TW201619593A - Illumination intensity control apparatus and method, and optical inspection system - Google Patents

Abstract

An optical inspection system and an illumination intensity control apparatus and method for the same are provided, The apparatus (10) includes a solid state illumination source (15) for inspection of objects, and circuitry (20, 64, 68, 22, 43, 45, 50, 55) that is configured to perform an initial calibration process that selects a fixed voltage supply level for application to the solid state illumination source, and to apply to the solid state illumination source a sequence of voltage pulses (110) having the selected fixed voltage supply level, thus causing the solid state illumination source to generate a sequence of fixed-intensity illumination pulses for inspecting the objects.

Description

Irradiation intensity control device and method, and optical inspection system

SUMMARY OF THE INVENTION The present invention relates generally to illumination sources, and more particularly to methods and systems for illumination intensity control.

Various circuits for controlling illumination sources such as laser diodes and light emitting diodes (LEDs) are known in the prior art. For example, U.S. Patent No. 6,323,598 describes a plurality of illumination sources each comprising at least one light-emitting diode, which are connected in series or in parallel by a switching circuit in accordance with an applied input voltage. The disclosure of this U.S. patent is incorporated herein by reference. When the applied input voltage crosses a threshold during the traversing of the operating range of the applied input voltage, the switching circuit switches the illumination from the series connection to the parallel connection, or vice versa. Since the light-emitting diodes within the illumination source are switched from a series connection to a parallel connection at a defined kick-over point, the voltage-luminance characteristic changes on the opposite side of the inflection point. The resulting overall voltage-luminance characteristic has greater brightness variability across the entire operating range of the applied input voltage, and the number of luminance variations is not limited to only one portion of the operating range.

U.S. Patent No. 7,356,058 describes an adaptive laser diode driver capable of driving various laser diode types and different laser diodes of the same type while ensuring the lifetime of the diode and It has the best optical performance when its temperature changes. The disclosure of this U.S. patent is incorporated herein by reference. The driver adaptively changes the voltage level of the input data signal to achieve full current switching and short rise and fall times under extreme modulation conditions. This is performed by continuously monitoring the output signal of a laser diode. Based on the monitored signal, a modulated current is adjusted, and in response, the low level and the high level of the input data signal are set. According to an embodiment, the adaptive laser diode driver can be integrated into an optical line terminal (OLT) or an optical network unit (passive optical network (PON)) ( Optical network unit; ONU).

US Patent No. 7,899,098 describes a laser diode driver integrated circuit (IC) for a transmitter or transceiver having one or more of a plurality of transmitters or transceivers for monitoring the transmitter or transceiver A circuit of forward voltages of the laser diodes to enable an immediate assessment of the operating conditions of the or the laser diodes. The disclosure of this U.S. patent is incorporated herein by reference.

One embodiment of the present invention provides an apparatus comprising a solid state illumination source for inspecting an object, and an electrical circuit. The circuit is configured to: perform an initial calibration process selected to apply to a fixed voltage supply level of the solid state illumination source; and apply a complex number of the selected fixed voltage supply level to the solid state illumination source A sequence of voltage pulses, thereby causing the solid state illumination source to generate a sequence of a plurality of fixed intensity illumination pulses for use in verifying the objects.

In some embodiments, the circuit includes a capacitor for charging the capacitor to the selected fixed voltage supply level prior to each of the voltage pulses and discharging the charged capacitor by the solid state illumination source Each of the voltage pulses is generated. In other embodiments, the circuit does not recalibrate the fixed voltage supply level during the sequence of the illumination pulses.

In some embodiments, the solid state illumination source is an illumination source in which one of the voltage supply levels and the emitted optical intensity changes among the individual illumination sources, and the circuit is configured to perform the An initial calibration process to compensate for one of the changes in the relationship. In other embodiments, the solid state illumination source includes a light emitting diode and a switch, and the circuit includes a driver circuit for applying the sequence of the voltage pulses to the switch to cause the light emitting diode The body produces these illumination pulses.

In some embodiments, the circuit is configured to measure an optical intensity of light reflected from the object under test and select the fixed voltage supply level based on the measured optical intensity. In other embodiments, the circuit includes an image detector for acquiring images of the objects to be inspected and a processor for measuring the optical intensity by processing the images. In some embodiments, the circuit includes an imaging detector for directly measuring the intensity of the solid state illumination source and a processor for measuring the optical intensity by processing the images. In an alternative embodiment, the circuit is operative to digitize a current flowing through the solid state illumination source and select the fixed voltage supply level based on the digitized current.

In certain embodiments, the solid state illumination source comprises one or more light emitting diodes. In other embodiments, the solid state illumination source comprises one or more laser diodes.

In some embodiments, the circuit is operative to select both the voltage supply level and a respective duration of one of the voltage pulses. In other embodiments, the circuit is operative to select a plurality of voltage supply levels and durations of the plurality of respective types of voltage pulses. In still other embodiments The circuit is operative to select such illumination pulses to provide one of a predefined illumination intensity for a minimum duration.

In accordance with an embodiment of the present invention, a method is also provided that includes operating a solid state illumination source for verifying an object. An initial calibration process is performed that is selected for application to one of the solid state illumination sources for a fixed voltage supply level. A sequence of a plurality of voltage pulses having the selected fixed voltage supply level is applied to the solid state illumination source, thereby causing the solid state illumination source to generate a sequence of a plurality of fixed intensity illumination pulses for use in verifying the objects.

According to an embodiment of the invention, an optical inspection system is also provided, comprising a circuit, an imaging detector and a solid illumination source. The solid state illumination source is used to illuminate the item for inspection. The imaging detector is configured to acquire images of the illuminated objects. The circuit is configured to: measure an optical intensity of one of the light reflected from the object to be inspected; perform an initial calibration process, the initial calibration process selecting a fixed voltage applied to the solid-state illumination source according to the measured optical intensity Supplying a level; and applying a sequence of a plurality of voltage pulses having the selected fixed voltage supply level to the solid state illumination source for verifying the objects.

In some embodiments, the circuitry is operative to measure the optical intensity in at least one image acquired by the imaging detector having an object of known reflectivity. In other embodiments, the circuit is configured to measure the optical intensity in a plurality of images of the plurality of objects to be inspected acquired by the imaging detector, and measure the optical intensity in the objects. Average.

10‧‧‧Inspection system

15‧‧‧pulse solid-state illumination source

20‧‧‧ camera

22‧‧‧ Processor

25‧‧‧Solid Optics / Optical Diodes

26‧‧‧Optical devices

30‧‧‧ Capacitors

35‧‧‧Power field effect transistor switch

43‧‧‧Logic/Timing Control Circuit

45‧‧‧Adjustable regulator

50‧‧‧Power supply

55‧‧‧ drive

64‧‧‧ filter

68‧‧‧ Analog to Digital Converter

110‧‧‧pulse

120‧‧‧ mark

130‧‧‧ mark

200~216‧‧‧Steps

VHI‧‧‧ voltage

VLO‧‧‧ voltage

The invention will be more fully understood from the following detailed description of embodiments of the invention, in which: FIG. 1a is a block diagram schematically illustrating an embodiment for controlling one in accordance with an embodiment of the present invention. One of the intensities of the pulsed illumination source; Figure 1b shows an example of a pulsed illumination source in which the optical devices are connected in series; Figure 1c shows an example of a pulsed illumination source in which the optical devices are connected in parallel; The figure is a graph showing a signal waveform in a system for controlling the intensity of a pulsed illumination source according to an embodiment of the invention; and FIG. 3 is a flow chart schematically illustrating a method according to the present invention. An embodiment is a method for calibrating a pulsed illumination source.

Overview

Some optical inspection systems use pulsed optical illumination sources. In a typical inspection system, a series of objects to be inspected (for example, a flat panel display or a semiconductor wafer) are placed on a moving stage, and the objects are processed by an image detector such as a camera. Imaging. The objects move relative to the camera while light pulses from the source illuminate the moving objects at short pulse intervals. The inspection system analyzes the acquired image, for example, to detect manufacturing defects. This type of pulsed imaging helps prevent blurring of acquired images due to object movement.

