Hybrid frequency synthesizer and method

Abstract

Embodiments include a hybrid frequency synthesizer that includes a direct digital synthesizer configured to generate a digital output signal having a frequency determined by an input signal received from an externally generated signal source. The hybrid frequency synthesizer further includes a delta-sigma modulator configured to generate a delta-sigma modulated signal based on the digital output signal, the delta-sigma modulator being coupled to the direct digital synthesizer. The hybrid frequency synthesizer also includes a digital-to-analog converter configured to convert a delta-sigma modulated signal into an analog output signal, the digital-to-analog converter coupled to the delta-sigma modulator. Additionally, the hybrid frequency synthesizer includes a bandpass filter configured to remove interfering frequencies from the analog output signal, the bandpass filter coupled to the digital-to-analog converter; and a phase locked loop , which is coupled to the bandpass filter and driven by a reference signal received from the bandpass filter.

Description

[0001] Cross References to Related Applications [0002] This application claims the benefit of US Patent Application Serial No. 14 / 815,523, filed July 31, 2015, which is incorporated herein in its entirety. technical field [0003] The present application relates generally to frequency synthesizers and methods thereof. In particular, this application relates to hybrid frequency synthesizers including phase locked loops driven by direct digital synthesizers. Background technique [0004] Many electronic systems, including audio and communication systems, need to generate high quality, flexible signal sources for use as, for example, local oscillators, sample clocks, frequency modulators, or the like. For this purpose, such systems typically incorporate signal or frequency synthesizers that can tune within a few microseconds across the entire frequency band available for a given output signal. [0005] One conventional type of frequency synthesizer is a phase-locked loop (...

AI Technical Summary

Problems solved by technology

[0011] However, the existing DDS driven PLL hybrid system 100 still suffers from certain disadvantages in that it lacks the ability to provide a practical, high performance solution

For example, due at least in part to N-bit DAC 110, system 100 is expensive and consumes a large amount of power

Furthermore, the prior art system 100 is susceptible to spurious tones because the N-bit DAC 110 is a weighted Nyquist digital-to-analog converter with a spurious-free dynamic range that limits the spurious performance of the DDS system 102

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