Voltage-level shifter

Abstract: A voltage level shifter is provided which complies with the situation that a voltage source of an input signal supplies a low voltage and/or a large potential difference exists between a voltage source of an input signal and a voltage source of a voltage level shifter. When the input signal transits from an "L" level to the "H" level, a MOS transistor to be turned off is surely controlled to be turned off, and a voltage level of an output signal of the voltage level shifter is surely fixed at the "L" level while surely preventing flow of a through current.

Description: BACKGROUND OF THE INVENTION The present invention relates to a voltage-level shifter. A semiconductor device using a plurality of voltage sources requires a voltage-level shifter for shifting potentials of signals to potential levels of the respective voltage sources. A voltage-level shifter in the prior art will be described below. Fig. 5 shows a circuit structure of a conventional voltage-level shifter in the prior art, and Fig. 7 shows an operation timing of the conventional voltage-level shifter. In these figures, I30 indicates an input signal, 030 indicates an output signal, VCC indicates a first voltage source, VPP indicates a second voltage source, VSS indicates a ground voltage source, 3001 indicates a voltage-level shifter, Qn3001 and Qn3002 indicate N-channel MOS transistors, Qp3001 and Qp3002 indicate P-channel MOS transistors, and N3001 indicates a node name. A circuit structure in Fig. 5 will be described below. The input signal I30 is connected to a source of the N-channel MOS transistor Qn3001 and a gate of the N-channel MOS transistor Qn3002. A gate of the N-channel MOS transistor Qn3001 is connected to the first voltage source VCC, and a source of the N-channel MOS transistor Qn3002 is connected to the ground voltage source VSS. A source of the P-channel MOS transistor Qp3001 and a source of the P-channel MOS transistor Qp3002 are connected to the second voltage source VPP. A drain of the N-channel MOS transistor Qn3001, a drain of the P-channel MOS transistor Qp3001 and a gate of the P-channel MOS transistor Qp3002 are connected together. The output signal 030 is connected to a drain of the N-channel MOS transistor Qn3002, a gate of the P-channel MOS transistor Qp3001 and a drain of the P-channel MOS transistor Qp3002. Fig. 6 shows a basic structure of the voltage-level shifter in Fig. 5. The structure in Fig. 6 differs from that in Fig. 5 in that an N-channel MOS transistor Qn3001' is supplied on its gate with a signal formed by inverting the input signal by an inverter INV32, has a source connected to the voltage source VSS of the input signal, and has a drain connected to the P-channel MOS transistor Qp3202. In other words, the structure in Fig. 31 eliminates the inverter circuit INV32 by employing the appropriate connection structure of the N-channel MOS element Qn3001, but performs the same operation as the basic structure in Fig. 6. Accordingly, the operation will be described below only in connection with the structure in Fig. 5. Referring to an operation timing diagram of Fig. 7, the operation will be described below. When the input signal I30 is at the "L" (Low) level, the node N3001 is at the "L" level, the N-channel MOS transistor Qn3002 is off, P-channel MOS transistor Qp3002 is on, output signal 030 is at the "H" level set by the second voltage source VPP, and the P-channel MOS transistor Qp3001 is completely off. When the input signal I30 transits from the "L" level to the "H" level, the N-channel MOS transistor Qn3002 is completely turned off, the node N3001 attains a potential (VCC-Vtn) which is lower than the potential of the first voltage source VCC by a threshold voltage (Vtn) of the N-channel MOS transistor Qn3001, and the P-channel MOS transistor Qp3002 is substantially turned off. Then, the output signal 030 attains the "L" level, the P-channel MOS transistor Qp3001 is completely turned off, the node N3001 attains the potential of the second voltage source VPP, and the p-channel MOS transistor Qp3002 is completely turned off. Fig. 8 shows another voltage-level shifter. This voltage-level shifter amplifies both the maximum and minimum values of an amplitude of an input signal to produce a signal having a large amplitude. The voltage-level shifter includes a signal inverter circuit 50 inverting the input signal, a positive level shifter 51 which receives the input signal and an output signal of the signal inverter circuit 50 to amplify the maximum value of the amplitude of the input signal, a negative level shifter 52 which receives the input signal and the output signal of the signal inverter circuit 50 to amplify the minimum value of the amplitude of the input