Low-power high-performance NS-SAR-based front-ends for biomedical applications

Abstract

Recently, various biomedical research has been widely conducted. A low-power, high-performance analog front end is required in most biomedical applications. We present three analog front-end types by using noise-shaping SAR (NS-SAR) ADC. Each analog front end has been applied to an ultrasound capsule endoscope, a neural recording system, and a bio-signal acquisition system. First, ultrasound imaging is widely used for diagnosing patients because it can obtain biocompatible images at a low cost. Due to the miniaturization of ultrasound transducers, they have recently been applied to various fields, such as catheters and endoscopes. Recently, research on ultrasound capsule endoscopy has gotten attention. Unlike conventional video images, ultrasound capsule endoscopy has the advantage of obtaining images of the subsurface tissues and being easy for patients to swallow because of its small size. This paper presents a 20 MHz receiver circuit and on-chip transmitter for an ultrasound capsule endoscopy. The integrated circuit was fabricated on a 0.18 μm BCD process and consumed 2.3 mW in the receiver. Electrical stimulation of the brain has been widely used to treat patients with psychological disorders such as Parkinson’s disease, epilepsy, essential tremor, and depression. For more effective treatments, closed loop neuromodulation has been developed to operate with feedback information obtained by monitoring associated neural signals. However, in this closed-loop system, when the recording and stimulation regions are close to each other, incurring undesired artifacts in the recording signals. In order to obtain brain neural signals even with disturbances caused by stimulation artifacts, low power and high dynamic range NS-SAR ADC and low amplification analog front end are combined. The integrated circuit was fabricated on a 0.18 μm rf process and achieved the maximum FoM on a 0.18 μm process. Finally, research on systems that record other bio-signals is being conducted in addition to brain neural signals. As the interest in health care using bio-signals increases and the wearable device market grows, bio-signal recording technology is applied to various wearable devices. In this work, we propose a noise-shaping SAR ADC based on a delta-sigma modulator (DSM) structure that has a high input impedance while reducing circuit noise and broadening the input signal range compared to previous works. In addition, we proposed a new truncation error-shaping technique that utilizes the NS-SAR ADC. The integrated circuit was fabricated on a 65 nm process and achieved maximum input signal range and SNDR results. The input impedance was amplified without using an additional amplifier.