OUTPUT CIRCUIT

An output circuit outputs an output signal having an amplitude VCCH responsive to an input signal having an amplitude VCCL. The output circuit includes: first and second p-type transistors connected in series between VCCH and an output terminal; a first n-type transistor grounded at its source and receiving a first signal at its gate; a third p-type transistor connected to VCCH at its source, connected to the gate of the first p-type transistor at its drain, and receiving a second signal at its gate; and a first diode connected between the drains of the first n-type transistor and the third p-type transistor.

BACKGROUND

The present disclosure relates to a high-voltage output circuit using low-withstand voltage transistors.

With the recent scaling of semiconductor processes, the internal power supply voltages of semiconductor integrated circuits are becoming lower, and the operations of semiconductor integrated circuits are being sped up. Also, transistor withstand voltages are becoming increasingly lower. On the other hand, some of various interfaces require a high voltage due to their specifications. In view of this, a high-voltage output circuit using low-withstand voltage transistors has become necessary.

In order to form a high-voltage output circuit using low-withstand voltage transistors, it has been conventionally done to distribute a voltage to be applied to transistors using configurations such as one of cascoding low-withstand voltage transistors and one of inserting multiple stages of diodes.

Japanese Unexamined Patent Publication No. 2013-90278 discloses an output circuit outputting a high-voltage signal, which uses low-withstand voltage transistors. This output circuit is configured so as to avoid direct application of a high voltage across the gate-source/drain and source-drain of a low-withstand voltage transistor.

However, the output circuit disclosed in the cited patent document has the following problems. Since there are a rise in the low level of the output signal and an occurrence of an unwanted current between power supply and ground, the reliability is low. Also, since sufficient drive capability cannot be obtained from low-withstand voltage transistors, the circuit is not suitable for high-speed operation.

An objective of the present disclosure is implementing a highly-reliable output circuit suitable for high-speed operation using low-withstand voltage transistors.

SUMMARY

According to the first mode of the present disclosure, an output circuit for outputting an output signal responsive to an input signal having an amplitude corresponding to a first power supply voltage from an output terminal, the output signal having an amplitude corresponding to a second power supply voltage greater than the first power supply voltage, includes: first and second p-type transistors connected in series between a second power supply supplying the second power supply voltage and the output terminal; a first n-type transistor grounded at its source and receiving a first signal responsive to the input signal at its gate, the first signal having an amplitude from a ground voltage to a first predetermined voltage; a third p-type transistor connected to the second power supply at its source, connected to a gate of the first p-type transistor at its drain, and receiving a second signal responsive to the input signal at its gate, the second signal having an amplitude from the first predetermined voltage to the second power supply voltage; and a first diode including one diode or a plurality of serially connected diodes, connected between the drain of the third p-type transistor and a drain of the first n-type transistor.

According to the above mode, when the input signal is in a low level, the second signal responsive to the input signal becomes a first predetermined voltage. The third p-type transistor, connected to the second power supply at its source and receiving the first predetermined voltage at its gate, turns on under the condition of (second power supply voltage—first predetermined voltage) being greater than the threshold voltage, and its drain becomes the second power supply voltage. Since the first p-type transistor, of which the gate is connected to the drain of the third p-type transistor, receives the second power supply voltage at its gate, it fully turns off. It is therefore possible to avoid a rise in the low level of the output signal and an occurrence of an unwanted current between power supply and ground, and thus a highly-reliable output circuit can be implemented.

According to the second mode of the present disclosure, an output circuit for outputting an output signal responsive to an input signal having an amplitude corresponding to a first power supply voltage from an output terminal, the output signal having an amplitude corresponding to a second power supply voltage greater than the first power supply voltage, includes: first and second p-type transistors connected in series between a second power supply supplying the second power supply voltage and the output terminal; first and second n-type transistors connected in series between a ground terminal and the output terminal; a first circuit receiving a first signal responsive to the input signal, the first signal having an amplitude from a ground voltage to a first predetermined voltage, the first circuit giving a signal to a gate of the second p-type transistor; and a second circuit receiving a second signal responsive to the input signal, the second signal having an amplitude from the first predetermined voltage to the second power supply voltage, the second circuit giving a signal to a gate of the second n-type transistor.

