A 12-bit 1.25MS/s cyclic analog-to-digital converter (ADC) is designed and fabricated in 90nm CMOS technology, and only occupies an active area as small as 0.037mm². The proposed ADC is composed of a non-binary AD convertion stage, and a on-chip non-binary-to-binary digital block includes a built-in radix-value self-estimation scheme. Therefore, althouh a non-binary convertion architechture is adopted, the proposed ADC is the same as other stand-alone binary ADCs. The redundancy of non-binary 1-bit/step architecture relaxes the accuracy requirement on analog components of ADC. As a result, the implementation of analog circuits such as amplifier and comparator becomes simple, and high-density Metal-Oxide-Metal (MOM) capacitors can be used to achieve a small chip area. Furthermore, the novel radix-value self-estimation technique can be realized by only simple logic circuits without any extra analog input, so that the total active area of ADC is dramatically reduced. The prototype ADC achieves a measured peak signal-to-noise-and-distortion-ratio (SNDR) of 62.3dB using a poor DC gain amplifier as low as 45dB and MOM capacitors without any careful layout techniques to improve the capacitor matching. The proposed ADC dissipated 490µW in analog circuits at 1.4V power supply and 1.25Msps (20MHz clocking). The measured DNL is +0.94/-0.71LSB and INL is +1.9/-1.2LSB at 30kHz sinusoidal input.