Design and test of high-speed mixed-signal/RF circuits and systems is undergoing a transformation due to the effects of process variations stemming from the use of scaled CMOS technologies that result in significant yield loss. To this effect, post-manufacture tuning for yield recovery is now a necessity for many high-speed electronic circuits and systems and is typically driven by iterative test-and-tune procedures. Such procedures create new challenges for manufacturing test and built-in self-test of advanced mixed-signal/RF systems. In this paper, key test challenges are discussed and promising solutions are presented in the hope that it will be possible to design, manufacture and test ¿truly self-healing¿ systems in the near future.

High-volume manufacturing of current generation orthogonal frequency division multiplexing (OFDM) transceivers mandates testing for error-vector-magnitude (EVM) at production testing. During EVM test, a modulated RF input signal is down-converted and demodulated to obtain the output baseband digital data and EVM is computed by processing the baseband digital data. Hence, production testing of OFDM devices would require such modulation- and demodulation-capable automated test equipment (ATE) to perform EVM test. Such capabilities significantly add up to the cost of the ATE, thereby increasing the overall cost of testing. Moreover, test time for EVM can be relatively long compared to other tests due to the need to average over a large number of data bits. In this paper, we propose a methodology for testing EVM using multi-tone signals sourced from inexpensive signal sources that generate standard constellations. Moreover, introducing null carriers in the multi-tone test stimulus enables accurate characterization of system noise with reduced number of data bits. This enables significant speedup in EVM testing. We present the theory to corroborate the proposed approach along with simulation and hardware results. The proposed test method also has the potential to significantly reduce EVM test time under production test conditions.

Polar radio architectures are attractive due to the ability to implement them using largely digital architectures. However, testing for specs such as EVM incurs significant test time due to the large numbers of symbols that need to be transmitted. In our approach, EVM is modeled as a function of the system static non-idealities (IQ mismatch, gain, IIP3 parameters) and dynamic non-idealities (VCO phase noise). Using a multi-tone test stimulus, the static and dynamic non-idealities are estimated first. The data generated is used to predict EVM using machine learning methods with high accuracy while incurring minimal test time.

In this paper, a process tunable, continuously adaptive wireless front end architecture and related adaptation algorithms are presented that allow an RF transceiver to function at minimum power irrespective of channel conditions and process variability induced performance loss in the RF front end and baseband interface. Current wireless transceiver front ends are designed for worst case channel conditions and a limited degree of post manufacture tuning is performed to compensate for process variations. It is shown how the proposed architecture can result in significant power savings over current practice without compromising system-level bit error rate. The adaptation methodology is applied to a WLAN transceiver design and hardware measurement data for an adaptive receiver is presented.

Frequency modulation is used in many important communication and wireless applications. A key defining characteristic of frequency modulated systems is the constant amplitude of the transmitted signal making it impossible to use envelope-based built-in test (BIT) techniques. In this paper, an efficient BIT technique for such transmitters using lowpass filters is proposed. The proposed BIT technique is low-cost and has minimal impact on RF transmitter performance. It can also be used to efficiently test devices such as voltage-controlled oscillators (VCOs), phase locked loops (PLL) etc through frequency discrimination. Simulation results and hardware measurements demonstrate the feasibility of the proposed approach.

In production testing of wireless systems, measurement of EVM (a critical spec that is directly related to bit error rate) incurs significant test time due to the large numbers of symbols that need to be transmitted for reasons of accuracy. In our approach, EVM is modeled as a function of the system static non-idealities (IQ mismatch, gain, IIP3 parameters) and dynamic non-idealities (system noise, VCO phase noise). Using a selected subset of the OFDM tones, the static parameters are calculated first. These are then used to facilitate noise estimation using a back-end constellation compensation and noise amplification procedure. The data generated is used to predict EVM using machine learning methods. Significant reduction in test time is achieved with little loss in test accuracy.

In this paper, a novel adaptive calibration technique for advanced RF front-ends is proposed in which sensors are implanted in the transmitter and the observed device test response to a special calibration test is compared against the known golden response to the same. Tuning 'knobs' which are built into the circuit are then used to minimize the error between the observed response and the golden response using an iterative tuning approach. In addition to circuit-level tuning, adaptive digital compensation techniques are employed in the baseband processor. It is shown that this results in increased transmit signal dynamic range over existing techniques and accurate loopback testing of the transceiver modules.

Production testing of digitally modulated transceivers such as those based on orthogonal frequency division multiplexing (OFDM) has become challenging, particularly in the context of measuring specifications such as error-vector-magnitude (EVM) which require the use of precision test equipment with digital modulation capability and low noise floor. Moreover, test time is an issue due to the need to transmit and receive a large number of data bits for accurate test measurement. In this paper, a multi-tone based test method is presented for accurately measuring the EVM and noise specifications of a wireless device. We present the theory behind the proposed approach along with simulation results. The proposed test method is low-cost, and has the potential to significantly reduce EVM test time under production test conditions.

Modern wireless transceiver systems are often overdesigned to meet the requirements of low bit error rate values at high data rates under worst-case channel operating conditions (interference, noise, multi-path effects). This results in circuits being designed with ldquosufficientrdquo margins leading to lower efficiency and high power consumption. In this paper, we develop an adaptive power management strategy for RF systems that optimally trades-off power vs. performance for the RF front-end to maintain operation at or below a specified maximum bit error rate (BER) across temporally changing operating conditions. As the communication channel degrades, more power is consumed by the RF front end and vice versa. Since the maximum bit-error rate specification is not violated, minimum voice or video quality through the wireless channel is always guaranteed.

Digital predistortion is used as a compensation technique in communication systems to minimize the effect of power amplifier non-linearity while increasing its operational efficiency. Prior linearization schemes use the receiver chain to feed data to the baseband processor that adaptively adjusts the predistortion coefficients. The procedure is iterative, requires many test applications, is sensitive to receiver quality, and is not suitable for RF communication front ends in which the mixer, LNA and PA are dynamically reconfigured to adapt to changing operating conditions. In the proposed scheme, a single multi-sine diagnostic test is applied from the baseband, and the response of the transmitter is captured via a response envelope detector. A novel unified methodology for co-tuning predistortion coefficients along with the PA bias voltage based on response diagnosis is proposed, thereby, enabling the transmitter to operate at high efficiency and linearity.

In the recent days, ultra-wide band (UWB) has drawn significant attention as an emerging wireless standard. While the multiband (MB) orthogonal frequency division multiplexing (OFDM) PHY standards (IEEE 802.15.3a) are still being formulated, the first set of UWB devices is set to hit the consumer market by the end of 2005. For MB-OFDM UWB devices to be successful in the marketplace it is necessary for their manufacturing and test costs to be very low. To reduce the cost of production test, we propose 'alternate' tests for complex UWB transmitter specifications viz. EVM and complementary CDF (CCDF). The non-idealities present in UWB transmitters are a result of nonlinearities in DACs and ADCs, as well as the phase noise of the local oscillator (LO) used in the front-end of the transmitter. In this paper, production cost is minimized by reducing test time as well as using low-cost test equipment for performing the tests. The production tests generated for EVM and CCDF are easy to apply in a production test environment using a low-cost ATE and provides up to 10times savings in test time and 3times savings in test cost