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A VCO-based MASH delta-sigma ADC architecture is introduced that uses multi-rating of the two stages. The architecture allows for low power and high speed operation and is insensitive to the VCO linearity. To demonstrate this architecture, a prototype consisting of a first-order switched-capacitor (SC) integrator with a 4-bit quantizer operating at 100MHz is followed by a second-stage VCO-based ADC operating at 1.2GHz. The chip is implemented in a 130nm 1P8M CMOS process. The measured SNDR is 77dB for a 4MHz signal bandwidth with a power consumption of 13.8mW from a 1.3V supply. The resulting FoM is 298fJ per conversion.