Bus advancements improve cell-phone connections
By Brian Dipert -- EDN, March 18, 2004
The ever-increasing amount of data flowing between various subsystems in modern cell phones, coupled with unrelenting pressure to reduce the phones’ cost and size, creates considerable engineering challenges that two interconnect innovations strive to solve (Picture). Focusing first on the image sensor-to-application processor for camera-inclusive phones (for camera-inclusive phones) and application-processor-to-display links, National Semiconductor has evolved the WhisperBus technology that it acquired when it bought Vivid Semiconductor to come up with the MPL (Mobile Pixel Link) bus. Traditional multibit parallel-LVCMOS interfaces are bulky, and they become increasingly noisy and power-hungry as their speeds climb.
MPL, in contrast, is a single-ended, two-wire (data and strobe), bidirectional, low-swing-current-mode approach that, in its first silicon implementation, can provide 83-Mbps point-to-point throughput—for example, 320×240-pixel frames at 18-bit color depth and 60-frame/sec video rates. National’s first MPL-enabled products are the 85-cent (1000) LM2501, in a 24-bump CSP, which can implement an 8-bit YUV camera-to-processor interface, and the $1.26 LM2502 in 49-contact LLC, whose two data channels support 16-bit processor buses and dual displays. National expects that, in the long term, it will license its MPL transceiver cores for integration into others’ chips rather than remain as a supplier of stand-alone devices. To stimulate overall market growth, the company offers the specifications for MPF in an open, royalty-free manner, similar to the approach Silicon Image (www.siliconimage.com) took with DVI a few years ago.
With its low-voltage dual-port memories, IDT (International Device Technology) focuses on the bidirectional bus that links the application and baseband processors in cell phones. Latest generation CDMA-1X EV-DO, 802.11b and other leading-edge wireless networks exceed 1-Mbps speeds and, in the process, overwhelm the 1.5-Mbps (minus software and protocol overhead) UART- or low speed USB interprocessor-communication channels in today’s phones. IDT’s alternative approach comprises a family of memory-mapped, 1.8V dual-port RAMs, including the 70P248 and 70P258 low-power variants, which also offer I/O-voltage flexibility to 3.3V LVCMOS levels. All devices are now available in sample quantities and will enter volume production next quarter. Table 1 provides product-family details.
Integrated Device Technology, 1-408-727-6116, www.idt.com.
National Semiconductor, 1-408-721-5000, www.national.com.
