The WiMAX Wait Is Over

The receiver's IIP3 figure measures +5 dBm. The noise figure is less than 6 dB, including the switch and filter losses. Total RF gain is 100 dB with an automatic gain control (AGC) of 40-dB gain control range. The transmitter section is optimized for OFDM and supports HD-FDD as well as TDD operation.

These ICs are made with gallium-arsenide (GaAs) heterojunctionbipolar-transistor (HBT) technology. An external power amplifier, also available from SiGe, is required.

In this vein, the SE7380L is a GaAs pseudomorphic high electron mobility transistor (PHMET) single-pole doublethrow (SPDT) switch that's used for transmit-receive switching. It features low insertion loss and high linearity for maximum dynamic range with OFDM and high-level modulation schemes.

Another major RF chip supplier, Texas Instruments, recently announced a complete portfolio of RF chip sets for WiMAX and other wireless broadband applications (Fig. 5). They are the TRF11xx for 2.5 GHz, TRF12xx for 3.5 GHz, and TRF24xx for 5.8 GHz. They target basestation and CPE equipment for WiMAX and Korea's similar WiBro broadband wireless system.

The TRF1115 and TRF1216 receive (RX) chips include the low-noise amplifier (LNA) and downconverting mixer for 2.5- and 3.5-GHz receivers. These match up with the TRF1112 and TRF1212 second mixer, two LOs, and a programmable gain amplifier. The output at 44 MHz feeds the ADC.

On the transmit (TX) side, the TRF1121 or TRF1221 upconvert 25-MHz IF from the DAC at 2.5 and 3.5 GHz, respectively. Two LOs are included. The TRF1122 and TRF1222 provide a second upconversion. Separate power amplifiers (PAs) for higher output, the TRF1123 and TRF1223, also are available for 2.5 and 3.5 GHz. They can drive the antenna directly or serve as drivers for higher-power PAs.

The 5.8-GHz chip set is a bit different. This two-chip set consists of an RF and IF transceiver. The TRF2432 IF chip interfaces to the baseband ADCs and DACs. It works with the TRF2436 RF front end. A 374-MHz surface-acoustic-wave (SAW) IF filter separates the two chips. This chip set supports both the 5.8- and 4.9-GHz bands.

Other TI parts that fall into the WiMAX arena include the ADS5500 ADCs, the DAC5687 DACs, the GC5016 digital up/downconverter, and the GC1115 crest factor reduction chip. Moreover, TI's TMS320-TC16482 DSP chip runs at 1 GHz, making it a good fit with WiMAX signal processing.

No chips are currently available for 802.16e products, but some are on the way. Intel is working on such chips in cooperation with Nokia. Nokia sees some potential in incorporating WiMAX in some of its high-end cell phones. Adaptix, a basestation and CPE manufacturer, is rumored to be working on a mobile system that uses OFDMA-TDD. Finally, Philips Semiconductor has been focused on the mobile segment, with products expected next year.