Solid-state image capturing element and electronic device
Solid-state image capturing elements are disclosed. In one example, a solid-state image capturing element includes a noise-cancelling-signal generating circuit connected to a pixel power source. It executes a gain change and a polarity inversion on a first noise cancelling signal to output a second noise cancelling signal. The element also includes a DA converter that outputs a reference signal and converts a current of the second noise cancelling signal into a voltage to superpose the converted voltage on the reference signal; a comparator that receives inputs of the reference signal and a pixel signal and outputs an inversion signal according to the pixel signal and a gain setting; a counter that converts an inversion timing of the comparator into a digital value; and a gain controlling unit that outputs, when changing a gradient of the reference signal and an input capacity to execute a gain control on the comparator.
1. A solid-state image capturing element comprising:
a pixel that outputs a pixel signal;
a noise-cancelling-signal generating circuit connected to a pixel power source that supplies electric power to the pixel, the noise-cancelling-signal generating circuit configured to:
generate a first noise cancelling signal for cancelling a power-source noise of the pixel power source; and
execute, on the first noise cancelling signal, a gain change and a polarity inversion based on a gain controlling signal to output a second noise cancelling signal;
a Digital-to-Analog (DA) converter configured to:
generate a reference signal as a ramp signal to output the generated reference signal; and
convert a current of the second noise cancelling signal into a voltage to superpose the converted voltage on the reference signal;
a comparator where the reference signal and the pixel signal are input to a main body part of the comparator via an input capacity connected to one of terminals of a differential pair, the comparator outputting an inversion signal having a timing according to the pixel signal and a gain setting;
a counter that converts an inversion timing of the comparator into a digital value; and
a gain controlling unit that outputs, when changing a gradient of the reference signal and the input capacity to execute a gain control on the comparator, the gain controlling signal based on a change amount in the input capacity.
2. The solid-state image capturing element according to claim 1 , wherein
the comparator includes an input capacity changing unit including:
a first capacitor that is connected between an input terminal and one of the terminals of the differential pair;
a plurality of second capacitors whose one ends are connected to the one terminal of the differential pair; and
a plurality of switches that connects in parallel the second capacitors and the first capacitor to each other.
3. The solid-state image capturing element according to claim 1 , wherein
the noise-cancelling-signal generating circuit includes:
a pixel-power-source inputting unit to which the pixel power source is connected;
a first noise-cancelling-signal generating unit that converts a pixel-power-source voltage input via the pixel-power-source inputting unit into a current to generate the first noise cancelling signal; and
a gain changing/inverting circuit that executes a gain change and a polarity inversion on the first noise cancelling signal based on the gain controlling signal.
4. The solid-state image capturing element according to claim 3 , wherein
the gain changing/inverting circuit includes:
a first transistor group constituted of a plurality of transistors connected in parallel and through which a current amount proportional to a current amount of the first noise cancelling signal is able to flow;
a second transistor group constituted of a plurality of transistors connected in parallel, serially connected to the first transistor group, and through which a predetermined constant current is able to flow; and
a third transistor group connected in parallel to the first transistor group, and capable of outputting the second noise cancelling signal.
5. The solid-state image capturing element according to claim 4 , further comprising:
the third transistor group; and
a fourth transistor group constituting a current mirror circuit, and capable of adjusting a gain of the second noise cancelling signal to output the adjusted gain.
6. An electronic device comprising:
a pixel array unit in which a plurality of pixels is arranged in array, each of the plurality of pixels outputting a pixel signal;
a noise-cancelling-signal generating circuit connected to a pixel power source that supplies electric power to the pixels, the noise-cancelling-signal generating circuit configured to:
generate a first noise cancelling signal for cancelling a power-source noise of the pixel power source; and
execute, on the first noise cancelling signal, a gain change and a polarity inversion based on a gain controlling signal to output a second noise cancelling signal;
a DA converter configured to:
generate a reference signal as a ramp signal to output the generated reference signal; and
convert a current of the second noise cancelling signal into a voltage to superpose the converted voltage on the reference signal;
a comparator where the reference signal and the pixel signal are input to a main body part of the comparator via an input capacity connected to one of terminals of a differential pair, the comparator outputting an inversion signal having a timing according to the pixel signal and a gain setting;
a counter that converts an inversion timing of the comparator into a digital value;
a gain controlling unit that outputs, when changing a gradient of the reference signal and the input capacity to execute a gain control on the comparator, the gain controlling signal based on a change amount in the input capacity; and
an image-data processing unit that processes image data based on an output from the counter.