KEYWORDS: Terahertz radiation, Field effect transistors, Clocks, Sensors, Signal to noise ratio, Antennas, Circuit switching, Signal attenuation, Signal detection, CMOS sensors
A switched-capacitor integrator readout circuit for FET-based terahertz (THz) detectors was fabricated in a 0.13 μm standard CMOS technology. The designed readout circuit is suitable for implementation in pixel arrays due to its compact size and power consumption. In order to find the optimum bias point of the FET detector, responsivity, noise equivalent power (NEP) and signal-to-noise ratio (SNR) curves in function of the FET gate voltage (VG) have been measured for an arbitrary number of 10 accumulation cycles and two different operating clock frequencies. A responsivity peak of 1.8 kV/W was obtained with a clock frequency of 200 kHz, and of 1.3 kV/W at 400 kHz. A minimum NEP of 7.3 nW/√Hz was obtained with a 400 kHz clock frequency, while at 200 kHz the NEP is 8.5 nW/√Hz. The presented THz measurements with 100 accumulation cycles at 200 kHz and 400 kHz clock frequencies show a SNR improvement after each operation cycle, which means 500 and 1000 measurements per second with on-off modulation of the source, respectively. A test structure containing only a FET detector and a bowtie THz antenna was used to evaluate the impact of the readout circuit in the FET THz detection.
In this work an antenna-coupled diode-based microbolometer implemented in a 0.35μm CMOS technology with a low-cost
maskless micromachining post-process is proposed. The device is suspended above the substrate on an oxide
membrane by removing the silicon underneath. It is composed of an antenna connected to a matched load, which heats
up proportionally to the captured electromagnetic radiation, and heat sensing elements. These elements consist of several
series polysilicon diodes placed near the antenna load, while an identical set of diodes is also included as a reference to
track ambient temperature variations.
Theoretical calculations and preliminary temperature characterization of polysilicon diodes have been performed.
Different antenna sizes have been used so as to obtain detectors for 0.5THz, 1.0THz, and 2.0THz frequency operation.
Thanks to the use of a standard CMOS technology, in the same chip a custom designed readout circuit has been
integrated with the objective to maximize the performance of the detectors through signal amplification and filtering.
KEYWORDS: Signal to noise ratio, Sensors, High dynamic range image sensors, High dynamic range imaging, CMOS sensors, Image sensors, Nickel, Image quality, Interference (communication), Quantization
There have been many reports of application-specific or custom designed high dynamic range (HDR) CMOS
image sensors. To achieve their extended dynamic range, these sensors utilize techniques that can
significantly degrade their signal-to-noise ratios (SNR). We utilize a simplified sensor model to compare two
HDR techniques with a conventional APS sensor regarding their SNR and dynamic range (DR). We perform a
new analysis of a mixed APS and time-to-saturation sensor that shows that it can detect similar high
illuminations levels that the multiple capture sensor without degrading the SNR at lower levels. Furthermore,
the time-to-saturation sensor can be adjusted on-the-fly to detect specific illumination levels with optimized
image quality.
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