CMOS Capacitive Fingerprint Sensor Based on Differential Sensing Circuit with Noise Cancellation

Abstract

In this paper, we introduce a differential sensing technique for CMOS capacitive fingerprint detection. It employs a new capacitive-sensing cell structure with charge sharing detection and readout circuit. The proposed technique also can eliminate the effect of parasitic capacitances by employing parasitic insensitive switched-capacitor structure and so increases the sensitivity even under severe noisy conditions. It can also overcome the performance degradation caused by various conditions of finger surface by using a differential integrator and adjusting its number of integrations. In addition, the proposed architecture allows parallel detection of all sensing channels. It can, therefore, substantially speed up the detection process compared with conventional architectures. We implemented a prototype fingerprint sensor chip with an array of 20 × 16 sensor cells using a 130 nm CMOS process. Simulation experiments demonstrated that the proposed architecture provided an SNR gain of 54 dB, whereas a conventional single line sensing gives an SNR gain of only 13 dB.

Three-Dimensional Conductive Fingerprint Phantoms Made of Ethylene-Vinyl Acetate/Graphene Nanocomposite for Evaluating Smartphone Scanners

“…For capacitive scanning, both the conductivity and permittivity of the target (finger or phantom) are critical; conductivity is required for charge to flow during charging and discharging, whereas the permittivity of a material determines how much it is polarized by the electric field of the scanner. , The parasitic capacitance between the scanner and target is also inversely correlated with the distance, which facilitates the differentiation of feature (ridge) heights. The conductivity of EVA-G phantoms is 1.2 ± 0.1 × 10 –3 S/m, and the complex permittivity is 42 ± 4; both are about an order of magnitude lower than that of dry human skin (2.0–2.5 × 10 –2 S/m, and 550–1100 respectively) .…”

Monitoring of pulse signals with flexible paper-based graphene sensor

“…Energy storage bypass circuit ( shown in Fig. 2(a)) was designed with a capacitor of 0.1 μF is connected between the power supply and ground [14] to stabilize the supply voltage and enhance the signal stability by bypassing the AC noise.…”

Fingerprint Systems: Sensors, Image Acquisition, Interoperability and Challenges

“…The capacitive sensing technique is widely preferred in mobile and Internet of Things (IOT) applications due to the light weight, less power usage, reasonable cost-effectiveness, and convenience of embedding in the present applications [ 56 , 57 , 58 ]. There are several small and low-cost capacitive sensors identified in the literature [ 57 , 59 , 60 , 61 , 62 , 63 , 64 ]. However, most of the existing work experience the issues of finger sensitivity for wet and dry conditions and noisy environment.…”

“…A lot of research has explored integrating the fingerprint sensor in the mobile display and improving the stand-alone fingerprint sensing [ 57 ]. The research team [ 49 , 50 , 51 ] exploited on-display mutual capacitance to produce a prototype with finger-capture feature in mobile devices.…”