Joel L. Dawson

A 350

A 350 muW MSK direct modulation transmitter and a 400 muW OOK super-regenerative receiver (SRR) are implemented in 90 nm CMOS technology. The transceiver tunes 24 MHz in frequency steps smaller than 2 kHz and is designed to meet the specifications of the Medical Implant Communications Service (MICS) standard in the 402-405 MHz band. The transmitter meets MICS mask specifications with data rates up to 120 kbps, and the receiver has a sensitivity better than -99 dBm with a data rate of 40 kbps or -93 dBm with a data rate of 120 kbps.

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We present a 2.4-GHz asymmetric multilevel outphasing (AMO) power amplifier (PA) with class-E branch amplifiers and discrete supply modulators integrated in a 65-nm CMOS process. AMO PAs achieve improved modulation bandwidth and efficiency over envelope tracking (ET) PAs by replacing the continuous supply modulator with a discrete supply modulator implemented with a fast digital switching network. Outphasing modulation is used to provide the required fine output envelope control. The AMO PA delivers 27.7-dBm peak output power with 45% system efficiency at 2.4 GHz. For a 20-MHz WLAN OFDM signal with 7.5-dB PAPR, the AMO PA achieves a drain efficiency of 31.9% and a system efficiency of 27.6% with an EVM of 2.7% rms.

W CMOS MSK Transmitter and 400

Recent advances in the medical field are spurring the need for ultra-low power transceivers for wireless communication with medical implants. To deal with the growing demand for medical telemetry, the FCC commissioned the medical implant communications services (MICS) standard in 1999 in the 402-405 MHz band. This paper presents a 350 muW FSK/MSK direct modulation transmitter and a 400 muW OOK super-regenerative receiver (SRR) specifically optimized for medical implant communications. The transceiver is implemented in 90 nm CMOS and digitally tunes 24 MHz in frequency steps smaller than 2 kHz. The transmitter meets MICS mask specifications with data rates up to 120 kb/s consuming only 2.9 nJ/bit; the receiver has a sensitivity better than -99 dBm with a data rate of 40 kb/s or -93 dBm with a data rate of 120 kb/s consuming 3.3 nJ/bit. A frequency correction loop incorporating the base-station is prototyped to eliminate the need for a frequency synthesizer in the implant while still achieving frequency stability of less than 3 ppm.

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We describe a new outphasing transmitter architecture in which the supply voltage for each PA can switch among multiple levels. It is based on a new asymmetric multilevel outphasing (AMO) modulation technique which increases overall efficiency over a much wider output power range than the standard LINC system while maintaining high linearity. For demonstration, the overall transmitter is simulated in a 65nm CMOS process with HSUPA and WLAN signals. The simulation results show an efficiency improvement from 17.7% to 40.7% for HSUPA at 25.3dBm output power and from 11.3% to 35.5% for WLAN 802.11g at 22.8dBm while still meeting system linearity requirements.

W OOK Super-Regenerative Receiver for Medical Implant Communications

A compact, low-power, digitally-assisted sensor interface for biomedical applications is presented. It exploits oversampling and mixed-signal feedback to reduce system area and power, while making the system more robust to interferers. Antialiasing is achieved using a charge-sampling filter with a sinc frequency response and programmable gain. A mixed-signal feedback loop creates a sharp, programmable notch for interference cancellation. A prototype was implemented in a 0.18-μm CMOS process. The on-chip blocks operate from a 1.5-V supply and consume between 255 nW and 2.5 μW depending on noise and bandwidth requirements.

