Interpolation based timing recovery
First Claim
1. A communication apparatus for communicating with a further communication apparatus via a communication medium, comprising:
- a communication port for coupling to the communication medium;
a conversion apparatus for converting between respective analog and digital formats of a communication signal, including an analog port where said communication signal is presented in analog format, and a digital port where said communication signal is presented in digital format, said analog port coupled to the communication port with an input of an analog-to-digital converter and output of a digital-to-analog converter; and
said conversion apparatus including a compensator coupled to said digital port for modifying sample values in said digital format communication signal to compensate for a frequency difference between a time base used by said conversion apparatus and a further time base used by the further communication apparatus,said compensator including a receive compensator having an input coupled to said output of said analog-to-digital converter, and a transmit compensator having an output coupled to said input of said digital-to-analog converter, said transmit compensator having an input, and said digital port including said input of said transmit compensator and said output of said analog-to-digital converter.
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Accused Products
Abstract
The present invention provides a solution that eliminates both the voltage-controlled oscillator (“VXCO” 105) and its associated D/A converter (120) from the timing recovery scheme, thereby significantly reducing manufacturing costs for modems, such as asymmetric digital subscriber loop (“ADSL”) modems. The present invention also enables tracking of a wider frequency offset. The present invention provides this with a novel timing recovery scheme implemented entirely in the digital domain. The present invention includes a free running clock (205) as the sampling clock for the A/D (110) and D/A (115) converters, and interpolators (210, 220, 615 and 635) to correct timing errors for both the receive and transmit samples. The desired sample can be obtained based on its timing offset and its neighboring samples.
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Citations
19 Claims
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1. A communication apparatus for communicating with a further communication apparatus via a communication medium, comprising:
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a communication port for coupling to the communication medium; a conversion apparatus for converting between respective analog and digital formats of a communication signal, including an analog port where said communication signal is presented in analog format, and a digital port where said communication signal is presented in digital format, said analog port coupled to the communication port with an input of an analog-to-digital converter and output of a digital-to-analog converter; and said conversion apparatus including a compensator coupled to said digital port for modifying sample values in said digital format communication signal to compensate for a frequency difference between a time base used by said conversion apparatus and a further time base used by the further communication apparatus, said compensator including a receive compensator having an input coupled to said output of said analog-to-digital converter, and a transmit compensator having an output coupled to said input of said digital-to-analog converter, said transmit compensator having an input, and said digital port including said input of said transmit compensator and said output of said analog-to-digital converter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A communication apparatus for communicating with a further communication apparatus via a communication medium, comprising:
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a timing source for providing a timing signal; a conversion apparatus coupled to said timing source for converting between respective analog and digital formats of a communication signal based on said timing signal, said conversion apparatus including an analog port where said communication signal is presented in analog format, and a digital port where said communication signal is presented in digital format, said analog port for coupling to the communication medium;
said conversion apparatus including;a digital-to-analog converter having an output that defines said analog port, said digital-to-analog converter having an input; a compensator coupled to said digital port for compensating for a frequency difference between said timing signal and a further timing signal used by the further communication apparatus, said compensator having an output coupled to said input of said digital-to-analog converter and an input that defines said digital port; and said timing source operable independently of said compensator. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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19. A communication apparatus for communicating with a further communication apparatus via a communication medium, comprising:
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a timing source for providing a timing signal; a conversion apparatus coupled to said timing source for converting between respective analog and digital formats of a communication signal based on said timing signal, said conversion apparatus includes an analog-to-digital converter and a digital-to-analog converter, an analog port where said communication signal is presented in analog format and a digital port where said communication signal is presented in digital format, said analog port including an input of said analog-to-digital converter and an output of said digital-to-analog converter, said conversion apparatus further includes a compensator coupled to said digital port for compensating for a frequency difference between said timing signal and a further timing signal used by the further communication apparatus; and
said timing source operable independently of said compensator, said compensator including a receive compensator having an input coupled to said output of said analog-to-digital converter, and a transmit compensator having an output coupled to said input of said digital-to-analog converter, said transmit compensator having an input, and said digital port including said input of said transmit compensator and said output of said analog-to-digital converter.
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Specification