Germanium-silicon light sensing apparatus ii

Abstract

A circuit that includes: a photodiode configured to absorb photons and to generate photo-carriers from the absorbed photons; a first MOSFET transistor that includes: a first channel terminal coupled to a first terminal of the photodiode and configured to collect a portion of the photo-carriers generated by the photodiode; a second channel terminal; and a gate terminal coupled to a first control voltage source; a first readout circuit configured to output a first readout voltage; a second readout circuit configured to output a second readout voltage; and a current-steering circuit configured to steer the photo-carriers generated by the photodiode to one or both of the first readout circuit and the second readout circuit.

1 .- 30 . (canceled) 
     
     
         31 . A method for operating a circuit coupled to a photodiode configured to absorb photons and to generate photo-carriers, the method comprising:
 providing, to a first reset MOSFET transistor of a first readout circuit and to a second reset MOSFET transistor of a second readout circuit, a reset control voltage to set a first capacitor of the first readout circuit and a second capacitor of the second readout circuit to a preset voltage;   receiving, from the photodiode and by a current-steering circuit, a portion of the photo-carriers generated by the photodiode;   providing, to the current-steering circuit, one or more control voltages to steer the portion of the photo-carriers to one or more of the first readout circuit or the second readout circuit, wherein one or more of a first voltage provided by the first capacitor or a second voltage provided by the second capacitor changes in response to receiving the portion of the photo-carriers;   determining, based on the first voltage provided by the first capacitor or the second voltage provided by the second capacitor, voltage value for a first shutter control voltage or a second shutter control voltage; and   providing, to (i) a first shutter MOSFET transistor having a drain terminal coupled to the first readout circuit, the first shutter control voltage or to (ii) a second shutter MOSFET transistor having a drain terminal coupled to the second readout circuit, the second shutter control voltage to control one or more of (i) a voltage difference between the first voltage provided by the first capacitor and a voltage of a source terminal of the first shutter MOSFET transistor or (ii) a voltage difference between the second voltage provided by the second capacitor and a voltage of a source terminal of the second shutter MOSFET transistor;   wherein the first readout circuit is configured to output a first readout voltage, and the second readout circuit is configured to output a second readout voltage,   wherein the first capacitor is configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide the first voltage, and the first reset MOSFET transistor is configured to charge the first capacitor to a preset voltage,   
       wherein the second capacitor is configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide the second voltage, and the second reset MOSFET transistor is configured to charge the second capacitor to the preset voltage;
 wherein the first reset MOSFET transistor further comprises:
 a source terminal coupled to the first capacitor; 
 a drain terminal coupled to a first supply node; and 
 a gate terminal coupled to a control voltage source; 
 
 wherein the second reset MOSFET transistor further comprises:
 a source terminal coupled to the second capacitor; 
 a drain terminal coupled to the first supply node; and 
 a gate terminal coupled to the control voltage source, and 
 
 wherein the first supply node is configured to supply a supply voltage to the first reset MOSFET transistor and the second reset MOSFET transistor to charge the first capacitor and the second capacitor to the preset voltage. 
 
     
     
         32 . The method of  claim 31 , further comprising operating the first shutter MOSFET transistor or the second shutter MOSFET transistor in a saturation region or a subthreshold region. 
     
     
         33 . The method of  claim 31 , wherein the providing, to the current-steering circuit, one or more control voltages to steer the portion of the photo-carriers to one or more of the first readout circuit or the second readout circuit, further comprises providing, to the current-steering circuit, one or more control voltages to steer a first portion of the photo-carriers to the first readout circuit for a first period of time, and steer a second portion of the photo-carriers to the second readout circuit for a second period of time. 
     
