretically of zero and is used particularly when the voltage Vhsrc of the switch terminal reaches high values (tens or hundreds of V) is constituted by the circuit shown in Figure 2c in which the driver signal is stored in a memory element 220 comprising, for example, a "latch" SR 225. The switching-on and switching-off currents (Ion and Ioff) in this case serve solely for switching the memory element 220 and are therefore pulsed currents with a duration of a few hundreds of ns up to 1 µs. The signal is translated by means of current pulses generated as a result of a transition of the switching signal; in particular, a switching-on pulse is generated by the block 250 upon the transition of the switching signal from off to on whereas a switching-off pulse is generated by the block 255 upon the transition of the switching signal from on to off. This translation circuit which is known in the art has some disadvantages. In order to ensure the correct state of the latch 225 after the start-up stage, the circuit described above in fact requires the latch 225 to be connected to a very high resistance 230 which can orient the latch 220 correctly during the rise of the supply voltage of the driver; in practice, however, this resistance 230 cannot have excessively high values, thus producing a current consumption which can bring about discharge of the bootstrap capacitance. A further problem of the circuit known in the art is due to the fact that it cannot ensure congruence between the logic switching signals and their translated values since the translation takes place by means of pulses generated in relation to a transition of the switching signal and not in relation to its logic value. In fact, it is possible for a current pulse not to succeed in switching the memory element of the circuit, for example, by virtue of interference of short duration; in this case, the switch retains its previous state (open or closed) conflicting with the value of the switching signal applied. For example, if the switching signal changes from off to on, it generates a current switching-on pulse; if this pulse does not succeed in switching the switch, it will remain closed throughout the duration of the switching-on signal. The next transition of the switching signal from on to off will have no effect on the switch, simply confirming its already switched-off state; the switch will thus switch on only upon the subsequent transition of the switching signal from off to on. This problem is particularly serious in the case of a switching-off signal; if the switch is closed and the translator circuit does not succeed in storing the switching-off pulse, the switch remains closed with serious risks of damage to the components of the circuit. Document US-4 996 443 describes a circuit for level shift comprising a plurality of MOS transistors including transistors of different conductivity types. These problems of the prior art are avoided by the invention as claimed. The present invention provides a circuit for translating a switching signal (Ldrive) disposed between a first voltage level (0) and a second voltage level (Vdd) to a corresponding translated switching signal disposed between a third voltage level (Vhsrc) and a fourth voltage level (Vhstrap), the circuit comprising a first terminal (0), a second terminal (Vdd), a third terminal (Vhsrc) and a fourth terminal (Vhstrap) for supplying voltages at the first, second, third and fourth levels, driver means connected to the first and second supply terminals (0, Vdd) in order to derive, from the switching signal (Ldrive) applied to an input terminal of the driver means, a switching-on signal and a switching-off signal at a first output terminal and at a second output terminal, respectively, a bistable circuit connected to the first (0), third (Vhsrc) and fourth (Vhstrap) supply terminals, and comprising a first branch and a second branch, the branches comprising, respectively, a first transistor and a second transistor of a first type, each having a first terminal connected to the first supply terminal (0), a second terminal and a control terminal connected, respectively, to the first and second output terminals of the driver means, the bistable circuit being able to produce the translated switching signal at at least one output terminal thereof, characterized in that the first and second branches comprise, respectively, a third transistor and a fourth transistor of a second type complementary to the first type and each having a first terminal, a second terminal and a control terminal, the first terminals of both being connected to the fourth supply terminal (Vhstrap), the second terminal of each of them being connected to the control terminal of the other, and a fifth transistor and a sixth transistor of the second type connected between the respective second terminals of the first and second transistors and the respective second terminals of the third and fourth transistors and each having its control terminal connected to the third supply terminal (Vhsrc), the second terminal of the third or fourth transistor being the said at least one output terminal of the bistable circuit. Further features of the circuit according to the invention are defined in the annexed claim 1. The solution according to the present invention has a static consumption, that is upon completion of the switching, practically zero, since it has no active low-impedance path between the Vhstrap terminal and earth; this advantage is particularly important in the case of applications in