Methods and apparatus for a voltage-shifting readout circuit
Methods and device for a readout circuit according to various aspects of the present invention may operate in conjunction with a storage device selectively coupled to an input signal having a voltage value within a first voltage range. A comparator may compare the voltage value of the input signal to a predetermined threshold voltage. A level-shifting circuit may shift the first voltage value of the input signal to a second voltage value within a second voltage range if the first voltage value of the input signal is greater than the predetermined threshold voltage.
1. A readout circuit, comprising:
a storage device selectively coupled to an input signal and configured to sample the input signal, wherein the input signal has a first voltage value within a first voltage range;
a comparator coupled to the input signal, wherein the comparator compares the first voltage value of the input signal to a predetermined threshold voltage; and
a level-shifting circuit coupled to the storage device and responsive to the comparator, wherein the level-shifting circuit shifts the first voltage value of the input signal to a second voltage value within a second voltage range if the first voltage value of the input signal is greater than the predetermined threshold voltage.
2. The readout circuit of claim 1 , wherein the storage device comprises a top and bottom plate.
3. The readout circuit of claim 2 , wherein the level-shifting circuit comprises a first switch to selectively couple the bottom plate of the storage device to a first reference voltage.
4. The readout circuit of claim 3 , wherein the level-shifting circuit comprises a second switch to selectivity couple the bottom plate of the storage device to a second reference voltage to subtract an offset value from the input signal.
5. The readout circuit of claim 4 , wherein the comparator transmits a control signal to the level-shifting circuit to couple the second switch to the second reference voltage.
6. The readout circuit of claim 1 , further comprising a buffer coupled to the storage device.
7. The readout circuit of claim 1 , further comprising a delta sigma modulator coupled to the level-shifting circuit and operative at the second voltage range, wherein the modulator converts the input signal into a digital signal.
8. The readout circuit of claim 1 , wherein the level-shifting circuit subtracts an offset value from the sampled input signal if the input signal is greater than the predetermined threshold voltage.
9. The readout circuit of claim 1 , wherein the comparator provides a most significant bit signal to a data formatting unit according to the input signal.
10. A imaging system, comprising:
a pixel array comprising pixels arranged in rows and columns;
a storage device comprising a top plate and a bottom plate, wherein the top plate is coupled to the pixel array and samples the voltage of an input pixel signal, and wherein the sampled input pixel signal has a first voltage range;
a comparator coupled to the storage device, wherein the comparator compares the sampled input pixel signal to a predetermined threshold voltage;
a level-shifting circuit coupled to the bottom plate of the storage device and responsive to the comparator, wherein the level-shifting circuit shifts the sampled input pixel signal to a second voltage range if the sampled input pixel signal exceeds the predetermined threshold voltage;
an analog-to-digital converter coupled to the level-shifting circuit and configured to convert the sampled input pixel signal to a digital signal; and
an output device coupled to the analog-to-digital converter and configured to display an image according to the digital signal.
11. The imaging system of claim 10 , wherein the level-shifting circuit comprises a first switch to selectively couple the bottom plate of the storage device to a first reference voltage.
12. The imaging system of claim 11 , wherein the level-shifting circuit further comprises a second switch to selectivity couple the bottom plate of the storage device to a second reference voltage to subtract an offset value from the input signal.
13. The imaging system of claim 12 , wherein the comparator provides a control signal to the second switch to couple the second switch to the second reference voltage.
14. The imaging system of claim 10 , wherein, further comprising a buffer coupled between the storage device and the analog-to-digital converter.
15. The imaging system of claim 10 , wherein the comparator converts and transmits the most significant bit of the input signal to a data-formatting unit.
16. The imaging system of claim 10 , wherein analog-to-digital converter comprises a delta-sigma modulator.