Mc-680dcc reference Design Note
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MC-680DCC Reference Design Note
AbstractThe purpose of this reference design note is to describe the functionality of the Texas Instruments (TI) MC-680DCC 1394-based digital PC camera and to give reference design information concerning the production version of its chipset. This beta version of the MC-680DCC camera, as well as the production chipset, is capable of sending full motion VGA resolution video to the computer over the IEEE1394-1995 200 megabits per second serial interface. The user can control all camera functions including exposure, frame rate, white balance, saturation, gamma, brightness, and focus, by sending asynchronous commands to the camera from the PC. The camera receives these commands and performs the appropriate digital signal processing or these functions can be controlled automatically by the camera. By doing this processing in the camera, the resource burden on the computer is minimized. Also included in this note are the installation of hardware and software, operation of hardware and software, the camera specifications, the basic camera architecture for the beta release, and the preliminary production reference design notes including schematics. FeaturesThe MC-680DCC offers the advantage of 24-bit true color digital video processing. This gives superior video quality at higher sustained data rates. The MC-680DCC utilizes the IEEE 1394-1995 high-speed serial bus for isochronous video communications and asynchronous control of camera operation at a data rate of 200Mbit/sec. This bus allows non-compressed full motion digital video at rates of 30 frames/sec. Using this serial connection eliminates the need for expensive video capture cards. The camera incorporates proprietary digital image processing techniques. These techniques enable the camera to achieve excellent color accuracy and resolution. The use of a custom advanced CMOS Video Signal Processing VSP ASIC allows for both the advanced digital imaging processing techniques and for advanced color space conversion. This enables multiple output formats required for a multipurpose video conferencing camera. In addition, it allows for low power operation enabling the camera unit to be powered by a notebook computer operating on battery power. ApplicationsThe MC-680DCC is a very low cost digital color camera. Its low cost and features make it well suited to many applications including:
The MC-680DCC’s resolution is 640 (H) X 480 (V) with 7.4m square pixels. This resolution meets the VGA square pixel standards. Hardware InstallationTo operate the MC-680DCC camera, it is necessary to connect the camera, via a 6-conductor 1394 cable, to a 1394 port on a computer. It is expected that over the next several months, a 1394 port will be included on the motherboard of most new computers. This port can be added to an older computer that contains a PCI slot using the TI FireWire 1394 Serial Bus Design Kit (TSBKPCI). This kit contains a 1394 evaluation PCI card, 1394 cable, Lynx Software for Windows 95, and various data sheets and users guide. The instructions for installing this card are included with the kit, but it is as simple as installing the 1394 PCI card into a free slot and installing the software. This kit is available from your authorized TI distributor. To use the MC-680DCC camera, it is necessary to connect the 1394 cable from the computers 1394 port to the camera. The power used by the camera is transferred over this cable. To insure proper connection and power up, the red LED on the top of the front board of the camera should light up. This shows that the camera was initialized correctly and is ready to send video data to the computer. The beta version of the MC-680DCC camera will run under Windows 95 using the TI DISP demonstration software or under Microsoft’s new Windows operating system code-named Memphis. The software installation below, as well as the software operation section, covers the DISP demonstration software under Windows 95. Under Windows Memphis, the camera utilizes its plug-and-play compatibility to load the correct drivers. Video can be displayed by using the built in VidCap32 video display utility. The camera is also compatible with Microsoft’s Net Meeting under Windows Memphis. Software InstallationThe current version of the software, version 1.05, is in beta release. This software was developed by TI Digital Image Sensor Products (DISP) as evaluation software for the IEEE1394-1995 camera interface. It will only run TI beta MC-680DCC cameras and will only work with the TI PCI Lynx 1394 chipset. All other cameras on the bus will be ignored. The software is designed to run under Microsoft Windows 95 on the minimum system as listed below: 133 MHz Pentium processor 16 Megabytes system memory 10 Megabytes hard drive space Video card capable of 640x480 resolution @ 65K colors A 1394 port or one free PCI slot
