Optical reader with adaptive exposure control

• US 6,230,975 B1
• Filed: 10/07/1999
• Issued: 05/15/2001
• Est. Priority Date: 08/25/1995
• Status: Expired due to Term

• Current Assignee: PTO (Safe Fleet Holdings LLC)
• Original Assignee: PTO (Safe Fleet Holdings LLC)
• Inventors: Olmstead, Bryan L., Colley, James E.
• Primary Examiner(s): TREMBLAY, MARK STEPHEN
• Application Number:
  US09/414,676
• Time in Patent Office: 586 Days
• Field of Search: 235/462.06, 235/462.25, 235/462.32
• US Class Current: 235/462.06
• CPC Class Codes: G06K 7/10752 Exposure time control
• CPC Class Codes: G06K 7/1093 sensing, after transfer of the image of the data-field to an intermediate store, e.g. storage with cathode ray tube
• CPC Class Codes: H04N 25/40 Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled
• CPC Class Codes: H04N 25/533 by using differing integration times for different sensor regions
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• CPC Class Codes: H04N 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

An optical or symbol reader including CMOS circuitry preferably integrated on a single chip. A CMOS optical reader chip comprises a CMOS imaging array having a plurality of pixels each with a dedicated pixel-site circuit. Charge is accumulated at each pixel location transferred upon demand to a common bus. In a preferred embodiment, exposure time of the imaging array is controlled using a feedback loop. One or more exposure control pixels are positioned adjacent to or within the imaging array and receive light along with the imaging array. The charge of the exposure control pixel or pixels is measured against a threshold level, and the amount of time taken to reach the threshold level determines the time exposure of the pixels of the imaging array. CMOS signal processing circuitry is employed which, in combination with the exposure control circuitry, minimizes time-to-read over a large range of light levels, while performing spatially optimal filtering. Clocking cycles and control signals are time-adjusted in accordance with the varying output frequency of the imaging array so as to provide invariant frequency response by the signal processing circuitry. A multi-dimensional CMOS imaging array is also provided having simultaneous pixel exposure with non-destructive readout of the pixel contents.

Claims

1. An optical reader comprising:

a common output bus;

an imaging array comprising a plurality of pixels, each pixel connected to said common bus and comprising a photo-sensitive element and a pixel circuit connected to said photo-sensitive element;

an address decoder outputting a plurality of pixel select signals, each of said pixel select signals connected to a different pixel;

an adaptive exposure control circuit; and

a plurality of pixel reset signals responsive to said adaptive exposure control circuit, said pixel reset signals separately and individually controlling overlapping exposure periods for each pixel based on a relative level of light detected simultaneously by said adaptive exposure circuit and said imaging array each pixel select signal being asserted for reading out its pixel and each pixel reset signal being asserted during the time when its pixel is selected for resetting the pixel and starting a new exposure period for the pixel.

2. An optical reader comprising:

a common output bus;

an imaging array comprising a plurality of pixels, each pixel connected to said common bus and comprising a photo-sensitive element and a pixel circuit connected to said photo-sensitive element;

an address decoder outputting a plurality of pixel select signals, each of said pixel select signals connected to a different pixel, said address decoder asserting said pixel select signals in a repeating, uninterrupted sequence so as to generate a continuous stream of pixel data on said common bus; and

an adaptive exposure control circuit, said adaptive exposure control circuit comprising at least one stand-alone photo-sensitive detector not used in said image array, said stand-alone photo-sensitive detector connected to a comparator, wherein said adaptive exposure control circuit controls overlapping exposure periods for each pixel based on a relative amount of light detected simultaneously by said stand-alone photo-sensitive detector and said imaging array.

3. An integrated optical reader comprising:

an imaging array fabricated using a CMOS process and located on a CMOS chip, said imaging array comprising a plurality of individually accessible pixels;

a clock generator outputting an imaging array clocking signal at a variable clock frequency, said imaging array clocking signal having a new clock pulse to initiate each new pixel readout and controlling a rate at which data from said individually accessible pixels is read out; and

an adaptive exposure control circuit, said adaptive exposure control circuit adjusting an exposure time of said pixels by adjusting said variable clock frequency, said adaptive exposure control circuit fabricated using a CMOS process and located on said CMOS chip.

