The present application claims priority from Japanese patent application JP 2007-238672 filed on Sep. 14, 2007, and JP 2008-065084 filed on Mar. 14, 2008, the contents of which are hereby incorporated by reference into this application.
This invention relates to a load drive circuits supplying a high and a low voltage to a load and to a semiconductor device having one or a plurality of load drive circuits integrated on a single semiconductor substrate. In particular, this invention relates to a semiconductor device and load drive circuit provided with a short-circuit protection circuit preventing failure of a circuit supplying high voltage to a load, such as a scan drive for a plasma display, as a result of short-circuiting between adjacent pins.
Furthermore this invention relates to a delay circuit provided in both the load drive circuit and the semiconductor integrated circuit and used in the above load drive circuit for example in a timing generation circuit or a pulse generation circuit. In particular, the invention relates to a delay circuit compensating for fluctuations over a delay period resulting from thermal fluctuations.
JP-A-2005-284242 discloses short-circuit protection for a scan driver. In particular,
JP-A-2006-325084 discloses a circuit which, for a short period of time after a drive circuit is switched to an ON position, maintains an output voltage by a stray capacitance.
In particular,
The present inventors examined techniques for short-circuit protection in scan drivers prior to this application. FIG. 23 in JP-A-2005-284242 a circuit using a technique of short-circuit protection for a scan drive.
However this circuit changes an output after a fixed time period from a Hi level to a HiZ level and maintains the Hi level in the output load capacity. As a result, the present inventors realized that after the fixed time period, if there is noise in the output, the output potential can not be maintained to the Hi level since there is not an element to drive the output.
FIG. 1 in JP-A-2006-325084 shows an arrangement of maintaining an output voltage using a stray capacitance in the scan driver circuit.
However the present inventors realized that when an output is short-circuited to a ground potential in this circuit, a potential always exists in the gate emitter of the IGBT and thus short-circuit protection is not enabled.
The present inventors have proposed a load drive circuit as shown in
A conventional example of a delay circuit 500 is shown in
However the delay time of a conventional delay circuit is determined by the characteristics of the individual transistors and the stages in the inverter circuit. Thus fluctuations in the ambient temperature result in large fluctuations in the delay time of individual inverter circuits and as a result large fluctuations in the delay time of the delay circuit after a number of stages.
For example, as shown in
A representative example of this invention is described hereafter. In other words, a load drive circuit according to this invention is a load drive circuit supplying a high and a low voltage to a load. The load drive circuit has a first semiconductor switching element, a diode, a second semiconductor switching element, two MOS field-effect transistors having a first conductivity type and two MOS field-effect transistors having a second conductivity type. The first semiconductor switching element is connected between a first power supply and an output terminal. The diode is connected to a cathode via the output terminal and to an anode via the first semiconductor switching element. The second semiconductor switching element is connected between the output terminal and a second power supply supplying a lower potential than the first power supply. The two MOS field-effect transistors having a first conductivity type control the first semiconductor switching element and the two MOS field-effect transistors having a second conductivity type of an opposite conductivity type to the first conductivity type control the first semiconductor switching element. The output terminal is maintained in a first state, a second state having a lower voltage than the first state, a third state having a higher impedance than the first and second states, and a fourth state having a higher impedance than the first and second states and a lower impedance than the third state by the application of a gate drive signal, being a signal applied to the gate terminal of the MOS field-effect transistors having a second conductivity type. The output terminal is maintained in the fourth state for a fixed time period and a voltage equal to the first state is maintained. When the output terminal short circuits, the current flowing between the first power supply and the second power supply is stopped.
A semiconductor device according to this invention has a plurality of load drive circuits provided for a single output bit, the load drive circuits integrated on common semiconductor substrates to form a plurality of output bits and the load drive circuit having the characteristics described above.
