Patent ID: 7057430
Filing Date: 2006-06-06
Classification: H03B,H03K,H03L,H04J

Abstract:
1. A clock shaping device, provided in a transmission apparatus and compensating for network synchronization, for receiving an input of a back-up clock signal in sync with a reference clock signal from a master station and supplied from a clock supply apparatus and an input of reception data from a transmission path, and generating a reception clock signal through timing-extraction from said reception data, said device comprising: a first clock signal selection portion that receives an input of said reception clock signal and an input of said back-up clock signal, selects either of said clock signals by a first selection signal inputted from outside, monitors, when said reception clock signal is being selected, a loss in said selected reception clock signal, and switches said selected reception clock signal to said back-up clock signal upon detection of said loss; a quartz crystal oscillation circuit that oscillates at a predetermined frequency; a second clock signal selection portion that receives an input of a clock signal from said first clock signal selection portion and an input of a clock signal from said quartz crystal oscillation circuit, selects either of said clock signals by a second selection signal inputted from outside, monitors, when said back-up clock signal is being selected, a loss in said selected back-up clock signal, and switches said back-up clock signal to said clock signal from said quartz crystal oscillation circuit upon detection of said loss; a voltage controlled oscillation circuit having a frequency that varies with a control voltage being supplied, and generates and outputs a feedback loop output signal; a phase comparison portion that generates a phase difference signal based on a result of comparing said feedback loop output signal from said voltage controlled oscillation circuit and a clock signal outputted from said second clock signal selection portion; and a loop filter that smoothes said phase difference signal and outputs said phase difference signal in the form of said control voltage, wherein the voltage controlled oscillation circuit includes a forward feedback oscillation loop circuit that outputs said feedback loop output signal and a forward feedback oscillation loop output signal, said forward feedback oscillation loop circuit including: