Patent ID: 7872645
Filing Date: 2011-01-18
Classification: H04N

Abstract:
1. An image sensing chip, comprising: an active pixel sensor array including a plurality of pixels arranged in rows and columns; and a built in self test circuit coupled to the active pixel sensor array, the built in self test circuit including: a controller adapted to be coupled to external circuitry through a programming port, wherein the controller is configured to be programmed to perform desired tests on the active pixel sensor array in response to receiving programming signals from the external circuitry through the programming port; a data collection circuit coupled to column lines of the active pixel sensor array and adapted to receive a reference voltage, the data collection circuit operable for each accessed row of pixels in the sensor array to compare a voltage developed on each column line to the reference voltage and to generate corresponding output signals indicating whether the voltages on the respective column lines are less than or greater than the reference voltage; and wherein the controller is coupled to the data collection circuit and to the output port and the controller is operable to process the output signals from the data collection circuit and generate a test results signal indicating whether the sensor array has passed or failed a test; a test digital-to-analog converter coupled to the data collection circuit and operable to develop the reference voltage having a stair-step characteristic responsive to a digital control signal; a plurality of registers, each register coupled to receive the digital control signal and coupled to the data collection circuit to be clocked by a corresponding output signal; an addition circuit having a first input coupled to the register and having a second input, the addition circuit operable to sum values on the first and second inputs and output an average value; and a register coupled to the addition circuit to receive the average value and operable to provide the average value on the second input.