Analog-digital converter, image sensor system and camera device

An analog-digital converter comprising:

• a reference signal generation circuit for generating a reference signal whose voltage value increases or decreases over time;
• n comparators arranged in a first direction with a predetermined cell pitch and corresponding respectively to n input voltages, each comparator comparing a voltage value of a reference signal with an input voltage corresponding to the comparator;
• n counters corresponding respectively to the n comparators, each counter performing a count operation in synchronism with a predetermined clock so as to output a count value at a point when an output of the comparator corresponding to the counter is inverted;
• and
• n digital memories corresponding respectively to the n counters, each digital memory storing the count value output from the counter corresponding to the digital memory, wherein
• each of the n comparators includes a current source transistor for supplying a reference current, and
• the current source transistor is formed by a plurality of unit transistors connected in series whose gates are given a bias voltage for supplying the reference current.

An analog-digital converter comprising:

• a reference signal generation circuit for generating a reference signal whose voltage value increases or decreases over time;
• n amplifiers arranged in a first direction with a predetermined cell pitch and corresponding respectively to n input voltages, each amplifier amplifying an input voltage corresponding to the amplifier;
• n comparators corresponding respectively to the n amplifiers, each comparator comparing a voltage value of the reference signal with an input voltage which has been amplified by the amplifier corresponding to the comparator;
• n counters corresponding respectively to the n comparators, each counter performing a count operation in synchronism with a predetermined clock so as to output a count value at a point when an output of the comparator corresponding to the counter is inverted;
• and
• n digital memories corresponding respectively to the n counters, each digital memory storing the count value output from the counter corresponding to the digital memory, wherein
• each of the n amplifiers includes a current source transistor for supplying a predetermined current, and
• the current source transistor is formed by a plurality of unit transistors connected in series whose gates are given a bias voltage for supplying the predetermined current.

An image sensor system comprising:

• n×m pixel portions arranged in a two-dimensional matrix of n columns by m rows, each pixel portion generating a charge according to an amount of incident light thereupon;
• a vertical scanning circuit for selecting the n×m pixel portions row by row;
• n readout circuits corresponding respectively to n pixel columns of the n×m pixel portions, each readout circuit generating a pixel voltage according to the charge generated by one of the n pixel portions selected by the vertical scanning circuit that corresponds to the readout circuit;
• an analog-digital converter for converting the n pixel voltages generated by the n readout circuits to n digital values;
• and
• a horizontal scanning circuit for successively transferring the n digital values obtained by the analog-digital converter as captured data, wherein
• each of the n readout circuits includes a current source transistor which forms a source follower circuit together with a pixel portion corresponding to the readout circuit, and
• the current source transistor is formed by a plurality of unit transistors connected in series whose gates are given a reference voltage for supplying a readout current.