signal, and a positive/negative level shifter 53 which receives output of the positive and negative level shifters 51 and 52 to compose them. However, in the voltage-level shifters of the conventional structures shown in Figs. 5 and 7, when the input signal I30 transits from the "L" level to the "H" level, the N-channel MOS transistor Qn3002 is completely off, and the P-channel MOS transistor Qp3002 is substantially off as already described. In particular, if the first voltage source VCC supplies a low voltage, and/or a large potential difference exists between the first and second voltage sources VCC and VPP, the P-channel MOS transistor Qp3002 is on. Therefore, a through current flows from the second voltage source VPP to the ground voltage source VSS via the N-channel MOS transistor Qn3002 and the P-channel MOS transistor Qp3002, which causes a disadvantage that the voltage level of the output signal 030 cannot fixed at the "L" level. The conventional voltage-level shifter shown in Fig. 8 requires three level shifters and hence many transistors forming them, and is constructed to compose the shifted outputs of the positive and negative level shifters, resulting in reduction of the operation speed. SUMMARY OF THE INVENTION An object of the invention is to provide a voltage-level shifter which can operate as follows if a voltage source of an input signal supplies a low voltage and/or a large potential difference exists between a voltage source of an input signal and a voltage source of a voltage-level shifter. When the input signal transits from an "L" level to the "H" level, an MOS transistor to be turned off is surely controlled to be turned off, and a voltage level of an output signal of the voltage-level shifter is surely fixed at the "L" level while surely preventing flow of a through current. This object is attained by the features of claim 1. Preferred embodiments of the invention are subject matter of the dependent claims. Other objects, features and advantages of the invention will appear more fully from the following detailed description thereof taken in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings showing preferred embodiments of the invention: Fig. 1 shows a structure of a first embodiment of a voltage-level shifter of the invention; Fig. 2 shows an operation timing of the first embodiment of the voltage-level shifter of the invention; Fig. 3 shows a structure of a second embodiment of the voltage-level shifter of the invention; Fig. 4 shows an operation timing of the second embodiment of the voltage-level shifter of the invention; Fig. 5 shows a structure of a voltage-level shifter in the prior art; Fig. 6 shows a basic structure of the voltage-level shifter in the prior art; Fig. 7 shows an operation timing of the voltage-level shifter in the prior art; and Fig. 8 shows a structure of another conventional voltage-level shifter. DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the invention will be described below with reference to the drawings. [First Embodiment] A voltage-level shifter of a first embodiment of the invention will now be described below. Fig. 1 shows a circuit structure, and Fig. 2 shows an operation timing. I12 indicates an input signal, 012 indicates an output signal, VCC indicates the first voltage source, VPP indicates the second voltage source, and VSS indicates the ground voltage source. 1201 indicates a voltage-level shifter, Qn1201 and Qn1202 indicate N-channel MOS transistors, Qn1203 indicates an N-channel MOS transistor (fifth N-channel MOS transistor), Qn1204 indicates an N-channel MOS transistor (sixth N-channel MOS transistor), Qp1201 and Qp1202 indicate P-channel MOS transistors, Qp1203 indicates a P-channel MOS transistor (sixth P-channel MOS transistor), and N1201-N1203 indicate node names. The circuit structure in Fig. 1 will be described below. In the voltage-level shifter1201, the input signal I12 is connected to a source of the N-channel MOS transistor Qn1201, a source of the N-channel MOS transistor Qn1204 and a gate of the N-channel MOS transistor Qn1202. Sources of the N-channel MOS transistors Qn1202 and Qn1203 are connected to the ground voltage source VSS. Sources of the P-channel MOS transistors Qp1201 and Qp1202 are connected to the second voltage source VPP. Sources of the P-channel MOS transistor Qp1203 and Qp1204 are connected to the first voltage source VCC. The node 1201 is connected to a drain of the N-channel MOS transistor Qn1201, a drain of the N-channel MOS transistor Qn1204, a drain of the P-channel MOS transistor Qp1201 and a gate of the P-channel MOS transistor Qp1202. The output signal 012 is connected to a drain of the N-channel MOS transistor Qn1202, a gate of the P-channel MOS transistor Qp1201, a drain of the