MLX90255

Linear Optical Array

MLX90255 Linear Optical Array

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Rev 1.0 31-May-01

Application Note: MLX90255 Demo Board

The demo board described in this document facilitates the evaluation of the MLX90255xx Linear Optical

Arrays. The board provides the necessary timing and clock signals to support both the on-board imaging

device or an externally connected sensor. The designer is then free to investigate the properties and

performance of the device without having to design and construct an external support circuitry. A

regulated DC power supply between 6 and 10V is the only input signal. An oscilloscope is required for

observation and analysis of the output signals.

Features and Benefits

• 128 x 1 Sensor-Element Organization (1 Not Connected, 1 dummy, 128 real, 1 dummy, 1

Dark Pixel)

• 385 DPI sensor pitch

• High Linearity and Uniformity for 256 Gray-Scale

• High Sensitivity: 1.7V @ 10µW/cm 2 @ 0.7ms integration time

• Special Gain Compensation for use with single LED light source

• Output Referenced to Ground

• Single 5V Supply

• Operation to 1MHz

Applications

• position Sensing

• electrical Power Assist Steering (EPAS)

• spectrometer Applications

Functional Diagram

General Description

The MLX90255xx linear sensor array consists of

a 128 x 1 array of photodiodes, associated

charge amplifier circuitry and a pixel data-hold

function that provides simultaneous integration

start and stop times for all pixels. The pixels

measure 200µm (H) by 66 µm (W) and there is 8

µm

spacing

between

pixels.

Operation

is

simplified by internal control logic that requires

only a Serial Input (SI) pulse and a clock signal.

The

sensor

consists

of

128

photodiodes

arranged in a linear array. Light energy falling on

a photodiode generates photocurrent, which is

integrated by the active integration circuitry

associated with that pixel. During the integration

period, a sampling capacitor connects to the

output of the integrator through an analog

switch. The amount of charge accumulated at

each pixel is directly proportional to the light

intensity and the integration time. The output

and reset of the integrators is controlled by a

132-bit shift register and reset logic. An output

cycle is initiated by clocking in a logic 1 on SI.

This causes all 132 sampling capacitors to be

disconnected from their respective integrators

and starts an integrator-reset period.