3-transistor source follower-per-detector unit cell for 2-dimensional focal plane arrays

Abstract

A Source-Follower-per-Detector (SFC) unit cell [12], a two dimensional array [30] of same and a method of operating the two dimensional array. Each unit cell is constructed with but three transistors [14, 16, 22] and is coupled to an associated radiation detector [10] for receiving an output signal therefrom. A method includes a first step of (a) reading out a first row (N) of unit cells by asserting a first row enable signal for causing each of the unit cells of the row (N) to impress an electrical signal onto an associated output signal line. The electrical signal has a magnitude that is a function of the associated detector output signal. The method includes an additional step of (b) simultaneously resetting another row of unit cells each of which has a reset input coupled to and responsive to the assertion of the first row enable signal line.

What is claimed is: 
     
       1. A readout unit cell circuit for coupling to a radiation detector, comprising: a node having a capacitance associated therewith, the node being coupled to a radiation detector for storing charge generated by the detector;   first switching means coupled to the node and responsive to an assertion of an enabling signal for periodically impressing an electrical signal onto an output signal line, the electrical signal having a magnitude that is a function of the charge stored by the capacitance; and   second switching means coupled to the node for periodically resetting the node to a predetermined signal level; wherein   the unit cell is one of a plurality of unit cells organized into at least two groups, wherein each group contains a plurality of unit cells that are each coupled in common to an associated enabling signal, and wherein the second switching means is coupled to and is responsive to the assertion of an enabling signal associated with another group of unit cells.   
     
     
       2. A readout unit cell circuit as set forth in claim 1 wherein the first switching means is comprised of a first transistor means and a second transistor means and wherein the second switching means is comprised of a third transistor means. 
     
     
       3. A readout unit cell circuit as set forth in claim 1 wherein the unit cell is disposed in a row (N) of a two dimensional array of unit cells, and wherein the second switching means is coupled to and is responsive to the assertion of an enabling signal associated with a physically adjacent row (N+1). 
     
     
       4. A readout unit cell circuit as set forth in claim 1 wherein the unit cell is disposed in a row (N) of a two dimensional array of unit cells, and wherein the second switching means is coupled to and is responsive to the assertion of an enabling signal associated with a physically nonadjacent row (N+m), where m is an integer greater than one. 
     
     
       5. A readout unit cell as set forth in claim 1 wherein the plurality of unit cells are provided on a common substrate with a plurality of radiation detectors. 
     
     
       6. A readout unit cell as set forth in claim 1 wherein the plurality of unit cells are provided on a first substrate and wherein a plurality of radiation detectors are provided on a second substrate. 
     
     
       7. A method of operating a two dimensional array of unit cells organized as rows and columns of unit cells, each unit cell being coupled to an associated radiation detector for receiving an output signal therefrom, comprising the steps of: reading out a first row (N) of unit cells by asserting a first row enable signal for causing each of the unit cells of the row (N) to impress an electrical signal onto an associated output signal line, the electrical signal having a magnitude that is a function of the associated detector output signal; and   simultaneously resetting another row of unit cells each of which has a reset input coupled to and responsive to the assertion of the first row enable signal.   
     
     
       8. A method as set forth in claim 7 wherein the step of simultaneously resetting resets a physically adjacent row of unit cells that was previously read out. 
     
     
       9. A method as set forth in claim 7 wherein the step of simultaneously resetting resets a physically nonadjacent row of unit cells that was previously read out. 
     
     
       10. A two dimensional array of unit cells organized as rows and columns of unit cells, each unit cell being coupled to an associated radiation detector means for receiving an output signal therefrom, comprising: means for reading out a first row (N) of unit cells including means for asserting a first row enable signal for causing each of the unit cells of the row (N) to impress an electrical signal onto an associated output signal line, the electrical signal having a magnitude that is a function of the associated radiation detector means output signal; and   means associated with each unit cell of a second row of unit cells for resetting the second row of unit cells to a predetermined signal condition, each of the unit cell resetting means having a reset input coupled to and responsive to the assertion of the first row enable signal line.   
     
     
       11. A two dimensional array of unit cells as set forth in claim 10 wherein each unit cells comprises: a node having a capacitance associated therewith, the node being coupled to the associated radiation detector for storing charge generated by the detector;   wherein the means for reading out is comprised of first switching means coupled to the node and responsive to an assertion of an associated row enable signal for periodically impressing the electrical signal onto the associated output signal line; and   wherein the means for resetting is comprised of second switching means coupled to the node for periodically resetting the node to the predetermined signal condition.   
     
