Automatic level control circuit

Details Automatic level control circuit Automatic level control circuit

G - Physics

01

R

356/2, 324/58

G01R 31/28 (2006.01) G01R 31/309 (2006.01) H04N 1/403 (2006.01) H05K 1/00 (2006.01)

Patent

CA 1186737

ABSTRACT OF THE DISCLOSURE An automatic level control (ALC) circuit for use with a light beam scanning apparatus which apparatus is used to inspect printed circuit boards is disclosed. The printed circuit board contains a pattern of conducting surfaces on an insulating substrate. Light interaction with the conductors causes a detector assembly portion of the scanning apparatus to produce a first set of signals called conductor signals while light interaction with the substrate causes the detector assembly to produce a second set of signals called substrate signals. A first corrected reference signal corresponding to the conductor signals is generated during an initial adjustment period and is provided to summing circuitry where it is summed with conductor and substrate signals from the scanning apparatus. When the first reference signal is summed with conductor signals a near zero level summed conductor signal is produced. Substrate signals added to the fixed level first reference signal produce summed substrate signals with a non-zero value. A programmable high voltage power supply portion of the detector assembly is responsive to adjustment signals to change the level of the substrate signals produced by the detection assembly. During second time intervals of selected beam sweeps during the adjustment period when only substrate signals are produced, the summed substrate signals are compared with a preselected substrate value and correction signals are generated in response to the comparison. The output of the programmable power supply is changed in response to the correction signals. Eventually, the value of the summed substrate signals becomes substantially the same as the preselected substrate value.

413833

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