Pallab Midya

Sensorless current mode control-an observer-based technique for DC-DC converters

Sensorless current mode (SCM) control is an observer method that provides the operating benefits of current mode control without current sensing. SCM has significant advantages over both conventional peak and average current-mode control techniques in noise susceptibility and dynamic range. The method supports both line and bulk load regulation, and reduces control complexity to a single loop. The static and dynamic performance of SCM are analyzed and verified experimentally for DC-DC converters. Performance in continuous and discontinuous modes compares favorably to conventional techniques when noise is not a factor, but is significantly better when noise and wide load ranges are a concern. The SCM method encompasses one-cycle control as a special case; the general SCM method is introduced here as a public domain control technique.

High-fidelity PWM inverter for digital audio amplification: Spectral analysis, real-time DSP implementation, and results

A complete digital audio amplifier has been developed, implemented and tested. The process is entirely computational, and the output load and filter are the only analog components in the system. The process makes use of digital signal processing and a switching power stage to provide both high fidelity and high efficiency, beginning with a digital audio data stream. The advantages of naturally-sampled pulse-width modulation (PWM) are discussed in depth, including spectral analysis and comparisons to uniformly-sampled PWM. It is shown that natural PWM does not introduce audible distortion at switching frequencies consistent with power electronics practice. Interpolation methods for sample data conversion to natural PWM are discussed, and error analysis is presented based on Lagranges Expansion Theorem. Noise-shaping processes are used to support high fidelity with practical values of time resolution. A counter conversion process enforces switching dead time in the inverter gate signals. The experimental full-bridge inverter implementation demonstrates that miniaturization is possible. A complete test system delivered more than 50 W into an 8 /spl Omega/ load with an efficiency of 80% and total harmonic distortion plus noise of 0.02%.

Tracking power converter for supply modulation of RF power amplifiers

This paper describes a tracking power converter and the controller IC for its implementation. The tracking power converter is used for supply modulation of a linear RF power amplifier. Supply modulation improves RF power amplifier efficiency for variable envelope RF signals. This system maximizes tracking bandwidth (/spl sim/160 kHz), ripple suppression (/spl sim/70 dB) and power conversion efficiency (/spl sim/92%) with a relatively low switching frequency (800 kHz).

Linear switcher combination with novel feedback

A linear regulator and switching power converter parallel combination with novel control is presented. The power converter is setup to operate without output feedback while the linear regulator operates with output feedback. The control scheme minimizes the linear regulator current for maximum efficiency. A higher order L-C filter reduces ripple. This circuit is appropriate for supply modulation of RF power amplifiers.

Digital correction of PWM switching amplifiers

Pulsewidth modulated (PWM) signals for driving a switching audio amplifier can be synthesized in the digital domain with extremely high linearity and precision. However, nonidealities associated with the power stage degrade output performance. A method to digitally correct for these nonidealities, resulting in very low total harmonic distortion (THD) and high signal-to-noise ratio (SNR) performance, is presented. This method also provides excellent rejection of power supply noise which is otherwise absent in digital PWM amplifiers. To meet noise requirements for hi-fi audio, the feedback structure is a fourth-order structure which shapes the noise beyond the audio band. The method has been implemented on a bread board, and state-of-the-art performance was achieved. Total harmonic distortion of 85 dB and dynamic range of 100 dB was measured using Audio Precision test equipment.

Quadrature integral noise shaping for generation of modulated RF signals

This paper introduces a method to produce a modulated RF signal using a digital pulse signal switching at the carrier frequency. The entire modulation and amplification lineup is implemented in the digital domain. Integral Noise Shaping (INS) is used to create the baseband signals (I, Q) as digital PWM signals which are then mixed with a pair of digital carrier signals. All the edges of the digital pulse modulated signal line up with an edge of a fixed frequency clock signal at twice the carrier frequency. The resulting digital signal has high linearity and low quantization noise. All switching spurs and the quantization noise can be cleaned up with a bandpass filter with reasonable Q factor. Simulation results are presented for an offset tone test signal.

Noise properties of pulse-width modulated power converters: open-loop effects

The pulse-width modulation (PWM) process in DC-DC and DC-AC power converters introduces characteristic nonlinear behavior. When PWM is performed in the presence of noise, specific effects are seen on the duty ratio and consequently on the output of the converter. Small-signal concepts do not model nonlinear noise issues. Here, the probability density function of the duty ratio and its implications are obtained analytically, given external noise that follows a Gaussian distribution. The results are verified with Monte Carlo simulation and confirmed by experiments. For a DC-DC converter, noise is shown to introduce a DC shift at the output. The degree of nonlinear effect on a converter depends on the noise derivative level. For an inverter, noise can produce significant DC offset at the output. Closed-form expressions from the analysis can be used to evaluate noise sensitivity of a design.

High-fidelity PWM inverter for audio amplification based on real-time DSP

A complete digital audio amplifier has been developed, implemented and tested. It makes use of digital signal processing and a switching power stage to provide both high fidelity and high efficiency. It includes innovative signal processing and hardware techniques. It delivers 51 W into an 8-/spl Omega/ load with an efficiency of 82% and a total harmonic distortion plus noise of 0.022%.

Two sided latched pulse width modulation control

A control scheme is presented in which both edges of the PWM signal are modulated. The PWM signal is latched to prevent multiple transitions. The sawtooth ramp is replaced by a triangular wave derived from a digital clock, which is particularly suitable for high frequency operation. Additionally, the two sided PWM halves the response time.

An all-digital universal RF transmitter [CMOS RF modulator and PA]

This paper presents a CMOS class-D PA with on-chip all-digital RF modulator. The IC is fabricated in a 0.18 /spl mu/m digital CMOS process with MIM capacitors. The die size is a square 2.5 mm on each side. The active area used for the modulator (excluding the pads and bypass capacitance) is 0.315 mm/sup 2/. The class D PA shows 75 dB IM, -50 dB feedthrough, and puts out 19.6 dBm at >69% drain efficiency from a 1.8 V supply. The modulator operates in the IQ domain, without the use of bias control nor envelope modulation.