DE3427986A1 - CIRCUIT ARRANGEMENT FOR CONTROLLING LIQUID CRYSTAL DISPLAYS - Google Patents

Description

. "'.'; Deutsche Thomson-Brandt GmbH

/.:...- - - Fos'tfach 2G60

- - - 7730 Villingen-Schwenningen

3427986 ^{23 3uli 153A}

- * 'T-PA 516

PATENT APPLICATION

Circuit arrangement for the control of liquid crystal displays.

The invention is based on a circuit arrangement as described in the preamble of the patent claim is.

As is well known, LC displays are made up of many segments exist, controlled in multiplex operation. For this purpose, the individual segments and their counter-electrodes become matrix-like summarized. By creating a AC voltage each individual segment can be displayed by placing two opposing segments can be controlled at the same time. Microprocessors are used to control the segments of the LC display, the corresponding control voltages are applied to the outputs. The control voltages come via LCD driver ICs to the LC display unit. [Programmer's Reference Manual, Hitachi, Edition GuIi 1981, 40-1-12, page 42 "Liquid Crystal Display, Circuit-Block Diagram). These driver ICs are expensive components and it is part of the invention." the task is to save them. The object is achieved by the invention specified in claim 1 solved.

• Deutsche Thomson-Brandt GmbH

/ Plague compartment 20 60

Sheet - 4 - · ■ 7730 Vilüngen-Schwenningen

July 23, 19'k 'T-PA 516

The advantage of the invention lies in the low manufacturing costs and in a higher reliability.

The essence of the invention is explained below using an exemplary embodiment.

FIG. 1 shows the arrangement of the segments and control lines of an LC display

FIG. 2 shows the curves of the control voltages j necessary for a display

FIG. 3 shows the circuit arrangement for controlling the display;

FIG. 4 shows the circuit arrangement for controlling the display j

FIG. 5 shows a further dimensioning example for a circuit arrangement with tri-state outputs.

A display field for displaying Numbers and symbols. In Figure 1a, several segments are combined into groups and via segment lines S1 to S1Q controllable. In FIG. 1b, the "* electrodes of the same shape opposite the segments of FIG. 1a are shown, which can be controlled via so-called common lines C1 to C4, whereby these segments are also combined into groups are. The lines S1 to S10 and C1 to C4 are matrix-like arranged so that each individual element of the display is separately and individually controllable. There is always only the element for Displayed to which the corresponding control voltage is applied via lines S1 to S10 and C1 to C4.

. ".. · .. · - - Oeutsche Thomson-Brandt GmbH

-. . "; _ ·: ^ Osifach 20 60

Sheet - ο - ■ '■ - ·.: .- - - 7780 Villingen-Schwenningen

3427986 July 23, 19 = ^

T-PA 51B

In Figure 2a-h, for example, the control voltages for the segment lines S1 and S2 and the common lines C1 to C4 are shown. Due to the phase position of the signals on lines S1 and S2 in relation to the phase position of the signals on lines C1 to C4, a character formed from the segments can be displayed. In the example shown according to FIGS. 1 and 2, the characters "TUNING" and "FM" are displayed, since the voltages according to FIGS. 2a and 2e as well as FIGS. 2b and 2s have the correct phase relationship to one another for a display. H)

In Figure 3, a circuit constructed according to the feature of the invention is shown. An LC display 1 with the inputs C1 to C4 and S1 to S10 are connected to a control unit

connected. At the output A1 of the microprocessor 2 is a square wave of constant amplitude and phase, the are switched cyclically via the analog switch 3 to the inputs C1 to C4 of the LC display '. The analog switches 3 are controlled via control outputs A2 to A5, whereby a multiplex operation of the display is achieved. With the one shown Example is a microprocessor with open drain outputs, for which a pull-up resistor 4 is required. To generate the correct control voltage for the Inputs C1 to C4 are voltage dividers 5 for the operating voltage -'- U placed at whose divider points the output A1 the control unit 2 is placed via the analog switch 3. The analog switch 3 shown can be omitted if a Microprocessor with tri-state outputs is used. The inputs S1 to S10 of the display are connected to the outputs B1 to B10 of the microprocessor switched. For this purpose, inputs S1 to S10 are tapped off voltage dividers 6 and above Resistors 7 at the outputs B1 to BIO of the control unit 2.

