Black Spot Hardware
ambient temperature. Once again 35◦C is much lower than 85◦C.
The third chip to analyse is the linear regulator. The regulator chosen is a
3.3  from
nalog Devices, Inc. and its datasheet gives a maximum junction temperature
of 150◦C and a thermal coefficient of θJA
= 62.3◦C/W. Using Equation 5.5 this gives
TJREG = 35 + 62.3 × 573 × 10
This is also well below the maximum quoted.
This brief analysis shows that the camera modules can operate at an ambient tempera- ture of 35◦C with passive cooling without exceeding the maximum operating temperatures given in the three main components data sheets.
System with external SDR M
With the processor family and image sensor chosen a decision was made whether to use an SDR M external to the Blackfin (Figure 5.4) or to rely solely on the internal SR M avail- able. Using external SDR M has advantages as it allows buffering of a full image frame in memory that is not possible with limited internal SR M. This is particularly useful for debugging as it allows an entire image to be captured and relayed to software for analysis. It also simplifies image processing algorithms as they can operate on data from anywhere within the entire image. Without SDR M only portions of an image can be processed at a given time requiring algorithms to be adapted to work in this manner. These two reasons make a strong case for using SDR M.
However, there are disadvantages to using external SDR M. These are the added hard- ware complexity, increased potential for corruption of data due to noise, increased part count, potentially increased size, and increased cost. For this prototype the part count, size, and cost are of lesser importance. Complexity and noise are important issues, how- ever.
By adding SDR
M complexity is increased.
Firstly, routing the PCB is more difficult as a
M requires many tracks for transferring data between the Blackfin.
of these extra lines on the PCB makes routing the PCB more difficult and time consuming. lso, the SDR M requires a 133 MHz clock. high speed clock such as this is a source of switching noise and the PCB would require careful design to avoid this noise coupling with data lines on the board. This again makes routing more difficult and time consuming and increases the chances of producing a board that cannot be used. Finally, SDR M running at 133 MHz is slower than the internal SR M meaning that the processor may have to wait to process data and this could slow the system down. Careful design and use of the caching