Using this procedure listed above, the software should be installed properly. This demo software is a BETA TEST VERSION and could have bugs. The use of this software application is understood to be fully at the risk of the customer. Camera OperationThe beta version of the MC-680DCC camera is designed to perform most of the digital video processing functions inside the camera, therefore, minimize the processing burden on the CPU. These functions, including exposure, brightness, gain, sharpness, gamma, white balance, shutter, focus, and various transfer modes are explained in detail below. The exposure, brightness, and gain functions perform video processing on the image signal in the analog domain. The exposure controls the electronic integration function of the TC236P sensor by sending a clear pulse on the ODB line to clear all charge from the sensors image area. This clear pulse, which is set through an asynchronous 9-bit word sent from the computer, can vary the integration time from 250 sec to 0.133 seconds. The gain and the brightness control the analog gain control (AGC) and the DC offset, respectively, before the signal enters the analog-to-digital converter. These three functions can also be controlled automatically by the camera. The exposure and the gain will be set to give center weighted, properly exposed video while the brightness keeps a constant dark level through the varying gain settings. The sharpness, gamma, and white balance functions are digital signal processes that improve the video quality. The sharpness control utilizes a two stage, digital sharpness filter to improve edge enhancement in the video signal. The gamma control implements a digital correction factor that is equivalent to the 0.45 analog gamma standard and may be switched on or off. The white balance control modifies the color balance of the video to allow for correct white balancing under different types of illumination. This white balance has been defaulted to the correct values for fluorescent lighting conditions typical in an office environment. This white balance will need to be adjusted for different lighting conditions such as incandescent or natural light. Auto white balance can be incorporated into the software to automatically correct these color balance factors for various lighting conditions. The shutter function allows for control of extended integration time within a given transfer mode. This allows the user to easily change the integration time which yields better performance in low light levels. Using this feature sacrifices frame rate in a given mode in exchange for increased sensitivity. The focus control controls the position of the focus mechanism by sending a position value to the focus state machine. A reference position for the focus mechanism is determined upon camera power up by stepping to a known position given by an IR emitter/detector module. The stepping motor will step the motor from its current position to the new position given by the computer. Utilizing this position method of focusing, it is possible to perform an auto focus routine in software and send the correctly focused position data to the camera. The last function performed in the camera is the implementation of different video transfer modes. The beta version of the MC-680DCC supports the transfer modes listed in Table 1 below.
Table 1: MC-680DCC Beta Camera Capabilities. These capabilities can be verified in the MC-680DCC test software by selecting the Camera Capabilities selection under the Camera menu while the camera is operating. There is also the capability of the camera to operate in 25, 12.5, 6.25, 3.13 frames per second. These alternate frame rates allow the camera to operate without any color rolling or flickering due to 50Hz lighting typical in European and Japanese areas. The optical lens used with this camera is a five-element glass lens with an aperture of F=2.0. The selection of this lens was based on the cameras typical operating environment of being indoors and observing a person sitting at a computer. While the camera can function outside in full sunlight, better performance can be achieved by utilizing a neutral density filter of 2.0. This will improve the video performance by allowing an increased integration time for proper exposure, which minimizes any resulting smear. Software OperationTo demonstrate the capabilities of the MC-680DCC camera, TI DISP has developed evaluation software that operates under the Microsoft Windows 95. This software allows the user to operate the camera in any transfer mode the camera is capable of and control all aspects of the video processing on board the camera. The software will only work with the beta version of the MC-680DCC camera that is interfaced to a 1394 port utilizing the TI PCI Lynx 1394 chipset. All other cameras on the bus will