A chip-area efficient capacitor-less CMOS LDO with active feedback and damping zero compensation

A chip-area efficient capacitor-less low-dropout regulator for on chip application with active feedback and damping-zero compensation to minimize compensation capacitance and slew-rate enhancement circuit to speed up transient response is presented in this paper. The idea has been modeled and simulated in a standard 0.35μm CMOS process. From simulated results, the implemented regulator can operate from supply voltage of 2.4V to 3.3V with a minimum dropout voltage of 0.2V at maximum load current of 100mA. With I_Q of about 30μA, the regulator only needs a small total on-chip compensation capacitance of 1.5pF. © 2010 IEEE

Comparative studies of common fix-frequency controls for reference tracking and enhancement by end-point prediction

This paper analyzes the dynamics of reference tracking in switched-mode power converters in terms of both large-signal and small-signal perspectives. Common control schemes, namely, voltage mode, current mode, and V ²-control, are compared for their performance in reference tracking. For small-signal analysis, loop gains and reference-to-output transfer functions are analytically derived and verified by the proposed Matlab-based frequency response simulator. In the case of multiple-loop control like V ²-control, different loop gains are clarified for their application in load transient or reference tracking. Practical circuit-level design considerations are given to current-mode control for achieving fast reference tracking, while end-point prediction (EPP) is used to improve V ²-control, which is inherently slow in reference tracking. The effect of EPP on transfer function is then explained in details. A V ²-controlled buck converter with EPP is fabricated. The measured reference-tracking response shows ten times improvement in tracking speed and verifies the effectiveness of EPP in V²-control. © 2006 IEEE

Design considerations of recent advanced low-voltage low-temperature- coefficient CMOS bandgap voltage reference

The design considerations of CMOS bandgap voltage references focusing on low-voltage and low-temperature-coefficient methodologies are discussed in this paper. Some recently reported circuits of bandgap voltage references are included and analyzed. Moreover, a CMOS voltage reference is also addressed. © 2004 IEEE

A sub-1-V 15-ppm/°C CMOS bandgap voltage reference without requiring low threshold voltage device

A sub-1-V CMOS bandgap voltage reference requiring no low threshold voltage device is introduced in this paper. In a CMOS technology with V_thn ≈ \V_thp\ ≈ 0.9 V at 0°C, the minimum supply voltage of the proposed voltage reference is 0.98 V, and the maximum supply current is 18 μA. A temperature coefficient of 15 ppm/°C from 0°C to 100°C is recorded after trimming. The active area of the circuit is about 0.24 mm²

A two-phase switching hybrid supply modulator for RF power amplifiers with 9% efficiency improvement

A hybrid supply modulator consisting of a parallel operation of a high-drive, low output impedance, wideband class-AB linear amplifier and a high-efficiency, wideband, low-ripple switching amplifier is presented for the application of polar transmitters. At system level, a two-phase switching is employed to lower the inductor current ripple so that both the output ripple and power loss are reduced. On-chip feed-forward bandpass filter is used to extend the tracking bandwidth of the switching amplifier, without hurting the stability of parallel control loop or the need to increase switching frequency. At circuit level, the output impedance of the linear amplifier is lowered by optimizing the design of super source-follower output stage. Inductor current sharing and two-phase ramp generator are implemented for realizing the two-phase switching scheme. Fabricated in a 0.35- m CMOS process, the prototype chip measures 9% static efficiency improvement over the conventional single-phase switching design in the back-off power level. Dynamic efficiency is enhanced by 8-12% by enabling the bandpass filter. Successful tracking of a 4 MHz 0.4-2.8 V full-wave rectified sine wave and a WCDMA envelope signal is demonstrated. © 2006 IEEE

Soft-start circuit with duty ratio controlled voltage clamping and adaptive sizing technique for integrated DC-DC converters

A novel soft-start technique with charge-pump based staircase clamping voltage generator to eliminate the inrush-current and over-shoot voltage is presented. Proper duty cycle is introduced as a new freedom to control the soft-start speed which enables a fully on-chip design to reduce the cost of the converter. In addition, adaptive sizing method is presented to control the charging current for boost converters when the output voltage is less than the input voltage. A boost DC-DC converter is implemented with a 0.35μrn CMOS process. Simulation results show a smooth start-up with load range from 0-500mA. © 2010 IEEE

A monolithic 2nd-order boundary controller for buck converter with fast transient response

It is well known from control theory that 2nd-order boundary control is able to achieve a faster transient response over the conventional hysteretic control. However, no available monolithic 2nd-order boundary controller for buck converter has not been found. The main challenges of designing this controller are the implementation of the non-invasion output capacitor current sensor and the hardware calculation of both positive and negative squared terms in the 2nd-boundary control law. This paper overcomes those challenges and successfully designed and fabricated the controller with a standard 0.35μm CMOS process. Measurement results show that, during a 400mA load current step change, the controller is able to regulate a 4MHz buck converter output voltage to return to its nominal value within one ON/OFF switching action (1μs) with less than 50mV overshoot/undershoot. The measured highest power efficiency is about 94%. © 2010 IEEE

Fixed-frequency adaptive-on-time boost converter with fast transient response and light load efficiency enhancement by auto-frequency-hopping

An integrated fixed-frequency adaptive-on-time DC-DC converter with fast transient response and high light load efficiency is presented. To achieve fixed frequency at continuous conduction mode, the on-time is adaptively controlled to force the switching frequency tracks the reference frequency with less than +/-0.5% error within the whole operating range. To enhance the light load efficiency as well as reduce EMI noise problem, the on-time is adjusted to maintain the switching frequency hops between 1MHz and 1MHz/N where N = 2 i and i = 1 to 5 according to the loads without load current sensor. © 2011 JSAP (Japan Society of Applied Physi