Praveen Varma Nadimpalli

CMOS fast-settling time low pass filter associated with voltage reference and current limiter for low dropout regulator

In this work, a fast turn-on settling low dropout regulator (LDO) with current limiter is presented. Dynamically operating the proposed current limiter using a decent current comparator protects the IC from any damage when an overload condition occurs or the output of the regulator is shorted. A novel low pass filter associated with voltage reference circuit, which provides highly filtered reference voltage and fast settling time, is implemented to minimize output noise due to voltage reference noise. The LDO with proposed low pass filter and current limiter has been implemented in a 0.6µm n-well CMOS process. The LDO dissipates 65µA quiescent current at 150mA full load condition and its output noise is 407.8nV/√Hz at 100Hz. Turn-on settling time of the LDO is 45µsec and threshold current of the current limiter is set to 230mA of output load current.

RF induced communication errors in RFFE MIPI controlled Power Amplifiers

As the number of RF components increases inside mobile devices, the industry has rapidly adopted and utilized MIPIs RFFE serial bus specification [1] to communicate with these devices and reduce the amount of control line routing between components. However, the use of a serial bus within the RF front end increases the risk that RF energy, particularly from the Power Amplifier (PA), can corrupt the RFFE bus communication. RF coupling to areas such as the RFFE serial clock (SCLK) signal seen within the PAs RFFE state machine can result in communication errors with the PA. This coupling can be to the SCLK signal itself, or to the PAs CMOS controllers ground reference. PA designers must pay special attention to the positioning and design of the CMOS controller and the internal routing of signals to the controller to avoid these problems. This paper provides a detailed analysis of how RF energy coupling to the internal CMOS controller can create “glitches” on the SCLK signal that cause communication errors. A simple example is provided to illustrate how choices in PA module layout can significantly impact these issues. A natural extension of these concepts applies to phone or radio board layouts, too.

A fast transient response shunt low dropout regulator

In this paper, the proposed shunt regulator is presented. Compared with a series voltage regulator, the shunt voltage regulator gives wideband power supply rejection (PSR) and fast transient response at the expense of large quiescent current. In this paper, a novel shunt regulator architecture is proposed to achieve the genuine characteristic of a shunt regulator with small quiescent current. The proposed shunt regulator transient response is 3.98μsec over full load current rising step and it is at least 3.5 times faster than series regulator. PSR characteristic of the proposed shunt regulator shows −22.4 dB up to 200 kHz.