P-channel MOS transistor Qp1202, a gate of the P-channel MOS transistor Qp1203 and a gate of the N-channel MOS transistor Qn1203. The node N1203 is connected to a drain of the P-channel MOS transistor Qp1203, a drain of the N-channel MOS transistor Qn1203 and a gate of the N-channel MOS transistor Qn1204. The fifth and sixth N-channel MOS transistors Qn1203 and Qn1204 as well as the sixth P-channel MOS transistor Qp1203 form a potential control circuit (electric charge supply circuit) 120. An operation will be described below with reference to the operation timing diagram of Fig. 2. When the input signal I12 is at the "L" level, the node N1201 is at the "L" level, the N-channel MOS transistor Qn1202 is off, and the P-channel MOS transistor Qp1202 is on. At this time, the output signal 012 is at the potential of the second voltage source VPP and thus at the "H" level. At this time, the N-channel MOS transistor Qn1203 is on, the P-channel MOS transistor Qp1203 is off, and the node N1203 is at the "L" level. The N-channel MOS transistor Qn1201 is on, the N-channel MOS transistor Qn1204 is off, and the P-channel MOS transistor Qp1201 is off. When the input signal I12 transits from the "L" level to the "H" level, the node N1201 initially attains lower one between the potential of (VCC-Vtn) and the potential of the first voltage source VCC, because the output signal 012 is at the potential of the first voltage source VCC. Assuming that VPP is 3.0V, VCC is 1.5V and Vtn is 0.7V, the node N1201 attains the potential of the first voltage source VCC, i.e., 1.5V. Thereafter, the N-channel MOS transistor Qn1202 is turned on, and the P-channel MOS transistor Qp1202 is substantially turned off. The output signal 012 attains the "L" level, the N-channel MOS transistor Qn1203 is turned off, the P-channel MOS transistor Qp1203 is turned on, and the node 1203 is set to the potential of the first voltage source VCC. The N-channel MOS transistor Qn1201 is turned off, the N-channel MOS transistor Qn1204 is turned on, and the P-channel MOS transistor Qp1201 is turned on, so that the node N1201 is set to the potential of the second voltage source VPP, and the P-channel MOS transistor Qp1202 is completely turned off. The foregoing voltage-level shifter has such a feature that, when the input signal I12 transits from the "L" level to the "H" level, the potential of the node N1201 is set to that of the first voltage source VCC, whereby the P-channel MOS transistor Qp1202 is substantially turned off. Thereby, it is possible to suppress a through current flowing from the second voltage source VPP to the ground voltage source VSS via the N-channel MOS transistor Qn1202 and the P-channel MOS transistor Qp1202. Also, the voltage level of the output signal 012 can be rapidly fixed at the "L" level. In particular, even when the first voltage source VCC supplies a low voltage, and/or there is a large potential difference between the first and second voltage sources VCC and VPP, the voltage level of the output signal 012 can be rapidly fixed at the "L" level. [Second Embodiment] A voltage-level shifter of a second embodiment of the invention will now be described below. Fig. 3 shows a circuit structure, and Fig. 4 shows an operation timing. I12 indicates an input signal, 012 indicates an output signal, VCC indicates the first voltage source, VPP indicates the second voltage source, and VSS indicates the ground voltage source. 1201 indicates a voltage-level shifter, Qn1201 and Qn1202 indicate N-channel MOS transistors, Qn1404 indicates an N-channel MOS transistor (seventh N-channel MOS transistor), Qp1201 and Qp1202 indicate P-channel MOS transistors, and N1201 indicates a node name. The circuit structure in Fig. 3 will be described below. In the voltage-level shifter1201, the input signal I12 is connected to a source of the N-channel MOS transistor Qn1201, a source of the N-channel MOS transistor Qn1404, a gate of the N-channel MOS transistor Qn1404 and a gate of the N-channel MOS transistor Qn1202. A source of the N-channel MOS transistor Qn1202 is connected to the ground voltage source VSS. Sources of the P-channel MOS transistors Qp1201 and Qp1202 are connected to the second voltage source VPP. The node 1201 is connected to a drain of the N-channel MOS transistor Qn1201, a drain of the N-channel MOS transistor Qn1404, a drain the P-channel MOS transistor Qp1201 and a gate of the P-channel MOS transistor Qp1202. The output signal O12 is connected to a drain of the P-channel MOS transistor Qp1202, a gate of the P-channel MOS transistor Qp1 01, a drain of the P-channel MOS transistor Qp1202 and a gate of the N-channel MOS transistor Qn1201. The seventh N-channel MOS transistors Qn1404 forms a potential control circuit (electric charge supply