According to the above mode, while the gate of the second p-type transistor is controlled with the signal output from the first circuit, the gate of the second n-type transistor is controlled with the signal output from the second circuit. It is therefore possible to adjust the signals given to the gates of the second p-type transistor and the second n-type transistor independently so that the operations of these transistors be individually optimum. With this, since the drive capability of the second p-type transistor and the second n-type transistor can be sufficiently exploited, an output circuit suitable for high-speed operation can be implemented.

According to the third mode of the present disclosure, an output circuit for outputting an output signal responsive to an input signal having an amplitude corresponding to a first power supply voltage from an output terminal, the output signal having an amplitude corresponding to a second power supply voltage greater than the first power supply voltage, includes: first and second n-type transistors connected in series between a ground terminal and the output terminal; a third n-type transistor grounded at its source, connected to a gate of the first n-type transistor at its drain, and receiving a first signal responsive to the input signal at its gate, the first signal having an amplitude from a ground voltage to a first predetermined voltage; a first p-type transistor connected to a second power supply supplying the second power supply voltage at its source, and receiving a second signal responsive to the input signal at its gate, the second signal having an amplitude from the first predetermined voltage to the second power supply voltage; and a first diode including one diode or a plurality of serially connected diodes, connected between a drain of the first p-type transistor and the drain of the third n-type transistor.

According to the above mode, when the input signal is in a low level, the second signal responsive to the input signal becomes a first predetermined voltage. The first p-type transistor, connected to the second power supply at its source and receiving the first predetermined voltage at its gate, turns on under the condition of (second power supply voltage—first predetermined voltage) being greater than the threshold voltage, and its drain becomes the second power supply voltage. Since the gate of the first n-type transistor is connected to the drain of the third n-type transistor, it receives a voltage reduced from the second power supply voltage by a forward voltage of the first diode. With this, since the gate-source voltage of the first n-type transistor can be sufficiently made high, the drive capability can be sufficiently exploited. Therefore, an output circuit suitable for high-speed operation can be implemented.

According to the present disclosure, a highly-reliable output circuit suitable for high-speed operation can be implemented using low-withstand voltage transistors.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described hereinafter with reference to the accompanying drawings. Note that, in the following description, “VCCL” and “VCCH” denote power supply voltages or power supplies themselves, and “GND” denotes a ground voltage or a ground terminal. The power supply voltage VCCH is greater than the power supply voltage VCCL. Also, “H” and “L” represent the logic levels of a signal, where “H” represents a high level and “L” a low level. “Z” denotes an output terminal or output signal of an output circuit.

Also, in the following description, MOS transistors are used as an example of transistors. The threshold voltage of a p-type MOS transistor (abbreviated as a PMOS appropriately) is denoted by Vthp, and the gate-source voltage thereof is denoted by Vgsp. The threshold voltage of an n-type MOS transistor (abbreviated as an NMOS appropriately) is denoted by Vthn, and the gate-source voltage thereof is denoted by Vgsn. The forward voltage of a diode is denoted by Vf.

Note that “P**” is used as the character of a PMOS, “N**” is used as the character of an NMOS, and “D**” is used as the character of a diode (* is a numeric). Also, to avoid complication of description, expression of a PMOS, an NMOS, and a diode may be simplified, such as “a PMOS P**” being simplified as “P**”, for example.

First Embodiment

FIG.1is a circuit diagram showing a circuit configuration of an output circuit according to the first embodiment. An output circuit1shown inFIG.1outputs an output signal Z having an amplitude VCCH responsive to an input signal IN having an amplitude VCCL. The input signal IN having the amplitude VCCL is a signal that becomes GND when it is L and VCCL when it is H. The output signal Z having the amplitude VCCH is a signal that becomes GND when it is L and VCCH when it is H.

As shown inFIG.1, the output circuit1includes PMOSs P11and P12connected in series between the power supply VCCH and the output terminal Z and NMOSs N11and N12connected in series between the ground terminal GND and the output terminal Z. The output circuit1also includes: a circuit11that outputs a signal PG given to the gate of P11; a circuit12that outputs a signal BP given to the gate of P12; a circuit13that outputs a signal NG given to the gate of N11; and a circuit14that outputs a signal BN given to the gate of N12. The output circuit1further includes a signal conversion circuit10that converts the input signal IN into signals NH and NL responsive to the input signal IN. The signal NH is a signal having an amplitude of VCCL to VCCH, i.e., a signal becoming VCCL when it is L and VCCH when it is H. The signal NL is a signal having an amplitude of GND to VCCL, i.e., a signal becoming GND when it is L and VCCL when it is H.

