Active pixel sensor imaging system

Patent metadata

Field	Value
Publication number	US-9344655-B2
Application number	US-201514754394-A
Country	US
Kind code	B2
Filing date	Jun 29, 2015
Priority date	Jun 30, 2014
Publication date	May 17, 2016
Grant date	May 17, 2016

Abstract

An active pixel sensor imaging system is disclosed. In one aspect, the system includes a plurality of active pixel sensor circuits arranged into an array of rows and columns. Each active pixel sensor is connected to a supply line and a column line, and operable to generate a voltage output through the column line corresponding to a detected light intensity. The system includes a current sensing circuit, located external to the plurality of active pixel sensor circuits and connected to the supply line. The current sensing circuit is implemented as a current mirror for sensing a current through an active pixel sensor circuit readout transistor. The system includes a feedback circuit, located external to the plurality of active pixel sensor circuits and connected to the column line, to a current generator and to the current sensing circuit. The feedback circuit is implemented as a classAB current mirror configured for controlled quiescent current.

First claim

What is claimed is:

1. An active pixel sensor imaging system, comprising:
a plurality of active pixel sensor circuits arranged into an array of rows and columns, at least one of said active pixel sensor circuits being connected to a supply line and a column line and operable to generate a voltage output through the column line corresponding to a detected light intensity;
a current sensing circuit, located external to the plurality of active pixel sensor circuits and connected to the supply line, the current sensing circuit being implemented as a current mirror for sensing a current through an active pixel sensor circuit readout transistor; and
a feedback circuit, located external to the plurality of active pixel sensor circuits and connected to the column line, to a current generator and to the current sensing circuit, the feedback circuit being implemented as a classAB current mirror configured for controlled quiescent current.

2. The system of claim 1 wherein the feedback circuit is designed to present a different current gain for a rising and a falling slope of the column line output voltage.

3. The system of claim 1 wherein the feedback circuit is designed to have a transfer function with two linear segments, each having a different slope.

4. The system of claim 3 wherein an inflection point between the two linear segments is defined by a reference current generated within the feedback circuit.

5. The system of to claim 4 , wherein the classAB current mirror comprises a push-pull current mirror stage where a ratio of a first pair of transistors determines a gain for currents above the reference current and a ratio of a second pair of transistors determines a gain for currents below the reference current.

6. The system of claim 5 , wherein the first pair of transistors are PMOS transistors and the second pair of transistors are NMOS transistors.

7. The system of claim 1 , wherein the classAB current mirror comprises a pair of transistors to control the quiescent current according to a Monticelli bias scheme.

8. The system of claim 7 , wherein the classAB current mirror comprises a bypass capacitor connected between two gate voltage sources of a plurality of classAB stage transistors.

9. The system of claim 1 , wherein the current sensing circuit is implemented as a low-swing current mirror designed to reduce its input impedance to the supply line at a first connection node.

10. The system of claim 8 , wherein the impedance at the first connection node between the supply line and the current sensing circuit is designed to be lower than a second connection node between the feedback circuit and the column line, such as to obtain a non-dominant pole at the first connection node.

11. An electronic device comprising an active pixel sensor imaging system according to claim 1 .

Assignees

• Imec Vzw

Inventors

• Terryn Steven
• Thite Mandar

Classifications

• H04N25/709 Primary

  Circuitry for control of the power supply · CPC title

• H04N25/76

  Addressed sensors, e.g. MOS or CMOS sensors · CPC title

• H03F3/505 Primary

  with field-effect devices · CPC title

• H03F2203/5012

  the source follower has a controlled source circuit, the controlling signal being derived from the drain circuit of the follower · CPC title

• H03F3/085

  using opto-couplers between stages · CPC title