which it is necessary to reduce current consumption to the minimum. Moreover, this solution enables the congruence between the input logic signal and the translated output signal to be maintained even in the presence of interference since the translation takes place in relation to the switching signal and not only to its leading or trailing edge. Various embodiments of the present invention will now be described by way of example with reference to the appended drawings, in which: Figure 1 shows schematically a switching system in which the translation circuit of the present invention can be used, Figures 2a, 2b and 2c show schematically three switching systems comprising various translation devices of the prior art, Figure 3 shows schematically a translation circuit which is similar to the level shift circuit known from US-A 4 996 443. Figure 4 shows a preferred embodiment of the translation circuit according to the present invention, Figure 5 shows the structure of the logic element of Figure 4, Figure 6 shows schematically a translation circuit complementary to that of Figure 3. With reference now to the drawings and, in particular, with reference to figure 3 (Figures 1, 2a, 2b and 2c have already been described above) a translation circuit is shown schematically. The translation circuit 300 has four terminals for supplying voltages at the earth (0V), Vdd, Vhsrc and Vhstrap levels, respectively. The circuit 300 has an input terminal for a switching signal Ldrive which is disposed between the first two voltage levels, that is, it can assume one or other of two values between 0V and Vdd. This switching signal Ldrive is applied to driver means constituted, in the embodiment illustrated, by a buffer 305 and by an inverter 310 (supplied between vdd and earth) which output, respectively, a switching-on signal (on) and a switching-off signal (off) which are complementary to one another. The two signals, that is, the switching-on signal on and the switching-off signal off, are then applied to a bistable circuit constituted by two branches each comprising three transistors 315, 335, 325 and 320, 340, 330, respectively; this bistable circuit is connected to the earth (0V), Vhsrc and Vhstrap supply terminals as described in detail below. In particular, the switching-on signal (on) is applied to the gate of an nMOS transistor 315 the source of which is connected to the earth terminal; similarly, the switching-off signal (off) is applied to the gate of an nMOS transistor 320, the source of which is connected to the earth terminal. The translation circuit 300 then comprises two pMOS transistors 325 and 330, the sources of which are connected to the supply terminal Vhstrap; the gate of the transistor 325 is connected to the drain of the transistor 330 and the gate of the transistor 330 is connected to the drain of the transistor 325. The translation circuit 300 has an output for the translated switching signal (hdrive) connected to the drain of the transistor 330. Clearly, this switching signal hdrive can also be derived from the drain of the transistor 325 by means of an inverter supplied between Vhsrc and Vhstrap; alternatively, it is possible to obtain two separate outputs, one for a translated switching-on signal hon (obtained from the drain of the transistor 330) and one for a translated switching-off signal hoff (obtained from the drain of the transistor 325). The translated switching signal (Hdrive) is disposed between the voltage levels Vhsrc and Vhstrap; in this embodiment, it can assume the value Vhstrap or a value close to Vhsrc. Two further respective pMOS transistors 335 and 340 are connected between the two nMOS transistors 315 and 320 and the two pMOS transistors 325 and 330. As shown in the drawing, the drain (D) of the transistor 335 is connected to the drain of the transistor 315 and the source (S) of the transistor 335 is connected to the drain of the transistor 325; similarly, the drain (D) and the source (S) of the transistor 340 are connected to the drain of the transistor 320 and to the drain of the transistor 330, respectively. The gate terminals of both of the transistors 335 and 340 are connected to the supply terminal Vhsrc. The transistors 315, 320, 335 and 340 have structures which are resistant to high voltages since their drains undergo voltage swings from 0V to Vhstrap; for example, the drains of the transistors 315 and 335 are at a voltage of 0V when the transistor 315 is conducting whereas they are at the Vhstrap voltage when the transistors 325 and 335 are conducting. In particular, the two pMOS transistors 335 and 340 operate as voltage translators preventing the voltages at the gate electrodes of the transistors 325 and 330 from assuming values such as to cause breakdown of the gate oxide. In order to describe the operation of the circuit, an initial condition in which the transistors 320, 325 and 335 are on whilst the transistors 315, 330 and 340 are off will be considered. It is now assumed that the switching signal Ldrive adopts the value on; this value generates an on signal equal to Vdd via the buffer 305 whereas the off signal produced by the inverter 310 is zero (0V). The transistor 315 is thus switched on whilst the transistor 320 is switched off. The voltage at the drain of the pMOS transistor 335 thus falls to zero, bringing this transistor close to being switched off, that is, with a voltage between gate and source close to the threshold voltage. The voltage at the gate of the pMOS transistor 330 consequently falls to the voltage Vhsrc (plus