Note that the voltage when the signal NH is L and the voltage when the signal NL is H are not necessarily the same, i.e., VCCL. It is however preferred that the voltage when the signal NH is L and the voltage when the signal NL is H be the same.

The circuit11includes a PMOS P21, a diode D11, and an NMOS N21placed in series between the power supply VCCH and the ground terminal GND. P21is connected to VCCH at its source, receives the signal NH at its gate, and is connected to the anode of D11at its drain. N21is connected to GND at its source, receives the signal NL at its gate, and is connected to the cathode of D11at its drain. The drain of P21is connected to the gate of P11, to give the signal PG.

The circuit12includes a PMOS P22, a diode D21, and an NMOS N22placed in series between the power supply VCCL and the ground terminal GND. P22is connected to VCCL at its source, receives the signal NL at its gate, and is connected to the anode of D21at its drain. N22is connected to GND at its source, receives the signal NL at its gate, and is connected to the cathode of D21at its drain. The drain of P22is connected to the gate of P12, to give the signal BP.

The circuit13includes a PMOS P23, a diode D31, and an NMOS N23placed in series between the power supply VCCH and the ground terminal GND. P23is connected to VCCH at its source, receives the signal NH at its gate, and is connected to the anode of D31at its drain. N23is connected to GND at its source, receives the signal NL at its gate, and is connected to the cathode of D31at its drain. The drain of N23is connected to the gate of N11, to give the signal NG.

The circuit14includes a PMOS P24, a diode D41, and an NMOS N24placed in series between the power supply VCCH and the power supply VCCL. P24is connected to VCCH at its source, receives the signal NH at its gate, and is connected to the anode of D41at its drain. N24is connected to VCCL at its source, receives the signal NH at its gate, and is connected to the cathode of D41at its drain. The drain of N24is connected to the gate of N12, to give the signal BN.

Note that, while the diodes D11, D21, D31, and D41are each illustrated as having one diode element, they may have a plurality of diode elements connected in series. The number of serially connected diode elements may be determined appropriately depending on the value of the power supply voltage and the value of the transistor withstand voltage.

Note also that, as the diodes D11, D21, D31, and D41, a self-biased transistor of which the gate is connected to its drain may be used in place of the diode element. A p-type or n-type transistor can be used in this case.

FIG.2shows a circuit configuration of the signal conversion circuit10. As shown inFIG.2, the signal conversion circuit10includes four inverters IV10, IV11, IV12, and IV13connected in series and a level shifter100. The inverters IV10, IV11, IV12, and IV13are constituted by low-withstand voltage transistors. The input signal IN is given to the input of the inverter IV10, and the signal NL is output from the output of the inverter IV13. When the input signal IN is L (GND), the signal NL becomes L (GND), and when the input signal IN is H (VCCL), the signal NL becomes H (VCCL). The level shifter100receives an output IN1of the inverter IV10and an output IN2of the inverter IV11as its inputs, and outputs the signal NH. When the input signal IN is L (GND), the signal NH becomes L (VCCL), and when the input signal IN is H (VCCL), the signal NH becomes H (VCCH).

FIG.3shows a circuit configuration of the level shifter100. As shown inFIG.3, the level shifter100includes four PMOSs PM1, PM2, PM3, and PM4. The sources of PM1and PM2are connected to the power supply VCCL, and the sources of PM3and PM4are connected to the power supply VCCH. The output IN2of the inverter IV11is given to the gate of PM1, and the output IN1of the inverter IV10is given to the gate of PM2. The gate of PM3is connected to the drains of PM2and PM4. The gate of PM4is connected to the drains of PM1and PM3, and serves as the output node of the signal NH.

Note that the circuit configuration of the signal conversion circuit10is not limited to that shown inFIGS.2and3. Any other configuration may be used if only the signal NL becomes L (GND) and the signal NH becomes L (VCCL) when the input signal IN is L (GND), and the signal NL becomes H (VCCL) and the signal NH becomes H (VCCH) when the input signal IN is H (VCCL).

FIG.16shows a circuit configuration of an output circuit disclosed in the cited patent document as a contrast example. The output circuit shown inFIG.16, like the output circuit1described above, outputs an output signal Z having an amplitude VCCH responsive to an input signal IN having an amplitude VCCL.