be ignored. For the software to display video from the camera, the software must initialize the camera. There are two methods to initialize a camera depending upon whether a camera is connected before or after the software program is started. If the software is run after the camera is connected, the program’s main window, with its menu bar, and the video window are started. If the program is started before the camera is connected, only the main window appears. To initialize a recently connected camera, the “New Camera” option under the “File” menu must be selected. A camera selection window appears with a list of all cameras attached to the 1394 bus. Select the appropriate camera and click the “New” option to initialize the video window. The camera controls are controlled through three menu functions that bring up three control windows. The camera color controls are controlled through “Color Control” option under the “Camera” menu. These controls include brightness, exposure, sharpness, white balance including U and V, gamma correction, shutter, and gain. Beside each of these control sliders is an automatic control check box. If this box is available to be checked, the respective control can be optimized and automatically controlled by the camera. The focus control window is accessed through the “View Control” option on the “Camera” menu. This window controls the focus mechanism position. The slider moves the focus mechanism from infinity focus to near focus (~10cm). The transfer mode window can be selected through the “Transfer Mode” option under the “Camera” menu. This window selects between the various transfer modes available. The modes available for a given camera are displayed through the “Camera Capabilities” option under the “Camera” menu. This software has several methods of capturing, saving, and printing the video data that is sent by the camera. Video can be saved by selecting the “Save Video” option under the “File” menu. The video is saved in the *.avi format. Still images can be frozen on the screen, saved to disk in *.bmp or *.eps format, copied to the clipboard, or printed directly to a printer. These options are available under the “View” “File”, and “Edit”menus. Camera Specifications
Table 2: Camera Specifications Beta Camera ArchitectureThe beta version of the MC-680DCC camera is designed around three PC boards. The front board, containing the image sensor and analog processing, the middle board, containing the digital control and signal processing, and the rear board, performing the serial 1394 communications. These boards and their functionality are described below. The front board, called the 236-5 board, contains the main sensing element, the image sensor. This camera uses the TI DISP TC236P image sensor. This sensor is a frame transfer Charge Coupled Device (CCD) that contains 658x496 active imaging pixels, 22 dark reference pixels per line, 4 dark lines, and a single-phase storage area. This storage area, effectively an analog memory, allows the camera architecture to be designed without using costly external frame memory. This sensor board also contains the CCD driver circuitry, TI’s TLC976DGG ADC, switching power supplies, and stepping motor driver circuitry used for mechanized focus. The TLC976DGG performs all analog processing on the CCD pixel information including correlated double sampling (CDS), DC offset, and analog gain control (AGC). Currently on the beta prototype boards, two digital-to-analog converters are utilized to control the DC offset and AGC functions. The middle board, called the 10K50-4 board, contains two electronically programmable logic devices (EPLD). They perform all of the TC236P sensor timing, CDS interface, ADC clock, digital signal processing, and 1394 interface. The sensor timing, the CDS interface clocks, and the ADC clock works in conjunction with the computer to send video information as it is requested. During a wait state, the image data is kept in the on-chip storage area of the TC236P sensor until another request for data is received. At this point, another line of video is read out of the sensor’s memory. The integration timing of the sensor, also controlled by these EPLDs, is varied depending upon either the signal processing feedback during automatic exposure control or by the computer in manual mode. These EPLDs also control all of the digital signal processing of the video information and the communication with the 1394 chipset. The back board, called the 1394-4 board, contains the 200 megabit per second 1394 interface chipset. This chipset contains two ICs, the Link-Layer and the Phy-Layer. This board also includes the 3.3-volt switching power supplies. This power supply accepts the 1394 specified voltage range of 8 to 40 volts and efficiently generates the 3.3 volts needed by the 1394-4 and the 10K50-4 boards. Preliminary Production Reference DesignTo succeed