the threshold voltage of the transistor 335) so that the pMOS transistor 330 becomes conductive. At the same time, the switching-on of the transistor 330 causes the voltage of the terminal hdrive to rise to values close to the voltage level Vhstrap. The source terminal of the pMOS transistor 340 is also charged to the voltage Vhstrap so that the transistor 340 is switched on; at the same time, the gate of the pMOS transistor 325 is brought to the voltage Vhstrap so that the transistor 325 is switched off. During the switching-off stage, the operation of the translation circuit 300 is equivalent to that described above for the switching-on stage. In particular, the voltage at the hdrive node assumes a value which, if the threshold voltage of the transistor 340 is ignored, is equal to the voltage Vhsrc. The circuit shown has no active low-impedance path between the supply terminal Vhstrap and earth; the circuit according to the present invention therefore has a static consumption, that is upon completion of the switching, practically zero. Moreover, with the solution proposed there is no risk of loss of congruence between the input logic signal and the translated output signal since the translation takes place throughout the duration of the switching signal and not only in relation to the leading or trailing edge. Although the substrate terminals (bulk gates) of the transistors 334 and 340 may, generally, be connected to the respective sources, in the embodiment shown in Figure 3, both of these terminals are connected to the supply terminal Vhstrap. In fact, owing to capacitive coupling, it is possible that the voltage at the source of one of these transistors may temporarily fall below the value of its drain voltage. The measure of the connection of the bulk gates to the supply terminal Vhstrap and not to the source of the same transistor ensures that the substrate voltage of the transistor cannot fall to a value below that of its own drain, thus reducing the risk of damage to the component. The preferred embodiment of the translation circuit according to the present invention is now described with reference to Figure 4; the components in common with the circuit of Figure 3 are indicated by the same reference numerals. The translation circuit 400 comprises, as described with reference to Figure 3, the two nMOS transistors 315 and 320, to the gates of which the switching-on signal (on) and the switching-off signal (off) derived from the switching signal Ldrive by means of a buffer and an inverter (not shown in the drawing) are applied, respectively; the further pMOS transistors 325, 330, 335 and 340 are connected as described above with reference to Figure 3. The output taken from the drain of the transistor 330 is connected to the gate of a pMOS transistor 405, and the output taken from the drain of the transistor 325 is connected to the gate of a pMOS transistor 410; the sources of both of the pMOS transistors 405 and 410 are connected to the supply terminal Vhstrap. The drains of the two transistors 405 and 410 are connected to the drains of an nMOS transistor 415 and of an nMOS transistor 420, respectively. The gate of the transistor 415 is connected to the drain of the transistor 420 and the gate of the transistor 420 is connected to the drain of the transistor 415; the sources of both of the transistors 415 and 420 are connected to the supply terminal Vhsrc. The output constituted by the drain of the transistor 420 provides the translated switching-on signal hon, and the output constituted by the drain of the transistor 415 provides the translated switching-off signal hoff. The component constituted by the transistors 405-420 operates as a further voltage translator enabling the translated control signal (hdrive) to reach the value Vhsrc, eliminating the difference due to the threshold voltages of the transistors 335 and 340. The translation circuit 400 then comprises two further pMOS transistors 425 and 430. The sources of both of the transistors 425 and 430 are connected to the supply terminal Vhstrap; the drain of the pMOS transistor 425 is connected to the drain of the transistor 335 and the drain of the pMOS transistor 430 is connected to the drain of the transistor 340. The two transistors 425 and 430 have structures which are resistant to high voltages since their drains (as explained above with reference to the transistors 315, 320, 335 and 340) undergo voltage swings of from 0V to Vhstrap. The gate terminals of both of the transistors 425 and 430 are normally kept at a voltage Vhstrap so that both of the pMOS transistors are off. The transistor 430 is controlled at its own gate by means of a voltage pulse (pon) of amplitude Vhstrap-Vhsrc generated upon the transition of the translated switching signal (hdrive) from the translated off value (hoff) to the translated on value (hon); similarly, the gate of the transistor 425 is controlled by a voltage pulse (poff) of amplitude Vhstrap-Vhsrc generated upon the transition of the signal hdrive from the value hon to the value hoff. The duration of these voltage pulses pon and poff is typically no longer than 400 ns, for example, one hundred ns. The two transistors 425 and 430 improve the operation of the translation circuit, reducing the switching time. With reference, for example, to the transistor 430 (similar considerations apply to the transistor 425), it is connected to the drains of the two transistors 320 and 340. As indicated above, these transistors have structures which are resistant to high voltages and