We investigate the light-current-voltage characteristics and emission spectra of 2.3 THz quantum cascade laser operating in the negative differential resistance (NDR) region. It was shown that the formation of electric field domains (EFDs) leads to a large number of discontinuities on the current-voltage and the total optical power on current characteristics. Measurements of emission spectra at different current (before the NDR region and in the NDR region) shows that the formation of EFDs results in decrease of the output intensity, but does not influence on Fabry-Perot multi-mode structure of THz QCL. The developed theoretical model predicts the formation of EFDs in the NDR region and qualitatively explain the experimental results.

A low power regenerative comparator is very useful in Successive Approximation Register (SAR) type Analog to Digital Converter (ADC) for a Wireless Sensor Node (WSN). A regenerative type comparator generates output pulses by comparing input with a reference input. This paper deals with control of a power with an adjustable duty cycle. The regenerative comparator with an adjustable duty cycle and a positive feedback of a latch will help in improving accuracy, speed and also in achieving the less power consumption. The optimum value of a duty cycle is determined with metastability timing constraints. The proposed low power regenerative comparator circuit is designed and simulated by using TSMC 180 nm CMOS technology. The comparator consumes power as low as 298.54 nW with a regenerative time 264 ps at 1 V power supply.