The output circuit of the contrast example shown inFIG.16has the following problems.

(1) When the input signal IN=L, the output signal Z is expected to be L (GND). However, in the output circuit ofFIG.16, since PG=VCCH−|Vthp| when IN=L, P11fails to be completely turned off. Therefore, a rise in the low level of the output signal Z occurs, and if this rise exceeds input level specifications of a circuit that receives the output signal Z, a communication error will occur. Also, because of P11failing to become completely off, an unwanted current occurs in the path of VCCH→P11→P12→N12→N11→GND. This hastens the deterioration of transistors and wires, causing decrease in reliability.

(2) In the output circuit ofFIG.16, the same signal VG is given to the gates of P12and N12. Therefore, since sufficient drive capability cannot be obtained by combining the withstand voltage value of a low-withstand voltage transistor and the voltage value of VCCH, the circuit is not suitable for high-speed operation.

For example, assume that VCCH=1.8 V and the withstand voltage value of the transistors is 1.5 V. When IN=H and Z=H, P11is turned on, whereby a node a becomes VCCH. Therefore,

where Vgsp12is the gate-source voltage of P12. Also, when IN=L and Z=L, N11is turned on, whereby a node b becomes GND. Therefore,

where Vgsn12is the gate-source voltage of N12. In general, the current capability of a transistor is higher as its gate-source voltage is higher. It is therefore preferable to set the voltage of the signal VG so that both |Vgsp12| and |Vgsn12| be maximum. To do so, the signal VG=0.9 V is preferable, where

As a result, the transistors P12and N12, to which 1.5 V can be applied as the gate-source voltage, are to be driven with application of 0.9 V, indicating that sufficient drive capability cannot be obtained from P12and N12.

(3) In the output circuit ofFIG.16, the output of an inverter IV1operating with VCCL is given to the gate of N11as the signal NG. Therefore, a sufficient drive capability may not be obtained from N11depending on the value of VCCL.

For example, assume that VCCL=0.8 V, VCCH=1.8 V, and the withstand voltage value of the transistor is 1.5 V. When IN=L and Z=L, the output of the inverter IV1, i.e., the signal NG becomes VCCL (0.8 V), and therefore,

where Vgsn11is the gate-source voltage of N11.

As a result, the transistor N11, to which 1.5 V can be applied as the gate-source voltage, is to be driven with application of 0.8 V, indicating that sufficient drive capability cannot be obtained from N11.

Operation of Output Circuit of First Embodiment

The operation of the output circuit1of the first embodiment will be described. As an example, assume the following.

VCCL=0.8VVCCH=1.8Vwithstand voltage value of transistor=1.5 Vthreshold voltage of transistor |Vthp|=|Vthn|=0.5 Vforward voltage of diode Vf=0.4 V

FIG.4shows potentials of nodes in the output circuit1ofFIG.1when IN=L (GND=0 V). The signal conversion circuit10outputs L (0.8 V) as the signal NH and L (0 V) as the signal NL.

At this time, P21, P22, P23, and P24are all turned on since

Also, N21, N22, N23, and N24are all turned off since

Since P21is turned on, the signal PG output from the circuit11becomes VCCH (1.8 V). Therefore, the gate-source voltage |Vgsp11| of P11becomes 0 V, whereby P11can be completely turned off. Also, at this time, in the circuit11, the potential of a cathode11bof D11becomes 1.4 V, reduced from the potential of the signal PG by Vf (0.4 V) of D11.

The signal BP is output from the circuit12and the signal BN is output from the circuit14. That is, the signal BP and the signal BN can be controlled independently. Since P22is turned on, the signal BP output from the circuit12becomes VCCL (0.8 V). At this time, in the circuit12, the potential of a cathode21bof D21becomes 0.4 V, reduced from the potential of the signal BP by Vf (0.4 V) of D21. Since P24is turned on, the signal BN output from the circuit14becomes 1.4 V, reduced from VCCH (1.8 V) by Vf (0.4 V) of D41. Therefore, compared with the contrast example, the gate-source voltage |Vgsn12| of N12can be made high, which is suitable for high-speed operation.

Since P23is turned on, the signal NG output from the circuit13becomes 1.4 V, reduced from VCCH (1.8 V) by Vf (0.4 V) of D31. Therefore, compared with the contrast example, the gate-source voltage |Vgsn11| of N11can be made high, which is suitable for high-speed operation.

