Low-power Instrumentation Amplifier Research Articles

Improvement of Gain Accuracy and CMRR of Low Power Instrumentation Amplifier Using High Gain Operational Amplifiers

Background: Sensing of biomedical signals is crucial for monitoring of various health conditions. These signals have a very low amplitude (in μV) and a small frequency range (<500 Hz). In the presence of various common-mode interferences, biomedical signals are difficult to detect. Instrumentation amplifiers (INAs) are usually preferred to detect these signals due to their high commonmode rejection ratio (CMRR). Gain accuracy and CMRR are two important parameters associated with any INA. This article, therefore, focuses on the improvement of the gain accuracy and CMRR of a low power INA topology. Objective: The objective of this article is to achieve high gain accuracy and CMRR of low power INA by having high gain operational amplifiers (Op-Amps), which are the building blocks of the INAs. Methods: For the implementation of the Op-Amps and the INAs, the Cadence Virtuoso tool was used. All the designs and implementation were realized in 0.18 μm CMOS technology. Results: Three different Op-Amp topologies namely single-stage differential Op-Amp, folded cascode Op-Amp, and multi-stage Op-Amp were implemented. Using these Op-Amp topologies separately, three Op-Amp-based INAs were realized and compared. The INA designed using the high gain multistage Op-Amp topology of low-frequency gain of 123.89 dB achieves a CMRR of 164.1 dB, with the INA’s gain accuracy as good as 99%, which is the best when compared to the other two INAs realized using the other two Op-Amp topologies implemented. Conclusion: Using very high gain Op-Amps as the building blocks of the INA improves the gain accuracy of the INA and enhances the CMRR of the INA. The three Op-Amp-based INA designed with the multi-stage Op-Amps shows state-of-the-art characteristics as its gain accuracy is 99% and CMRR is as high as 164.1 dB. The power consumed by this INA is 29.25 μW by operating on a power supply of ±0.9V. This makes this INA highly suitable for low power measurement applications.

Low-power Bulk-driven Subthreshold OTA and CCII+ Cells based Instrumentation Amplifier for LF Applications

This paper at onset describes a low-power, bulk-driven, folded cascode (FC-OTA) and second generation positive current conveyor (CCII+) operating in weak inversion region with ± 0.35 V DC bias supply. The designed 2 or 3 numbers of CCII+ cells are utilized to compose an instrumentation amplifier (IA), which dissipates a total power of 3.847 µW or 5.768 µW. The OTA cell as the input core in CCII+ circuitry consumes a power of 287 nW, whereas the CCII+ cell consumes total power of 1918 nW. The CCII+ cell uses an OTA which is followed by two-CMOS class AB inverters to realize the X and Z terminals of CCII+ cell. Further, these CCII+ cells are utilized to get low power IA usable in analog front ends of DSP processor for amplifying sensed signal with very high-common mode rejection ratio (CMRR) and high-power supply rejection ratio (PSRR). This IA is simulated using tanner EDA tool of version 16.1 in 180 nm n-tub standard CMOS process technology. This IA consumes less power and is usable as variable gain amplifier for low- frequency bio-signal as well as sub-audio frequency range signal processing.

Low power DDA-based instrumentation amplifier for neural recording applications in 65 nm CMOS

The low power instrumentation amplifier (IA) presented in this paper has been designed to be the front-end of an integrated neural recording system, in which common-mode rejection ratio (CMRR), input referred noise and power consumption are critical requirements. The proposed IA topology exploits a differential-difference amplifier (DDA) whose differential output current drives a fully differential, high-resistance, transimpedance stage, with an embedded common-mode feedback loop to increase the CMRR. This stage is followed by a differential-to-single-ended output amplifier. Low-power operation has been achieved by exploiting sub-threshold operation of MOS transistors and adopting a supply voltage of 1 V. Simulation results in a commercial 65 nm CMOS technology show a 1 Hz to 5 kHz bandwidth, a CMRR higher than 120 dB, an input referred noise of 8.1 μVrms and a power consumption of 1.12 μW.

