Sixth‐order differential Sallen‐and‐Key switched capacitor LPF using a‐IGZO TFTs

Abstract

This paper presents sixth-order fully differential active low pass RC and switched-capacitor (SC) filters using N-type IGZO thin-film transistors for flexible wearable continuous health monitoring systems. As a first step, a low-gain amplifier using a diode-connected load and a fully differential amplifier is designed with positive feedback based on capacitor bootstrapping. These amplifiers present a gain around 5.03 and 40 dB, respectively, whereas their respective GBW product are around 450 and 200 kHz. Then these amplifiers are employed to realize biquads, with which a sixth-order Sallen-Key lowpass RC and SC filters are implemented. The SC filter realized with low-gain DDA has shown a simulated THD of −30.9 dB, SFDR of 30.1 dB, and a power consumption of 456 μW. On the other hand, the SC filter presents a THD of −31.4 dB, SFDR of 32.2 dB, and a power consumption of 573 μW with highgain differential difference amplifier (DDA) when a power supply of 10 V is used. Circuit simulations have been carried out in Cadence Virtuoso using in-house IGZO TFT models. KEYWORDSactive RC filters, differential amplifier and health monitoring system, IGZO TFT, switched capacitor filters 1 | INRODUCTION Continuous health monitoring of post hospitalized cardiac patients is vital. In present scenario, most of the cardio vascular system activities are being monitored using ECG and BP measurements using cuffs, which limit the mobility of the patients and need human interaction. Nevertheless, few wearable devices were reported with standard CMOS technology, 1-4 where these systems are bulky (due to the battery weight), rigid, and expensive. In order to get rid of these drawbacks and to guarantee user comfort, biomedical self-contained wearable systems implemented with low-cost flexible electronics would be a perfect solution, where circuits can be driven by printed batteries. 5,6 Among other semiconductor technologies (a-Si: H TFT and organic TFT) that allow flexible electronics due to compatibility with low-temperature fabrication (≥150°C), 7,8 amorphous indium gallium zinc oxide thin-film transistors

Mostly Passive Δ - Σ ADC with a-IGZO TFTs for Flexible Electronics

“…Because of which, CMOS circuit techniques cannot be adapted directly and new design techniques need to be investigated. Till date many a-IGZO TFT based circuits have been reported on flexible substrates such as amplifiers [11], [12], [13], ring oscillators [14], filters [15], bootstrapping circuit [5] and rectifiers [16]. The work done towards analog-to-digital Converters (ADCs) with oxide TFTs is very limited, though they are critical functional blocks to implement systems of practical importance.…”

Positive‐negative DC‐DC converter using amorphous‐InGaZnO TFTs

“…However, these converters need to be designed using only n-type transistors due to a lack of stable p-type transistors with oxide semiconductors. 4 Many works report on amplifiers, 5,6 data converters, 7,8 filters, 9 and other circuits 10,11 with a-IGZO TFTs. Nevertheless, the work done on DC-DC converters, with this technology, is limited.…”

An AMOLED Pixel Circuit Based on LTPS Thin-film Transistors with Mono-Type Scanning Driving

“…Although different AMOLED backplane solutions have been discussed over the past decades [3,4], for state-of-the-art AMOLED displays, low-temperature poly-silicon thin-film transistors (LTPS TFTs) show better performance. Compared with other types of TFTs, LTPS TFTs exhibit higher mobility and better stability in terms of electrical characteristics [5,6]. However, the drawbacks of LTPS TFTs lie in the obvious variations in the threshold voltage (V TH ) and mobility [7,8], which hinder the implementation of high-quality AMOLEDs with uniform display for larger dimensions.…”