N11is turned on, making the potential of the node b 0 V, and N12is turned on, whereby Z=L (0 V). The potential of the node a becomes a value obtained by adding |Vthp| (0.5 V) to the potential (0.8 V) of the signal BP, i.e., 1.3 V.

As a result of the operation as described above, the gate-source/drain voltages and source-drain voltages of all the transistors fall within the withstand voltage value (1.5 V).

FIG.5shows potentials of nodes in the output circuit1ofFIG.1when IN=H (VCCL=0.8 V). The signal conversion circuit10outputs H (1.8 V) as the signal NH and H (0.8 V) as the signal NL.

At this time, P21, P22, P23, and P24are all turned off since

Also, N21, N22, N23, and N24are all turned on since

Since N21is turned on, the signal PG output from the circuit11becomes 0.4 V, increased from GND (0 V) by Vf (0.4 V) of D11.

Since N22is turned on, the signal BP output from the circuit12becomes 0.4 V, increased from GND (0 V) by Vf (0.4 V) of D21. Therefore, compared with the contrast example, the gate-source voltage |Vgsp12| of P12can be made high, which is suitable for high-speed operation. Since N24is turned on, the signal BN output from the circuit14becomes VCCL (0.8 V). At this time, in the circuit14, the potential of an anode41aof D41becomes 1.2 V, increased from the potential of the signal BN by Vf (0.4 V) of D41.

Since N23is turned on, the signal NG output from the circuit13becomes GND (0 V). Therefore, N11is turned off since |Vgsn11|1=0 V. Also, at this time, the potential of an anode31aof D31becomes 0.4 V, increased from the potential of the signal NG by Vf (0.4 V).

P11is turned on, making the potential of the node a VCCH (1.8 V), and P12is turned on, whereby Z=H (1.8 V). The potential of the node b becomes a value obtained by subtracting |Vthn| (0.5 V) from the potential (0.8 V) of the signal BN, i.e., 0.3 V.

As a result of the operation as described above, the gate-source/drain voltages and source-drain voltages of all the transistors fall within the withstand voltage value (1.5 V).

According to this embodiment, the problems of the contrast example described above can be solved.

Specifically, in the output circuit1, by giving the signal NH to the gate of P21in the circuit11, P21can be fully turned on. Since this can sufficiently increase the H level of the signal PG up to VCCH, P11can be completely turned off. It is therefore possible to avoid a rise in the L level of the output signal Z and an occurrence of an unwanted current between VCCH and GND (problem (1) is solved).

In the output circuit1, while the signal BP output from the circuit12is given to the gate of P12, the signal BN output from the circuit14is given to the gate of N12. With this, the signals BP and BN can be adjusted so that the operations of P12and N12become optimum individually. Therefore, since sufficient drive capability can be obtained from P12and N12, the circuit is suitable for high-speed operation (problem (2) is solved).

In the output circuit1, the signal NG output from the circuit13is given to the gate of N11, and the signal NG is generated independently of VCCL in the circuit13. Therefore, when the input signal IN is L, the gate-source voltage of N11can be made high, and thus the circuit is suitable for high-speed operation (problem (3) is solved).

Therefore, according to this embodiment, it is possible to implement, using low-withstand voltage transistors, the output circuit1that is high in reliability because there is neither a rise in the L level of the output signal Z nor an occurrence of an unwanted current between power supply and ground, and also suitable for high-speed operation because sufficient drive capability can be obtained from low-withstand voltage transistors.

Second Embodiment

FIG.6is a circuit diagram showing a circuit configuration of an output circuit according to the second embodiment. Like the output circuit1of the first embodiment, an output circuit2shown inFIG.6outputs an output signal Z having an amplitude VCCH responsive to an input signal IN having an amplitude VCCL. The basic configuration of the output circuit2is similar to that of the output circuit1. In the output circuit2, circuits11A,12A,13A, and14A each having added components are provided in place of the circuits11,12,13, and14. Also, pulse generation circuits21and22are added.

In the circuit11A, D11in the circuit11is replaced with a plurality of (four in the figure) serially connected diodes D11a, D11b, D11c, and D11d, and an NMOS N41is added. The source and drain of N41are connected to a node11bbetween D11band D11cand to a node11dbetween D11dand N21.

