National Semiconductor Corporation

Brian D Segerstedt

Bumha Lee

Willem J Kindt

Christina P Phan

A method and apparatus for system offset calibration using an overranging ADC is provided. The overranging ADC is configured to convert an analog signal into an intermediary digital signal. The conversion range of the overranging ADC is extended beyond the full dynamic range of the ADC system. The intermediary digital signal has more bits than the digital output signal. A digital fine offset adjustment circuit is configured to provide the digital output signal by digitally subtracting a fine offset from the intermediary digital signal and decoding the intermediary digital signal. The digital output signal has approximately no offset, and has approximately no loss in dynamic range.

Method and apparatus of system offset calibration with overranging ADC

A digital-to-analog converter (DAC) comprises a current DAC, first and second resistance circuits, and an operational transconductance amplifier (OTA). The first resistance circuit is coupled between a first node and an output of the OTA. The second resistance circuit is coupled between the first node and a power supply node. The current DAC is arranged to provide an analog current to a first node in response to a digital input signal. The OTA has a first input that receives a stable DC reference voltage signal, and a second input that is coupled to the first node. A charge pump provides the local supply voltage of the OTA to improve the system dynamic range. The output voltage corresponds to the sum of the voltages across the first and second resistance circuits. An increase in the current produced by the current DAC causes a decrease in the output voltage.

Digital-to-analog converter with a shifted output and an increased range

An image sensor is disclosed that contains pixel cells that can individually provide a real-time output signal that is proportional to the instantaneous magnitude of incident radiation upon each pixel cell. The individual real-time output signals can be used to construct an electronic image. Additionally, the pixel cells of the image sensor can be used to collectively provide an accumulated real-time output signal that is proportional to the instantaneous magnitude of incident radiation upon a plurality of selected pixel cells. A propagated signal from a source such as a laser can be used to illuminate a target in an image. A reflection from the target can be detected in the accumulated real-time output signal. The range to the target can be determined using the round-trip propagation time between the sensor and the target of a propagated signal.

Integrated range finder and imager

An active pixel sensor cell array including a XDR reset signal generation circuit configured to generate XDR reset signals having user-selected levels, and an XDR reset signal generation circuit for use with such an array. The XDR reset signal generation circuit includes a digital-to-analog converter (DAC) coupled to receive control bits which determine the level and time of assertion of each XDR reset signal, and a level shifting circuit coupled to the output of the DAC. In response to the control bits (typically a sequence of multi-bit words), the circuit asserts a time-varying XDR reset potential. The XDR reset potential's amplitude as function of time (during each integration period) determines the breakpoints of each cell's response curve. The level shifting circuit includes a reference transistor, whose current density matches that of the reset transistors inside the cells, which shifts the potential at the DAC's output upward by an amount equal to the reference transistor's threshold voltage (which matches the threshold voltage of each reset transistor of the cell array or a row of the cell array) to produce the XDR reset potential. To cause the control bits asserted to the DAC to establish breakpoints which in turn cause the analog-to-digital converter (ADC) of the image sensor array to assert (predictably) an expected set of digital output bits in response to each read of a cell exposed to light of known intensity, both the ADC and the DAC operate at the same reference voltage, and the level shifting circuit's reference transistor's biasing matches that of the reset transistors inside the cells.

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Redwood City, CA, United States of America

Brian D Segerstedt