A 14-bit 12 μV/LSB resolution A/D converter for sensors using only digital circuit with low-pass filter effect

A compact, high-resolution A/D converter (ADC) for sensors is presented. The basic structure is a completely digital circuit including a ring-delay line with delay units (DUs), along with a frequency counter, latch and encoder. The operating principles are, firstly, the delay time of the DU is modulated by the A/D conversion voltage; secondly, the delay pulse passes through a number of DUs within a sampling time, and the number of DUs through which the delay pulse passes is output as conversion data, Compact size and high resolution were realized with an ADC having a circuit area of 0.45 mm(2) (0.8 mum CMOS) and a resolution of 12 muV (10 kHz). Sample holds are unnecessary, and a low-pass filter function eliminates high-frequency noise simultaneously with A/D conversion. This ADC can be shrunk and operated at low voltage, so it is an ideal means to lower the cost and power consumption.