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

• US 7,413,126 B2
• Filed: 02/12/2007
• Issued: 08/19/2008
• Est. Priority Date: 01/09/2003
• Status: Expired due to Term

• 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.
• Primary Examiner(s): LE, THIEN MINH
• Application Number:
  US11/705,545
• Publication Number:
  US 20070228170A1
• Time in Patent Office: 554 Days
• Field of Search: 23546201-46245, 235/472.01, 235/472.02, 235/472.03, 235/454, 235/455, 235/470, 235/494
• US Class Current: 235/462.06
• 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. A bar code reading apparatus for use in reading decodable bar code indicia, said bar code reading apparatus comprising:

an M×

N 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 analog-to-digital converter being controlled so that an N-bit range of said analog-to-digital converter substantially spans a dynamic range of said excitation as sensed by said sensor;

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

a display capable of displaying an indicia being read.

2. The bar code reading apparatus of claim 1, wherein said range of illumination includes approximately 70,000 Lux to substantially zero Lux.

3. The bar code reading apparatus of claim 1, wherein said sensor comprises a selected one of a CCD sensor having a plurality of pixels and a CMOS sensor having a plurality of pixels.

4. The bar code reading apparatus of claim 1, wherein said dynamic range of said excitation is measured temporally.

5. The bar code reading apparatus of claim 1, wherein said dynamic range of said excitation is measured spatially.

6. The bar code reading apparatus of claim 1, further comprising an illumination source for illuminating said encoded symbol.

7. The bar code reading apparatus of claim 6, wherein said illumination source for illuminating said encoded symbol comprises at least one LED.

8. The bar code reading apparatus of claim 6, wherein said illumination source for illuminating said encoded symbol comprises a laser diode.

9. The bar code reading apparatus of claim 6, wherein said illumination source for illuminating said encoded symbol comprises a scanner for scanning illumination from said illumination source across said encoded symbol.

10. The bar code reading apparatus of claim 1, further comprising an imaging system of which said sensor that senses an excitation is a component.

11. The bar code reading apparatus of claim 10, wherein said imaging system comprises a stationary optical system.

12. The bar code reading apparatus of claim 1, further comprising a trigger for initiating an action of said bar code reading apparatus.

13. The bar code reading apparatus of claim 1, wherein said bar code reading apparatus is provided in a hand held configuration.

14. The bar code reading apparatus of claim 13, further comprising a trigger for initiating an action of said bar code reading apparatus.

15. The bar code reading apparatus of claim 1, wherein said analog-to-digital converter is controlled responsively to a dynamic range of a signal from said sensor.

16. The bar code reading apparatus of claim 1, wherein said analog-to-digital converter is controlled, responsively to operating conditions of said sensor.

17. The bar code reading apparatus of claim 1, wherein said analog-to-digital converter is controlled with use of at least one reference voltage applied to said analog-to-digital converter.

18. The bar code reading apparatus of claim 1, wherein said analog-to-digital converter is controlled with use of first and second reference voltages applied to said analog-to-digital converter.

19. The bar code reading apparatus of claim 1, wherein said sensor is a CMOS sensor.

20. The bar code reading apparatus of claim 1, wherein said sensor is a color sensor.

21. An optimized analog-to-digital converter (ADC) circuit, comprising:

a detector configured to output an analog signal responsive to a detected excitation;

an ADC configured to receive said analog signal and output an optimized N-bit digital representation of said analog signal, where N is a positive integer greater than 1; and

a microprocessor configured to adjust at least one reference voltage so that a difference between observed minimal and maximal levels of said analog signal is one of;

less than a pre-defined threshold value, more than a pre-defined threshold value, said at least one reference voltage being outputted to said ADC.

22. An optimized optical reader comprising the optimized ADC converter circuit of claim 21, wherein said detector is provided by an M×

N color image sensor, and wherein said optical reader incorporates a display.

23. An optimized analog-to-digital converter (ADC) circuit, comprising:

a detector configured to output an analog signal responsive to a detected excitation;

an ADC configured to receive said analog signal and output an optimized N-bit digital representation of said analog signal, where N is a positive integer greater than 1; and

a digital-to-analog converter (DAC) configured to output at least one reference voltage to said ADC, said DAC being controlled to adjust said at least one reference voltage so that a difference between observed minimal and maximal levels of said analog signal is one of;

less than a pre-defined threshold value, more than a pre-defined threshold value.

24. An optimized optical reader comprising the optimized ADC converter circuit of claim 23, wherein said detector is provided by an M×

N color image sensor, and wherein said optical reader incorporates a display.

25. An apparatus for use in reading decodable indicia, comprising:

a sensor configured to sense under ambient illumination conditions an excitation carrying information representing an encoded symbol, said sensor further configured to output an analog signal responsive to said excitation;

an analog-to-digital converter (ADC) configured to receive said analog signal and to output optimized digital data in an N-bit representation, where N is a positive integer greater than 1, said ADC being controlled so that an N-bit range of ADC substantially spans 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 encoded symbol;

wherein said is devoid of an illumination source.

26. The apparatus of claim 25, wherein said sensor is an M×

N color image sensor, and wherein said apparatus includes a display.

27. An apparatus for use in reading decodable indicia, comprising:

a sensor configured to sense under ambient illumination conditions an excitation carrying information representing an encoded symbol, said sensor further configured to output an analog signal responsive to said excitation;

an analog-to-digital converter (ADC) configured to receive said analog signal and to output optimized digital data in an N-bit representation, where N is a positive integer greater than 1;

a microprocessor that manipulates said optimized digital data, thereby providing accurate decoding of said encoded symbol; and

a source of illumination configured to be controlled by said microprocessor to operate at various intensities, said source of illumination further configured to simulate different illumination levels for at least one of;

testing said optical reader, calibrating said optical reader.

28. The apparatus of claim 27, wherein said sensor is an M×

N color image sensor, and wherein said apparatus includes a display.

29. A method for decoding decodable indicia, said method comprising the steps of:

providing an apparatus having an image sensor outputting an analog image signal and an analog-to-digital converter (ADC) for digitizing said analog image signal, said ADC being controlled by at least one reference voltage;

in a calibration mode of operation, subjecting said apparatus to a plurality of different illumination conditions, and compiling a look-up table; and

in a field use mode of operation, retrieving a value of said at least one reference voltage from said look up table based upon a measured difference between observed minimal and maximal levels of said analog image signal.

30. The method of claim 29, wherein said providing step includes the step of providing an M×

N color image sensor, and further providing on said apparatus a display.

31. An apparatus for use in reading bar codes, comprising:

an image sensor configured to output an analog signal;

an analog-to-digital converter (ADC) configured to receive said analog signal and output an optimized N-bit digital representation of said analog signal, where N is a positive integer greater than 1; and

a control circuit configured to adjust at least one reference voltage responsively to a level of illumination sensed by said apparatus, said at least one reference voltage being outputted to said ADC.

32. The apparatus of claim 31, wherein said sensor is an M×

N color image sensor, and wherein said apparatus includes a display.

33. An apparatus for use in reading bar codes, comprising:

an image sensor configured to output an analog signal;

an analog-to-digital converter (ADC) configured to receive said analog signal and output an optimized N-bit digital representation of said analog signal, where N is a positive integer greater than 1;

a look-up table including a multitude of reference voltage values; and

wherein said apparatus is configured to retrieve at least one reference voltage value from said look-up table, said reference voltage value being outputted to said ADC.

34. The apparatus of claim 33, wherein said sensor is an M×

N color image sensor, and wherein said apparatus includes a display.