Analog-to-digital converter with automatic range and sensitivity adjustment

• US 20050006475A1
• Filed: 05/10/2004
• Published: 01/13/2005
• Est. Priority Date: 01/09/2003
• Status: Active Grant

• Current Assignee: Hand Held Products Incorporated (Honeywell International Inc.)
• Original Assignee: Hand Held Products Incorporated (Honeywell International Inc.)
• Inventors: Pankow, Matthew W., Bremer, Edward C., Meier, Timothy P., Pettinelli, John A. Jr., Livingston, Joseph T.
• Granted Patent: US 7,175,092 B2
• Time in Patent Office: Days
• US Class Current: 235/454
• CPC Class Codes: G06K 7/10851 Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device basic electronic circuitry H03
• CPC Class Codes: H03M 1/182 the feedback signal controlling the reference levels of the analogue/digital converter

Abstract

The invention is a system and method for providing optimized accuracy and precision in analog-to-digital conversions of data. In an embodiment of the invention, an A/D converter is configured by setting two separately definable reference voltages that are controlled by a microprocessor. The A/D converter range is as wide as, or slightly greater than, a dynamic range of the analog signal to be converted. The microprocessor adjusts at least one reference voltage. The A/D converter receives analog signals from a sensor. The dynamic range of the signal from the sensor, or the sensor operating conditions, are used to define the reference voltages. The converted data is provided to a data processor at a rate controlled by a clocking signal. In a method according to the invention, the A/D converter is operated using the features described above. The accuracy and the precision of the converted data are thereby optimized.

Claims

1. An improved optical reader for reading decodable indicia, comprising:

a sensor that senses an excitation carrying information representing an encoded symbol and that provides an analog signal responsive to said excitation at an output terminal;

an analog-to-digital converter configured to receive said analog signal from said sensor output terminal at an analog data input terminal, and to provide optimized digital data in an N-bit representation, where N is a positive integer greater than 1, said N-bit range of said analog-to-digital converter substantially spanning a dynamic range of said excitation as sensed by said sensor; and

a microprocessor that manipulates said optimized digital data, thereby providing accurate decoding of said digital data under a range of illumination conditions.

2. The improved optical reader of claim 1, further comprising a display.

3. The improved optical reader of claim 1, wherein said range of illumination includes approximately 70,000 Lux to substantially zero Lux.

4. The improved optical reader of claim 1, wherein said sensor comprises a selected one of a CCD sensor having a plurality of pixels and a CMOS senor having a plurality of pixels.

5. The improved optical reader of claim 1, wherein said sensor comprises a selected one of a television camera, a digital camera, and a video camera.

6. The improved optical reader of claim 1, wherein said dynamic range of said excitation is measured temporally.

7. The improved optical reader of claim 1, wherein said dynamic range of said excitation is measured spatially.

8. The improved optical reader of claim 1, further comprising an illumination source for illuminating said encoded symbol.

9. The improved optical reader of claim 8, wherein said illumination source for illuminating said encoded symbol comprises at least one LED.

10. The improved optical reader of claim 8, wherein said illumination source for illuminating said encoded symbol comprises a laser diode.

11. The improved optical reader of claim 8, wherein said illumination source for illuminating said encoded symbol comprises a scanner for scanning illumination from said illumination source across said encoded symbol.

12. The improved optical reader of claim 1, further comprising an imaging system of which said sensor that senses an excitation is a component.

13. The improved optical reader of claim 12, wherein said imaging system comprises a stationary optical system.

14. The improved optical reader of claim 12, wherein said imaging system comprises a scanner for scanning illumination from said illumination source across said encoded symbol.

15. The improved optical reader of claim 1, further comprising a trigger for initiating an action of said reader.

16. The improved optical reader of claim 1, wherein said improved optical reader is provided in a hand held configuration.

17. The improved optical reader of claim 16, further comprising a trigger for initiating an action of said reader.

18. A least-significant-bit-optimized analog-to-digital converter circuit, comprising:

an analog-to-digital converter having a first reference voltage input terminal, a second reference voltage input terminal, an analog data input terminal, and a digital data output terminal providing data in an N-bit representation, where N is a positive integer greater than 1;

a first reference voltage source that provides a first reference voltage to said first reference voltage input terminal;

a second reference voltage source that provides a second reference voltage to said second reference voltage input terminal;

a detector that detects an excitation and that provides an analog signal responsive to said excitation to said analog data input terminal; and

a microprocessor-based controller that controls said first reference voltage and said second reference voltage;

whereby said microprocessor-based controller adjusts at least one of said first and said second reference voltages to cause said N-bit range of said analog-to-digital converter to substantially span a dynamic range of said excitation as detected by said detector, thereby optimizing a value of a least-significant bit of said analog-to-digital converter with respect to said excitation.

19. The analog-to-digital converter circuit of claim 18, wherein a difference between said first and said second reference voltages is a rational number times a characteristic voltage, a denominator of said rational number being a full scale value of an M-bit representation of the number of bits of at least one of a first D/A converter and a second D/A converter.

20. The analog-to-digital converter circuit of claim 18, wherein said analog-to-digital converter further comprises a clock signal input terminal for receipt of a clock signal that determines an N-bit data rate under control of said microprocessor-based controller.

21. The analog-to-digital converter circuit of claim 18, wherein said detector comprises a selected one of a CCD sensor having a plurality of pixels and a CMOS sensor having a plurality of pixels.

22. The analog-to-digital converter circuit of claim 18, wherein said dynamic range of said excitation is measured temporally.

23. The analog-to-digital converter circuit of claim 18, wherein said dynamic range of said excitation is measured spatially.

24. The analog-to-digital converter circuit of claim 18, further comprising a microprocessor that receives an N-bit digital output datum from said analog-to-digital converter.

25. The analog-to-digital converter circuit of claim 24, wherein said microprocessor that receives digital output data manipulates said digital output data to interpret an encoded symbol.

26. The analog-to-digital converter circuit of claim 18, wherein said microprocessor-based controller, said first reference voltage source, and said second reference voltage source are integrated in a single integrated circuit.

27. An optical reader comprising said least-significant-bit-optimized analog-to-digital converter circuit of claim 18.

28. The optical reader of claim 27, further comprising an illumination source for illuminating an encoded symbol.

29. The optical reader of claim 28, wherein said illumination source for illuminating said encoded symbol comprises at least one LED.

30. The optical reader of claim 28, wherein said illumination source for illuminating said encoded symbol comprises a laser diode.

31. The optical reader of claim 28, wherein said illumination source for illuminating said encoded symbol comprises a scanner for scanning illumination from said illumination source across said encoded symbol.

32. The optical reader of claim 27, further comprising an imaging system of which said detector that detects an excitation is a component.

33. The optical reader of claim 32, wherein said imaging system comprises a stationary optical system.

34. The optical reader of claim 32, wherein said imaging system comprises a scanner for scanning illumination from said illumination source across said encoded symbol.

35. The optical reader of claim 27, further comprising a trigger for initiating an action of said reader.

36. The optical reader of claim 27, wherein said optical reader is provided in a hand held configuration.

37. The optical reader of claim 36, further comprising a trigger for initiating an action of said reader.