Transcript CCD
Reading from a charge coupled device (ccd) © D Hoult 2010 ODWS Each pixel in a ccd consists of a photoelectric cell and a capacitor (to store the charge emitted) © D Hoult 2010 ODWS Each pixel in a ccd consists of a photoelectric cell and a capacitor (to store the charge emitted) The voltage across the capacitor is proportional to the charge stored © D Hoult 2010 ODWS Each pixel in a ccd consists of a photoelectric cell and a capacitor (to store the charge emitted) The voltage across the capacitor is proportional to the charge stored and hence to the intensity of the illumination of the pixel © D Hoult 2010 ODWS The pixels in this diagram have been magnified... © D Hoult 2010 ODWS The pixels in this diagram have been magnified... quite a lot ! © D Hoult 2010 ODWS This ccd has not yet been exposed to light © D Hoult 2010 ODWS After exposure, the capacitors in the illuminated © D Hoult 2010 ODWS pixels now store a small charge The data are read 1 pixel at a time © D Hoult 2010 ODWS First, all the voltages are “shifted” towards a special row of pixels at one end of the chip © D Hoult 2010 ODWS First, all the voltages are “shifted” towards a special row of pixels at one end of the chip © D Hoult 2010 ODWS First, all the voltages are “shifted” towards a special row of pixels at one end of the chip © D Hoult 2010 ODWS Now the data voltages are “shifted”, one at a time, towards a pixel at the end of that special row © D Hoult 2010 ODWS After each shift, the voltage in the special pixel is © D Hoult 2010 ODWS read and stored in memory After each shift, the voltage in the special pixel is read and stored in memory, in this case, zero © D Hoult 2010 ODWS voltage = V © D Hoult 2010 ODWS voltage = 0 © D Hoult 2010 ODWS voltage = 0 © D Hoult 2010 ODWS voltage = V © D Hoult 2010 ODWS voltage = 0 © D Hoult 2010 ODWS voltage = V © D Hoult 2010 ODWS voltage = 0 © D Hoult 2010 ODWS voltage = 0 © D Hoult 2010 ODWS voltage = V © D Hoult 2010 ODWS voltage = V © D Hoult 2010 ODWS voltage = V © D Hoult 2010 ODWS voltage = V © D Hoult 2010 ODWS voltage = V © D Hoult 2010 ODWS voltage = 0 © D Hoult 2010 ODWS