Analog Signal Processing in CMOS Technology

Analog signal processing in complementary metal–oxide–semiconductor (CMOS) technology underpins a vast array of applications ranging from biomedical sensing and environmental monitoring to wireless communications and industrial instrumentation. At its core, this discipline exploits continuous-time circuits to condition, filter and analyse real-world phenomena without the quantisation inherent to digital conversion. Advances in device scaling and low-voltage design have driven the emergence of compact, power-efficient transconductors, conveyors and oscillators, enabling direct integration of front-end signal-conditioning blocks on digital chips. Key challenges include managing thermal and flicker noise, minimising mismatch and distortion, and maintaining linearity across wide dynamic ranges. Current-mode architectures, employing active elements such as operational transconductance amplifiers (OTAs) and current conveyors, have gained prominence for their bandwidth, simplicity and amenability to low-voltage operation. Meanwhile, voltage-mode filters and biquadratic sections continue to evolve towards electronically tunable, resistor-less topologies. These developments are complemented by novel quadrature oscillators and adaptive feedback schemes that facilitate on-chip frequency synthesis and phase-sensitive detection. Collectively, CMOS-based analog processing techniques are pivotal for next-generation smart sensors, low-power wearable devices and mixed-signal SoCs.

Research from Nature Portfolio

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Research from all publishers

In the bio-instrumentation domain, current-mode interfaces employing second-generation voltage and current conveyors have been shown to furnish low-noise, high-speed conditioning for electrochemical and optical sensors, yielding improved signal fidelity and reduced power consumption compared with traditional operational-amplifier-based readouts. Another strand of work has introduced sub-1 V, nanowatt multiple-input OTAs to realise fifth-order Butterworth low-pass filters optimised for electrocardiogram acquisition; operation in the subthreshold region affords microwatt-level dissipation and robust PVT (process-voltage-temperature) tolerance. Additionally, analytic synthesis methods have yielded multifunction current-feedback operational-amplifier (CFOA) biquadratic filters and fully uncoupled quadrature oscillators in 0.18 µm CMOS, delivering independent electronic control of resonant frequency and quality factor alongside compact area, low distortion and facile integration.

Analog Signal Processing in CMOS Technology publication trend

The graph below shows the total number of articles in analog signal processing in cmos technology across all publications each year (not limited to Nature Index journals).

Technical terms

CMOS: A semiconductor technology combining p- and n-channel MOS transistors used to implement integrated circuits with low static power.

Operational Transconductance Amplifier (OTA): An amplifier whose differential input voltage controls output current, fundamental for voltage-controlled filters.

Current Conveyor (CCII): A current-mode active building block that transfers current from input to output terminals with high bandwidth.

Second-Generation Voltage Conveyor (VCII): The dual of a CCII providing an easy-to-read output voltage alongside current conveyance.

Quality Factor (Q): A dimensionless parameter indicating the selectivity or sharpness of a resonant filter’s frequency response.

References

1. A Survey on Current-Mode Interfaces for Bio Signals and Sensors. Sensors (2023).
2. 0.5 V Fifth-Order Butterworth Low-Pass Filter Using Multiple-Input OTA for ECG Applications. Sensors (2020).
3. Analytical Synthesis of High-Pass, Band-Pass and Low-Pass Biquadratic Filters and its Quadrature Oscillator Application Using Current-Feedback Operational Amplifiers. IEEE Access (2021).