VCO based Nyquist-rate ADC with F_VCO of F_s/2

Relentless pursuit of Moore's law, while providing immense speed, power, and cost benefits in digital circuits, has thrown open many challenges in analog circuit design, especially analog-to-digital converter (ADC) design. Present day ADC's must be able to achieve an extremely high level of performance in terms of both resolution and bandwidth. High-resolution and high-bandwidth input modulated parallel ΔΣ-ADCs have been proposed earlier [1]. However, the large size of a conventional ΔΣ-ADC severely constrains the amount of parallelism. Voltage Controlled Oscillator (VCO) based 1^st-order noise-shaped ADCs being mostly digital in nature can exploit the scaling trend and can therefore be realized in a small area. Thus, using VCO based 1^st-order noise-shaping, a large amount of parallelism can be achieved to enable the design of high-resolution, high-bandwidth ADCs. This work provides an intuitive explanation of input modulated parallel ADCs and proposes a 32-channel VCO based ADC operating at a sampling rate, Fs, of 200 MHz and achieving an SNR of 65-dB, with the VCOs in each channel oscillating at a meagre frequency, F_vco = F_s/2 = 100 MHz.