A 0-dB STF-Peaking 85-MHz BW 74.4-dB SNDR CT ΔΣ ADC With Unary-Approximating DAC Calibration in 28-nm CMOS

Abstract

This article presents a continuous-time (CT) analog-to-digital converter for wireless communication systems with a high tolerance against blockers. The zero-cancellation technique is introduced to eliminate the peaking in the signal transfer function (STF) to achieve better out-of-band-blocker immunity. An on-chip unary-approximating calibration is implemented to calibrate the mismatch of the outer current-steering digital-to-analog converter. A discrete-time (DT) second-order noise-shaping (NS) 2b/cycle asynchronous successive-approximation-register (ASAR) quantizer further reduces the quantization noise and the excess loop delay, achieving a CT-DT hybrid sixth-order NS without suffering from neither the problem of the CT-DT transfer function matching in a CT multistage NS topology nor the stability issue in a singleloop fully CT sixth-order topology. The prototype is fabricated in 28-nm bulk CMOS and is clocked at 1.7 GHz. With a bandwidth of 85 MHz, the analog-to-digital converter achieves 0-dB peaking STF, 74.4-dB signal to noise and SNDR and 87.5-dB spuriousfree dynamic range, while consuming 61.8-mW power, resulting in an excellent Schreier Figure-of-Merit (FoM S ) of 165.8 dB. Index Terms-2 b/cycle asynchronous successiveapproximation-register (ASAR), continuous-time (CT) analog-to-digital converter (ADC), flat signal transfer function (STF), noise-shaping (NS) QTZ, on-chip digital-to-analog converter (DAC) calibration, out-of-band blocker (OBB). I. INTRODUCTIONT HE ever more crowded radio spectrum causes great challenges to the design of wireless communication systems, in terms of increasing signal bandwidth (BW) as well as spectral performance. This makes continuous-time (CT) analog-to-digital converters (ADCs) more attractive for use in wireless applications due to their high dynamic range (DR), good power efficiency and implicit anti-aliasing property [1]-[3]. Fig. 1 shows the received spectrum at the antenna of the long-term-evolution advanced (LTE-A) standard [2], [4], [5]. For an inter-band contiguous carrier Manuscript

VCO-ADCs with a Quadrature Band-Pass Noise-Transfer-Function

“…Therefore, the front-end ADC must deal with out-of-band power, which supposes, firstly, possible saturation of the ADC and, secondly, aliasing of the blockers within the band of interest. Continuous-time Σ∆ modulators are robust against this phenomenon due to their inherent anti-aliasing filtering and the possibility of designing appropriate signal-transfer-functions to remove blockers [109]. Nevertheless, analog integrators and quantizers are needed, so the digital nature we are seeking is partially hidden.…”

“…As an application example, we are supposing that we have to deal with three out-of-band components at f 1 = 60 MHz, f 2 = 70 MHz and f 3 = 90 MHz (e.g. LTE-A standard [109]) for an application bandwidth of 60 MHz. The required pulse shaping filter h(t) to remove those blockers may result from the convolution of three square pulses (first-order sinc functions) of width T 1 = 1/f 1 , T 2 = 1/f 2 , and T 3 = 1/f 3 , respectively.…”