A delay circuit according to this invention has a first inverter circuit, a second inverter circuit and a fifth MOS field-effect transistor. The first inverter circuit has a first MOS field-effect transistor having a first conductivity type and inputting an input signal and a second MOS field-effect transistor having a second conductivity type being opposite to the first conductivity type and inputting an input signal. The first MOS field-effect transistor and the second MOS field-effect transistor are connected in complementary pairs between a positive power supply and a ground potential. The second inverter circuit has a third MOS field-effect transistor having a first conductivity type and inputting an output signal of the first inverter circuit and a fourth MOS field-effect transistor having a second conductivity type. The third MOS field-effect transistor and the fourth MOS field-effect transistor are connected in complementary pairs between a positive power supply and a ground potential. The fifth MOS field-effect transistor having a second conductivity type is connected in parallel between the first inverter circuit and the second inverter circuit. The first MOS field-effect transistor and the fifth MOS field-effect transistor have substantially equivalent thermal characteristics.
As described above, a semiconductor device according to this invention has a plurality of load drive circuits provided for a single output bit, the load drive circuits and delay circuits integrated on common semiconductor substrates. The load drive circuit has the characteristics described above. The delay circuit has the characteristics described above.
According to this invention, it is possible to provide a scanning device with short-circuit protection. In particular, even in the event of a fluctuation in the ambient temperature, short-circuit protection of a load drive circuit such as a scan drive is ensured to a greater degree by using a delay circuit having an approximately fixed delay time.
The delay circuit of this invention has a MOS field-effect transistor and two inverter circuits. The MOS field-effect transistor having a first conductivity type is connected between a positive power supply and a ground potential and receives an input signal or an output signal from an inverter circuit in a previous stage. The two inverter circuits have MOS field-effect transistors having a second conductivity type opposite to the first conductivity type connected in complementary pairs thereto. Furthermore a MOS field-effect transistor having a second conductivity type opposite to the first conductivity type is connected in parallel between the two inverter circuits.
This arrangement allows normal operation of short-circuit protection functions in a load drive circuit according to this invention irrespective of the ambient temperature. Thus even in the event of fluctuation in the ambient temperature, the delay time of the delay circuit is approximately fixed.
A load drive circuit according to this invention is a load drive circuit which supplies a high and a low voltage to a load and is provided with a first semiconductor switching element connected between a first power supply and an output terminal, a diode being connected to a cathode via the output terminal and to an anode via the first semiconductor switching element, a second semiconductor switching element connected between the output terminal and a second power supply supplying a lower potential than the first power supply, two MOS field-effect transistors having a first conductivity type controlling the first semiconductor switching element, two MOS field-effect transistors having a second conductivity type of an opposite type to the first conductivity type controlling the first semiconductor switching element. The output terminal is maintained in a first state, a second state having a lower voltage than the first state, a third state having a higher impedance than the first and second states, and a fourth state having a higher impedance than the first and second states and a lower impedance than the third state by the application of a gate drive signal, being a signal applied to the gate terminal of the MOS field-effect transistors having a second conductivity type. The output terminal being maintained in the fourth state for a fixed time period, a voltage equal to the first state being maintained and when the output terminal short circuits, the current flowing between the first power supply and the second power supply is stopped.
This arrangement enables short-circuit protection for a load drive circuit. In particular, it is possible to ensure short-circuit protection in a load drive circuit more accurately by using a delay circuit on the input side, that is to say, a delay circuit having an approximately fixed delay time in the delay circuit even during fluctuations in ambient temperatures in order to normal operation of short-circuit protection in a load drive circuit irrespective of ambient temperatures.
Furthermore a semiconductor device according to this invention has a number of load drive circuits equal to the number of output bits provided with respect to a plurality of output bits. The load drive circuits are integrated on common semiconductor substrates. In another embodiment, a plurality of load drive circuits and the above delay circuits are integrated on common semiconductor substrates.
Thus the invention provides a delay circuit having an approximately fixed delay time irrespective of fluctuations in the ambient temperature. Therefore use of the delay circuit provides a load drive circuit such as a scan drive with a short-circuit protection function which operates normally even in the event of fluctuation in the ambient temperature.
