| 摘要 |
A small size transistor based photodiode readout circuit 100 in accordance with the present invention comprises a cascode transistor M<SUB>C</SUB> connected to the output of a photodiode. The cascode transistor M<SUB>C</SUB> is connected via an integrating node to a reset transistor M<SUB>R</SUB>, an integrating capacitor C<SUB>INT</SUB> and to a buffering transistor M<SUB>B</SUB>. When an appropriate signal is applied to switch M<SUB>S</SUB> via input RO it is closed and a signal can pass from M<SUB>B</SUB> to the output, the signal being a function of the voltage on the integrating capacitor C<SUB>INT</SUB>. The cascode transistor M<SUB>C</SUB> connected between the output of a photodiode D<SUB>PH</SUB> and the rest of said readout circuit 100 is operable to decouple the parasitic capacitance C<SUB>PH</SUB> of the photodiode D<SUB>PH</SUB> from the rest of the readout circuit 100, and in particular the capacitance of the integrating capacitor C<SUB>INT</SUB>. As a result, the signal integrated by the integrating capacitor C<SUB>INT</SUB> has a good linear relationship with the output of the photodiode D<SUB>PH</SUB>, and the output signal of the readout circuitry 100 has a relatively high linearity and relatively high gain, whilst the readout circuit 100 is provided within a relatively small area. |