     
         34 . An optical sensor comprising:
 a photodiode configured to absorb photons and to generate photo-carriers;   a first readout circuit configured to output a first readout voltage; the first readout circuit comprising:
 a first capacitor configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide a first voltage; and 
 a first reset MOSFET transistor configured to charge the first capacitor to a preset voltage; 
   a second readout circuit configured to output a second readout voltage; the second readout circuit comprising:
 a second capacitor configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide a second voltage; and 
 a second reset MOSFET transistor configured to charge the second capacitor to the preset voltage; 
   a first shutter MOSFET transistor comprising:
 a source terminal; 
 a drain terminal coupled to the first readout circuit; and 
 a gate terminal coupled to a first control voltage source; 
   a second shutter MOSFET transistor comprising:
 a source terminal; 
 a drain terminal coupled to the second readout circuit; and 
 a gate terminal coupled to a second control voltage source; and 
   a current-steering circuit configured to steer a portion of the photo-carriers generated by the photodiode to one or more of the first readout circuit or the second readout circuit,
 wherein, during operation of the circuit, the first shutter MOSFET transistor is configured to receive, from the first control voltage source, a first control voltage to control a voltage difference between the first voltage provided by the first capacitor and a voltage of the source terminal of the first shutter MOSFET transistor, and 
 wherein, during operation of the circuit, the second shutter MOSFET transistor is configured to receive, from the second control voltage source, a second control voltage to control a voltage difference between the second voltage provided by the second capacitor and a voltage of the source terminal of the second shutter MOSFET transistor; 
   wherein, the first control voltage source and the second control voltage source are the same, and the first control voltage and the second control voltage are the same.   
     
     
         35 . The optical sensor of  claim 34 , wherein the first reset MOSFET transistor further comprises:
 a source terminal coupled to the first capacitor;   a drain terminal coupled to a first supply node; and   a gate terminal coupled to a third control voltage source,   wherein the second reset MOSFET transistor further comprises:
 a source terminal coupled to the second capacitor; 
 a drain terminal coupled to the first supply node; and 
 a gate terminal coupled to the third control voltage source, 
 wherein the first supply node is configured to supply a supply voltage to the first reset MOSFET transistor and the second reset MOSFET transistor to charge the first capacitor and the second capacitor to the preset voltage. 
   
     
     
         36 . The optical sensor of  claim 34 , wherein the first readout circuit further comprises:
 a first source follower circuit coupled to the first capacitor and configured to output the first readout voltage, and   wherein the second readout circuit further comprises:
 a second source follower circuit coupled to the second capacitor and configured to output the second readout voltage. 
   
     
     
         37 . The optical sensor of  claim 34 , wherein the current-steering circuit further comprises:
 a first current steering MOSFET transistor comprising a gate terminal coupled to a fourth control voltage source; and   a second current steering MOSFET transistor comprising a gate terminal coupled to a fifth control voltage source.   
     
     
         38 . The optical sensor of  claim 34 , wherein the photodiode includes a light absorption region supported by a substrate, and the current-steering circuit further comprises a well region in the substrate for collecting photo-carriers generated by the light absorption region. 
     
     
         39 . The optical sensor of  claim 34 , wherein the circuit is configured to (a) control the first control voltage such that the voltage difference between (i) the first voltage provided by the first capacitor and (ii) the voltage of the source terminal of the first shutter MOSFET transistor is equal to or greater than a predetermined percentage of the preset voltage, and
 wherein the circuit is configured to:
 (a) control the second control voltage such that the voltage difference between (i) the second voltage provided by the second capacitor and (ii) the voltage of the source terminal of the second shutter MOSFET transistor is equal to or greater than the predetermined percentage of the preset voltage; or 
 (b) control the first control voltage such that the voltage difference between (i) the first voltage provided by the first capacitor and (ii) the voltage of the source terminal of the first shutter MOSFET transistor is equal to or greater than a predetermined threshold, and 
   wherein the circuit is configured to control the second control voltage such that the voltage difference between (i) the second voltage provided by the second capacitor and (ii) the voltage of the source terminal of the second shutter MOSFET transistor is equal to or greater than the predetermined threshold.   
     
     
         40 . The optical sensor of  claim 34 , wherein the photodiode includes a light absorption region comprising germanium or germanium silicon. 
     
     
         41 . The optical sensor of  claim 34 , wherein the first readout circuit further comprises:
 a first source follower circuit coupled to the first capacitor and configured to output the first readout voltage, and   wherein the second readout circuit further comprises:   a second source follower circuit coupled to the second capacitor and configured to output the second readout voltage.   
     
     
         42 . The optical sensor of  claim 34 , wherein the first readout circuit is configured to output a first readout voltage, and the second readout circuit is configured to output a second readout voltage. 
     
     
         43 . The optical sensor of  claim 42 , wherein the first capacitor is configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide the first voltage, and the first reset MOSFET transistor is configured to charge the first capacitor to a preset voltage. 
     
