DPLL circuit having holdover function
AssigneeFujitsu Limited
InventorKoji Nakamuta
Life of this patent
Estimating the term…
Abstract
The invention relates to a digital synchronization network, and provides a DPLL circuit having a holdover function that generates a high-precision reference clock with a temperature correction to perform a free-running frequency control at a holdover time. In a holdover mode of the DPLL circuit using a DDS, the DPLL circuit having a holdover function adds a correction value calculated from a temperature characteristic of a slave oscillator to a fixed DDS control value during a detection of a holdover, thereby changing the DDS control value according to the temperature characteristic.
Claims3
A digital phase locked loop (DPLL) circuit having a holdover function that adds a correction value calculated from a temperature characteristic of a slave oscillator to a fixed direct digital synthesizer (DDS) control value during a detection of a holdover, thereby changing the DDS control value according to the temperature characteristic, in a holdover mode of the DPLL circuit using the DDS.
A DPLL circuit having a holdover function, the DPLL circuit comprising:
- a temperature sensor that detects an ambient temperature;
- a characteristic holder that holds a temperature-frequency variation characteristic of a slave oscillator;
- a correction value converter that gives a DDS control correction value, based on a detection signal from the temperature sensor and information held in the characteristic holder;
- a holdover circuit that gives a DDS control value immediately before the occurrence of a trouble as a fixed value;
- an adder that adds a DDS control correction value from the correction value converter and a DDS control value of the holdover circuit, and outputs the sum;
- and
- a selector that selectively outputs one of an output from the adder and an output from a DLF, wherein
- the selector selects an output from the adder, and controls the DDS, in a holdover mode.
Dependencies are inferred from the claim text.