Electrical pulse counters – pulse dividers – or shift registers: c – Systems – Using shift register
Reexamination Certificate
1999-11-12
2001-10-09
Wambach, Margaret R. (Department: 2816)
Electrical pulse counters, pulse dividers, or shift registers: c
Systems
Using shift register
C377S079000
Reexamination Certificate
active
06301323
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a circuit arrangement as part of a shift register to control switch elements arranged in the form of a chain or a matrix.
BACKGROUND INFORMATION
Switch elements arranged in the form of a chain or a matrix are controlled, in particular, by addressing row or column circuits of a liquid crystal screen. Liquid crystal screens have a matrix-shaped arrangement of pixels with a switch element being assigned to each pixel. The switch elements are often thin-layer transistors. The image information is applied to the columns and is written row by row into the pixel memory (pixels) via the switch elements. To select the rows, shift registers preferably manufactured using the same technology as the pixels are regularly used.
German Patent No. 43 07 177 describes a circuit arrangement as part of a shift register for controlling switch elements arranged in the form of a chain or a matrix. In particular, this circuit is used to control switch elements in rows of an active matrix for a liquid crystal screen. According to the present invention, the circuit should have no more than seven transistors operating as switches and no more than two capacitors, with some capacitors, together with one capacitor operating as a bootstrap capacitor forming an output stage and at least one additional transistor forming the charge and discharge stage for the bootstrap capacitor. In addition, the circuit is controlled by four clock signals, which are phase shifted 90° one in relation to the other, so that no cross currents appear in the circuit. The output signal going to the row circuit depends directly on the shape of the shift register clock signal in this circuit. In this way, the circuit has few transistors, yet the shape of the output signal is determined.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a circuit arrangement as part of a shift register with which switch elements arranged in the form of a chain or a matrix can be controlled more effectively or more variably, yet with a relatively reduced number of transistors being required.
The present invention is based on a circuit arrangement as part of a shift register to control switch elements arranged in a chain or matrix form. To control the circuit arrangement, four clock signals, phase shifted 90° in relation to one another, are available. The fact that in addressing rows or columns of a matrix no arbitrary pulse sequences are required as shift information is taken into account here. Instead, it is sufficient to shift an input pulse through all stages of the shift register prior to applying the next input pulse to the input of the first stage. The present invention contemplates that in the circuit arrangement as part of a shift register at least one transistor switches through a signal that is independent of the shift clock signals to the output, depending on the information to be shifted, in order to control the switch elements. This feature has the advantage that the signal form that has been switched through can be adjusted to the needs of the output. Thus, for example, when controlling the rows of an active matrix for liquid crystal screens, the selection voltage curve can be individually adjusted to the characteristics of the thin layer transistors arranged in the rows, thereby achieving the desired charge characteristics of the pixels affected.
In order to prevent the transistors controlled by the different shift clock signals from becoming conductive simultaneously, allowing cross currents to flow, it is proposed that the clock signals, phase shifted by 90° with respect to one another, be substantially non-overlapping.
In order to avoid undesirable output signals, it is furthermore proposed that two selection signals (
111
,
112
) be provided, which are alternatingly connected to adjacent circuit arrangements of the shift register and have non-overlapping signal forms that are phase shifted 180° with respect to one another.
It is furthermore advantageous if the circuit arrangement has no more than eight effective transistors, which operate as switches. Thus the circuit is substantially independent of the characteristics of the transistors in the amplifier range, since the operating point of the transistors when switched on is always in the starting range. Due to the reduced number of transistors (no more than eight), a high degree of efficiency is achieved in manufacturing such circuits with a relatively compact design.
In a particularly advantageous embodiment of the circuit arrangement according to the present invention, the circuit includes two clocked inverters connected in series with an output stage connected between them. The inverter stages preferably each have three transistors connected in series. This arrangement has the advantage that the circuit can be implemented with only three crossovers not considering the relatively problem-free crossovers of supply lines. The output stage is preferably formed by at least two transistors with at least one bootstrap capacitor. Using a first transistor with a bootstrap capacitor, the selection signal can be switched through to the output with a relatively low resistance. With the second transistor of the output stage, which preferably also has a capacitor at the control electrode, the information to be shifted can be completely isolated from the output side. Even if the output were to be short-circuited, the information to be shifted in the shift register would not be affected. These features result in improved resistance of the circuit arrangement to interference.
In order to achieve manufacturing technology compatibility with the control matrices of an active liquid crystal display, it is proposed that the circuit be manufactured using thin film technology. The circuit arrangement is particularly well-suited for manufacture using amorphous silicon technology, polysilicon technology or polycadmium technology. It is advantageous if the transistors are field-effect transistors of the n-MOS enhancement type. They can be manufactured in a particularly advantageous manner and, when large-surface thin film technology is used, result in a simple manufacturing process with high manufacturing yields.
A particular advantage is obtained when the circuit arrangement is used for controlling row and/or column circuits of liquid crystal screens.
REFERENCES:
patent: 5517543 (1996-05-01), Schleupen et al.
patent: 5631940 (1997-05-01), Fujikura
patent: 0 615 250 (1994-09-01), None
Edwards, M.J., “NMOS and CMOS Polysilicon Drive Circuits For Liquid Crystal Displays”, IEEE Proceedings: Circuits Devices and Systems, vol. 141, No. 1, pp. 50-55 (Feb. 1, 1994).
Kenyon & Kenyon
Robert & Bosch GmbH
Wambach Margaret R.
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