PI0512WS Page 4 of 8 – July 26, 2001

EOS

EOS

AVIDEO

RESET

BIAS

SHIFT REGISTER

START

CLK

START

CLK

PI0512WS

VDD

Note: Quantum Efficiency (QE) can be calculated by dividing the responsivity by the area of

the sensor's element and multiplying the resulting ratio by the energy per photon in electron

volts (eV).

The dark current is typically about 1 pA at 25

dark current will contribute dark-signal charges and these charges will increase as direct

function of integration time and superimpose on the image signal charges.

Self-Scanning Circuit

Figure 5 shows a simplified electrically equivalent circuit diagram of the photodiode array.

Every photodiode in the array is connected to a common output video line by a MOS switch.

Impinging photons generate charge that is collected on each imaging photodiode when the

switch is open. As the shift register sequentially closes each MOS switch, the stored charge,

which is proportional in amount to the light exposure, from each corresponding photodiode is

readout onto the video line. The output charge on the video line from each photodiode pixel is

typically sensed by an external charge-integrating amplifier. The shift register is activated with

the entry of the start pulse. This pulse propagates through each shift register stage and

activates the MOS switches sequentially. When the pulse reaches the last shift register stage,

the fourth and last dummy pixel is readout and end-of-scan (EOS) output is held high for one

clock cycle.

Figure 5. Simplified circuit diagram of PI0512WS photodiode array.