US Patent 7425915 Frequency modulation based flash ADC

An analog-to-digital converter converts a frequency-modulated signal into a digital signal. The frequency-modulated signal is supplied to multiple comparators, such as low-pass filters, which determine whether the signal falls within their frequency ranges. The outputs of the comparators are converted into a digital output signal, e.g., by fat-tree encoding. Each comparator has a differently tuned capacitive load to cause a phase delay in the input signal. When the phase-delayed and non-phase-delayed signals are supplied to a D-Flop, the phase delay is determined by whether the latch conditions are met.