Integrated circuits such as complementary metal-oxide semiconductors (CMOS) or charge-coupled devices (CCD) are used in processing analog image signals. For example, a CMOS or CCD imager device is a light sensitive integrated circuit that stores and outputs image data. Typically, image data is generated in the form of analog signals from pixels or image elements. A photosensitive section of a pixel reacts to exposure to light or photons which then drives an electrical charge into a storage element. CMOS and CCD image sensors are used in a wide variety of applications including digital cameras, surveillance systems, sensor systems and scanning systems. Analog signal processors are also used in a variety of other applications including temperature sensors, battery chargers, voice recognition circuits and many others.
Testing of individual devices comprising an integrated circuit is an essential part of integrated circuit production. Test result information is useful in identifying defective circuits and diagnosing problems relating to circuit operation and design. A number of techniques have been developed to perform circuit operating parameter measurements such as the use of test probes on test equipment which are applied to probe pads on integrated circuit wafers during production and testing of integrated circuits.
Conventional imager chip design also has made use of probe or test pads for use with measuring equipment in order to perform testing. Common techniques include provision of an on-chip probe pad which can be used with a test station probe to perform desired testing.
The use of probes and probe pads have previously provided satisfactory results in test processing. However, decreases in the size of dies as well as increase in circuit density of chips have resulted in increased difficulty in providing sufficient probe pads on the die to permit required test procedures to be carried out without extensive design effort in probe pad design. Also, improvements in test equipment design have not provided an adequate solution to reduction in die size, increased circuit density, increased chip complexity and increased testing requirements leading to constraints in probe pad availability.
Imager chip calibration in conjunction with test processing has also become more difficult as die size has decreased and circuit complexity has increased. Imager chip calibration typically is accomplished by use of test probe measurements accompanied by automatic or manual calibration of operational performance attributes of chip circuits or components. Calibration has been accomplished by use of various types of manual procedures or methods including the use of a laser to burn fuses associated with registers to program or set on-chip registers to a particular value which affects specific imager component operations.