A single chip synthesizer for generating a digital signal of tunable frequency with nearly no spurs.

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Technology abstract

A European Organization has invented a method and apparatus for generating a digital signal of tunable frequency. This hybrid configuration is a single chip synthesizer that enables the generation of a fractional reference frequency instead of fixed one. This invention can be used for reducing the phase error in the up/down radio conversion chain. The main advantage of this invention is that the output signal is spur free. 

Because of the novelty and the significant improvement that this invention offers compared to conventional and state-of-art synthesizers it is a very attractive option for demanding industries.

- Paris Rallis -

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Technology Description

This invention provides a method for creating: 

  • A signal generator outputting a digital signal of tunable frequency with a reduced spur level.
  • A fractional-N frequency synthesizer outputting a signal with a reduced spur level that can be implemented on a single chip.

This hybrid configuration is a single chip synthesizer that enables the generation of a fractional reference frequency instead of fixed one. The synthesizer has both a fractional-N and an integer-N output capability.
The method that this invention uses has the following steps:

  • Generating a periodic first analog signal and determining a sign of a first difference between a value of the first analog signal and a first control value (variable value)

Generating the digital signal of tunable frequency on the basis of the determined sign of the first difference, wherein the digital signal of tunable frequency is generated such that a subset of switches of the signal level are coincident with a respective sign flip of the determined sign of the first difference.

Innovations & Advantages

The main advantage of this invention is that the signal that is generated has no spurs. This means that this apparatus offers higher performance than other solutions available.
There are existing mechanisms for reducing the level of spurs but none of these removes the fractional spurs completely. Other fractional-N frequency synthesizers, which are implemented on a single chip are not able to reduce the levels of fractional spurs due to design considerations and space limitations.
Additionally hybrid fractional-N frequency synthesizers are not able to output spur-free frequencies due to sampling errors and digital-to-analog conversion. As a result the output of these hybrid fractional-N frequency synthesizers is not spur-free.
This innovative invention provides a strict separation of the analog domain from the digital domain and since spurs have their origin in the digital domain, such separation allows the overall spur level of the final digital output signal to be significantly limited.
Another advantage of the apparatus described is the single chip design. This means that it has a more compact size, which increases the flexibility for possible applications and reduces the costs.
The high performance and the mass reduction that this invention offers make it an attractive solution for demanding fields like space applications.

Further Information

Current and Potential Domains of Application

  • Space applications (satellite communication systems)
  • Wireless base stations
  • Broadband wireless access
  • Test and measurement equipment (instrumentation)
  • Telecommunication devices (mobile phones)
  • Wireless LAN (also for PAN, WAN and MAN) devices
  • Transmitting devices in a communication system (radio frequency link)
  • Broadcast systems such as radio and television (also in CATV)
  • Sonar and radar applications
  • Earth observation such as cartography
  • Weather forecast or monitoring
  • Military applications and guidance applications