A 12-b 18-GS/s RF Sampling ADC With an Integrated Wideband Track-and-Hold Amplifier and Background Calibration

We discuss a 12-b 18-GS/s analog-to-digital converter (ADC) implemented in 16-nm FinFET process. The ADC is composed of an integrated high-speed track-and-hold amplifier (THA) driving up to eight interleaved pipeline ADCs that employ open-loop inter-stage amplifiers. Up to 10 GS/s, the THA operates at the full sampling rate using a non-interleaved single sample network, thereby eliminating the interleaving sampling time and bandwidth mismatch. Above 10 GS/s, the THA is programmed to use two ping-ponged, or an optional (2 + 1) randomized, sample networks to spread the residual post-calibration interleaving spurs in the noise floor. The THA enables an input bandwidth of 18 GHz and employs dither injection and optional pseudorandom chopping. In the pipeline stages, dither-based background calibration detects and corrects gain, settling, memory, and kick-back errors. New dither-based background calibration algorithms are employed to detect and correct the arbitrary non-linearity in the form of integral non-linearity (INL) breaks and harmonic distortion up to the fifth order in the THA and in the references, DACs, and inter-stage open-loop amplifiers of the pipeline ADCs. Moreover, new dither-based background calibration is implemented to detect and correct the chopping non-idealities, memory errors, interleaving mismatches, and order-dependent randomization errors. Compared to the fastest state-of-the-art with similar performance, this ADC achieves 80% higher sample rate and 2.4× higher input bandwidth, and incorporates a THA that supports a 3.3× higher non-interleaved sample rate.

I. Introduction

Analog-to-digital converters (ADCs) with high sample rate, high input bandwidth, and low power consumption are needed in communication, instrumentation, and other applications to enable direct RF sampling, more integration, greater flexibility, and lower cost. By removing the mixers of heterodyne and homodyne receivers and positioning the ADC closer to the antenna, the RF signal can be directly digitized, which moves the majority of the signal processing to the digital domain. Moreover, supporting a Nyquist bandwidth that is greater than 8 GHz enables the whole signal band of interest in many applications to be in a single Nyquist zone, thereby eliminating the need for complicated anti-aliasing filtering and frequency planning.