A low-voltage low-power instrumentation amplifier based on supply current sensing technique

In this paper a new low-voltage low-power instrumentation amplifier (IA) is presented. The proposed IA is based on supply current sensing technique where Op-Amps in traditional IA based on this technique are replaced with voltage buffers (VBs). This modification results in a very simplified circuit, robust performance against mismatches and high frequency performance. To reduce the required supply voltage, a low-voltage resistor-based current mirror is used to transfer the input current to the load. The input and output signals are of voltage kind and the proposed IA shows ideal infinite input impedance and a very low output one. PSPICE simulation results, using 0.18 μm TSMC CMOS technology and supply voltage of ±0.9 V, show a 71 dB CMRR and a 85 MHz constant −3 dB bandwidth for differential-mode gain (ranging from 0 dB to 18 dB). The output impedance of the proposed circuit is 1.7 Ω and its power consumption is 770 µW. The method introduced in this paper can also be applied to traditional circuits based on Op-Amp supply current sensing technique.

Wireless Zero-Power Air Quality Electrochemical Sensor Card for Iot Applications

A new business card size very low cost wireless electrochemical sensor device for use with smartphones and connection to the IoT has been developed. The gas sensor platform uses amperometric gas sensors, AGS, herein demonstrated for CO but easily expanded to many other important airborne contaminants. The NFC based communication could revolutionize low cost personal monitoring of environmental air quality. The technology is based on a 2-electrode electrochemical gas sensor, and can be adapted to a 3-electrode configuration as well. The platform is adaptable to other electrochemically active gases including but not limited to formaldehyde, H2, H2S, alcohol, NO2, CL2, O3 or SO2. The application enables NFC equipped mobile phones and devices to communicate wirelessly with the sensor on demand. The phone app NFC provides all the power necessary to read the signal from the sensor and communicate the data to the smartphone. In this configuration the sensor needs no warm-up or stabilization time and has no need for a battery or power supply. By tailoring the electro-chemistry of the sensor, a zero external bias can be used and still maintain an effective response to the target analyte. For instance, testing has been performed using composite printed Pt electrodes and an aqueous electrolyte, packaged in a small cell (roughly 15mm x 15mm x 3.8mm). Properties such as stability and linearity have been studied and will yield a device with years of service in indoor, outdoor and workplace environments. A lower detection limit of about 200 ppb CO has been achieved making ambient air quality monitoring possible as well as CO alarms. We envision that this platform will be useful for many types of AGSs with differing electrode and electrolyte configurations for other gases. The sensor module’s electronics consist of a few passive components, an NFC communications chip with analog or digital inputs, and a low power instrumentation amplifier. With modern flexible electronics, and engineered antennae, the device can be reduced in size for embedding into just about anything. Including a printed battery enables the device to log in real time, and allows for a 3 electrode sensor configuration in a postage stamp size. Combining techniques such as screen printing of electrodes and electronics, reel to reel manufacturing, and conformal packaging, the cost to produce a complete gas detector can be less than a dollar each! This new capability allows widespread use in studies from environmental air quality to personal health and asset protection. Figure 1

Ultralow-Power Bioimpedance IC With Intermediate Frequency Shifting Chopper

A bioelectrical impedance IC with an intermediate frequency shifting chopper (IFSC) technique driven by a merged clock is presented. The proposed technique enables high-frequency impedance measurements with a narrow bandwidth low-power instrumentation amplifier (IA). The conventional series-connected double choppers required for the frequency shifting operation are replaced with a single chopper driven by a XNOR-merged clock. The proposed IC can measure bioelectrical impedance at a maximum excitation frequency of 1.24 MHz in an IA bandwidth of only 30 kHz. A DC trimming technique that uses a dummy impedance and anti-phase current source can adjust the output offset and prevent output saturation. This DC trimming technique also enables shifting of the impedance measurement scope. The proposed IC is fabricated using 0.13- $\mu \text{m}$ CMOS process, and is shown to achieve a dynamic range of 97.1 dB, and 52 $\mu \text{W}$ of power consumption.

Low-Power Instrumentation Amplifier IC Design for ECG System Applications

This paper describes the development of a low-power instrumentation amplifier (IA) intended for use in recording of the human electrocardiogram (ECG). With the wide-swing cascade bias circuit design, the IA realizes a very high power-supply rejection ratio (PSRR), and can be operated at signal supply voltage in the rage between 2.5 and 5.5 V. It was fabricated using 0.5um double-poly triple-metal CMOS technology, and occupies a die area of 0.2mm2.The amplifier provides a gain of 40 dB and has high common-mode rejection ration (CMRR) better than 100 dB. The IA has a power consumption of 160uW operating from a 3.3 V power supply.