-B-

-German Thomson-Brandt GmbH ^: Poütfach 2060

T-PA

The LC display is at a certain voltage UD between the intersection of a segment line and of a common line effective and e.g. switched off at 1/3 of this voltage UD. This becomes with 1/3 bias designated. The voltage divider 5 for the common lines C1 to C4 and the voltage dividers 6 for the segment lines S1 to Ξ10 are to be dimensioned in such a way that that a voltage swing of 4/3 of the voltage UD occurs at the taps for the common lines C1 to C4, so that either the full display voltage UD or 1/3 UD arises between the common and segment lines. at a display voltage UD of e.g. 3 volts, the potential on the common line must be between 4 volts and Q volts change when the segment line potential changes between 1 volt and 3 volts.

In Figure 4, a dimensioning example for the voltage dividers 5 and 6 is given, with which the required Stresses can be generated.

As shown in FIG. 2, the network for the common line is connected to the output A1 of the microprocessor 2 C1 placed. Depending on the switching status in the microprocessor arranged switching stage 12 and the analog switch result in the following voltages on common line C1:

a.} Analog switch 3 high resistance: 2 volts b.) Analog switch 3 low resistance,

Switching stage 12 low resistance: 0 volts c. Analog switch 3 low resistance, Switching stage 12 high resistance: 4 volts.

Deutsche Thomson-Brandt Gm'cH ■ - ... P.O. Box 20 60

Sheet - * T - 7730 Vülingen-Schwenningen

23. JIuIi 1GS ^ * ^ · T-PA 516

The network for the segment line S1 is applied to the output B1 of the microprocessor 2. JDepending on the switching status the switching stage 13 arranged in the microprocessor 2 result from the resistance values given in FIG the following voltages on segment line S1:

a.) Switching stage 13 high resistance: 3 volts, b.) Switching stage 13 low resistance: 1 volt.

If the microprocessor has tri-state outputs, so that the analog switches 3 can be omitted, they are Α-outputs like the B-outputs at the taps of the voltage divider 5 or 6.

A corresponding structure with the required dimensions is shown in FIG. At the tri-state outputs the resistors 14 and 7 are depending on the switching state of the stages 12 ', 13' at the outputs A and B on the positive operating voltage + U parallel to the resistor B or 10, or at reference potential parallel to the resistors 9 or 11 or the resistors 14 and 7 are switched off in a highly homologous manner. This is also the case with this circuit Voltage swing on the common line 4/3 of the display voltage UD, i.e. 4 volts. Since the undervoltage only drops to 0.5 volts, the upper voltage must be increased to 4.5 volts.

The example shown relates to an LC display with 4 common and 10 segment lines. Of course Any combination of the number of segment and common lines can be used.

-Γ

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Claims (3)

'"OeiJische Thomson-Brindt GmbH ν "* ■." "- ■■" P.O. Box 2060 Sheet \ 7730 Villingen-Schwenninaen T-PA 516 Claims Circuit arrangement for controlling a liquid crystal display consisting of several segments CLC display), in which the segments are put together in several groups and with an alternating voltage via segment lines and are opposite with the segments These counter-electrodes are adapted in shape and are also interconnected in several groups and which can be cyclically controlled via common lines in multiplex operation, with the segments and counter-electrodes are grouped together like a matri ^ that each individual segment can be displayed, the switching voltages for the segment and common lines of the outputs of a control unit are supplied or controlled, characterized in that that between the outputs (A, B) of the control unit which supply or control the switching voltages [2] and the segment and cornmon lines (C, S) of the LC display (1) passive voltage divider (5, 6) are switched. 2. Circuit arrangement according to claim 1, characterized in that the passive voltage divider (5, 6) are dimensioned in such a way that, depending on the switching status of the outputs (A, B) the control unit (2) the control voltages for the segment lines (S) and common lines (C) deliver. '"-" ■ ■ ·. German Thomson-Brandt GmbH / "" - ■ ::. -R: nsffach2060 ^Sheet "/" - ■ - ■ '. "* ..'.. '.. ■ 77C0 Villingen-Schwenningen 3427986 July 23, 1984 T-PA 516 3. Circuit arrangement according to claim 1, characterized in that between the operating voltage (U) and ground potential voltage divider (5, 6] are connected, the divider points with the Common or segment lines CC or S) are connected and that the tapping of the on the common lines CO lying voltage divider C5) cyclically to the with a square-wave alternating voltage applied Output (A1) of the control unit C2) are placed and that the taps of the voltage divider C6) connected to the segment lines CS) via series resistors (7) with which the alternating voltage for the segments of the LC display (1) supplying outputs CB) of the control unit (2) are connected, the resistors (8, 9) the voltage divider C5) and the resistors CIO, 11) the voltage divider CB) and the series resistors (7) are dimensioned such that at the taps of the voltage divider (5, 6) as a function of the output impedance of the outputs CA, B) (high or low resistance) for the display of the selected Segments required potentials arise.