The bidirectional neural interface is essential to realize the closed-loop neuromodulation, which is the core of next-generation neurological devices. For the bidirectional neural interface, a recording circuit with a high dynamic range (DR) is required to record the neural signal while stimulating the neuronal cells simultaneously. This article presents a voltage-controlled oscillator (VCO)-based neural-recording IC, which directly quantizes the input signal and achieves a large DR to process the small-amplitude neural signal in the presence of the large-amplitude stimulation artifact (SA). A feedback-controlled source degeneration is applied to the input transconductor circuit (Gm, in) by using a resistor digital-to-analog converter (R-DAC). It mitigates the circuit nonlinearity, resulting in a large signal-to-noise-and-distortion ratio (SNDR) and a high input impedance (Zin). The implemented neural-recording IC achieves 81.3-dB SNDR over 200-Hz signal bandwidth and 200-mVpp maximum allowable input range with consuming 3.9 μW per channel. The in-vitro measurement with prerecorded neural signal demonstrates that the original neural signal is well preserved in the presence of the large-amplitude artifact without any saturation or significant distortion.

Radiation sensor interface circuits can be mounted on sensor nodes in wireless sensor networks to detect radiation signals. They respond quickly to operators and command centers, allowing appropriate decisions to be made to mitigate nuclear power plant accidents. For instance, high-level radiation leaked from a reactor building during a nuclear plant accident can degrade the performance of the radiation sensor interface implemented by integrated circuits due to threshold voltage shift, leakage current change, and noise increase induced by radiation impact events. To obtain reliable signal measurements in the high radiation environment, radiation-hardening technologies must be applied to radiation sensor interface circuits. The radiation-hardened sensor interface circuit proposed in this article exploits a pair of charge-sensitive amplifiers (CSAs) in dual paths to equivalently cancel out the distorted output signals caused by radiation impacts on the circuits. In addition, a low-power, fully differential successive approximation register (SAR) analog-to-digital converter (ADC) is used to reduce the radiation effects by subtracting the radiation-induced noise of one input from the other. The implemented radiation sensor interface circuit can maintain its performance up to 1.0 mrad (SiO ₂ ) of irradiation with only 2.5 mW power consumption, while successfully sensing and transferring the radiation information to the downstream signal-processing network.

This paper presents a comprehensive design tutorial for four types of single-stage operational transconductance amplifiers (OTAs): (1) five-transistor OTAs, (2) telescopic cascode OTAs, (3) folded cascode OTAs, and (4) current mirror OTAs. These OTAs serve as fundamental building blocks in analog circuits. The operational principles of each OTA are reviewed, and the key performance metrics are derived through a hand analysis. These performance metrics encompass most crucial parameters, including small-signal parameters, frequency response, input and output swing ranges, rising and falling slew rates, nonidealities, and bias circuit simplicity. All of these metrics are verified and compared using the simulation. Furthermore, the practical applications of each OTA are summarized, and a case study demonstrates the enhancement of a neural recording amplifier’s performance through appropriate OTA selection. A thorough review of the essential building blocks will become a stepping stone to design high-performance analog amplifiers across diverse applications.

The capacitively coupled instrumentation amplifier (CCIA) is broadly used for neural signal acquisition. Although it is suitable for various biopotential recording applications, the CCIA is vulnerable to capacitor mismatches, which degrades the common-mode rejection ratio (CMRR). The neural signals with small amplitude can be easily contaminated by large-amplitude common-mode (CM) interferences due to the degraded CMRR. This paper presents a CMRR enhancement circuit for the CCIA, with which the capacitor mismatches can be compensated in a power-efficient manner. In the proposed CCIA, the gains of a pair of output stages are controlled separately to reject the output signals generated by the CM interferers in the presence of capacitor mismatches. Employing the proposed CMRR enhancement scheme, the implemented CCIA achieves a CMRR over 90 dB from 10 Hz to 1 kHz and 3.4-μVrms integrated input-referred noise (IRN) while only consuming 1.5 μW per channel.

Radiation sensor interfaces for battery-powered mobile dosimeters must consume low power to monitor the amount of radiation exposure over a long period. This paper proposes a power-efficient radiation sensor interface using a peak-triggered sampling scheme. Since the peak of the analog-to-digital converter’s (ADC’s) input represents radiation energy, our ADC only operates around the peak value thanks to the proposed sampling scheme. Although our ADC operates with a high sampling frequency, this proposed sampling scheme reduces the power consumption of the sensor interface because of the reduced operation time of the ADC. Our sensor interface does not have signal distortion caused by a conventional shaper because the interface quantizes the peak value using the high sampling frequency instead of the shaper. When the radiation input occurs once every 10 μs, the power consumption of the ADC with the proposed sampling scheme is only about 21.5% of the ADC’s power consumption when the ADC continuously operates. In this worst case, the fabricated radiation sensor interface in a 0.18-μm complementary metal-oxide-semiconductor (CMOS) process consumes only 1.11 mW.