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US 6,956,413 B2Granted
Ramp generator for image sensor ADC
AssigneeSTMicroelectronics S.r.l.
InventorToby Bailey
Life of this patent
Estimating the term…
Abstract
A ramp generator includes a resistance ladder supplied with a constant current. Switches are closed in sequence by a shift register to provide a stepped ramp output. The constant current is controlled by referencing an on-chip bandgap voltage that is used as an input to a feedback circuit controlling current through a reference resistor ladder.
Claims29
A ramp generator comprising:
- a plurality of resistance elements connected together in series to form a resistance ladder, with a node between each of the resistance elements;
- a current source connected to said resistance ladder for passing a controlled current therethrough;
- a plurality of switches connected between the nodes of said resistance ladder and a voltage output;
- and
- switch control means for closing at least some of said plurality of switches in a predetermined sequence, said switch control means comprising a shift register receiving a clock signal and including
- a plurality of shift register elements, each shift register element for a predetermined number of switches, and
- a plurality of multiplexers connected to said plurality of shift register elements, each respective multiplexer for connecting a corresponding switch register element to its predetermined number of switches.
4 more elements
An analog-to-digital converter comprising:
- a ramp generator comprising
- a plurality of resistance elements connected together in series with a node between each of the resistance elements,
- a current source connected to said plurality of resistance elements for passing a controlled current therethrough,
- a plurality of switches connected between the nodes of said plurality of resistance elements and a voltage output, and
- a switch controller for closing at least some of said plurality of switches in a predetermined sequence, said switch controller comprising a shift register including
- a plurality of shift register elements, each shift register element for a predetermined number of switches, and
- a plurality of multiplexers connected to said plurality of shift register elements, each respective multiplexer for connecting a corresponding switch register element to its predetermined number of switches;
- and
- comparing means having a first input for receiving a voltage at the voltage output of said ramp generator and a second input for receiving an analog voltage, said comparing means for comparing the two voltages.
6 more elements
An image sensor comprising:
- at least one analog-to-digital converter for converting pixel voltage signals to digital signals, said at least one analog-to-digital converter comprising
- a ramp generator comprising
- a plurality of resistance elements connected together in series with a node between each of the resistance elements,
- a current source connected to said plurality of resistance elements for passing a controlled current therethrough,
- a plurality of switches connected between the nodes of said plurality of resistance elements and a voltage output, and
- a switch controller for closing at least some of said plurality of switches in a predetermined sequence said switch controller comprising a shift register receiving a clock signal, said shift register including
- a plurality of shift register elements, each shift register element for a predetermined number of switches, and
- a plurality of multiplexers connected to said plurality of shift register elements, each respective multiplexer for connecting a corresponding switch register element to its predetermined number of switches;
- and
- a comparator having a first input for receiving a voltage at the voltage output of said ramp generator and a second input for receiving an analog voltage, said comparator for comparing the two voltages.
7 more elements
A method for operating a ramp generator comprising a plurality of resistance elements connected together in series with a node between each resistance element, & current source connected to the plurality of resistance elements, and a plurality of switches connected between the nodes and a voltage output, the method comprising;
- providing a controlled current through the plurality of resistance elements;
- and
- closing at least some of the plurality of switches, with a switch register receiving a clock signal, in a predetermined sequence for providing a voltage at the voltage output, wherein the shift register comprises
- a plurality of shift register elements, each shift register element for a predetermined number of switches, and
- a plurality of multiplexers connected to the plurality of shift register elements, each respective multiplexer for connecting a corresponding switch register element to its predetermined number of switches.
2 more elements
A ramp generator comprising:
- a resistance ladder including a plurality of resistance elements connected together with a node between each of the resistance elements;
- a controlled current source connected to said resistance ladder;
- a plurality of switches connected between the nodes of said resistance ladder and a voltage output;
- and
- a switch controller for operating said plurality of switches in a predetermined sequence, said switch controller comprising a shift register receiving a clock signal, wherein said shift register comprises
- a plurality of shift register elements, each shift register element for a predetermined number of switches, and
- a plurality of multiplexers connected to said plurality of shift register elements, each respective multiplexer for connecting a corresponding switch register element to its predetermined number of switches.
4 more elements
Dependencies are inferred from the claim text.