In the circuit12A, D21in the circuit12is replaced with a plurality of (four in the figure) serially connected diodes D21a, D21b, D21c, and D21d, and an NMOS N42is added. The source and drain of N42are connected to a node21bbetween D21band D21cand to a node21dbetween D21dand N22.

In the circuit13A, D31in the circuit13is replaced with a plurality of (four in the figure) serially connected diodes D31a, D31b, D31c, and D31d, and a PMOS P41is added. The source and drain of P41are connected to a node31abetween P23and D31aand to a node31cbetween D31band D31c.

In the circuit14A, D41in the circuit14is replaced with a plurality of (four in the figure) serially connected diodes D41a, D41b, D41c, and D41d, and a PMOS P42is added. The source and drain of P42are connected to a node41abetween P24and D41aand to a node41cbetween D41band D41c.

The pulse generation circuit21generates, from the signal NL, a pulse signal PP to be given to the gates of N41and N42. The pulse generation circuit22generates, from the signal NH, a pulse signal PN to be given to the gates of P41and P42.

FIG.7Ashows a circuit configuration example of the pulse generation circuit21, andFIG.7Bis a waveform diagram of the pulse signal PP. The amplitude of the pulse signal PP is the same as that of the signal NL, i.e., GND to VCCL. As shown inFIG.7B, at a rising transition of the signal NL from L to H, the pulse signal PP generates a pulse, remains H for a predetermined time, and then makes a transition to L. At a falling transition of the signal NL from H to L, the pulse signal PP remains L.

FIG.8Ashows a circuit configuration example of the pulse generation circuit22, andFIG.8Bis a waveform diagram of the pulse signal PN. The amplitude of the pulse signal PN is the same as that of the signal NH, i.e., VCCL to VCCH. As shown inFIG.8B, at a falling transition of the signal NH from H to L, the pulse signal PN generates a pulse, remains L for a predetermined time, and then makes a transition to H. At a rising transition of the signal NH from L to H, the pulse signal PN remains H.

Features of the output circuit2will be described taking the operation of the circuit11A as an example.FIG.9Ashows a circuit configuration of the circuit11A, andFIG.9Bis a waveform diagram of the signal PG output from the circuit11A. In this case, also, assume the following.

When the input signal IN makes a transition to H, the signals NH and NL make a transition to H accordingly. With the signal NL becoming H (0.8 V), N21turns on. The pulse signal PP generates a pulse at a transition of the signal NL to H and remains H for a predetermined period. Since N41is on during the period of the pulse signal PP being H, the node11band the node11dare shorted, becoming the same potential. At this time, the number of diodes between P21and N21becomes substantially two, thereby increasing the per-diode potential difference exerted on D1aand D11b. In a diode, due to its static characteristics, as the anode-cathode potential difference is greater, the current flowing through increases. Therefore, during the period of N41being on, the H to L transition of the signal PG is hastened.

In the waveform diagram of the signal PG shown inFIG.9B, the broken line A shows a change to be exhibited if N41is always off (four diodes), and the broken line B shows a change to be exhibited if N41is always on (two diodes). The operation of falling of the signal PG is faster in the broken line B because the per-diode potential difference is greater. The signal PG changes like the broken line B during the period of the pulse signal PP being H (period (1)) and like the broken line A during the period of the pulse signal PP being back to L (period (2)). As a result, the signal PG changes as shown by the solid line, where the H to L transition is hastened.

As described above, in the circuit11A, with the placement of the transistor N41, both ends of the series of D11cand D11d, out of the plurality of serially connected diodes, are shorted at a rising transition of the input signal IN, whereby the falling response of the signal PG can be hastened.

While, in the circuit configuration ofFIG.9A, both ends of the series of D11cand D11d, out of the plurality of serially connected diodes, are shorted through N41, the number of diodes to be shorted is not limited to two. For example, both ends of one diode may be shorted, or both ends of a series of three or more diodes may be shorted. Also, the positions of diodes to be shorted may be different from those inFIG.9A. For example, in the circuit configuration ofFIG.9A, both ends of the series of D11aand D11bmay be shorted, or both ends of the series of D11band D11cmay be shorted.

