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FROM EDN EUROPE: CMOS GSM transceiver
-- EDN, 3/1/2001
Silicon Laboratories has used its mixed-signal CMOS processes to build a complete RF front end for dual- and triple-band Global System for Mobile communications (GSM) and GPRS handsets. The Aero is a three-chip set that removes the need for an external IF SAW filter, VCOs, and around 60 discrete components (Picture). On the receive channel, Aero integrates three low-noise amplifiers (one per band), and on the transmit side, the chip set directly feeds the power amplifier and antenna switch. Aero's receiver is a low-IF design, which the company claims has advantages over the alternative direct-conversion, or zero-IF, architecture, especially when you implement Aero in a pure CMOS process. Design requirements are less stringent on the low-noise amplifier, mixer, and PLL blocks. (For example, Aero is 20 dB less demanding in PLL linearity.)
Silicon Labs digitises the low IF in a 13-MHz delta-sigma ADC, with digital mixing yielding I and Q signal components. The current design converts these back to the analogue domain to directly feed established baseband processors. A future design might keep those signals in the digital domain and feed them directly in to a suitable design of a baseband processor. The Aero chip set comprises the Si4200 transceiver in a 32-lead microlead-frame package, the Si4201 baseband interface in a similar 20-lead package, and the 28-lead Si4133 RF synthesiser. The chip set costs $8.62 each (10,000), and sampling is now under way.
—by Graham Prophet