A 2.4-GHz, 27-dBm Asymmetric Multilevel Outphasing Power Amplifier in 65-nm CMOS

We demonstrate energy-efficient low-complexity adaptive linearization for wideband handset power amplifiers (PAs). Due to power overhead and complexity, traditional wideband linearization techniques such as adaptive digital predistortion (DPD) thus far have not been used for wideband handset transmitters. Our energy-efficient lookup table training strategy resulted in a training energy of 1.83 nJ/entry for a 5-MHz bandwidth WiMAX orthogonal frequency division multiple access (OFDMA) transmission, which represents more than 40times improvement over state-of-the-art DPD implementations. Our experimental prototype transmitter achieves a maximum of 9.9-dB improvement of adjacent channel leakage power at 5.15-MHz offset with 22.0-dBm channel power in the 5-MHz bandwidth WiMAX-OFDMA transmission. This linearity improvement offers 26.5% savings in PA power consumption by reducing power backoff.

A 350μW CMOS MSK transmitter and 400μW OOK super-regenerative receiver for Medical Implant Communications

We present a new adaptive power amplifier (PA) linearization technique. We leverage analog Cartesian feedback (CFB) to train a Cartesian look-up table, reducing DSP and power amplifier modeling requirements to a minimum and eliminating model convergence as a design issue. Because the CFB system does not continuously operate, we overcome the bandwidth limitation traditionally associated with this technique. In addition, we exploit sample averaging to greatly relax the noise requirements of the analog feedback path. We implemented a prototype 900-MHz direct-conversion transmitter with a class-A PA. We measured a 10-dB reduction of out-of-band distortion products with no noise floor degradation for 40-MHz-bandwidth, 16-QAM test signals.

Asymmetric multilevel outphasing architecture for multi-standard transmitters

A 1.95-GHz asymmetric multilevel outphasing (AMO) transmitter with class-E GaN power amplifiers (PAs) and discrete supply modulators is presented. AMO transmitters achieve improved efficiency over envelope tracking (ET) transmitters by replacing the continuous supply modulator with a discrete supply modulator implemented with a fast digital switching network. Outphasing modulation is used to provide the required fine output envelope control. A 4-level supply modulator is implemented that allows for fast and efficient discrete envelope modulation with up to 28-V supply voltages using low-voltage gate drivers and time-alignment logic. With two class-E GaN PAs that achieve 62.5% power-added efficiency (PAE) at 40- dBm peak output power, the AMO transmitter delivers 42.6- dBm peak output power at 1.95-GHz. For a 16-QAM signal at 36-dBm output power, the transmitter achieves 44.2/42.8/41.4% average system efficiency and 2.0/2.1/3.1% EVM for 10/20/40-MHz channel bandwidth, respectively.

A Biomedical Sensor Interface With a sinc Filter and Interference Cancellation

As with many analog building blocks, DC offsets limit the accuracy of analog multipliers. Chopper stabilization, long applied to precision amplifiers, has been recently modified to be applicable to analog multiplication (Dawson and Lee, 2003). In this paper we present a general approach to chopper stabilization for analog multiplication. An IC fabricated in National Semiconductors 0.18mum process allowed us to characterize an array of the new multipliers, which represents the first thorough experimental characterization of the new technique. The prototype circuits exhibit an average output offset of 204muV, with a standard deviation of 23muV, while consuming 181muW of power each. These are the lowest reported measured offsets in the DC analog multiplier literature

Energy-Efficient Digital Predistortion With Lookup Table Training Using Analog Cartesian Feedback

Electrical Impedance Myography (EIM) is a non-invasive, painless clinical technique for the diagnosis and monitoring of a variety of neuromuscular diseases including amyotrophic lateral sclerosis and focal nerve injuries. It involves the application of a low-intensity alternating current to a muscle group and the measurement of the consequent surface voltage patterns. This paper presents a system for the rapid and accurate acquisition of data employing an interrogating signal composed of multiple tones with frequencies between 10 kHz and 4 MHz. The use of this composite signal makes possible measurement of impedance at multiple frequencies simultaneously. In addition, this system takes impedance measurements at multiple orientations with respect to the muscle fibers by means of an electronically reconfigurable electrode array and utilizes the linearity of muscle tissue to reduce the required measurement time. Testing of the EIM system on beef has established the capability of this system to rapidly detect the anisotropic conductive properties of muscle tissue at multiple frequencies.