In a typical inspection system, it is important to maintain accurate control of the intensity of the illumination of the pulsed illumination source. One possible way to control the intensity of the illumination is to apply current control to the current flowing through the source of illumination, since in the solid state source the emitted optical power is proportional to the current. However, maintaining a fixed current through one of the sources typically involves a complex and expensive high speed current feedback mechanism.

Embodiments of the invention described herein provide improved illumination intensity control Method and system. The disclosed technique uses voltage control rather than current control to maintain a constant illumination intensity. Although the relationship between voltage and illumination intensity can vary between different illumination sources, the inventors have found that this relationship remains stable over a very long period of time. The characteristic voltage associated with the optical diode device (eg, turn on knee voltage) may vary with heating or as manufacturing changes. However, once the voltage and pulse duration are first calibrated, they remain stable over a plurality of pulses and within a plurality of long pulse trains. Therefore, this can avoid recalibrating the fixed voltage supply level during long illumination pulse sequences.

In some embodiments described herein, the illumination source is coupled to a circuit. During an initial calibration process, the circuit is used to select a fixed voltage supply level to be applied to the illumination source after assessing that the optical output is at an appropriate power level for the inspection system to operate effectively.

In an exemplary embodiment, the circuit uses an (existing) camera of the inspection system to measure the intensity of the illumination and uses the measurements to calibrate the source voltage level. Alternatively or in addition, the circuit may digitize the current flowing through the solid state illumination source after low pass filtering and calibrate the source voltage level based on the digitized current.

In general, this type of recalibration is only rarely required due to the long-term stability of the relationship between voltage and illumination intensity. In an exemplary embodiment, voltage calibration is performed at the beginning of an inspection lot. After calibration, a long pulse train is generated without a recalibration. This long pulse train can be used to inspect multiple objects.

Compared to current control schemes, the disclosed voltage control mechanism has the advantages of simpler implementation, less printed circuit board area, less cost, and less prone to electromagnetic interference.

instructions

1a is a block diagram schematically illustrating a system 10 for controlling the intensity of a solid state illumination source (SSIS) 15 in accordance with an embodiment of the present invention. Solid state illumination source 15 includes solid state optics 25 coupled to a power field effect transistor (FET) switch 35, such as a laser diode (LD) or a light emitting diode (light emitting diode) Diode; LED). The optical signal from device 25 illuminates an object to be inspected (not shown) and the illuminated object is imaged by an imaging detector (e.g., a camera 20).

In the present example, system 10 is part of an inspection system for finding defects in a flat panel display. However, another option is that the disclosed techniques can be used in any other suitable application.

A processor 22 analyzes a plurality of images of the object identified by the system 10 for defect recognition and acquired by the camera 20. In some embodiments, processor 22 measures the intensity of light reflected from the imaged object as described in detail below, and this intensity measurement is used as part of an initial calibration process for the intensity of the illumination source. In other embodiments, system 10 includes an Analog-to-Digital Converter (ADC) 68 that is analogous to digital converter 68 to sample and digitize the current flowing through solid-state illumination source 15. In the example of Figure 1, the current is sensed by sensing one of the solid state illumination sources that is suitable for the voltage across the resistor. A filter 64, typically a low-pass filter (LPF), filters the sensed current and provides it to an analog to digital converter 68 for digitization. As will be explained below, the digitized current is fed back to the processor 22 and used for initial calibration.

The example of Figure 1a shows two types of sensors (camera 20 and analog to digital converter 68), all of which can be used as feedback inputs for initial calibration of the intensity of the illumination source. In various embodiments, only cameras, only analog to digital converters, or two To perform the calibration.

In some embodiments, processor 22 controls the illumination pulses via a logic/timing control circuit 43. Processor 22 typically acquires information from the camera and implements the calibration algorithm described below. The logic/timing control circuit 43 includes fast and instant electronic devices that receive location information of the moving object from the inspection system, for example, a controller, a field programmable gate array (FPGA), and a digital signal processor (digital). Signal processor; DSP) device. As will be explained further below, the logic/timing control circuit 43 also controls the camera trigger and illumination pulse duration.

Processor 22 outputs a digital value that is sent to an adjustable regulator 45 via logic/timing control circuit 43. The output of the adjustable regulator 45 regulates the voltage of a power supply 50. This voltage can charge a capacitor 30 of choice.