consequently have high stray capacitances. These stray capacitances would be charged during the switching stage only by the current supplied by the pMOS transistor 330 which cannot reach excessively high values (since the pMOS transistor 330 is of limited dimensions). The use of the further transistor 430 however enables these stray capacitances to be charged rapidly, thus making the o switching quicker. The circuit of Figure 4 then comprises a logic element 440 supplied between Vhsrc and Vhstrap. This logic element 440 receives as inputs the translated switching-on signal hon and the translated switching-off signal hoff and outputs the voltage pulse pon for controlling the gate of the transistor 430 and the voltage pulse poff for controlling the gate of the transistor 425, in addition to the translated switching signal hdrive. In order to describe the operation of the circuit, an initial condition in which the transistors 320, 325, 335, 405 and 420 are on whilst the transistors 315, 330, 340, 410, 415, 425 and 430 are off will be considered. It is now assumed that the switching-on signal adopts the value Vdd and the switching-off signal is thus zero (0V). During this switching-on stage, the transistor 315 is switched on whilst the transistor 320 is switched off. The pMOS transistor 335 is brought close to being switched off, that is, with a voltage between source and gate close to the threshold voltage; the transistors 330 and 410 consequently become conductive. At the same time, the switching-on of the transistor 410 causes the voltage at the node hon to rise to values close to the voltage Vhstrap. This transition of the node hon is detected by the logic of the element 440 which generates a translated switching signal hdrive, allowing the switch (not shown in the drawing) to be switched on. At the same time, the logic element 440 generates the voltage pulse pon (of amplitude Vhsrc). This pulse enables the pMOS transistor 430 to be switched on for a limited time interval starting from the start of the switching so as to charge the drains of the transistors 320 and 340 to the voltage Vhstrap; the pMOS transistor 340 therefore becomes conductive. The voltage Vhstrap at the source of the pMOS transistor 340 is applied to the gates of the pMOS transistors 325 and 405 which are therefore switched off. The voltage Vhstrap brought by the transistor 410 (which is conductive) to the gate of the nMOS transistor 415 switches it on, bringing the node hoff to the voltage Vhsrc. This voltage Vhsrc is also applied to the gate of the nMOS transistor 420 which is therefore switched off completing the translation and storage of the information relating to the switching signal. Moreover, as a result of the switching of the signal hdrive, the logic element 440 temporarily blocks the propagation of the signals hon and hoff towards the output of the translated switching signal hdrive; the duration of this masking is typically no longer than 100 ns, for example 50 ns. This measure prevents voltage variations at the nodes hon and/or hoff, due to the switching of the structure, from generating spurious transitions which could cause the switch (not shown in the drawing) to switch off early. During the switching-off stage, the operation of the translation circuit is equivalent to that described above for the switching-on stage; in particular, the transition of the node hoff from Vhsrc to vhstrap, detected by the logic component 440, generates a signal hdrive which is equal to zero and causes the switch (not shown in the drawing) to be switched off. An embodiment of the logic component 440 of Figure 4 will now be described with reference to Figure 5. The block 510 is a memory (latch) component which stores the value of the translated switching-on signal on (latched_hon), enabling the spurious transitions at the node hon to be masked during the switching of the system; similarly, the block 520 stores the translated switching-off signal hoff (latched_hoff) in order to mask the spurious transitions at the node hoff. The logic component 440 then comprises a sequential network 530 which can generate the translated switching signal hdrive, detecting the transitions of hon and hoff from Vhsrc to Vhstrap. This sequential network 530 also generates (as described in detail below) the pulsed logic signals pon and poff upon the transitions of the signal hdrive in order to pilot the transistors 430 and 425, respectively. The RC circuit 540, on the other hand, produces two masking signals (blank_on and blank_off) upon the switching of the signal hdrive; the duration of these masking signals is fixed by the time constant RC defined by the resistor 550 and the capacitor 560 (for example 50 ns). The masking signals blank_on and blank_off are applied, respectively, to the memory components 510 and 520 so as to block the propagation both of the signal hon and of the signal hoff. The durations of the voltage pulses pon and poff are defined by the durations of the masking pulses blank_on and blank_off and by the duration of the switching of the signals hon and hoff. For example, it is assumed that the signal hon switches from Vhsrc to Vhstrap with the consequent generation of the voltage pulse pon. This voltage pulse pon is maintained as long as the masking pulses blank_on and blank_off are active or the signal hoff has a value Vhstrap (that until it is switched to the value Vhsrc). If the switching of the terminal hoff terminates before the masking pulses blank_on/blank_off, the duration of the signal pon will therefore