Built-in EVM measurement for OFDM transceivers using all-digital DFT

Yılmaz, Emre; Nassery, Afsaneh; Ozev, Sule; Acar, Erkan

doi:10.1109/test.2009.5355625

Cited by 3 publications

(1 citation statement)

References 17 publications

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“…In [8], we proposed a built-in-self-test (BIST) method for EVM measurements. Our previous work relies on aa Gray coding scheme and accuracy degrades for large EVM levels due to code aliasing.…”

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Built-In EVM Measurement With Negligible Hardware Overhead

Yılmaz¹,

Nassery

Ozev

2014

IEEE Des. Test

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h BECAUSE OF ITS soft capacity and frequency diversity, orthogonal frequency division multiplexing (OFDM) has become the prevailing modulation scheme for modern RF transceiver systems. Modulation accuracy, specified in terms of error vector magnitude (EVM), is one of the most important transmitter parameters specified for OFDM transceivers. EVM encapsulates many nonidealities of the transmitter, including inter symbol interference, mismatches, nonlinearity, phase noise and spurs, and carrier leakage [1]. It is typically one of the few parameters specified for the transmitter and needs to be guaranteed.Recently, several researchers have proposed techniques for simplified EVM measurements. The goal in [2] is to limit the number of symbols that need to be transmitted/received within one frame as dictated by the normal operation mode. The complete receive operation is duplicated and conducted at the tester using a golden receiver on the load board. In [3], the authors propose an EVM measurement method that requires less number of symbols by increasing the sensitivity of EVM to transceiver system noise. A computationally efficient EVM measurement method for phase-only modulation schemes is presented in [4]. EVM test sequence is reduced in [5] by selecting sensitive corner cases into the test vector to shrink the test sequence.While there has been significant progress in reducing the overhead of EVM measurements, important challenges still remain, especially when it comes to multi-site testing. Multi-site environments typically share high-frequency channels that complicate board design and limit the number of parallel tested devices. Moreover, characterization of EVM requires sending many symbols spread over multiple frames and conducting the overall receive operation including the channel characterization and synchronization. The I and Q signals need to be captured and analyzed at the tester requiring access to these signals. Moreover, the complete receive operation needs to be duplicated by the test engineer and incorporated into the test program. This operation requires complex procedures to synchronize the transmitted and received frames and to estimate the channel characteristics. These steps complicate the test development process and may result in long test development times.The need to analyze the IQ signals, rather than the bit pattern, also puts a high burden on the tester. The IQ signals are typically digitized with a resolution of 8-12 bits [6]. This means that measuring EVM requires 16 to 24 bits of digital bandwidth between the tester and the device under test (DUT) just for Editor's notes: This article presents an all-digital, built-in method for measuring EVM that alleviates the need for sophisticated external test equipment and speeds up test application time.VHaralampos Stratigopoulos, TIMA Laboratory

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