This article presents a dual-loop noise-coupling (NC)-assisted continuous-time (CT) sturdy multistage noise-shaping (SMASH) Δ Σ modulator (DSM), employing 1.5-bit/4-bit quantizers. The proposed SMASH can equivalently work as an overall fourth-order DSM with 4-bit internal quantization. The NC applied in this CT SMASH DSM whitens the 1.5-bit quantization noise (QN) and further reduces its in-band tone power, while a finite-impulse response (FIR) filter integrated into the outermost feedback path suppresses the out-of-band (OOB) noise power of the multibit digital-to-analog converter (DAC) input. Together, they avoid any linearization technique for the multibit DAC. Sampled at 1.2 GHz, the 28-nm CMOS experimental prototype measures a signal-to-noise-and-distortion ratio (SNDR) of 76.6 dB and a spurious-free dynamic range (SFDR) of 87.9 dB over a 50-MHz bandwidth (BW), consuming 29.2 mW from 1.2-V/1.5-V supplies and occupying an active area of 0.085 mm. It exhibits a Schreier figure-of-merit (FoM) (SNDR) of 168.9 dB.