Abstract
This paper presents a new low-voltage CMOS structure for operational transconductance amplifier (OTA) exploiting the bulk-driven, the self-cascode and the multiple-input transistor techniques (MI). The multiple-input OTA (MIOTA) circuit operates in subthreshold region using 0.5V supply voltage and offers enhanced linearity. The MIOTA is developed for biopotential signal as well as electrocardiogram (ECG) signal processing circuit and it is exploited to design a 5th-order Chebyshev low-pass and 3rd-order band-pass filters with a dynamic range (DR) of 57.6 dB and 60.4 dB, and nanopower consumption of 50 nW and 60 nW, respectively. Due to the electronic tuning of cut-off frequency, the low-pass and band-pass filters are suitable for random noise and motion artifact noise reductions in biopotential signals. The circuits were designed in Cadence environment using the standard N-well <inline-formula> <tex-math notation="LaTeX">$0.18~\mu \text{m}$ </tex-math></inline-formula> TSMC CMOS technology. Intensive post-layout simulation results along with the process, voltage, temperature analysis (PVT) and Monte Carlo (MC) prove the robustness of the design. The chip area of the proposed MIOTA is 0.00725 mm<sup>2</sup> (<inline-formula> <tex-math notation="LaTeX">$118~\mu \text{m}\,\,\times 61.5\,\,\mu \text{m}$ </tex-math></inline-formula>). Compared with standard OTA the MIOTA offers simplification of filter topology and reduced number of active elements. In order to demonstrate these advantages, the MIOTA-based filter was also build using commercially available OTA LT1228. The experimental results of OTA LT1228 confirm both the filter functionality and the advantages of the proposed MIOTA.
Highlights
Nowadays, as people become more health conscious, the growing popularity of wearable devices is the factor to stimulate the transformation toward telehealth
If the multiple-input OTA (MIOTA) would be realized as a connection of n operational transconductance amplifier (OTA), each biased with n-times lower current, such a circuit would have lower dynamic range than the approach based on the input capacitive divider [31]
It is evident that the proposed filters offer the best FOM, less number of active devices, the lowest voltage supply and the best low voltage capability from all others OTA-C based filters [20, 22, 39, 40]
Summary
As people become more health conscious, the growing popularity of wearable devices is the factor to stimulate the transformation toward telehealth. It is worth noting that active devices with multiple-input like OTAs [31,32,33,34,42,43,44,45,46] or multipath dynamic comparators [48, 49] attracted the attention of the integrated circuit designers It is because these devices offer the advantage of arbitrary summing or subtracting the voltage signals at the inputs, allowing topology simplification and reducing the number of used components. The signal flow graph (SFG) is often used to describe the filter design, which allows easy transformation of the equations to particular values of the circuit elements It has been assumed, that the synthesized circuits will operate in a voltage mode and use only multiple-input transconductors and grounded capacitors.
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