What are Linear Image Sensors?

Fairchild Imaging makes CMOS 1421, a linear image sensor. This is an imaging device with a wide dynamic range of 94 dB or 52000:1, with excellent linearity. The device is a linear sensor, meaning it has 2048 x 1 high-resolution imaging sensors. Fairchild has designed this linear sensor for medical and scientific line scan applications such as optical inspection or fluorescent imaging that require wide dynamic range, high sensitivity, and low noise operation.

With several acquisition modes, this photodiode pixel has an optical area measuring 7 x 10 µm with a pitch of 7 µm and a fill factor of 85%, making the operation of this sensor very flexible:

  • Read after Integration: This mode is ideal for applications with high quality signals
  • Buffered Read after Integration: is a high speed mode that integrates the next line while reading the current line
  • Read on Integration: This is a non-CDS mode, allowing the highest speed of operation
  • Multiple Read during Integration: This mode is for low-light applications, permitting oversampling during integration

Other than the above, a programmed mode, accessible through JTAG interface, meets a wide range of specialized imaging requirements. Readout cycles in this mode are controllable through external signals.

CMOS 1421 has several features such as very low dark current, very low readout noise, and non-destructive readout for fowler sampling. Along with anti-blooming drain and electronic shutter, the CMOS 1421 also features two independent gain settings for each pixel. The entire device is enclosed in an RoHS compliant CLCC and PLCC package of 22.35 x 6.35 x 2.85 mm dimensions. The device consumes 40 mW of power while operating from 3.3 VDC. Major applications of linear image sensors are in microscopy, photon counting, and fluorescent imaging.

CMOS 1421 has a pixel array consisting of a photodiode, a pixel amplifier, and a sample and hold circuit. Along with the above, each pixel has a noise suppression circuitry and a gain register. While the pixel-level gain affects the device sensitivity, it also has a bearing on the noise and conversion factor of the sensor.

Linear image sensors from Fairchild use thinned back-illuminated large area arrays. Fairchild offers custom capabilities such as extreme spectral band detection, low noise active reset CMOS architecture, and high-resolution X-ray imagery using these sensors.

These linear image sensors are ideal for visible, ultra violet to visible, and visible to near infrared spectrometers, and their enhancement makes them suitable for spectroscopy applications. The design of their pixels being tall and narrow helps light distribution from a spectrometer’s grating. If provided with UV sensitivity, these sensors do not need extra UV coating.

CMOS 1421 displays superior linearity, which is of extreme benefit to spectroscopy measurements. The device also includes an electronic shutter along with a built-in timing generator, which are useful in spectroscopy. The device is suitable for several applications involving scientific, industrial, and commercial activities.

New sensors based on CMOS match features with those of CCDs. Featuring simpler external circuit design, and simpler operation, CMOS 1421 linear image sensors are suitable for spectroscopy, displacement measurement, barcode scanning, and imaging.