Logic/timing control circuit 43 is preferably used via driver 55 to apply a plurality of voltage pulses to the gate of field effect transistor 35. The voltage pulses are bi-directionally turned on and off by the current passing through the optics 25, which produces a pulsed output optical signal. When the field effect transistor 35 begins to conduct at the beginning of a pulse, the voltage is discharged via the optical device 25, thereby causing the illumination source to generate an illumination pulse.

The field effect transistor 35 reaches the role of an electrical switch. When the switch is turned off (ie, the field effect transistor does not allow current to pass from the drain to the source) and no current flows through the optical diode 25, the fixed voltage supply level set by the adjustable regulator 45 can be The capacitor 30 is charged. When the switch is closed (i.e., the field effect transistor conducts current), the voltage discharges and current flows through the optical diode 25, thereby generating light.

When the field effect transistor 35 conducts, the optical diode 25 and the field effect transistor 35 (for example) For example, the sum of the voltages at the two terminals of the optical illumination source 15) shown in Figure 1a is the output of the adjustable regulator 45, which acts as a voltage control source as referred to herein. The electrical switch shown in Figure 1a as field effect transistor 35 can be implemented by any suitable switching device and is not limited to field effect transistors (e.g., bipolar transistors).

For a typical optical diode 25 used in a pulsed optical illumination source 15 for an optical inspection system, the current through the diode 25 is varied when the pulse is in the range from 0.1 microseconds to 1000 microseconds. The level can range from 0.01 amps to 20 amps. Source 15 from the test system typically produces 10 to 5000 pulses per second.

The interpulse stability of the current passing through the optical diode 25 is fixed by several parameters. For example, such parameters include a fixed voltage supply level from the regulator output, a current-voltage characteristic of the optical diode, a pulse duration at the gate of the field effect transistor 35, and a field effect during current conduction. The voltage drop across the two ends of the transistor 35. The voltage drop at the two ends of the field effect transistor 35 is mainly dependent on the equivalent resistance between the 汲 terminal and the source terminal of the field effect transistor 35.

The inventors have found that the illumination power generated by source 15 that is integrated over the duration of the pulse remains stable over a long period of time. The power between the optical source pulses can be stabilized over a period of several weeks. In other words, for a given voltage output and one of the voltage pulses applied to the switch 35 for a given pulse duration (referred to herein as the illumination control parameter), a current having a very high interpulse stability flows through the optical diode.

Although the relationship between voltage and pulse duration and illumination intensity is stable, the actual relationship may vary between different illumination sources. Thus, in some embodiments, processor 22 performs an initial calibration process that sets the appropriate voltage and pulse duration.

In a typical calibration process, processor 22 begins by: setting A low voltage level is gradually increased and the voltage supply level is gradually increased until a predetermined power level for valid operation of the verification system is measured from source 15. In some embodiments, the camera 20 is used to perform the measurement. In one embodiment, the system includes a plurality of cameras, and the calibration process is important to ensure that the illumination levels in all of the plurality of cameras are the same. Alternatively or in addition, filter 64 and analog to digital converter 68 can be used to perform the measurement.

The processor 22 is input to the steady state system 10 via a logic/timing control circuit 43, a "voltage control" input using an adjustable regulator 45 (eg, a selected fixed voltage supply level), and a "pulse duration control" of the driver 55. The selected drive condition is applied. These parameters are then used in one or more consecutive optical inspection sessions until a drift of the pulsed power level output occurs. These drive conditions are then recalibrated. In other embodiments, processor 22 monitors the average illumination power over a long time interval and modifies the output voltage if a change in illumination power is detected.

The configuration of the system 10 shown in Fig. 1a is an exemplary configuration, which is for the sake of clarity of the concept and is not intended to limit the embodiments of the invention. Alternatively, any suitable component configuration can be used to perform the functions of system 10 described herein. The source 15 in this exemplary configuration is not limited to optics 25 and switch 35, but may comprise any suitable combination of a plurality of electrical and/or optical components. Various components for calibrating and controlling the illumination intensity of source 15 (including processor 22, circuit 43, camera 20, adjustable regulator 45, driver 55, filter 64, analog to digital converter 68, and associated components) are This document is collectively referred to as a circuit. In alternate embodiments, any other suitable circuit configuration can be used.

