A Fully-Dynamic kT/C-Noise-Canceled SAR ADC with Trimming-Free Dynamic Amplifier

Nowadays, SAR ADC is popular due to the high energy efficiency. However, in high-resolution applications, the power and area are too large as the kT/C-noise requirement leads to a huge capacitive DAC. To solve this issue, several techniques to cancel the kT/C noise have been reported in 1 –3. Among them, 1–2 use an amplifier with static current to cancel the kT/C noise. Despite its effectiveness, it wastes much energy in low-duty-cycle circumstances (low sampling rate), since the static amplifier is always active even when the ADC works in the tracking mode. This static amplifier cannot be disabled to save power, since the static amplifier wakes up slowly and it is unknown when the next sampling instance will come, i.e., in event driven applications. Also, in some commercial ADC products, such as AD7982 4, it is a significant consideration to have no static current in the tracking mode, and their fully-dynamic operation is highlighted as an important feature. To realize dynamic operation, 3 proposes a fully-dynamic kT/C-noise cancellation in a noise-shaping SAR. Nevertheless, it requires an accurate gain of dynamic amplifier to cancel the kT/C noise. This leads to an extra trimming during test, which increases the cost severely for commercial products.