RF Test, Adaptation and Self-Healing

System Level Self-Healing of RF Transceivers

CMOS technology scaling has exacerbated the effects of process variations on circuit level performance and has driven the need for post-manufacture tuning of high-performance RF systems. In this work, a new iterative built-in testing and tuning approach for RF transceiver systems is proposed that uses: (a) the baseband processor to stimulate the RF front end in loopback mode using DSP-generated multitones, (b) the output of the receiver and sensors designed into the RF signal path to acquire the response of the front-end to the applied stimulus, (c) assessment of all the relevant transceiver specifications in a single data acquisition from the observed front-end response and (d) iterative testing and tuning of the RF front end using DSP-activated tuning control until all the RF front end performance specifications are within acceptable bounds with minimal impact on overall power consumption. The proposed methodology enables yield recovery of devices not possible with earlier methods, avoids local minima, is validated on a set of industrial devices and can be implemented at low cost.

Key Publications : VTS 2010, IEEE D&T 2014

Process-Variation Tolerant Low-Noise Amplifier

A self compensating process variation tolerant RF Low Noise Amplifier (LNA) is demonstrated. A novel non–intrusive mixing technique is proposed which enables minimal intrusion negative feedback in RF circuits making them process variation tolerant. The proposed design technique provides 18% yield improvement over comparable conventional LNA under severe process variation.

Key Publications : ISCAS 2008

Low-cost AM/AM & AM/PM Testing of RF Power Amplifiers

This work develops a simple, practical yet easily realizable method for low cost measurement of phase and amplitude distortions in radio frequency power amplifiers (RF PA). Amplitude-to-amplitude (AM-AM) and amplitude-to-phase (AM-PM) distortions are two significant distortion effects in PAs at high output power levels, causing out of band interference in the transmitted signal and bit errors in the received signal. Traditional measurements of amplitude and phase distortion in RF PAs require the use of expensive vector network analyzers. In this work, we propose the use of phase-to-amplitude conversion to develop a low cost and accurate test methodology for AM-AM and AM-PM measurement using simple load board test circuitry along with software based difference generation and peak detection mechanisms. Using either simple sine wave stimulus with power sweep or a single amplitude modulated RF stimulus, both distortion effects can be measured with high accuracy for nominal devices as well as over process and voltage variations, while allowing significant reduction in test cost.

Key Publications : ITC 2009, TVLSI 2012

Testing of Polar RF Transceivers

This work presents a Built-in self-test (BIST) solution for polar transmitters with low cost. Polar transmitters are desirable for portable devices due to higher power efficiency they provide compared to traditional Cartesian transmitters. However, they generally require iterative test/measurement/calibration cycles. The delay skew between the envelope and phase signals and the finite envelope bandwidth can create inter modulation distortion (IMD) that leads to the violation of the spectral mask and error vector magnitude (EVM) requirements. Typically, these parameters are not directly measured but calibrated through spectral performance analysis using expensive RF equipment, leading to lengthy and costly measurement/calibration cycles. Characterization and calibration of these parameters inside the device would reduce the test time and cost considerably. In this work, we propose a technique to measure the delay skew and the finite envelope bandwidth, two parameters that can be digitally calibrated, based on the measurement of the output of the receiver in the loop-back mode. Simulation and hardware measurement results show that the proposed technique can characterize the targeted impairments in the polar transmitter accurately.

Key Publications : VTS 2013, DATE 2014

Low-cost IQ Mismatch BIST

This work proposes a cost and time efficient accurate DSP based measurement and compensation methodology for I/Q imperfections in quadrature transceivers through phase-to-­amplitude conversion using no hardware overhead. The proposed one-shot technique utilizes equation based optimum test stimulus estimation and power detection mechanisms. Circuit simulations presented show that both gain and phase mismatch can be measured with high accuracy. Hardware validation of the methodology provide for impairment estimation accuracy of within 0.5% for gain and 4.5% for phase.

Key Publications : IMS 2010