To reduce the amount of space taken up in settop boxes, TDK Semiconductor has designed a low-speed single-chip modem that connects directly to a transformer-less data access arrangement (DAA) interface.
The company has designed the 2400bit/s modem to work with a Silicon Laboratories interface chip through a capacitive interface that performs the function normally handled by a transformer. The interface circuitry has been integrated into the modem instead of needing a separate line driver to pass signals through the six parallel 1000pF-range capacitors.
TDK opted to use the Krypton Isolation KR2963 silicon DAA for its design. That company was bought by Silicon Laboratories in August, which holds a much larger market share in silicon DAAs but which tend to include a codec. Silicon Laboratories made its own two-chip 2400bit/s modem with DAA. Having bought Krypton in August, the company now holds three key patents for the capacitive isolation technology needed for silicon DAAs.
Analog Devices and Conexant also make silicon DAAs. However, Silicon Laboratories is currently suing Analog Devices and 3Com over patent infringement. The case is set for trial in March 2001.
Many of the other transformer-less DAA designs use optocouplers to achieve the necessary isolation between the telephone line and the modem itself.
For its single-chip modem, TDK has based the design on a previous generation.
Neil Harrison, director of European sales for the company, said: "We decided two years ago to introduce a single-chip design that could be driven by AT commands," said
Because its device is intended to operate in settop boxes and other networked equipment to support back-channel communications, the company aims to add more firmware to the microcontroller inside.
Joel Chlodnik, product line marketing manager for TDK Semiconductor, said: "The next version will implement a TCP/IP stack in the modem. It will use AT commands to control TCP/IP communications, using enhanced firmware in the modem."
TDK Semiconductor, which is to be spun out by its parent in the spring of next year, plans further moves into other parts of digital settop boxes. As the company already has a higher proportion of modem shipments going into European designs, it has chosen to design an OFDM [orthogonal frequency domain multiplexing] demodulator.
"A lot of the tuner can manufacturers are looking to put the demodulator in the can, and that is where we are focused. We have built a low-power 2.5V core for a 0.25um process. We are using a low-power DSP core that we have licensed in," said Williams.