Shift register
At least one embodiment the present invention a plurality of unit circuits connected in multiple stages, to normal operation when the unit circuits are simultaneously turned on to output high-level output signals. When a shift register malfunctions, so that output signals provided by previous- and subsequent-stage unit circuits are simultaneously set to high level, malfunction restoration circuits and included in a unit circuit detect the malfunction in at least one embodiment. The malfunction restoration circuit provides a high voltage to a node, thereby forcibly pulling down an output signal. Also, the malfunction restoration circuit forcibly discharges another node, so that a charge accumulated in a capacitance is released. As a result, the shift register in malfunction can be instantaneously restored to normal operation. At least one embodiment of the present invention is suitable for driver circuits or suchlike of display devices and imaging devices.
1. A shift register having a plurality of unit circuits connected in multiple stages and operating based on multiple-phase clock signals, the unit circuits being configured by transistors of the same conductivity type, the shift register comprising:
a detection circuit for outputting an active detection signal upon detection of the unit circuits being activated; and
a restoration execution circuit for deactivating the unit circuits based on the active detection signal,
wherein the unit circuits each include,
an output control transistor having one of the multiple-phase clock signals provided to a first conductive terminal and connected at a second conductive terminal to an output terminal;
a pre-charge circuit for providing an on-voltage to a control terminal of the output control transistor while an input signal is at on-level;
a discharge circuit for providing an off-voltage to the control terminal of the output control transistor; and
an output reset transistor having an off-voltage provided to a first conductive terminal and connected at a second conductive terminal to the output terminal, and
the restoration execution circuit activates the discharge circuit, thereby providing an off-voltage to the control terminal of the output control transistor, wherein,
the unit circuits each include the restoration execution circuit, and
the detection circuit provides the active detection signal to the unit circuits upon detection of all output signals from two or more unit circuits being activated, the two or more unit circuits being arbitrarily selected from either even- or odd-numbered-stage unit circuits connected to the same clock signal line.
2. The shift register according to claim 1 , wherein,
the detection circuit further includes an initialization circuit to be activated upon reception of an external initialization signal, and
the restoration execution circuit activates the discharge circuit upon activation of the initialization circuit.
3. The shift register according to claim 2 , wherein the restoration execution circuit provides an on-voltage to the control terminal of the output reset transistor upon activation of the initialization circuit.
4. A shift register having a plurality of unit circuits connected in multiple stages and operating based on multiple-phase clock signals, the unit circuits being configured by transistors of the same conductivity type, the shift register comprising:
a detection circuit for outputting an active detection signal upon detection of the unit circuits being activated; and
a restoration execution circuit for deactivating the unit circuits based on the active detection signal,
wherein the unit circuits each include,
an output control transistor having one of the multiple-phase clock signals provided to a first conductive terminal and connected at a second conductive terminal to an output terminal;
a pre-charge circuit for providing an on-voltage to a control terminal of the output control transistor while an input signal is at on-level;
a discharge circuit for providing an off-voltage to the control terminal of the output control transistor; and
an output reset transistor having an off-voltage provided to a first conductive terminal and connected at a second conductive terminal to the output terminal, and
the restoration execution circuit activates the discharge circuit, thereby providing an off-voltage to the control terminal of the output control transistor, wherein,
the unit circuits each include the restoration execution circuit, and
the detection circuit detects the number of activated unit circuits based on outputs from all the unit circuits, and outputs the active detection signal corresponding to the number.
5. The shift register according to claim 4 , wherein,
the detection circuit includes:
a number detection circuit for outputting a number detection signal corresponding to the number of activated unit circuits among the plurality of unit circuits, and
a signal output circuit for outputting the active detection signal to the restoration execution circuit when the number detection signal from the number detection circuit exceeds a predetermined range,
the number detection circuit includes:
a resistive element, and
a plurality of parallel-connected transistors connected at their gate terminals to their respective output terminals of the unit circuits, the transistors being connected at their first conductive terminals to one terminal of the resistive element, and
a potential at a connection point between the resistive element and the first conductive terminal of each of the transistors is outputted to the signal output circuit.
6. A shift register having a plurality of unit circuits connected in multiple stages and operating based on multiple-phase clock signals, the unit circuits being configured by transistors of the same conductivity type, the shift register comprising:
a malfunction restoration circuit for restoring the shift register to normal operation upon malfunction, wherein,
the unit circuits each include,
an output control transistor having one of the multiple-phase clock signals provided to a first conductive terminal and connected at a second conductive terminal to an output terminal;
a pre-charge circuit for providing an on-voltage to a control terminal of the output control transistor while an input signal is at on-level;
a discharge circuit for providing an off-voltage to the control terminal of the output control transistor; and
an output reset transistor having an off-voltage provided to a first conductive terminal and connected at a second conductive terminal to the output terminal, and
the malfunction restoration circuit includes,
a detection circuit for outputting an active detection signal upon detection of the unit circuits being activated; and
a restoration execution circuit for deactivating the unit circuits based on the active detection signal,
the shift register further comprising a reset signal generation circuit for generating a reset signal which is normally at on-level and changes to off-level when the input signal is set to on-level, wherein,
the reset signal generation circuit includes,
a first transistor having one of the multiple-phase clock signals provided to a control terminal, the provided signal being the same as that provided to the first conductive terminal of the output control transistor;
a second transistor having one of the multiple-phase clock signals provided to a control terminal, the provided signal differing from that provided to the first conductive terminal of the output control transistor, the second transistor being connected at a first conductive terminal to a second conductive terminal of the first transistor; and
a third transistor having the input signal provided to a control terminal, connected at a first conductive terminal to a second conductive terminal of the second transistor, and having an off-voltage provided to a second conductive terminal, and
a connection point between the second and third transistors is connected to a control terminal of the output reset transistor.