Uncertainty of asynchronous analog-to-digital converter output state

The fundamental difference between the classical signal value quantization and the quantization of the asynchronous time intervals is that there is only one quantization noise component in the former instead of two independent components in the latter. The quantization of a given time interval may result in two different values of a digital code depending on the phase of the reference clock in relation to the beginning of the discretized time interval. The problem of uncertainty of state on the output of asynchronous analog-to-digital converter (A-ADC) is illustrated and analyzed in the paper. It is shown that the noise introduced by the clock-based quantization in A-ADCs is 3 dB higher than that in the conventional ADCs. As a result, the resolution of the A-ADC is a half bit worse than the resolution of the classical ADC with the signal value quantization. The time quantization of the asynchronous time interval may be modeled by random rounding operation. The advantages and disadvantages of clock-based asynchronous time quantization is discussed in details.