circuit) 140. An operation will be described below with reference to the operation timing diagram of Fig. 4. When the input signal I12 is at the "L" level, the node N1201 is at the "L". level, the N-channel MOS transistor Qn1202 is off, the N-channel MOS transistor Qn1404 is off and the P-channel MOS transistor Qp1202 is on. The output signal O12 is at the potential of the second voltage source VPP and thus at the "H" level. The P-channel MOS transistor Qp1201 is off, and the N-channel MOS transistor Qn1201 is on. When the input signal I12 transits thereafter from the "L" level to the "H" level, the N-channel MOS transistor Qn1202 is turned on, and the node N1201 initially attains lower one between the potential of (VPP-Vtn) and the potential of the first voltage source VCC, because the output signal 012 is initially at the potential of the second voltage source VPP. Assuming that VPP is 3.0V, VCC is 1.5V and Vtn is 0.7V, the node N1201 attains the potential of the first voltage source VCC of 1.5V. Thereafter, the P-channel MOS transistor Qp1202 is substantially turned off, and the output signal O12 attains the "L" level. Further, the P-channel MOS transistor Qp1201 is turned on, the N-channel MOS transistor Qn1201 is turned off, the node N1201 attains the potential of the second voltage source VPP, and the P-channel MOS transistor Qp1202 is completely turned off. The foregoing voltage-level shifter has such a feature that, when the input signal I12 transits from the "L" level to the "H" level, the node N1201 is set to the potential of the first voltage source VCC, whereby the P-channel MOS transistor Qp1202 is substantially turned off. Thereby, it is possible to suppress a through current flowing from the second voltage source VPP to the ground voltage source VSS via the N-channel MOS transistor Qn1 02 and the P-channel MOS transistor Qp1202. Also, the voltage level of the output signal O12 can be rapidly fixed at the "L" level. In particular, even when the first voltage source VCC supplies a low voltage, and/or there is a large potential difference between the first and second voltage sources VCC and VPP, the voltage level of the output signal 012 can be rapidly fixed at the "L" level.

Claims: A voltage-level shifter comprising: a high voltage power source (Vpp); first and second P-channel MOS transistors (Qp1201, Qp1202); and a first N-channel MOS transistor (Qn1201) including: a source receiving an input signal (I12); a drain connected to a drain of said first P-channel MOS transistor (Qp1201) and a gate of said second P-channel MOS transistor (Qp1202); and a second N-channel MOS transistor (Qn1202) including: a gate receiving said input signal (I12); a source that is grounded (Vss); and a drain, the potential of which serves as an output signal (O12), wherein said high voltage power source (Vpp) is connected to each source of said first and second P-channel MOS transistors (Qp1201, Qp1202), and wherein a gate of the first N-channel MOS transistor receives said output signal (O12), said voltage-level shifter further including: a potential control circuit (120, 140) which has a third N-channel MOS transistor (Qn1204, Qn1404), a source of which receives the input signal (I12) and a drain of which is connected to the drain of the first N-channel MOS transistor (Qn1201), said potential control circuit controlling a potential of the gate of the third N-channel MOS transistor (Qn1204) to a set potential at a "H" level (Vcc) when the input signal is at the "H" level, and controlling the potential of the gate of said second P-channel MOS transistor (Qp1202) to the ground potential (Vss) when the input signal is at the "L" level. The voltage-level shifter according to claim 1, wherein the potential control circuit (120) includes a sixth P-channel MOS transistor (Qp1203) and a fifth N-channel MOS transistor (Qn1203) connected in series and the third N-channel MOS transistor (Qn1204); each of the sixth P-channel MOS transistor (Qp1203) and the fifth N-channel MOS transistor (Qn1203) receives on its gate the output signal (O12) of the level shifter, the sixth P-channel MOS transistor (Qp1203) is connected to the voltage source (Vcc) of the input signal (I12), and the fifth N-channel MOS transistor (Qn1203) is grounded; the third N-channel MOS transistor (Qn1204) has a gate connected to a connection between the sixth P-channel MOS transistor (Qp1203) and the fifth N-channel MOS transistor (Qn1203). The voltage-level shifter according to claim 1, wherein the third N-channel MOS transistor (Qn1404) receives on its gate the input signal (I12).

Inventors: HIRANO HIROSHIGE, HIRANO, HIROSHIGE
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD
Application year: 1995
Main classification: H03K19
IPC codes: H03K19