In some embodiments, the circuit of Figure 1a can be used to simultaneously drive one or more optical illumination sources 15, for example, a plurality of optically connected sources connected in series and disposed on a small printed circuit board (PCB). source. In other embodiments, one or more sources are each individually The circuits are driven separately, each of the one or more sources being individually calibrated with their respective steady state drive conditions.

All or any portion of the components of system 10 may be implemented in a hardware form on a printed circuit board or any suitable substrate, or may be one or more application-specific integrated circuits (ASICs). Or implement a Field Programmable Gate Array (FPGA). Additionally or alternatively, some of the components of system 10 can be implemented using software, or any suitable combination of hardware or software.

In still other embodiments, for example, processor 22 can be used in any portion of system 10 to perform or coordinate any of the functions of system 10 described herein, such as for analyzing acquired images. Processor 22 typically includes a general purpose computer that is programmed in software to perform one of the functions described herein. The software can be downloaded to the computer in electronic form, for example via a network, or alternatively or additionally, can be provided on non-transitory tangible media (such as magnetic memory, optical memory or electronic memory) and/or Store software.

Figure 1b shows an example of a solid state illumination source (SSIS) 15 in which the illuminating solid state source 26 is connected in series. Several illumination sources can be connected in series. In this example, the current through all of the different solid state sources is equal.

Figure 1c shows an example of a solid state illumination source (SSIS) 15 in which the illuminating solid state source 26 is connected in parallel. Several illumination sources can be connected in parallel. In this example, the voltage across all of the different solid state sources is equal.

2 is a graph schematically illustrating a plurality of signal waveforms in a system 10 for controlling the intensity of a pulsed illumination source 15 in accordance with an embodiment of the present invention.

Four pulses 110 are shown in this example. That is, applied to the field via the driver 55 A pulse train of the gate of the effect transistor 35 (the electrical switch in Fig. 1). The TTL levels shown are from VHI (switch open) to VLO (switch closed), where VHI and VLO are any suitable TTL voltages. The pulse width from a mark 120 to a mark 130 illustrates the on pulse and may have a typical value from 0.1 microseconds to 1 millisecond and above. The time interval between pulses can vary depending on the pulse duration and provides a pulse duty cycle as shown in FIG.

Inspection system calibration scheme

3 is a flow chart that schematically illustrates one method for calibrating a pulsed illumination source 15 in system 10 in accordance with an embodiment of the present invention. The following description begins with the inspection of an object in response to one of the new types, which requires the setting of a new inspection protocol (and in particular a new pulse voltage level).

In an exemplary embodiment, the inspection process involves examining multiple types of items (and thus involving multiple scenarios). In this case, the method of Fig. 3 is repeated for each object type. The article can include one of the actual samples being tested (eg, a flat panel display, a printed circuit board, a wafer), or one of the targets having a known reflectivity.

The method begins with system 10 (typically processor 22 or control circuit 43) setting a voltage pulse level to a certain initial value at a voltage adjustment step 200. This voltage level is set by controlling the adjustable regulator 45.

Subsequently, at a measurement step 208, system 10 measures the intensity of the illumination from the pulses reflected by the object. As described above, the intensity measurement can be performed by acquiring one or more images using the camera 20 and processing the images by the processor 22 to estimate the illumination intensity. Alternatively or in addition, the measurement can be performed by digitizing the current flowing through the SSIS 15 using an analog to digital converter 68 and feeding back the digitized current to the processor 22.

Subsequently, at an inspection step 212, the system checks if the current illumination intensity is sufficient. If not, the method loops back to step 200 above, in which the system adjusts the pulse voltage level as needed (ie, if the measured intensity is too low, the pulse voltage level is increased, and vice versa).

If the measured illumination intensity is appropriate, the system proceeds to verify an item of the type in question at a test step 216. Typically, during the inspection phase, the system re-evaluates the intensity of the illumination from time to time (e.g., by branching to step 208). If necessary, the system adjusts the pulse voltage level to maintain the appropriate illumination intensity.

