1. Field of the Invention
The present invention relates to a flip-flop circuit, a shift register and a scan driving circuit using the same for a display device and, more specifically, relates to a flip-flop circuit, which permits an inverse change-over of the input and output, in other words permits a so called bidirectional operation and limits the circuit scale increase thereof, a shift register which is constituted by the flip-flop circuit, of which shift operation control in positive and reverse directions is performed easily and which is suitable for a scan driving circuit in a small sized and thinned display device, and a scan driving circuit therefor.
2. Background Art
For a flip-flop circuit used in an IC circuit, a D type flip-flop circuit in a master slave form in which inverters are connected in a loop shape as shown in FIG. 4 is often used. Further, in the drawing, CK is a clock signal, *CK is an inverted clock signal with regard to the phase thereof, numeral 1 is a latch circuit at the master side and 2 is another latch circuit at the slave side.
Herein, the master side latch circuit (a master flip-flop) 1 is constituted by two inverters 3a and 3b and two transmission gates 4a and 4c operating as analog switches, and the slave side latch circuit (a slave flip-flop) 2 is constituted by two inverters 3d and 3e and two transmission gates 5a and 5b operating as analog switches.
When the flip-flop circuit constituted by these elements operates as master and slave, the transmission gates 4a and 5b and the transmission gates 4b and 5a are respectively turned “ON/OFF” in an inverted phase timing. In this flip-flop circuit a terminal 11 operates as the input side and a terminal 12 operates as the output side.
Now, symbol “*” in the drawing implies an inverted signal which is used throughout the specification in the same meaning.
The assignee of the present application applied an application relating to a bidirectionally operable flip-flop circuit which is an improvement of FIG. 4 flip-flop circuit and permits an inverting change-over of the input and output as Japanese Patent Application Number 62-246345 (now patented as JP-B-6-54860). FIG. 5 shows the above improved bidirectionally operable flip-flop circuit.
6 and 7 are respectively transmission gates similar to the transmission gates 4a and 4b as shown in FIG. 4, and 8 is a transmission gate added at the side of the output terminal 12 in the flip-flop circuit as shown in FIG. 4. In this D type flip-flop circuit at the back side of the transmission gate 8 an input and output terminal 14 is provided in place of the output terminal 12 in FIG. 4, and the input terminal 11 in FIG. 4 is designated as an input and output terminal 13. In this circuit, placing the transmission gate 5a at the center, a flip-flop 9a and a flip-flop 9b are disposed in symmetry and a symmetric structure is formed as a whole. Therefore, any one of the flip-flops 9a and 9b can be selected as a master flip-flop and the other as a slave flip-flop, thereby, a bidirectionally operable D type flip-flop circuit which permits an inverting changing-over of the output and input is constituted. A shift register which makes use of such flip-flop circuit can select its shift direction. Such selection can be performed by exchanging the master and slave of the flip-flop (latch circuit) 9a and the flip-flop (latch circuit) 9b constituting the shift register.
However, when constituting a shift register with the bidirectionally operable flip-flop circuit as shown in FIG. 5, although it is easy to selectively set the shift direction in any one of two directions afterward, however, if it is required to constitute a shift register which is operable bidirectionally in dynamic manner, it is necessary to introduce an operation control circuit which exchanges the master and slave flip-flop of the D-flip-flops in the respective stages of the shift register.
Such as in a LCD display device and a LED display device, in case when displaying a display image as a mirror display, a dynamic reverse scanning is required. Further, such as in an organic EL display device, in order to improve display brightness simultaneous scanning of a panel divided into top and bottom two parts in opposite directions from top and bottom in vertical direction is effected. Therefore, for the scan driving circuit in these types of display devices a bidirectionally operable shift register is necessitated.
On the other hand, in view of the small sizing and thinning requirement for these types of devices it is not preferable to increase the circuit scale thereof. However, if a shift register is constituted by making use of the bidirectionally operable flip-flop circuit as shown in FIG. 5 and the same is used as a driving circuit for bidirectional scanning in a display device, an input and output control circuit which controls timing of the transmission gate 4a and the transmission gate 8 disposed respectively at both sides of the input and output depending on the input and output directions and clock CK is necessitated for respective stages of the shift register which causes a problem of increasing the circuit scale thereof.