     
       12. A two dimensional array of unit cells as set forth in claim 11 wherein the first switching means is comprised of a first transistor means and a second transistor means and wherein the second switching means is comprised of a third transistor means. 
     
     
       13. A two dimensional array of unit cells as set forth in claim 11 wherein the unit cell is disposed in the row (N) and wherein the second switching means is coupled to and is responsive to the assertion of the row enable signal associated with a physically adjacent row (N+1). 
     
     
       14. A two dimensional array of unit cells as set forth in claim 11 wherein the unit cell is disposed in the row (N) and wherein the second switching means is coupled to and is responsive to the assertion of a row enable signal associated with a physically nonadjacent row (N+m), where m is an integer greater than one. 
     
     
       15. A two dimensional array of unit cells as set forth in claim 11 wherein the rows are sequentially read out in an interlaced manner as even rows followed by odd rows and wherein the unit cell is disposed in the even row (N) and wherein the second switching means is coupled to and is responsive to the assertion of a row enable signal associated with a physically nonadjacent even row (N+2). 
     
     
       16. A two dimensional array of unit cells as set forth in claim 10 wherein the two dimensional array of unit cells is provided on a common substrate with a plurality of radiation detectors. 
     
     
       17. A two dimensional array of unit cells as set forth in claim 10 wherein the two dimensional array of unit cells is provided on a first substrate and wherein a plurality of radiation detectors are provided on a second substrate. .Iadd. 
     
     
       18.  A readout cell for coupling to an output of a radiation detector, comprising: an input node for coupling to an output of a radiation detector, said input node having a capacitance coupled thereto for storing a charge that is output by the radiation detector;   first switching means coupled between said input node and a first predetermined signal level, said first switching means being responsive only to a first enabling signal for resetting said input node to the first predetermined signal level; and   second switching means coupled between said input node and an output node, said second switching means being responsive only to a second enabling signal for impressing an electrical signal onto said output node, the electrical signal having a magnitude that is a function of a magnitude of a charge that is stored on said capacitance;   wherein said first switching means is comprised of: a first transistor having a drain terminal coupled to the first predetermined signal level, a source terminal coupled to the input node, and a gate terminal coupled to the first enabling signal; and   wherein said second switching means is comprised of a second transistor that is coupled in series with a third transistor, said second transistor having a source terminal coupled to said output node, a drain terminal coupled to a source terminal of said third transistor, and a gate terminal coupled to said input node, and wherein said third transistor has a drain terminal coupled to a second predetermined signal level and a gate terminal coupled to said second enabling signal. .Iaddend. .Iadd.19. A readout cell as set forth in claim 18 wherein said readout cell is a member of a first group that is comprised of a first plurality of said readout cells, wherein the second enabling signal is a group select signal that, when asserted, causes the second switching means of each of said first plurality of readout cells within the first group to impress the electrical signal onto an associated one of said output nodes, and wherein the first enabling signal is a group select signal of a second group that is comprised of a second plurality of said readout cells. .Iaddend.     
     
     
        .Iadd. 0.  A readout cell for coupling to an output of a radiation detector, comprising: an input node for coupling to an output of a radiation detector, said input node having a capacitance coupled thereto for storing a charge that is output by the radiation detector;   a first transistor having a drain terminal coupled to a first predetermined signal level, a source terminal coupled to the input node, and a gate terminal coupled to a first enabling signal, said first transistor being responsive to the first enabling signal for resetting said input node to the first predetermined signal level; and   a second transistor having a source terminal coupled to a readout cell output node, a drain terminal coupled to a source terminal of a third transistor, and a gate terminal coupled to said input node, said third transistor having a drain terminal coupled to a second predetermined signal level and a gate terminal coupled to a second enabling signal, said second transistor and third transistor being responsive to the second enabling signal for impressing an electrical signal onto said output node, the electrical signal having a magnitude that is a function of a magnitude of a charge that is stored on said capacitance. .Iaddend. .Iadd.21. A readout cell as set forth in claim 20 wherein said readout cell is disposed within a first row that is comprised of a first plurality of said readout cells, wherein the second enabling signal is a row select signal that, when asserted, causes the second transistor and the third transistor of each of said first plurality of readout cells within the first row to impress the electrical signal onto an associated one of said output nodes, and wherein the first enabling signal is a row select signal of a second row that is comprised of a second plurality of said readout cells. .Iaddend.