be equal to that of these pulses (for example 50 ns); if, on the other hand, the switching of the node hoff terminates afterwards, the voltage pulse pon will have a longer duration (for example 300 ns). Persons skilled in the art will appreciate that the foregoing description can also be applied with the nMOS transistors replaced by pMOS transistors and vice versa. Similar considerations also apply if some of the MOS transistors are replaced by suitable bipolar NPN and PNP transistors, the gate, source and drain terminals being replaced by the appropriate base, emitter and collector terminals. A translation circuit complementary to that of Figure 3 is shown schematically, for example, with reference to Figure 6. The translator circuit 600 has an input terminal for a switching signal hdrive disposed between Vhsrc and Vhstrap (where Vhsrc may even assume very high values, for example 100 V) and an output terminal for a corresponding switching signal Ldrive between 0V and Vdd (for example 5V). This switching signal hdrive is applied to an inverter 605 and to a buffer 610 (supplied between Vhsrc and Vhstrap) which output, respectively, a switching-on signal (hon) and a switching-off signal (hoff) which are complementary to one another. The switching-on signal (hon) and the switching-off signal (hoff) are applied, respectively, to the gates of a pMOS transistor 615 and of a pMOS transistor 620, the sources of which are connected to the supply terminal Vhstrap. The translation circuit 600 then comprises two nMOS transistors 625 and 630, the sources of which are connected to the earth terminal (0V); the gate of the transistor 625 is connected to the drain of the transistor 630 and the gate of the transistor 630 is connected to the drain of the transistor 625. An output for the switching signal Ldrive is connected to the drain of the transistor 630. Two further nMOS transistors 635 and 640 are connected between the two respective pMOS transistors 615 and 620 and the two nMOS transistors 625 and 630; the gate terminals and the substrate terminals (bulk gates) of both of the transistors 635 and 640 are connected, respectively, to the supply terminal Vdd and to the earth terminal (0V). The transistors 615, 620, 635 and 640 have structures which are resistant to high voltages since their drains undergo voltage swings from Vhstrap to 0V. The operation of the circuit 600 is complementary to that of the circuit 300 shown in Figure 3; in particular, it should be noted that the switching-on signal (hon) and the switching-off signal (hoff) are active at the low value Vhsrc. Similar considerations apply to the production of a circuit complementary to that shown in Figure 4.

Claims: A circuit (300) for translating a switching signal (Ldrive) disposed between a first voltage level (0) and a second voltage level (Vdd) to a corresponding translated switching signal (hdrive) disposed between a third voltage level (Vhsrc) and a fourth voltage level (Vhstrap), the circuit comprising: a first terminal (0), a second terminal (Vdd), a third terminal (Vhsrc) and a fourth terminal (Vhstrap) for supplying voltages at the first, second, third and fourth levels, driver means (305, 310) connected to the first and second supply terminals (0, Vdd) in order to derive, from the switching signal (Ldrive) applied to an input terminal of the driver means, a switching-on signal (on) and a switching-off signal (off) at a first output terminal and at a second output terminal, respectively, a bistable circuit connected to the first (0), third (Vhsrc) and fourth (Vhstrap) supply terminals, and comprising a first branch and a second branch, the branches comprising, respectively, a first transistor and a second transistor (315, 320) of a first type each having a first terminal connected to the first supply terminal (0), a second terminal and a control terminal connected, respectively, to the first and second output terminals of the driver means (305, 310), the bistable circuit being able to produce the translated switching signal (hdrive) at least one output terminal thereof, the first and second branches comprise, respectively, a third transistor and a fourth transistor (325, 330) of a second type complementary to the first type, and each having a first terminal, a second terminal and a control terminal, the first terminals of both (325, 330) being connected to the fourth supply terminal (Vhstrap), the second terminal of each of them being connected to the control terminal of the other and a fifth transistor and a sixth transistor (335, 340) of the second type, first terminals thereof being connected to the respective second terminals of the first and second transistors (315, 320), second terminal thereof being connected to the respective second terminals of the third and fourth transistors (325, 330) and control terminals thereof being connected to the third supply terminal (Vhsrc), the second terminal of the third or fourth transistor (325, 330) being the said at least one output terminal of the bistable circuit, the translator circuit being characterized by comprising: a first charge transistor (425) and a second charge transistor (430) of the second type, each having a control terminal, a first terminal connected to the fourth supply terminal (Vhstrap) and a second terminal, the second terminals of the first and second charge transistor (425, 430) being connected to the first terminals of the fifth and sixth transistors (335, 340), respectively, for charging said first terminals of the fifth and sixth transistors. A