TSL401

128

× 1 LINEAR SENSOR ARRAY

SOES011 – MARCH 1996

2

POST OFFICE BOX 655303

POST OFFICE BOX 1443

Terminal Functions

TERMINAL

DESCRIPTION

NAME

NO.

DESCRIPTION

AO

3

Analog output

CLK

2

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

GND

6, 7

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

NC

5, 8

No internal connection

SI

1

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

VDD

4

Supply voltage. Supply voltage for both analog and digital circuits.

detailed description

The sensor consists of 128 photodiode pixels, arranged in a linear array. Light energy striking a pixel generates

photocurrent, which is then integrated. The amount of charge accumulated at each pixel is directly proportional

to the light intensity on that pixel and the integration time. The integration time is the interval between two

consecutive output periods.

A 128-bit shift register controls the output period of the device. An output period is initiated by applying a logic

level 1 to SI for one positive-going clock edge (see Figure 1). This logic one is clocked through a 128-bit shift

register, in which one bit is associated with each pixel. When a given bit is high, the associated pixel signal is

coupled to the analog output (AO) through an output amplifier. When the bit goes low, the integrator is reset.

AO is a source follower that requires an external pulldown resistor. The source-follower configuration permits

an analog wired-OR hookup of multiple devices. When the device is not in the output phase, the output is in a

high-impedance state. The output is nominally 0 V for no light input and 2 V for a nominal full-scale output.

The TSL401 is intended for use in a wide variety of applications, including mark and code reading, optical

character recognition (OCR) and contact imaging, edge detection and positioning, and optical linear and rotary

encoding.