A Wide Band High Linearity CT-∑Δ Converter for Receivers Reaching 1.75 Gb/s Using 16384 QAM

Higher order quadrature amplitude modulation (QAM) schemes enable increased data rates as well as improved spectral efficiency and thereby empower the evolution of future mobile communication standards. A key component in the receive chain is the analog-to-digital converter (ADC). Performance metrics are usually extracted using narrow-band signals such as high-purity single or two-tone sine waves. As an alternative, this paper describes gigabit rate receiver characterizations using complex wide-band signals with modulation depths up to 16384-QAM. This is possible by the use of a wide-band Sigma-Delta ADC with > 60 dB dynamic range with a bandwidth of 250 MHz. The complete digital signal processing chain is described, which features a linear equalizer and a low-pass decimation filter to recover the transmitted symbols. The influence of various transceiver design choices, such as the pulse shaping filter are measured. For the mitigation of interference from of out-of-band signals, high linearity is essential. This is shown by a sine-wave interference test showing RMS error-vector-magnitudes (EVM) under different linearity conditions. Here, EVMs of less than 0.2% are presented with 1.75 Gb/s transmission speed enabling future mobile communications.