5. The integrated optical reader of claim 3, further comprising a signal processing circuit connected to an output signal from said imaging array, wherein said clock generator adjusts a frequency of a clock connected to said signal processing circuit in correspondence with adjusting said variable clock frequency.

12. The integrated optical reader of claim 5, wherein said signal processing circuit comprises a synchronous digital filter.

13. The integrated optical reader of claim 12, wherein said synchronous digital filter comprises a finite impulse response filter responsive to said clock connected to said signal processing circuit, such that adjustment of said variable clock frequency provides invariant time domain response of said finite impulse response filter with respect to said output signal from said imaging array.

14. The integrated optical reader of claim 12, wherein said synchronous digital filter comprises an infinite impulse response filter responsive to said clock connected to said signal processing circuit, such that adjustment of said variable clock frequency provides invariant time domain response of said infinite impulse response filter with respect to said output signal from said imaging array.

4. An integrated optical reader comprising:

an imaging array fabricated using a CMOS process and located on a CMOS chip, said imaging array comprising a plurality of individually accessible pixels;

means for generating a periodic reading cycle of fixed duration;

a clock generator outputting a clocking signal, said clocking signal controlling read out of said individually accessible pixels at a constant rate once each reading cycle;

a light measurement exposure circuit, said light measurement exposure circuit fabricated using a CMOS process and located on said CMOS chip; and

means for regulating a duty cycle of pixel exposure time individually for each pixel in response to an amount of light simultaneously detected by said light exposure measurement circuit and said imaging array.

7. The integrated optical reader of claim 4, wherein said means for generating a periodic reading cycle of fixed duration comprises an oscillator connected to said light exposure measurement circuit, said oscillator outputting a periodic clear signal for resetting said light exposure measurement circuit at the start of each exposure cycle, and wherein said means for regulating a duty cycle of pixel exposure time individually for each pixel comprises:

a serial shift register connected to said light exposure measurement circuit and responsive to a shutter signal output therefrom, said shift register having a plurality of tapped stages; and

a plurality of reset control signals output from said tapped stages of said shift register, each pixel connected to one of said reset control signals, whereby an exposure period for the pixel is controlled in response to propagation of said shutter signal along the tapped stages of said serial shift register so as to sequentially assert said reset control signals, said reset control signals remaining asserted until the next periodic clear signal output by said oscillator propagates down said serial shift register to sequentially clear said reset signals.

6. An integrated optical reader, comprising:

an imaging array fabricated using a CMOS process and located on a CMOS chip, said imaging array comprising a plurality of individually accessible pixels;

means for generating a periodic reading cycle of fixed duration;

a clock generator outputting a clocking signal, said clocking signal controlling read out of said individually accessible pixels at a constant rate once each reading cycle;

a light measurement exposure circuit, said light measurement exposure circuit fabricated using a CMOS process and located on said CMOS chip; and

means for regulating a duty cycle of pixel exposure time individually for each pixel in response to an amount of light detected by said light exposure measurement circuit;

wherein said means for regulating a duty cycle of pixel exposure time individually for each pixel comprises an exposure period delay calculator connected to said light exposure measurement circuit, said exposure period delay calculator generating once each reading cycle a variable exposure delay period inversely proportional to said amount of light detected by said light exposure measurement circuit and holding each pixel in a reset state for said variable exposure delay period at the start of the exposure period for each pixel.

8. An optical reader, comprising:

a plurality of photosensitive pixels;

a plurality of pixel control signals connected to said photosensitive pixels;

a clock generator;

a readout clock signal output from said clock generator and connected to said pixel control signals, said readout clock signal comprising a separate clock pulse to initiate selection of each pixel in a designated sequential order, whereby an exposure time for said photosensitive pixels is controlled; and

an exposure control circuit receiving light collection information from at least one of said photosensitive pixels, said clock generator adjusting a frequency of said readout clock signal in response to said light collection information received by said exposure control circuit.

15. The optical reader of claim 8, further comprising a signal processing circuit connected to a common output signal from said photosensitive pixels, wherein said clock generator adjusts a signal processing clock frequency of a clock connected to said signal processing circuit in correspondence with adjusting said readout clock signal frequency.

