Readout circuit for an optical sensing charge injection device facilitating an extended dynamic range

In a charge injection device (CID) for optical sensing having an extended dynamic range, the combination comprising

• A. n optical sensor elements (E.sub.1-n) arranged in an array on a substrate, each element when reversely biased and suitably pulsed, forming a potential well in which optically induced charges may be stored, the charge which accumulates with the bias disconnected causing a reduction in depth of said potential well, the depth of which may be reestablished by periodically resetting said bias over a prolonged charge integration period, said optically induced charge being detectable after periodic resetting by application of an injection pulse adequate to collapse said potential well, or detectable without injection until the sensor element is reset,
• B. a readout circuit, comprising
• (1) n input terminals (IT.sub.1-n) each connected to one of said n sensor elements (E.sub.1-n), a first node including a primary sensing line (PLS), a second node including a secondary sensing line (SLS), and a primary (PTO) and a secondary (STO) signal output,
• (2) (i) a first voltage source (VR) suitable for reversely biasing said sensor elements,
• (ii) n parallel bias reset switches (S1.sub.1-n), each for connecting a corresponding sensor element to said first voltage source (VR),
• (iii) a primary reset switch (S3) for connecting said primary sensing line to said first voltage source (VR);
• and
• (iv) a secondary reset switch (S10) for connecting said secondary sensing line to said first voltage source (VR),
• (3) n primary select switches (S2.sub.1-n) for connecting successive sensor elements to said primary sensing line for primary readout,
• (4) n secondary select switches (S4.sub.1-n) for connecting successive sensor elements to said secondary sensing line for secondary readout,
• (5) primary pulse injection means (CI) for application of said injection pulse coupled to said primary sensing line and via said primary select switch (S2.sub.j) to each (jth) sensor element for removing stored charge from said selected element, the leading edge of said injection pulse collapsing the potential well, and the trailing edge of said injection pulse reestablishing said potential well,
• (6) a first and second correlated double sampling circuit (CDS) connected respectively to said primary (PLS) and said secondary (SLS) sensing lines for providing a primary (PTO) and a secondary (STO) readout signal,
• (7) timing means including
• (i) a scanning shift register connected to control said primary (S2.sub.1-n) and said secondary (S4.sub.1-n) select switch for establishing a primary and a secondary select interval respectively for each (jth) sensor element, the secondary select interval of the jth sensor element occurring during the primary select interval of the (j+1)th sensor element, and
• (ii) a timing generator for timing the operation of said scanning shift register, said switches, said charge injection means (CI), and said correlated double sampling circuits,
• said primary sensing line in each sensor element readout interval (t.sub.p) after resetting, being connected to said jth sensor element via primary select switch S2.sub.j during the primary select interval, said jth sensor element being successively sampled by said first correlated double sampling circuit, pulsed by said primary charge injection means (CI), and resampled by said first correlated double sampling circuit to provide said primary readout signal (PTO), the charge integration period for primary readout being approximately (n-1) sensor element readout intervals with resetting occurring every sensor element readout interval for sensitive low signal operation,
• said secondary sensing line in each sensor element readout interval (t.sub.p), after resetting, being connected to said (j-1)th sensor element via secondary select switch S4.sub.j-1 during the secondary select interval, said (j-1)th sensor element being twice sampled by said second double sampling circuit over a charge integration period (t.sub.si) to provide said secondary readout signal (STO), the charge integration period for secondary readout taking place within a single sensor element readout interval for unsaturated large signal operation.