Abstract: The present invention provides methods and apparatus for rapidly starting or bringing an oscillating device to its resonant frequency, and operating deflection amplitude. The invention is particularly applicable for use with an oscillating mirror used as the scanning engine of a laser printer. Control circuitry of the oscillating device first determines the resonant frequency of the device and then adjusts or increases the duty cycle of successive energy drive pulses until a selected deflection amplitude is reached. Energy drive pulses at the resonant frequency of the device and the adjusted duty cycle are then provided to maintain oscillation of the device. In a laser printer, a single sensor is used to determine the deflection amplitude of the resonant beam sweep by determining the spacing or timing between a pair of the sensors pulses.

Abstract: A method that allows a digital communications system to detect the presence of transmitted messages in noisy environments. The system includes an OFDM transmitter and an OFDM receiver. The OFDM transmitter converts a digital signal to be transmitted to a plurality of sub-signals, each corresponding to a respective sub-carrier frequency. The signal is a packet including a preamble field having a known data pattern. The transmitter pre-codes the preamble data pattern, maps the data to corresponding phase information, converts the sub-signals to the time domain, and converts the sub-signals to analog form for subsequent transmission. The OFDM receiver receives the transmitted sub-signals, converts the sub-signals to digital form, converts the sub-signals to the frequency domain, and subjects the sub-signals to preamble detection processing to detect the signals' presence.