This article proposes a new low-impedance transient-current enhanced (LTE) buffer, which is applied for low-dropout regulator (LDO) with large off-chip capacitor. The LTE buffer is based on current-shunt feedback technique and two ac coupling networks, which can achieve an extremely low output impedance and high charging/discharging current of the gate of power transistor at load transient response, while maintaining low-quiescent current consumption under the full-load range. In addition to containing the LTE buffer, the proposed LTE-LDO employs recycling-folded-cascode amplifier as the error amplifier, which has the advantage of high loop gain, loop bandwidth, and current efficiency. Meanwhile, simple Miller compensation with a nulling resistor is employed for frequency compensation and a complete small-signal analysis under different load current conditions is given in this article. This design has been implemented in semiconductor manufacturing international corporation 0.18 $\mu$ m complementary metal–oxide–semiconductor process and the experimental results show that the quiescent current consumption is about 48 $\mu$ A, and the maximum current efficiency of the LTE-LDO is 99.976 $\%$ . The measured transient response shows that under the condition of 1 $\mu$ F load capacitance, when the load current changes to 200 mA/100 ns, the output voltage change is 76 mV.

In this study, a local positive feedback technique is proposed to enhance the performance of the folded cascode (FC) operational transconductance amplifier (OTA) when working in its saturation region. The enhanced FC-OTA has a higher gain bandwidth (GBW), higher DC gain and higher slew rate (SR) over its conventional counterparts and popular recycling FC-OTAs. The proposed enhanced FC-OTA is implemented by reusing the current generated by the input transistors through the proposed local positive feedback loop to provide additional transconductance and negative resistance. It is then fabricated with SMIC 180nm process. To verify the effectiveness of the proposed FC-OTA performance enhancement strategy, extensive mathematical analysis, small-/large-signal stability analysis, simulation and experimentation are thoroughly investigated in this study. Simulation and experimental results agree well with the theoretical analysis and the expected performances, which corroborates the control design.

This letter proposes an ultra-wideband and high-gain antipodal tapered slot antenna (ATSA) with gradient refractive index (GRIN) lens. The GRIN lens consisting six metamaterial lenses is placed in the maximum radiation direction of the ATSA to greatly enhance its radiation capability. We found that the proposed GRIN lens antenna has a wide impedance bandwidth of 175.7% (0.84 - 13 GHz) and -3 dB gain bandwidth of 65.8% (5.86 - 11.6 GHz). Its gain is averagely increased by 4.81 dB in the whole operating band, and the maximum gain reaches 20.55 dBi at 9.5 GHz. The simulation and measured results demonstrate that the designed GRIN lens antenna has excellent performance and is suitable for short-pulse ground penetrating radar systems. It also provides reference for other occasions that require high-gain and wideband antennas.

Adaptive bias scheme, which can be used to provide a current proportional to the current flowing through the power transistor under high current load, avoiding the need for providing additional large fixed bias current to the circuit, has been adopted in many low-dropout regulators (LDO). When an adaptive bias scheme is applied to an LDO with a current mirror buffer, although a low chip area consumption and a better transient response can be achieved, the loop gain of LDO at high-load current and loop bandwidth at low load are still low. In previous works, multiple small-gain stages can effectively improve the gain and bandwidth but may lead to stability problems or even need to consume large currents to ensure stability, thus affecting current efficiency. This article proposes the multiple adaptive current feedbacks technique for small-gain stages in adaptively biased low dropout regulator (AB-LDO) with a current mirror buffer, improving the loop gain and bandwidth and eliminating the need for frequency compensation to meet stability requirements. Moreover, in the case that multiple adaptive bias loops can be introduced after the proposed technique is applied to this design, an intuitive and simple method is adopted to analyze the whole circuit. The designed AB-LDO was fabricated in Semiconductor Manufacturing International Corp (SMIC) 0.18- $\mu$ m process. The measured results show that the designed LDO realizes 30.75-mV transient performances with a step of 10 ns.

A super class‐AB bulk‐driven (BD) operational transconductance amplifier (OTA) with improved slew rate (SR) is presented. The proposed OTA utilises bulk flipped voltage follower for the BD input stage and a nonlinear current mirror for the active load to enhance the SR of conventional BD counterpart. Both the traditional and the proposed OTA, have been simulated on the UMC 180 nm process, and results show that the proposed BD OTA achieves a 350% SR enhancement with only 25% increased power dissipation compared with the conventional one.