The circuits12A,13A, and14A also operate similarly to the circuit11A. That is, in the circuit12A, when the signal NL becomes H, N22turns on. Since N42is on during the period of the pulse signal PP being H, the node21band the node21dare shorted, becoming the same potential, whereby the H to L transition of the signal BP is hastened. In the circuit13A, when the signal NH becomes L, P23turns on. Since P41is on during the period of the pulse signal PN being L, the node31aand the node31care shorted, becoming the same potential, whereby the L to H transition of the signal NG is hastened. In the circuit14A, when the signal NH becomes L, P24turns on. Since P42is on during the period of the pulse signal PN being L, the node41aand the node41care shorted, becoming the same potential, whereby the L to H transition of the signal BN is hastened.

As described above, according to this embodiment, the falling response of the signals PG and BP given to the gates of P11and P12can be hastened, and also the rising response of the signals NG and BN given to the gates of N11and N12can be hastened. In this way, high-speed operation of the output circuit can be achieved.

Note that, in place of N41of the circuit11A and N42of the circuit12A, PMOSs may be provided. In this case, an inverted signal of the pulse signal PP may just be given to the gates of the PMOSs. Also, in place of P41of the circuit13A and P42of the circuit14A, NMOSs may be provided. In this case, an inverted signal of the pulse signal PN may just be given to the gates of the NMOSs.

Third Embodiment

FIG.10is a circuit diagram showing a circuit configuration of an output circuit according to the third embodiment. Like the output circuit1of the first embodiment, an output circuit3shown inFIG.10outputs an output signal Z having an amplitude VCCH responsive to an input signal IN having an amplitude VCCL. The basic configuration of the output circuit3is similar to that of the output circuit1. In the output circuit3, circuits11B,12B,13B, and14B each having added components are provided in place of the circuits11,12,13, and14.

In the circuit11B, serially connected diodes D12and D13are additionally provided between the power supply VCCH and the drain of P21. Also, an NMOS N31is additionally provided between P21and D11. The signal NH is given to the gate of N31.

In the circuit12B, a diode D22is additionally provided between the power supply VCCL and the drain of P22.

In the circuit13B, serially connected diodes D32and D33are additionally provided between the ground terminal GND and the drain of N23. Also, a PMOS P31is additionally provided between D31and N23. The signal NL is given to the gate of P31.

In the circuit14B, a diode D42is additionally provided between the power supply VCCL and the drain of N24.

Features of the output circuit3will be described in comparison with the output circuit1of the first embodiment. As in the description of the first embodiment, assume the following.

VCCL=0.8VVCCH=1.8Vwithstand voltage value of transistor=1.5 V

First, usingFIGS.11A-11B, the operation of the circuit11in the output circuit1of the first embodiment will be described. As shown inFIG.11A, in the circuit11, the potentials of the signal PG and a node11ahave the same waveform. During the period of the input signal IN being H (period (1)), since N21is on, the potential of the signal PG becomes GND+Vf (0.4 V). During the period of the input signal IN being L (period (2)), since P21is on, the potential of the signal PG becomes VCCH (1.8 V) and the potential of the node11bbecomes VCCH−Vf (1.4 V). Therefore, the transistors are avoided from exceeding the withstand voltage value 1.5 V.

In the actual operation, however, there is a case where a signal is fixed to H or L for a long time (steady state).FIG.11Bshows a waveform diagram in a steady state, where the periods (1) and (2) are assumed to be sufficiently long. During the period of the input signal IN being H (period (1)), since N21is on, the potential of the signal PG is GND+Vf (0.4 V) initially. However, since a diode current responsive to the potential difference between the nodes11aand11bcontinues to flow to D11, the potential of the signal PG gradually decreases with the lapse of time. As a result, there is a possibility that P11and P21may exceed the withstand voltage value.

Also, during the period of the input signal IN being L (period (2)), since P21is on, the potential of the node11bis VCCH−Vf (1.4 V) initially. However, since the diode current responsive to the potential difference between the nodes11aand11bcontinues to flow to D11, the potential of the node11bgradually increases with the lapse of time. As a result, there is a possibility that N21may exceed the withstand voltage value.

In contrast to the above, in this embodiment, the circuit11B operates as follows. As shown inFIG.12A, in the circuit11B, N21and N31are on during the period of the input signal IN being H (period (1)). Therefore, the potential of the signal PG is a value obtained by dividing VCCH (1.8 V) by three diodes D11, D12, and D13, which is 0.6 V here. As a result, P11and P21are avoided from exceeding the withstand voltage value.

During the period of the input signal IN being L (period (2)), since P21is on, PG=VCCH (1.8 V). However, since N31is off, the potential of the node11ais

Therefore, since the potential of the node11bis determined to be 0.3 V or less, N21is avoided from exceeding the withstand voltage value.

