TSL218

512

× 1 PIXEL LINEAR ARRAY

SOES014B – AUGUST 1994 – REVISED NOVEMBER 1995

2

POST OFFICE BOX 655303

functional block diagram

Hold

and

Sample

1,7

VDD

2

3

SI

CLK

SO

6

AO

4

RL

(internal load)

Buffer

Output

Node

Sense

Amplifier

Differential

Generator

Reference

Dark-Pixel

Generator

Clock

512-Bit Shift Register

Q512

Q3

Q2

Q1

S512

S3

S2

S1

Reset

Nonoverlapping

Clock Generator

Pixel Selector Switch

512 Pixels

3

2

1

Pixel

Buffer

Pixel

Buffer

5

GND

Terminal Functions

TERMINAL

DESCRIPTION

NAME

NO.

DESCRIPTION

AO

4

Analog output

CLK

3

Clock. The clock controls charge transfer, pixel output, and reset.

GND

5

Ground (substrate). All voltages are referenced to the substrate.

SI

2

Serial input. SI defines the start of the data-out sequence.

SO

6

Serial output. SO signals the end of the data-out sequence.

VDD

1, 7

Supply voltage for both analog and digital circuits

detailed description

sensor elements

The line of sensor elements, called pixels, consists of 512 discrete photosensing areas. Light energy striking

a pixel generates electron-hole pairs in the region under the pixel. The field generated by the bias on the pixel

causes the electrons to collect in the element while the holes are swept into the substrate. The amount of charge

accumulated in each element is directly proportional to the amount of incident light and the integration time.

device operation

Operation of the 512

× 1 array sensor is a function of two time periods—an integration period during which

a charge is accumulated in the pixels and an output period during which signals are transferred to the output.

The integration period is defined by the interval between the externally supplied SI pulses and includes the

output period (see Figure 1). The required length of the integration period depends on the amount of incident

light and the desired output-signal level.