A Micropower Chopper CBIA Using DSL-Embedded Input Stage With 0.4 V EO Tolerance for Dry-Electrode Biopotential Recording.

A chopper instrumentation amplifier (IA) dedicated for bio-potential acquisition usually requires a linearized input stage for large electrode offset voltage accommodation. This linearization leads to excessive power consumption when sufficiently low input-referred noise (IRN) is required. We present a current-balance IA (CBIA) without the need for the input stage linearization. It uses two transistors to operate as an input transconductance stage and a dc-servo loop (DSL) at the same time. An off-chip capacitor completes the DSL by ac coupling the source terminals of the input transistors via chopping switches realizing a sub-Hz high-pass cutoff frequency for dc rejection. Fabricated in a 0.35-µm CMOS process, the proposed CBIA occupies 0.41 mm2 and consumes 1.19 µW from a 3 V dc supply. Measurements show that the IA achieves an input-referred noise of 0.91 µVrms over 100 Hz bandwidth. This corresponds to a noise efficiency factor of 2.22. Typical CMRR of 102.1 dB is achieved for zero offset and degraded to 85.9 dB when a ±0.3 V input offset was applied. Gain variation of 0.5% is maintained within the range of ±0.4 V input offset. The resulting performance meets well with the requirement for ECG and EEG recording using dry electrodes. A demonstration for the use of the proposed IA on a human subject is also provided.

A Compact Sub-µW CMOS ECG Amplifier With 57.5-MΩ Zin, 2.02 NEF, 8.16 PEF and 83.24-dB CMRR.

This paper presents a compact DDA-based fully-differential CMOS instrumentation amplifier dedicated for micro-power ECG monitoring. Only eight transistors are employed to realize a power-efficient current-sharing DDA. A RC network (using MOS pseudo resistors and poly capacitors) forms feedback loops around the DDA creating an ac-only amplification. The proposed amplifier is dc-coupled via gate terminals of the p-channel input transistors. It thus achieves sufficiently high input impedance over the entire ECG frequency range. Fabricated in a 0.35-µm CMOS process, the proposed amplifier occupies 0.0712 mm2. It operates from a 2 V dc supply with 336 nA current consumption. Measurements show that the amplifier attains its input impedance of 57.5 MΩ at 150 Hz and achieves 1.54 µVrms input-referred noise over 0.1-300 Hz. Noise and power efficiency factors are 2.02 and 8.16, respectively. At 50 Hz, the mean CMRR of 83.24 dB is obtained from 11-chip measurement. Experiments performed on a human subject confirm the functionality of the proposed amplifier in a real measurement scenario.

Optimization of 3-aminopropyltriethoxysilane functionalization on silicon nitride surface for biomolecule immobilization.

The 3-aminopropyltriethoxysilane (APTES) is a common method for biomolecule immobilization on silicon and silicon derivatives such as silicon nitride (Si3N4). However, there are many parameters which impact the efficiency of APTES modification such as APTES concentration and reaction time. Thus, various APTES concentrations (0.1%, 0.5%, 1%, 2%, 5%, and 10%) under different reaction times (15, 30, 60 and 120 min) were compared to achieve the optimal APTES modification condition which produced a thin and stable APTES layer on Si3N4 surface. The modified surfaces were characterized by contact angle (CA) measurement, Fourier transform infrared (FTIR) spectroscopy and spectroscopic ellipsometry to determine the wetting property, chemical bonding composition and surface thickness, respectively. In addition, biotin was used as a model to determine the effectiveness of APTES modification condition by coupling with glutaraldehyde (GA). The Alexa Flour 488 conjugated streptavidin was performed to visualize the presence of biotin using fluorescence microscopy due to the specifically binding between biotin and streptavidin. The atomic force microscopy (AFM) was utilized to determine the surface topology which was an indicator to demonstrate the agglomeration of APTES molecule. Moreover, ion sensitive field effect transistor (ISFET) was employed as a biosensor model to demonstrate the effect between surface thickness and sensitivity of biosensor. The results show that the APTES thickness is directly correlated to the APTES concentration and reaction time. Since the importance parameter for ISFET measurement is the distance between biomolecule and sensing membrane of ISFET, the thicker APTES layer negatively impacts the sensitivity of ISFET based biosensor because of the ion shielding effect. Therefore, these results would be valuable information for development of Si3N4 biosensor, especially ISFET based biosensor.

A bionics chemical synapse.

Implementation of the current mode CMOS circuit for chemical synapses (AMPA and NMDA receptors) with dynamic change of glutamate as the neurotransmitter input is presented in this paper. Additionally, circuit realisation for receptor GABA(A) and GABA(B) with an electrical signal which symbolises γ-Aminobutyric Acid (GABA) perturbation is introduced. The chemical sensor for glutamate sensing is the modified ISFET with enzyme (glutamate oxidase) immobilisation. The measured results from these biomimetics chemical synapse circuits closely match with the simulation result from the mathematical model. The total power consumption of the whole chip (four chemical synapse circuits and all auxiliary circuits) is 168.3 µW. The total chip area is 3 mm(2) in 0.35-µm AMS CMOS technology.