In the steady state, the circuit11B operates as shown inFIG.12B. During the period of the input signal IN being H (period (1)), N21and N31are on, and the potential of the signal PG is 0.6 V. At this time, since a steady current is occurring in D11, D12, and D13, PG=0.6 V remains constant even after the lapse of a sufficiently long time. As a result, P11and P21are avoided from exceeding the withstand voltage value.

During the period of the input signal IN being L (period (2)), P21is on, and PG=VCCH (1.8 V). However, since N31is off, the potential of the node11ais

Therefore, since the potential of the node11bis determined to be 0.3 V or less even after the lapse of a sufficiently long time, N21is avoided from exceeding the withstand voltage value.

As described above, with the placement of N31in the circuit11B, the voltage endurance of N21is secured irrespective of the number of stages of D11. It is therefore possible to minimize the number of stages of D11. Also, the potential of the signal PG when the input signal IN is H is determined by voltage division by D11to D13. Therefore, by reducing the number of stages of D11, the numbers of stages of D12and D13can also be reduced. This makes it possible to implement the circuit in a smaller area.

Also, in the circuit11B, the potential of the signal PG can be fixed to a given value depending on the number of diodes provided between VCCH and the drain of P21. For example, as shown inFIG.13, assume that diodes D14, D15, and D16are additionally provided between D13and VCCH. At this time, since a total of five diodes are present between the power supply VCCH and the signal line of PG, the potential of the signal PG is

The gate-source voltage |Vgsp11| of P11is then 1.5 (=1.8−0.3) V: i.e., it can be set at the maximum value for the transistor having a withstand voltage of 1.5 V. This voltage value remains constant even in the steady state. Therefore, P11can be used with its optimum drive capability.

The circuits12B,13B, and14B also operate similarly to the circuit11B. That is, in the circuit12B, when the input signal IN becomes H, making the signal NL H, N22turns on. At this time, the potential of the signal BP becomes a value obtained by dividing VCCL by two diodes D21and D22, and this remains constant even in the steady state.

In the circuit13B, during the period of the input signal IN being L, P23and P31are on. Therefore, the potential of the signal NG (H) is a value obtained by dividing VCCH by three diodes D31, D32, and D33, and this remains constant even in the steady state. During the period of the input signal IN being H, N23is on. Therefore, the potential of the signal NG (L) is GND, but, since P31is off, the potential of the node31bis

Therefore, since the potential of the node31ais determined to be 1.3 V or more, P23is avoided from exceeding the withstand voltage value even in the steady state.

In the circuit14B, when the input signal IN becomes L, making the signal NH L, P24turns on. At this time, the potential of the signal BN becomes a value obtained by dividing (VCCH −VCCL) by two diodes D41and D42, and this remains constant even in the steady state.

As described above, in this embodiment, the signals PG, BP, BN, and NG can be stabilized even when the signals are in the steady state where they are fixed to H or L for a long time. Also, the drive capability of the transistors can be enhanced within the range not exceeding the withstand voltage.

Note that the second embodiment and the third embodiment may be combined.

In the above embodiments, as each diode, a self-biased transistor of which the gate is connected to its drain may be used in place of the diode element. A p-type or n-type transistor can be used in this case.

FIGS.14A-14Dshow circuit configuration examples implemented using self-biased NMOSs as diodes, respectively corresponding to the circuits11B,12B,13B, and14B in the output circuit3of the third embodiment. InFIGS.14A-14D, the diodes are individually replaced with NMOSs, like the diode D11being replaced with an NMOS N101, for example.

FIGS.15A-15Dshow circuit configuration examples implemented using self-biased PMOSs as diodes, respectively corresponding to the circuits11B,12B,13B, and14B in the output circuit3of the third embodiment. InFIGS.15A-15D, the diodes are individually replaced with PMOSs, like the diode D11being replaced with a PMOS P101, for example.

Note that the voltage values of VCCL and VCCH and the withstand voltage and threshold voltage of the transistors used in the description of the above embodiments are mere examples and by no means intended to restrict the present disclosure.

According to the present disclosure, a highly-reliable output circuit suitable for high-speed operation can be implemented using low-withstand voltage transistors. The present disclosure is therefore useful in implementing high-performance, low-power semiconductor chips for communications, for example.