Abstract: The invention provides novel railroad ties manufactured from novel composite materials that possess excellent physical and performance characteristics matching or exceeding existing concrete RRTs. The RRTs of the invention can be readily produced from widely available, low cost raw materials by a process suitable for large-scale production with improved energy consumption and more desirable carbon footprint and minimal environmental impact.

Abstract: The invention provides novel railroad ties manufactured from novel composite materials that possess excellent physical and performance characteristics matching or exceeding existing concrete RRTs. The RRTs of the invention can be readily produced from widely available, low cost raw materials by a process suitable for large-scale production with improved energy consumption and more desirable carbon footprint and minimal environmental impact.

Abstract: Methods and apparatus to detect an over-current in switching circuits are described. An example method to detect an over-current in a switching circuit includes randomly selecting a sensor from a plurality of sensors operatively coupled to an output stage of the switching circuit; detecting a first voltage via the randomly selected sensor; and comparing the first voltage to a reference voltage to generate a signal, wherein the signal indicates a status of the output stage of the switching circuit.

Abstract: The summing comparator includes: a first integrator; a second integrator for receiving an output of the first integrator; and a comparator for switching when the output of the first integrator is greater than the output of the second integrator. The outputs of the first and second integrators are directly compared by the comparator without the necessity of a summing amplifier.

Abstract: A closed loop amplifier adapted to be directly connected to a battery having a battery voltage for powering the amplifier. The amplifier includes an amplifier stage having a node for receiving a control voltage for controlling a common mode voltage of the stage, a digital voltage indicator for generating a digital value corresponding to the battery voltage, and a common mode voltage supply providing the control voltage corresponding to the digital value.

Abstract: A closed loop amplifier adapted to be directly connected to a battery having a battery voltage for powering the amplifier. The amplifier includes an amplifier stage having a node for receiving a control voltage for controlling a common mode voltage of the stage, a digital voltage indicator for generating a digital value corresponding to the battery voltage, and a common mode voltage supply providing the control voltage corresponding to the digital value. In a preferred embodiment, a Class-D amplifier is powered by a power supply providing power by way of a power supply voltage node and a ground node, the amplifier having improved common-mode voltage control. A first integrator stage receives an input signal and provides an output signal, the integrator stage having a first common-mode reference voltage applied thereto for control of the common-mode voltage of the integrator stage.

Abstract: An amplifier system in accordance with an aspect of the present invention comprises a switching amplifier that drives a load with a pulse-width modulated (PWM) output signal that varies between first and second rails based on a first control input signal, and a common mode supply that provides a switching signal that varies between third and fourth rails to maintain a common mode voltage of the load at a level that is between the first and second rails.

Abstract: Multi-mode class-D amplifiers are disclosed. An example multi-mode class-D amplifier circuit having an analog input and a digital input disclosed herein comprises a single-mode class-D amplifier having an amplifier input, a smoothing filter having a filter input and a filter output, wherein the filter output is electronically coupled to the amplifier input, and a multiplexer electronically coupled to the filter input to select between at least one of the analog input and the digital input of the multi-mode class-D amplifier circuit.

Abstract: A Class-D amplifier system may include an input stage that includes an Nth order filter, where N>1. The input stage filters an input signal to provide a filtered output signal, an input of the input stage being configured to receive the input signal as a digital pulse-width-modulated (PWM) signal. A comparator provides a quantized output signal based on the filtered output signal. An output stage is connected between a first voltage rail and a second voltage rail. The output stage provides a switching output signal at an output that varies between the first voltage rail and the second voltage rail based on the quantized output signal. A feedback path connects the output of the output stage with the input of the input stage, such that the Nth order filter compensates for variations in at least one of the first voltage rail and the second voltage rail.

Abstract: The summing comparator includes: a first integrator; a second integrator for receiving an output of the first integrator; and a comparator for switching when the output of the first integrator is greater than the output of the second integrator. The outputs of the first and second integrators are directly compared by the comparator without the necessity of a summing amplifier.

Abstract: A Class-D amplifier system may include an input stage that includes an Nth order filter, where N>1. The input stage filters an input signal to provide a filtered output signal, an input of the input stage being configured to receive the input signal as a digital pulse-width-modulated (PWM) signal. A comparator provides a quantized output signal based on the filtered output signal. An output stage is connected between a first voltage rail and a second voltage rail. The output stage provides a switching output signal at an output that varies between the first voltage rail and the second voltage rail based on the quantized output signal. A feedback path connects the output of the output stage with the input of the input stage, such that the Nth order filter compensates for variations in at least one of the first voltage rail and the second voltage rail.

Abstract: An amplifier system in accordance with an aspect of the present invention comprises a switching amplifier that drives a load with a pulse-width modulated (PWM) output signal that varies between first and second rails based on a first control input signal, and a common mode supply that provides a switching signal that varies between third and fourth rails to maintain a common mode voltage of the load at a level that is between the first and second rails.