TEMPERATURE COMPENSATED MULTIPLE CHARACTER ELECTRONIC DISPLAY

• US 3,725,898 A
• Filed: 05/03/1971
• Issued: 04/03/1973
• Est. Priority Date: 05/03/1971
• Status: Expired due to Term

• Current Assignee: Joseph R. Canton
• Original Assignee: Joseph R. Canton
• Inventors: Canton, Joseph R.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Curtis, Marshall M.
• Application Number:
  US05/139,945
• Time in Patent Office: 701 Days
• Field of Search: 340/324R 346/76 219/216,506,201 178/30,89
• US Class Current: 347/194
• CPC Class Codes: G05D 23/2034 the sensing element being a semiconductor

Abstract

A temperature compensated multiple character electronic display is described. Each character position includes a multielement matrix controlled by a transistor. The collectors of all transistors of all matrices are common. The emitters of all transistors of a single character matrix are common, and are selectively connectable to ground so that the characters can be sequentially enabled. The corresponding elements of all character matrices are connected to a common control line and are actuated by a single character generator. The power sequentially applied to each character is controlled separately to maintain a uniform display under varying operating temperatures by sampling the voltage of the base-emitter junction of a transistor of the enabled character as a measure of its temperature, and then applying power to the character during the following display cycle that is related to the sampled temperature.

Claims

1. In a multiple character electronic display device, the combination of:

a plurality of character matrices, each of said character matrices having a plurality of thermally separated elements each including a heating means, means for sensing the temperature of each of the character matrices individually, and means responsive to said sensing means of a character matrix for selectively applying power to the heating means of the elements of the character matrix at a voltage level related to the temperature of said character matrix.

2. The combination defined in claim 1 wherein:

each character matrix includes at least one thermally separated element including a semiconductor diode junction in heat exchanging relationship with the heating means for sensing the temperature of the character matrix.

3. The combination defined in claim 2 wherein:

the diode junction is part of a transistor connected to control current through the resistive heating means, and the temperature of the diode junction is selectively sensed by closing the circuit in which the diode is located.

4. The combination defined in claim 3 wherein:

the diode is the base-emitter junction of the transistor, and the resistive heating means is connected in the collector circuit of the transistor.

5. The combination defined in claim 4 wherein:

the collectors of the transistors of the elements are completed through the resistive heating means of each character matrix to a common collector voltage supply line, the bases of the transistors of the elements are common, and the emitters of the transistors are separately connectable to an emitter supply voltage.

6. The combination defined in claim 1 wherein said power applying means includes:

circuit means for storing a voltage proportional to the temperature of a character matrix during a sample period, and circuit means for applying power that is proportional to the stored voltage to the heating elEments of said character matrix during a subsequent period.

7. In a multi-character electronic display device, the combination of:

a plurality of character matrices each comprising a plurality of thermally separated elements each including a heating element, first switching means for controlling the current through each individual heating element, temperature sensing means for each matrix for producing a signal representative of the temperature of the respective matrix, voltage supply means connected to each character matrix including means for adjusting the supply voltage in response to a signal from a temperature sensing means, second switching means for selectively enabling each of the character matrices for printing by connecting the voltage supply means to the respective character matrices and respective temperature means, and circuit means for decoding electrical data representative of characters and producing outputs for operating the switching means of the enabled matrix in a manner to heat the elements in a geometric pattern corresponding to the character represented by the character data.

8. The combination of claim 7 wherein:

at least one of the first switching means of each matrix comprises a transistor in heat exchange relationship with the heating element it controls, the heating element being connected in the collector circuit, and wherein the temperature of the respective matrix is sensed by passing a current through the base-emitter junction of the transistor and taking the offset voltage as a measure of the temperature of the matrix.

9. The combination of claim 8 wherein:

the second switching means are in the emitter circuits of the transistors used as temperature sensors.

10. In an electronic display, the combination of:

a plurality of matrices each comprised of a like number of semiconductor elements, each semiconductor element including a transistor formed in the element with a resistance in the collector circuit for heating the element when current is passed through the transistor, a separate control line common to the bases of the transistors of corresponding elements of the matrices, switch means for selectively opening the emitter circuits of the transistors of each matrix to permit enabling of only one selected matrix at a time, means for passing a current through one of the control lines and the base-emitter junction of the corresponding transistor of the enabled matrix to sense the temperature of the matrix, and means for applying power that is related in magnitude to the magnitude of the sensed temperature to the enabled matrix.

11. The combination of claim 10 wherein:

the means for applying power is circuit means for adjusting the voltage applied across the resistances and corresponding transistors.

12. The combination of claim 11 wherein the means for applying power includes:

means for sampling the offset voltage of the base-emitter junction of the enabled transistor during a sample period and storing the voltage during a succeeding energizing period, and means for regulating the voltage applied across the resistances and corresponding transistors in relation to the stored voltage during the energizing period.