Dual low voltage levels for control of transfer switch device in pixel array
A pixel array comprises at least one long exposure pixel, short exposure pixel, and a control circuit. The long exposure pixel comprises a first photodiode to generate charges, a first image signal generating module for generating a first image sensing signal; and a first transfer switch device for passing the charges to the first image signal generating module via a first transfer control signal. The control circuit sets the first transfer control signal to be a first predetermined control voltage when the long exposure pixel is in an long exposure phase, and then sets the first transfer control signal to be a second predetermined control voltage when the short exposure pixel is in a short exposure phase.
1. An image sensor, comprising:
a control circuit;
a pixel array, comprising:
at least one long exposure pixel, comprising:
a first photodiode, for sensing light to generate at least one charge;
a first image signal generating module, comprising a first reset transistor having a first terminal coupled to a first voltage source and a second terminal coupled to the first transfer switch device, for generating a first image sensing signal according to the charge generated by the first photodiode; and
a first transfer switch device, for passing the charge from the first photodiode to the first image signal generating module according to a first transfer control signal;
at least one short exposure pixel, comprising;
a second photodiode, for sensing light to generate at least one charge;
a second image signal generating module, comprising a second reset transistor having a first terminal coupled to the first voltage source and a second terminal coupled to the second transfer switch device, for generating a second image sensing signal according to the charge generated by the second photodiode; and
a second transfer switch device, for passing the charge from the second photodiode to the second image signal generating module according to a second transfer control signal;
wherein the control circuit sets the first transfer control signal to be a first predetermined control voltage to turn off the first transfer switch device when the long exposure pixel is in an long exposure phase, and then the control circuit sets the first transfer control signal to be a second predetermined control voltage slightly higher than the first predetermined control voltage to substantially turn off the first transfer switch device when the short exposure pixel is in a short exposure phase; wherein the control circuit asserts the first transfer control signal to be the second predetermined control voltage level before the short exposure phase ends;
an analog to digital converter, for generating a frame according to the first image sensing signal and the second image sensing signal.
2. The image sensor of claim 1 , wherein the long exposure pixel is beside the short exposure pixel.
3. The image sensor of claim 1 , wherein the long exposure pixels and the short exposure pixels are all provided in a row.
4. The image sensor of claim 1 , wherein the control circuit sets the first transfer control signal to be the first predetermined control voltage and the second control voltage before a reading operation for the long exposure pixel.
5. A pixel array, comprising:
a control circuit;
at least one long exposure pixel, comprising:
a first photodiode, for sensing light to generate at least one charge;
a first image signal generating module, comprising a first reset transistor having a first terminal coupled to a first voltage source and a second terminal coupled to the first transfer switch device, for generating a first image sensing signal according to the charge generated by the first photodiode; and
a first transfer switch device, for passing the charge from the first photodiode to the first image signal generating module according to a first transfer control signal;
at least one short exposure pixel, comprising;
a second photodiode, for sensing light to generate at least one charge;
a second image signal generating module, comprising a second reset transistor having a first terminal coupled to the first voltage source and a second terminal coupled to the second transfer switch device, for generating a second image sensing signal according to the charge generated by the second photodiode; and
a second transfer switch device, for passing the charge from the second photodiode to the second image signal generating module according to a second transfer control signal;
wherein the control circuit sets the first transfer control signal to be a first predetermined control voltage to turn off the first transfer switch device when the long exposure pixel is in an long exposure phase, and then the control circuit sets the first transfer control signal to be a second predetermined control voltage slightly higher than the first predetermined control voltage to substantially turn off the first transfer switch device when the short exposure pixel is in a short exposure phase; wherein the control circuit asserts the first transfer control signal to be the second predetermined control voltage level before the short exposure phase ends.
6. The pixel array of claim 5 , wherein the long exposure pixel is beside the short exposure pixel.
7. The pixel array of claim 5 , wherein the long exposure pixels and the short exposure pixels are all provided in a row.
8. The pixel array of claim 5 , wherein the control circuit sets the first transfer control signal to be the first predetermined control voltage and the second control voltage before a reading operation for the long exposure pixel.