The SAM itself comes in three parts, namely the i80134 analog front end (AFE), the i90816 digital controller, and the SAM host software (Fig. 1).
The CMOS AFE contains two 12-bit digital-to-analog converters (DACs) with an 8.8-MHz sampling rate and a 13-bit, pipeline analog-to-digital converter (ADC), also with an 8.8-MHz sampling rate. The ADC's bandwidth is 1.1 MHz. The incoming signal is externally filtered for attenuation of speech, plain-old telephone-system (POTS) signaling, and attenuation of echo signaling. It's then amplified by a low-noise programmable-gain stage and low-pass filtered. This prevents anti-aliasing and eliminates out-of-band noise. The filter bank is software configurable between the ATU-R and ATU-C modes.
The incoming 12-bit data on the transmit side is converted to an analog signal and filtered. A predriver buffers the signal for the external line driver, and in case of a short loop, provides attenuation of −15 to 0 dB. The digital interface to the processor is four bits wide in a delicate balance between power requirements and the possibility of introducing noise on the PCI bus. In full flight, the AFE consumes 0.5 W off a 3.3-V supply.
The i90816 controller contains dedicated hardware blocks. The DSP front end features digital filters for interfacing with the i80134 AFE. It also has a decimation/interpolation filter and a time-domain equalizer (TEQ). An execution core, controlled by a state machine, performs the conversion from the time to the frequency domain. (FFTs and iFFTs). A PCI core handles bus-interfacing tasks. The rest of the ADSL processing is completed by the host, using the SAM driver software (Fig. 2).
The driver software is based on the NDIS network miniport-driver models for Windows operating-system platforms. It consists of ATM stacks, ADSL handshaking, a DMT data pump, a miniport-driver interface, and a hardware chip-set interface based on the various ADSL and ATM protocols.
The symbol-buffer interface takes symbols one by one from memory for processing. The SAM hardware management configures the ATM power-down modes and the ADSL configuration layer for controlling hardware and software for operation in the various modes. The ATM protocol stack and cell-buffer interface mediate between the synchronous ATM protocol and the asynchronous ADSL layer. Beside these, the ADSL/ATM management interface lets the application software configure and control the modem, power down, ADSL activation, and other features.
The protocol and management stack make the ADSL appear Ethernet-like. (The RFC 1577, an extension of the IEEE 802.3 MAC interface, is an interface layer between the IP and ATM stacks.) The SAM comes with the company's ADSL tool software for management, configuration, control, and remote diagnostics.
Devices such as the SAM should proliferate quickly as CPUs jump in performance. According to ITeX, ADSL modems based on this architecture will be embedded in motherboards later this year. The i80134 comes in a 64-pin LQFP, while the i90816 digital chip is housed in a 160-pin PQFP. Also, the host software comes on a CD-ROM as assembled Windows 95, 98, 2000, and NT 4.0 object code.
Price & Availability
The chip set, with host software, is available now. Pricing is $25 per 1000, falling to $18 in high volumes.
Integrated Telecom Express Inc., 2710 Walsh Ave., Santa Clara, CA 95051; Sales Dept., (408) 980-8689; www.itexinc.com.