The embodiments of this invention will be described in further detail hereafter making reference to the drawings.
At a time t1, IN1 is placed at a Hi position and IGBT2 is placed in the ON position, IN2 is at a Lo position and IN3 is in the Hi position. Consequently IGBT1 is in the OFF position. At this time, the output DOUT is a Lo output.
At a time t2, NMOS 9c is ON and NMOS 9d is OFF since IN1 is at a Lo position and IGBT2 is in the OFF position, IN2 is at a Hi position and IN3 is in the Lo position, and PULSE_IN is synchronized with IN2 to a Hi position. Since NMOS 9c is ON, NMOS 9d is ON. Therefore a current flows through the diode 8 and the resistance elements 5a, 5b from PMOS 9b to the output DOUT. The electric potential difference produced by the resistance element 5b at this time takes the form of a positive bias on the gate emitter of IGBT1, and IGBT1 is placed in the ON position. A Zener diode 7 is provided to limit the potential between the gate emitters of IGBT1 in order to protect the IGBT gate. At this time, the output DOUT has an Hi output.
At a time t3, NMOS 9c is OFF since PULSE_IN is Lo. The level shift 9 is in a latching state, and even when the output. DOUT has a slightly reduced potential as a result of noise for example, PMOS 9b is retained slightly to an ON position. Since PMOS 9b is slightly in an ON position, a slight current flows to the output DOUT through the diode 8 and the resistance elements 5a, 5b from the PMOS 9b. This slight current is sufficient to maintain IGBT1 in an ON position and the output DOUT in a Hi state. As a result, even when the potential of the output DOUT decreases as a result of noise for example, the output DOUT can be forcibly returned to a Hi state and maintained in such a state. From the foregoing, an artificial Hi state is defined as a state in which a current which is smaller than a normal Hi output is applied and the output terminal is artificially maintained in a Hi state. In the example shown in
As shown in
The time interval between t3 and t2 takes a value which is greater than or equal a time sufficient to drive the output DOUT to a Hi position when there is not an output short circuit. When there is a short circuit, it is the time when the IGBT will not fail even when a saturation current flows in the IGBT 1.
In addition to the three states described above, in the example of a load drive circuit shown in
The illumination period of the plasma panel 407 is divided into a scan period and a sustain period. During the scan period, the scan driver 401 falls from a Hi potential to a Lo potential on consecutive scanning lines. At this time, no two scanning lines fall to a Lo position at the same time and only one scanning line falls to the Lo position. The address driver 402 supplies color information to the data line at positions on the plasma panel 407 falling to a Lo potential as a result of the scan driver 401. The points of intersection of data lines supplied with color information by the address driver 402 and scanning lines falling to a Lo potential due to the scan driver 401 are illuminated by preliminary discharge. After preliminary discharge is completed at all positions on the plasma panel 407, the illumination period of the plasma panel 407 shifts to the sustain period. During the sustain period, illumination resulting from preliminary discharge performed during the scan period is continued and an image is displayed on the plasma panel 407.
During the scan period, only one of the plural output bits in the scan driver 401 is always in a Lo state and the other bits are in a Hi state. At this time, when one output bit short circuits with an adjacent bit, a short circuit between a Hi state and a Lo state occurs. Generally since a high voltage is used to drive the plasma panel 407, failure of the scan driver may result from the generation of a short circuit. Furthermore there is no certainty that the plasma panel will not fail depending on how it is used. Use of a load drive circuit according to this invention which provides a short circuit protection function to the scan driver will prevent failure of the scan driver and the plasma panel.
The first conductivity type and the second conductivity type have mutually opposite polarity. In the example shown in
An input signal IN1 is connected to the gate of PMOS1a, NMOS1b. The output of an initial inverter constituted by PMOS1a and NMOS1b is connected to the gates of PMOS2a, NMOS2b. The output of a second stage inverter constituted by PMOS2a and NMOS2b is connected to the gate of NMOS3b.