in the growing PC camera market, it is necessary to have a competitive, very low cost camera chipset. To address this need, TI DISP is designing a chipset along with a reference design and a prototype of the production 1394 based PC camera. This chipset, along with these design tools, allows the customer to create a very low cost, high performance solution for the PC camera. This chipset consists of 6 ICs including the image sensor, main control/processing ASIC, sensor driver, analog-to-digital converter, and two 1394 serial interface ICs. These chips are discussed below. TC236P The main sensing element used in this camera is the TI TC236P image sensor. This sensor is capable of resolutions up to 640x480 pixels at 69dB of dynamic range. Utilizing the TI DISP ASIC, this sensor can generate 24-bit color video at a resolution of 640x480 at 30 frames per second. VSP ASIC The TI DISP ASIC is the main control/processing IC in the chipset. It represents considerable integration of various sections of the MC-680DCC beta cameras. This ASIC controls all of the timing functions for the TC236P image sensor, all timing requirements of the TLC976 CDS/ADC, all digital video processing algorithms, the 1394 chipset interface control logic, multiple stepper motor control logic for focus, zoom, ect., and two digital-to-analog converters (DAC) used in controlling the analog gain and offset levels. The ASIC utilizes several registers, which hold default values to perform these various functions. These registers are programmed in a small external E2 memory space. These registers are programmed with the correct values for each individual camera through TI DISP’s final test software. These values, for white balance, default focus, camera serial number, brightness, exposure, pulse positioning ect., are tested and programmed for each individual camera during final test. TMC57253DSB The TMC57253, along with two temperature stable discrete drivers, are used to interface between the VSP ASIC timing and the CCD. This interface is needed to generate the 12-volt voltage swings necessary in CCD clocking technology. The two discrete drivers were designed to minimize any signal propagation changes due to differing temperatures. These two drivers drive the reset and serial register clock lines. TLC976DGG The analog signal processing and analog-to-digital conversion is accomplished in the TLC976DGG. The analog signal from the CCD is capacitively coupled into this IC. The first stage to the analog processing is Correlated Double Sampling (CDS). This is accomplished through two clock pulses generated in the ASIC that sample the reset voltage and subtracts it from the pixel voltage. The AGC section increases the pixels voltage level to the correct point, which is determined by the ASIC. The DC component of this signal is adjusted to the correct level and fed to the 10-bit 20MHz analog-to-digital converter. TSB12LV31 & TSB21LV03 The last two chips in the chipset are the TSB12LV31 IEEE1394-1995 Link-Layer chip and the TSB21LV03 IEEE1394-1995 Physical-Layer. The Link-Layer IC performs the bidirectional asynchronous/isochronous data transfers to and from an IEEE 1394-1995 serial bus physical layer device. The Physical-Layer provides the functionality to implement a three-port node needed in a cable-based IEEE 1394-1995 network. It provides for initialization, arbitration, and packet reception and transmission. This device interfaces with the Link-Layer. Power Supplies The suggested power supply design, based from the MC-680DCC beta cameras, includes two separate switching power supplies. The back power supply provides 3.3 volt power to the two 1394 ICs, the E2 IC, and the VSP ASIC. The front power supply generates 20, 12, 10, and 5 volts necessary to operate the CCD, the ADC, the CCD drivers, and the stepper motor drivers. The system power supply design is divided into two separate power supply to allow for better power management. During low power mode, the front power supply can be powered down, effectively eliminating any current draw from the CCD, the ADC, the CCD drivers, or the stepper motor drivers. This allows for a very low current power down mode. Both power supplies are switching supplies to maximize DC-to-DC voltage conversion efficiencies, which minimizes the camera operating power. Focus Unit & Drivers The lens unit used on the MC-680DCC beta cameras utilizes a 2-phase, 10mm diameter, 62 ohm stepper motor to move a 5 element glass lens of F=2.0. To minimize the total cost of this focus/motor driver system, the motor drivers are designed using low cost discrete FETs arranged in 2 H-bridge configurations. This arrangement provides sufficient drive capability, low power, and low cost. Appendix APreliminary reference schematics Appendix BIEEE 1394 digital camera specification listed at: www.1394ta.org | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||