A Multi-GHz Inverter-Based ASDM With Distortion Cancellation

This brief proposes and demonstrates an asynchronous sigma-delta modulator (ASDM) which is based entirely on pseudo-digital inverters. To achieve multi-GHz operation, the proposed ASDM employs a delay-based approach, with a quantizer consisting of a cascade of pseudo-differential inverters. The loop filter is a Gm-RC low-pass filter with a Nauta transconductor 1, which consists of two input inverter pairs loaded by a self-coupled and cross-coupled inverter pair. By suitably sizing the loop filter, the non-linearity of the quantizer compensates the non-linearity of the transconductor. Fabricated in 28nm CMOS, the prototype oscillates at 6.9 GHz, achieving an SNDR of 46.5 dB and a dynamic range of 56.6 dB over a 500MHz bandwidth. The prototype occupies an area of 58 (μm)2, and consumes a power of 2.6mW from a 0.9V supply.