     
         44 . The optical sensor of  claim 43 , wherein the second capacitor is configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide the second voltage, and
 the second reset MOSFET transistor is configured to charge the second capacitor to the preset voltage   
     
     
         45 . The optical sensor of  claim 44 ,
 wherein the first reset MOSFET transistor further comprises:
 a source terminal coupled to the first capacitor; 
 a drain terminal coupled to a first supply node; and 
 a gate terminal coupled to a third control voltage source, 
   wherein the second reset MOSFET transistor further comprises:
 a source terminal coupled to the second capacitor; 
 a drain terminal coupled to the first supply node; and 
 a gate terminal coupled to the third control voltage source, 
   
       wherein the first supply node is configured to supply a supply voltage to the first reset MOSFET transistor and the second reset MOSFET transistor to charge the first capacitor and the second capacitor to the preset voltage. 
     
     
         46 . An optical sensor comprising:
 a photodiode configured to absorb photons and to generate photo-carriers;   a first readout circuit configured to output a first readout voltage, the first readout circuit comprising:
 a first capacitor configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide a first voltage; and 
 a first reset MOSFET transistor configured to charge the first capacitor to a preset voltage; 
   a second readout circuit configured to output a second readout voltage, the second readout circuit comprising:
 a second capacitor configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide a second voltage; and 
 a second reset MOSFET transistor configured to charge the second capacitor to the preset voltage; 
   a first shutter MOSFET transistor comprising:
 a source terminal; 
 a drain terminal coupled to the first readout circuit; and 
 a gate terminal coupled to a first control voltage source; 
   a second shutter MOSFET transistor comprising:
 a source terminal; 
 a drain terminal coupled to the second readout circuit; and 
 a gate terminal coupled to a second control voltage source; and 
   a current-steering circuit configured to steer a portion of the photo-carriers generated by the photodiode to one or more of the first readout circuit or the second readout circuit,
 wherein, during operation of the circuit, the first shutter MOSFET transistor is configured to receive, from the first control voltage source, a first control voltage to control a voltage difference between the first voltage provided by the first capacitor and a voltage of the source terminal of the first shutter MOSFET transistor, and 
 wherein, during operation of the circuit, the second shutter MOSFET transistor is configured to receive, from the second control voltage source, a second control voltage to control a voltage difference between the second voltage provided by the second capacitor and a voltage of the source terminal of the second shutter MOSFET transistor; 
   wherein the first readout circuit is configured to output a first readout voltage, and the second readout circuit is configured to output a second readout voltage,   wherein the first capacitor is configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide the first voltage, and the first reset MOSFET transistor is configured to charge the first capacitor to a preset voltage,   wherein the second capacitor is configured to integrate at least a portion of the photo-carriers generated by the photodiode to provide the second voltage, and the second reset MOSFET transistor is configured to charge the second capacitor to the preset voltage;   wherein the first reset MOSFET transistor further comprises:
 a source terminal coupled to the first capacitor; 
 a drain terminal coupled to a first supply node; and 
 a gate terminal coupled to a third control voltage source; and 
   wherein the second reset MOSFET transistor further comprises:
 a source terminal coupled to the second capacitor; 
 a drain terminal coupled to the first supply node; and 
 a gate terminal coupled to the third control voltage source, 
 wherein the first supply node is configured to supply a supply voltage to the first reset MOSFET transistor and the second reset MOSFET transistor to charge the first capacitor and the second capacitor to the preset voltage. 
   
     
     
         47 . The optical sensor of  claim 46 , wherein the current-steering circuit further comprises:
 a first current steering MOSFET transistor comprising a gate terminal coupled to a fourth control voltage source; and   a second current steering MOSFET transistor comprising a gate terminal coupled to a fifth control voltage source.   
     
     
         48 . The optical sensor of  claim 47 , wherein the photodiode includes a light absorption region supported by a substrate, and the current-steering circuit further comprises a well region in the substrate for collecting photo-carriers generated by the light absorption region. 
     
     
         49 . The optical sensor of  claim 46 , wherein the first readout circuit further comprises:
 a first source follower circuit coupled to the first capacitor and configured to output the first readout voltage, and   wherein the second readout circuit further comprises:   a second source follower circuit coupled to the second capacitor and configured to output the second readout voltage.   
     
     
         50 . The optical sensor of  claim 46 , wherein the photodiode includes a light absorption region comprising germanium or germanium silicon.