When IN1 is initially in a Low position at a time t1, PMOS1a is ON and NMOS1b is OFF. When PMOS1a changes to the ON position, a current flows from PMOS1a to IN2. Since NMOS3b is ON at this time, the current flowing from PMOS1a is drawn to LGND through NMOS3b in addition to flowing to IN2. In other words, the voltage of IN2 gradually increases.
Since NMOS3b is ON at a time t2, the voltage in IN2 gradually increases. However when the voltage of IN2 is greater than or equal to a fixed value at a time t3, since NMOS2b is ON and PMOS2a is OFF, OUT changes to a Low position and NMOS3b changes to OFF.
When NMOS3b is OFF at a time t3, the current flowing from PMOS1a is no longer drawn to LGND and the voltage in IN2 sharply increases.
The delay time is the time difference taken by an input voltage and an output voltage to respectively reach a certain voltage. The majority of the time difference of this delay circuit is determined by the interval t3 and t2 in
In the interval t3 and t2, when the ambient temperature is low, the current flowing from PMOS1a increases due to the decrease in the ON resistance value of PMOS1a. However, the current drawn to LGND via NMOS3b increases as a result of the decrease in the ON resistance value of NMOS3b. In other words, the decrease in the ON resistance value of PMOS1a and the decrease in the ON resistance value of NMOS3b cancel out and the delay time is the same as that at room temperature.
When the ambient temperature is high, the increase in the ON resistance value of PMOS1a cancels out with the increase in the ON resistance value of NMOS3b and the delay time is the same as that at room temperature.
As shown above, according to the present embodiment, it is possible to obtain an approximately fixed delay time even during fluctuation in the ambient temperature by connecting NMOS in parallel between the inverter circuit constituted by PMOS and NMOS which are connected in complementary pairs between the positive power supply and the ground potential. Alternatively the use of the delay circuit provides a load drive circuit having a short circuit protection function which operates during output short circuits and even during fluctuation in the ambient temperature.
A load drive circuit 100 has semiconductor switching elements 1, 2, diodes 3, 4, 8, resistance elements 5a, 5b connected in series, a Zener diode 7 connected in parallel with the resistance elements 5a, 5b, a level shift circuit 9, and a NAND element 10. The level shift circuit 9 has MOS field-effect transistors 9a, 9b having a first conductivity type (PMOS) and MOS field-effect transistors 9c, 9d having a second conductivity type (NMOS). The first conductivity type and the second conductivity type have mutually opposite polarity. In the example shown in
The output potential switching sequence of the load drive circuit 100 shown in
At a time t1, IN1 is Hi and IGBT2 is ON, IN2 is Lo and IN3 is Hi. Consequently IGBT1 is in the OFF position. At this time, the output DOUT is a Lo output.
At a time t2, NMOS 9c is ON and NMOS 9d is OFF since IN1 is Lo and IGBT2 is in the OFF position, IN2 is Hi and IN3 is Lo, and PULSE_IN is synchronized with IN2 to a Hi position. Since NMOS 9c is ON, NMOS 9d is ON. Therefore a current flows through the diode 8 and the resistance elements 5a, 5b from PMOS 9b to the output DOUT. The electric potential difference produced by the resistance element 5b at this time takes the form of a positive bias on the gate emitter of IGBT1, and IGBT1 is placed in the ON position. A Zener diode 7 is provided to limit the potential between the gate emitters of IGBT1 in order to protect the IGBT gate. At this time, the output DOUT has a Hi output.
At a time t3, NMOS 9c is OFF since PULSE_IN is Lo. The level shift 9 is in a latching state, and even when the output DOUT has a slightly reduced potential as a result of noise for example, PMOS 9b is retained slightly to an ON position. Since PMOS 9b is slightly in an ON position, a slight current flows to the output DOUT through the diode 8 and the resistance elements 5a, 5b from the PMOS 9b. This slight current is sufficient to maintain IGBT1 in an ON position and the output DOUT in a Hi state. As a result, even when the potential of the output DOUT decreases as a result of noise for example, the output DOUT can be forcibly returned to a Hi state and maintained in such a state. From the foregoing, an artificial Hi state is defined as a state in which a current which is smaller than a normal Hi output is applied and the output terminal is artificially maintained in a Hi state.
