Patent ID: 9686494
Date: 2017-06-20
CPC Classifications: H03K,H04N

Claim:
1. A semiconductor device comprising: a pixel area in which charge according to the amount of incident light is accumulated and which outputs pixel signals; an analog-to-digital converter that reads the pixel signals and outputs digital values each according to the magnitude of a corresponding one of the pixel signals using a ramp signal; and a ramp signal generating circuit that outputs the ramp signal, wherein the ramp signal generating circuit includes: a gradient initialization register that stores an initial gradient setting value indicating a gradient of the ramp signal during an initial gradient period in a preset sweep period; a first gradient setting register that stores a first gradient setting value indicating the gradient of the ramp signal during a first gradient period following the initial gradient period in the sweep period; a second gradient setting register that stores a second gradient setting value indicating the gradient of the ramp signal during a second gradient period following the first gradient period in the sweep period; a first gradient change timing setting register that stores a first change timing value indicating a timing for a change from the initial gradient period to the first gradient period; a second gradient change timing setting register that stores a second change timing value indicating a timing for a change from the first gradient period to the second gradient period; a counter that counts reference clocks received during the sweep period and outputs a count value; a switching control circuit that compares the count value with the first change timing value and compares the count value with the second change timing value to output a select signal; a selector that outputs one of the initial gradient value, the first gradient setting value, and the second gradient setting value in accordance with the select signal; and a ramp waveform generating circuit that outputs the ramp signal that changes linearly at a gradient according to the value output by the selector, wherein the ramp waveform generating circuit comprises: a current digital-analog conversion circuit that outputs an output current of a magnitude according to the value output by the selector, wherein the current digital-analog conversion circuit comprises a current mirror having a source side transistor connected to a current source and a plurality of branch-side transistors that outputs the output current, and the plurality of branch-side transistors is provided in association with the initial gradient value, the first gradient setting value and the second gradient setting value.