In some embodiments, circuitry in inspection system 10 can be used to calibrate and use two or more illumination intensities (ie, two or more pulse lengths versus voltage pairs). For example, system 10 can image several different types of areas on the object being inspected in the same scan such that each type of area is imaged using a different illumination intensity (different pulse length/voltage pair).

In some embodiments, the circuitry of system 10 controls both voltage and pulse duration. This dual control makes it possible to set various performance tradeoffs.

In embodiments where the output of camera 20 is used as an indication of illumination intensity, processor 22 can determine the illumination intensity in a variety of ways. In some embodiments, system 10 can image a particular object under inspection ("target") having a known reflectivity during the calibration process. Alternatively, calibration can be performed on the actual object to be inspected. Alternatively, as seen in Figure 1a, the camera can look directly at the output of the illumination source, or a portion of the output of the illumination source (e.g., via a partial beam splitter).

Although the embodiments described herein primarily address pulsed illumination control in an optical inspection system, the methods and systems described herein can also be used in which a pulsed illumination source is used. In other applications, for example in laser material processing.

Therefore, it is to be understood that the above-described embodiments are cited by way of example only, and the invention is not limited to what has been specifically shown and described herein. Rather, the scope of the present invention encompasses combinations and sub-combinations of the various features described above, as well as variations that would be apparent to those of ordinary skill in the art And retouching. The documents incorporated by reference in this patent application are hereby incorporated by reference in its entirety in the entire application in the application in When one of the definition conflicts is defined, only the definitions in this specification should be considered.

10‧‧‧Inspection system

15‧‧‧pulse solid-state illumination source

20‧‧‧ camera

22‧‧‧ Processor

25‧‧‧Solid Optics / Optical Diodes

30‧‧‧ Capacitors

35‧‧‧Power field effect transistor switch

43‧‧‧Logic/Timing Control Circuit

45‧‧‧Adjustable regulator

50‧‧‧Power supply

55‧‧‧ drive

64‧‧‧ filter

68‧‧‧ Analog to Digital Converter

Claims (30)