The point of difference between the load drive circuit in
The scan driver 300 as shown in
As described above, when an output DOUT short circuits with another output DOUT, the output DOUT is changed to a Lo potential by another bit and a saturation current flows to IGBT1. The time period from the time that the output DOUT short circuits with another output DOUT and saturation current starts to flow in IGBT1, saturation current continues to flow to IGBT1 until the time that IGBT1 no longer functions properly is called the permissible short-circuit time.
In (c) of
In contrast, when a temperature characteristics compensation delay circuit 600 as shown in this embodiment is used, the relationship between the permissible short-circuit time of IGBT1 and the pulse width is as shown in (d) of
The interval t2 and t3 takes a value which is greater than or equal a time sufficient to drive the output DOUT to a Hi position when there is not an output short circuit. When there is a short circuit, it is the time when IGBT will not fail even when a saturation current flows in the IGBT1.
In addition to the three states described above, in the example of a load drive circuit, it is possible to set both IGBT1 and 2 to an OFF position by setting IN1 to Lo, IN2 to Lo and IN3 to Hi and it is possible to place the output DOUT in a HiZ state. When the output DOUT is in a HiZ state, the DOUT potential can be freely set by another driver connected to DOUT.
The load drive circuit 100 shown in
However, the load drive circuit 100 shown in
The time for PULSE_IN as shown in
The temperature characteristics compensation delay circuit 600 in each stage is provided with a MOS field-effect transistor (NMOS) 3b having a second conductivity type connected in parallel between two inverters provided with MOS field-effect transistors 1a, 2a (PMOS) having a first conductivity type and MOS field-effect transistors 1b, 2b (NMOS) having a second conductivity type.
The first conductivity type and the second conductivity type have mutually opposite polarity. In the example shown in
An input signal IN1 is connected to the gate of PMOS1a, NMOS1b. The output of an initial inverter constituted by PMOS1a and NMOS1b is connected to the gates of PMOS2a, NMOS2b. The output of a second stage inverter constituted by PMOS2a and NMOS2b is connected to the gate of NMOS3b.
The output potential switching sequence of the temperature characteristics compensation delay circuit 600 shown in
The majority of the delay time is determined by the interval t3 and t2. When the ambient temperature is low in the interval t3 and t2, the decrease in the ON resistance value of PMOS1 cancels out with the decrease in the ON resistance value of NMOS3b and there is no difference with the delay time at room temperature. In the same manner, when the ambient temperature is high, the increase in the ON resistance value of PMOS1 cancels out with the increase in the ON resistance value of NMOS3b and there is no difference with the delay time at room temperature. Thus a delay circuit according to this invention can approximately fix the delay time even during fluctuations in the ambient temperature.
The pulse width of PULSE_IN which determines the transition time from a first state (Hi state) to a fourth state (artificial Hi state) is produced by the temperature characteristics compensation delay circuit 600 above, the inverter circuit 820 shown in
According to this embodiment, the period when the terminal OUT and the terminal OUT2 are low is the interval t3 and t4 as shown in
According to the embodiments of this invention, the output can be in a first state (Hi state), a second state (Lo state) having a lower voltage than the first state, a third state (HiZ state) having a higher impedance than the first and second states, and a fourth state (artificial Hi state) having a higher impedance than the first and second states and a lower impedance than the third state. Thus it is possible to use the characteristics of the fourth state (artificial Hi state) in order to protect the circuit from short circuits in the output terminal. Furthermore it is possible to use the characteristics of the third state (HiZ state) to freely set the potential of the output terminal. Thus it is possible to provide a load drive circuit having a short circuit protection function and which can be applied to a scan driver.
Number | Date | Country | Kind |
---|---|---|---|
2007-238672 | Sep 2007 | JP | national |
2008-065084 | Mar 2008 | JP | national |