translator circuit (300) according to Claim 1, in which the bistable circuit comprises a first output for a translated switching-on signal (hon) and a second output for a translated switching-off signal (hoff) constituted by the second terminals of the fourth and third transistors (330, 325), respectively. A translator circuit (400) according to Claim 2, comprising a further voltage translator circuit (405-420) having a first input and a second input connected, respectively, to the first and second outputs of the bistable circuit and at least one output for the translated switching signal (hdrive). A translator circuit (400) according to Claim 3, in which the further translator circuit (405-420) comprises: a seventh transistor (405) and an eighth transistor (510) of the second type, both having a first terminal connected to the fourth supply terminal (Vhstrap), the control terminals of the seventh and eighth transistors (405, 410) being the first and second inputs of the further translator circuit, respectively, a ninth transistor (415) and a tenth transistor (420) of the first type, both having a first terminal connected to the third supply terminal (Vhsrc), a second terminal of each of them being connected to the control terminal of the other and to the second terminal of the seventh or eighth transistor (405, 510), respectively, the second terminals of the ninth and tenth transistors (415, 420) being the said at least one output terminal of the further translator circuit (405-420). A translator circuit (400) according to Claim 4, in which the further translator circuit (405-420) comprises a first output for the translated switching-on signal (hon) and a second output for the translated switching-off signal (hoff), constituted by the second terminals of the tenth and ninth transistors (420, 415), respectively. A translator circuit (400) according to any one of Claims 1 to 5, further comprising logic means (440) having a first input and a second input connected, respectively, to the first and second outputs (hon, hoff) of the bistable circuit or of the further translator circuit (405-420), and a first output (pon) and a second output (poff), and being able to generate at the first output (pon) a first voltage pulse upon the transition of the translated switching signal (hdrive) from a translated switching-off value (hoff) to a translated switching-on value (hon) and, at the second output (poff), a second voltage pulse upon the transition of the translated switching signal (hdrive) from the translated switching-on value (hon) to the translated switching-off value (hoff), the control terminals of the first and second charge transistors (425, 430) being connected, respectively, to the second and first outputs (poff, pon) of the logic means (440). A translator circuit (400) according to Claim 6, in which the logic means (440) comprise a third output (hdrive) for the translated switching signal and means (510, 520, 540) for temporarily blocking the propagation of the translated switching-on signal (hon) and of the translated switching-off signal (hoff) upon a switching of the translated switching signal (hdrive). A translator circuit (400) according to Claim 7, in which the logic means (440) comprise: a first memory circuit (510) for storing the translated switching-on signal (hon) and a second memory circuit (520) for storing the translated switching-off signal (hoff), a sequential circuit (530) connected to the first and second memory circuits (510, 520) in order to generate the translated switching signal (hdrive) and the first and second voltage pulses (pon, poff), an RC circuit (540) connected to the translated switching signal (hdrive) in order to generate a first masking pulse (blank_on) for blocking the propagation of the translated switching-on signal (hon) and a second masking pulse (blank_off) for blocking the propagation of the translated switching-off signal (hoff), the first masking signal (blank_on) being applied to the first memory circuit (510) and the second masking signal (blank_off) being applied to the second memory circuit (520). A translator circuit (300,400) according to any one of Claims 1 to 8, in which the transistors of the first type are N-channel field-effect transistors and the transistors of the second type are P-channel field-effect transistors, the first terminals of the transistors being the drains, the second terminals being the sources and the control terminals being the gates. A translator circuit (300, 400) according to Claim 9, in which each of the fifth and sixth transistors (335, 340) has a substrate terminal connected to the fourth supply terminal (Vhstrap). A switching system (100) comprising: the circuit (150) for translating a switching signal (Ldrive) to a corresponding translated switching signal (hdrive) according to any one of Claims 1 to 10, an electronic switch (105) connected in a circuit by means of first and second terminals of the switch, one of the first and second terminals being connected to the third supply terminal (Vhsrc), and a driver (130) connected to the third and fourth supply terminals (Vhsrc, Vhstrap), to the translator circuit (150) and to a control terminal of the electronic switch (105) in order to receive the translated switching signal (hdrive) as an input and to output a signal for opening and closing the electronic switch (105).

Inventors: RIGAZIO LUCA, RIGAZIO, LUCA
Applicants: ST MICROELECTRONICS SRL, STMICROELECTRONICS S.R.L.
Application year: 1996
Main classification: H03K3
IPC codes: H03K3