An illumination intensity control apparatus comprising: a solid-state illumination source for inspecting an object; and a circuit for performing an initial calibration process for selecting a fixed voltage supply bit for application to the solid-state illumination source And applying a sequence of a plurality of voltage pulses having the selected fixed voltage supply level to the solid state illumination source, thereby causing the solid state illumination source to generate a sequence of a plurality of fixed intensity illumination pulses for verifying such object. The illumination intensity control device of claim 1, wherein the circuit includes a capacitor and is configured to charge the capacitor to the selected fixed voltage supply level prior to each of the voltage pulses, and by using the solid state illumination source The charged capacitor is discharged to generate each of the voltage pulses. The illumination intensity control device of claim 1 or 2, wherein the circuit does not recalibrate the fixed voltage supply level during the sequence of the illumination pulses. The illumination intensity control device according to claim 1 or 2, wherein the solid-state illumination source is an illumination source in which one of the voltage supply levels and the emitted optical intensity is changed among the individual illumination sources, and Wherein the circuit is operative to compensate for a change in the relationship by performing the initial calibration process. The illumination intensity control device according to claim 1 or 2, wherein the solid-state illumination source comprises a light-emitting diode and a switch, and wherein the circuit comprises a driver circuit, the driver circuit is configured to apply the voltage to the switch The sequence of pulses is such that the illumination diode produces the illumination pulses. The illumination intensity control device according to claim 1 or 2, wherein the circuit is configured to measure optical intensity of one of the light reflected from the object to be inspected, and select the solid according to the measured optical intensity Constant voltage supply level. The illumination intensity control device of claim 6, wherein the circuit includes an image detector for acquiring images of the objects to be inspected and processing for measuring the optical intensity by processing the images. Device. The illumination intensity control device of claim 6, wherein the circuit comprises an imaging detector for directly measuring the intensity of the solid state illumination source and for measuring the optical intensity by processing the images. A processor. The illumination intensity control device according to claim 1 or 2, wherein the circuit is configured to digitize a current flowing through the solid-state illumination source, and select the fixed voltage supply level according to the digitized current. The illumination intensity control device of claim 1 or 2, wherein the solid state illumination source comprises one or more light emitting diodes. The illumination intensity control device of claim 1 or 2, wherein the solid state illumination source comprises one or more laser diodes. The illumination intensity control device of claim 1 or 2, wherein the circuit is configured to select the voltage supply level and a corresponding duration of one of the voltage pulses. The illumination intensity control device of claim 1 or 2, wherein the circuit is configured to select a plurality of voltage supply levels and durations of the plurality of respective types of the voltage pulses. The illumination intensity control device of claim 1 or 2, wherein the circuitry is operative to select the illumination pulses to provide one of a predefined illumination intensity for a minimum duration. An illumination intensity control method comprising: operating a solid-state illumination source for detecting an object; Performing an initial calibration process that selects a fixed voltage supply level for application to the solid state illumination source; and applies one of a plurality of voltage pulses having the selected fixed voltage supply level to the solid state illumination source A sequence whereby the solid state illumination source produces a sequence of a plurality of fixed intensity illumination pulses for use in testing the objects. The illumination intensity control method of claim 15, wherein the step of applying the sequence of the voltage pulses comprises charging a capacitor to the selected fixed voltage supply level before each of the voltage pulses, and by using the solid state An illumination source discharges the charged capacitor to generate each of the voltage pulses. The illumination intensity control method of claim 15 or 16, comprising avoiding recalibrating the fixed voltage supply level during the sequence of the illumination pulses. The illumination intensity control method according to claim 15 or 16, wherein the solid-state illumination source is an illumination source in which one of the voltage supply levels and the emitted optical intensity changes among the individual illumination sources, and The step of performing the initial calibration process includes compensating for a change in the relationship. The illumination intensity control method of claim 15 or 16, wherein the solid-state illumination source comprises a light-emitting diode and a switch, and wherein the step of applying the sequence of the voltage pulses comprises applying the voltage pulse to the switch The sequence is such that the illumination diode produces the illumination pulses. The illumination intensity control method of claim 15 or 16, wherein the step of performing the initial calibration process comprises measuring optical intensity of one of the light reflected from the object to be inspected, and selecting the optical intensity according to the measured optical intensity Fixed voltage supply level. The illumination intensity control method of claim 20, wherein the step of measuring the optical intensity comprises Processing an image acquired by an imaging detector that images the object being inspected. The illumination intensity control method of claim 15 or 16, wherein the step of performing the initial calibration process comprises digitizing a current flowing through the solid-state illumination source, and selecting the fixed voltage supply bit according to the digitized current quasi. The method of controlling the intensity of illumination according to claim 15 or 16, wherein the solid-state illumination source comprises one or more light-emitting diodes. The illumination intensity control method of claim 15 or 16, wherein the solid state illumination source comprises one or more laser diodes. The illumination intensity control method of claim 15 or 16, wherein the step of performing the initial calibration process comprises selecting the voltage supply level and a respective duration of one of the voltage pulses. The illumination intensity control method of claim 15 or 16, wherein the step of performing the initial calibration process comprises selecting a plurality of voltage supply levels and durations of the plurality of respective types of the voltage pulses. The illumination intensity control method of claim 15 or 16, wherein the step of performing the initial calibration process comprises selecting to cause the illumination pulses to provide one of a predefined illumination intensity for a minimum duration. An optical inspection system comprising: a solid-state illumination source for illuminating an object for inspection; an imaging detector for acquiring an image of the illuminated object; and a circuit for: measuring from the Detecting an optical intensity of one of the light reflected by the object; performing an initial calibration process that selects a fixed voltage supply level applied to the solid state illumination source in accordance with the measured optical intensity; and applying the solid state illumination source have A sequence of a plurality of voltage pulses of the selected fixed voltage supply level is used to verify the objects. The optical inspection system of claim 28, wherein the circuitry is operative to measure the optical intensity in at least one image acquired by the imaging detector having an object of a known reflectivity. The optical inspection system of claim 28, wherein the circuit is configured to measure the optical intensity in a plurality of images of the plurality of objects to be inspected acquired by the imaging detector, and to be in the objects The measured optical intensity is averaged.