At this week’s International Solid State Circuits Conference (ISSCC 2008) in San Francisco, Calif., some sophisticated power amplifier (PA) architectures were unveiled by researchers from Axiom, Intel, Matsushita, NEC, and STMicroelectronics

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Sophisticated techniques such as envelope elimination and restoration (EER) or outphasing amplifiers have been known for some time, but have been difficult to implement in mobile communication terminals because they require high integration levels and fast operating frequencies. With advances in process technologies, those sophisticated methods are becoming a reality.

Likewise, the circuits for millimeter wave (mm-wave) applications have been rather expensive. However, with advances in low-cost RF CMOS, mm-wave CMOS PAs are becoming practical. Key issues like gain and power in this band have been addressed.

In fact, in this session on “RF and mm-Wave Power Amplifiers” (#31), eight novel designs are presented. NEC’s paper 31.1 demonstrates a 90 nm CMOS mm-wave transceiver with a PA achieving an output power of 8.4 dBm with a power gain of 10.3 dB and a PAE of 7.0%. In the paper titled “Tx and Rx front-ends for the 60 GHz band in 90 nm standard bulk CMOS”, NEC researchers described a mm-wave direct-conversion transceiver in standard 90 nm CMOS with careful consideration of reliability. In this design, the Tx includes a PA, a VGA, a driver amplifier (DA) and an I/Q modulator. While in the Rx section, two LNAs in series are followed by a VGA, a DA, and an I/Q demodulator. The PA uses 20 Ω transmission lines in its low-loss output matching network. According to the researchers, The complete Tx achieves a 6.0 dBm output power for a 2.6 Gbps QPSK signal.

Similarly, in paper 31.2, UC, Berkeley designers presented a differential 12.3 dBm output power PA with transformer inter-stage matching circuits. While Fujitsu in paper 31.3 showed PAs with short stub matching circuits at 60 GHz and 77 GHz which achieved 10.6 dBm and 6.3 dBm output power, respectively.

Three PAs with EER, PWM, and LINC algorithms followed in the session. Paper 31.4 by STMicroelectronics presented a single chip WCDMA envelope-restoration-type 27 dBm 46% PAE PA with 130 MHz operation switched mode power supply circuits. Paper 31.5 by U of Washington and Intel demonstrated a 28.6 dBm class-E PA with a pulse-width and pulse-position modulator. Pulse-width modulation is exploited here to achieve the highest PA output power ever demonstrated in 65 nm CMOS. A class-E PA with on-chip pulse-width and pulse-position modulator (PWPM) for envelope restoration is fabricated in 65 nm CMOS. The PA operates from a 2.5 V supply and occupies 1.3 × 1.6 mm2. It achieves a measured Pout of 28.6 dBm with a PAE of 28.5%. It can amplify phase-modulated signals and signals of limited peak-to-minimum ratios. It achieves rms EVM values of 1.2% and 4.6% for a GMSK signal with symbol rate of 270 kHz and a π/4-DQPSK signal with symbol rate of 192 kHz, respectively.

Operating on the principles of outphasing, a joint paper (#31.6) by UCLA and Matsushita discussed a programmable PA for a SDR transmitter that offers a 20 dBm output power. It incorporates a switching scheme to solve the problem of combining power in outphasing. It is tested for GSM, EDGE and WCDMA signals with 56%, 44%, and 30% efficiency, respectively.

On the multi-band cellular front, Axiom Microdevices introduced a fully integrated quad-band PA for GSM/GPRS, with integrated input and output matching and on-chip closed-loop power control and supply from 2.9 to 6 V, in standard 0.13 μm CMOS (#31.7). It uses a standard package with no oscillations, degradation, or failures for over 2,000 hours of operation at 6 V and 135 °C under a VSWR of 15:1 (all angles) and produces up to +35 dBm of RF power with a PAE of 48%.

Lastly, STMicroelectronics described a multi-mode, multi-band balanced SiGe PA module for GSM/EDGE/WCDMA. The integration of a 6 × 8 mm2 transmit power module for multi-mode (GSM/EDGE/WCDMA) and multi-band (850 to 900 MHz and 1800 to 2100MHz) operation hosts printed matching networks, on-glass 90° combiner, directional couplers, low-pass filters, and 2 SiGe balanced PAs capable of envelope and power tracking operation. The module delivers 34.9/32.9 dBm (PAE 54/45%) and 27/26 dBm (PAE 32/30%) in GSM/DCS and WCDMA modes, respectively.

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