16. The optical reader of claim 15, wherein said signal processing circuit comprises a synchronous digital filter.

17. The optical reader of claim 16, wherein said synchronous digital filter comprises a finite impulse response filter responsive to said clock connected to said signal processing circuit, such that adjustment of said readout clock signal frequency provides invariant time domain response of said finite impulse response filter with respect to said common output signal from said imaging array.

18. The optical reader of claim 16, wherein said synchronous digital filter comprises an infinite impulse response filter responsive to said clock connected to said signal processing circuit, such that adjustment of said readout clock signal frequency provides invariant time domain response of said infinite impulse response filter with respect to said common output signal from said imaging array.

9. An optical reader, comprising:

a plurality of photosensitive pixels;

a plurality of pixel select signals, each pixel select signal connected to a different photosensitive pixel;

a plurality of pixel reset signals, each pixel reset signal connected to a different photosensitive pixel, whereby assertion of a pixel select signal causes its corresponding photosensitive pixel to be read and assertion of a pixel reset signal while the photosensitive pixel is selected causes the photosensitive pixel to be reset and exposure of the photosensitive pixel to end, such that sequential assertion of said pixel select signals and said pixel reset signals provides a continuous and uninterrupted stream of pixel data in a series of repeating frames; and

an exposure control circuit receiving light collection information from at least one of said photosensitive pixels, said exposure control circuit adjusting a frequency of said pixel select signals and of said pixel reset signals in response to said light collection information, so as to vary a readout rate of said plurality of photosensitive pixels in response to a level of light exposure indicated by said light collection information.

10. An optical reader, comprising:

a plurality of photosensitive pixels, each of said photosensitive pixels capable of being separately selected for readout and separately reset;

a plurality of pixel outputs from said photosensitive pixels;

a common bus connected to said pixel outputs, said common bus receiving a continuous and uninterrupted stream of pixel data when said photosensitive pixels are sequentially selected; and

an exposure control circuit connected to said plurality of photosensitive pixels by a plurality of pixel control signals to provide individual selection and reset of said photosensitive signals, said exposure control circuit varying a readout rate of said photosensitive pixels in response to a level of light exposure of at least one of said photosensitive pixels, said readout rate increasing in response to an increase in said level of light and decreasing in response to a decrease in said level of light.

19. The optical reader of claim 10, further comprising

a controller for controlling sequential connection of said pixel outputs to said common bus, thereby providing a data signal;

a signal processing circuit connected to said common bus so as to receive said data signal from said common bus; and

a clock generator outputting a variable clock signal to said signal processing circuit;

wherein said clock generator adjusts said variable clock signal in order to vary said readout rate, said signal processing circuit adjusting its time domain response in tandem with the adjustment to said variable clock signal so as to maintain an invariant time domain response with respect to said data signal.

20. The optical reader of claim 19, wherein said signal processing circuit comprises a synchronous digital filter.

21. The optical reader of claim 20, wherein said synchronous digital filter comprises a finite impulse response filter responsive to said variable clock signal.

22. The optical reader of claim 20, wherein said synchronous digital filter comprises an infinite impulse response filter responsive to said variable clock signal.

23. The optical reader of claim 19, wherein said signal processing circuit comprises a synchronous transversal analog filter using bucket-brigade delay lines responsive to said variable clock signal.

24. The optical reader of claim 19, wherein said signal processing circuit comprises a synchronous delay line differentiator responsive to said variable clock signal.

11. A method of optical reading, comprising the steps of:

collecting light incident upon a plurality of photosensitive pixels;

controlling a light exposure time individually and separately for each photosensitive pixel by selectively asserting a reset signal associated with each photosensitive pixel;

reading light collection data from said photosensitive pixels on to a common output bus, said light collection data for each photosensitive pixel being read on to the common output bus just prior to the assertion of the reset signal associated with the photosensitive pixel so as to generate, by sequentially reading said photosensitive pixels in a repetitive pattern, a continuous and uninterrupted stream of pixel data on said common output bus; and

varying said exposure time in response to a level of light exposure from at least one of said photosensitive pixels, thereby varying a readout rate of light collection data on to the common output bus said readout rate increasing in response to an increase in said level of light and decreasing in response to a decrease in said level of light.