TC237B is a frame-transfer CCD image sensor designed for single-chip black-and-white NTSC television, computer, and special-purpose applications requiring low cost and small size.
The TC237B image sensing area is configured as 500 rows with 680 elements per row. Each row provides 22 elements for dark reference. The sensor's antiblooming function is based on an advanced lateral overflow drain concept. The sensor can operate as a 658 (horizontal) × 496 (vertical) sensor in true interlaced mode with low dark current. A key characteristic of the TC237B high-resolution sensor is its ability to capture a full 340,000 pixels per frame. The image sensor also provides high-speed image transfer capability and continuous electronic exposure control without the loss of sensitivity and resolution associated with other technologies. Through a high-performance architecture with reset and voltage reference generator, the charge voltage of each electron is converted to a signal voltage at 13μV. The signal is further buffered by a low-noise, two-stage source-follower amplifier to provide high output drive capability.
The TC237B sensor is fabricated using Texas Instruments' proprietary Advanced Virtual Phase (AVP) technology, which provides the device with high blue-light response, low dark current, high photoresponse uniformity, and single-phase clocking. The TC237B sensor operates over a temperature range of -10°C to 45°C.
This MOS device has limited built-in gate protection. During storage or handling, device pins should be shorted together, or the device should be placed in conductive foam. In circuit applications, unused inputs should always be connected to VSS. Under no circumstances should pin voltages exceed the absolute maximum ratings. Shorting OUT to VSS during operation should be avoided to prevent damage to the amplifier. The device may also be damaged if the output terminal is reverse-biased and excessive current is allowed to flow. Specific guidelines for handling such devices are contained in the Texas Instruments publication, Electrostatic Discharge Sensitive (ESDS) Devices and Assemblies Handling Guide.
The TC237B CCD image sensor consists of four basic functional blocks: the image sensing area, image storage area, serial register gates, and a low-noise signal processing amplifier block with charge detection node and independent reset. The locations of these blocks are identified in the functional block diagram.
When light enters the silicon of the image sensing area, electrons are generated and collected in the wells of the sensing elements. Antiblooming protection is provided by applying a DC bias to the overflow drain bias pin. To clear the image before the start of a new integration period (for implementing an electronic fixed shutter or electronic auto-iris), a pulse of at least 1μs is applied to the overflow drain bias. After integration is complete, the charge is transferred to the storage area. The transfer timing depends on whether the readout mode is interlaced or progressive scan. If progressive scan readout mode is selected, readout can be performed using one serial register, or at high speed using two serial registers. Row summation can be implemented prior to parallel transfer, which is useful for off-chip smear subtraction.
The 22 columns on the left edge of the image sensing area are shielded from incident light; these elements provide dark reference used for video black-level restoration in subsequent video processing circuits. In addition, four dark lines between the image sensing area and image storage area prevent charge leakage from the image sensing area into the image storage area.
The advanced lateral overflow drain structure is shared by two adjacent pixels and provides the sensor with several unique characteristics. By varying the DC bias on the drain pin, the antiblooming protection level can be controlled, with a trade-off against well capacity.
To clear the charge from the image area, a 10V pulse above the nominal DC bias level is applied for a duration of at least 1μs. This feature allows precise frame-by-frame control of integration time. The single-pulse clear function also reduces smear by eliminating charge accumulated in pixels prior to the start of integration.
