Alexander Chenakin’s research while affiliated with Matrix-Bio, Inc. and other places

This tutorial provides a brief introduction to the field of frequency synthesis. It starts with general definitions and requirements followed by a review of the main synthesizer architectures. Direct analog, direct digital, and indirect techniques are compared in terms of performance, circuit complexity, and cost impact. The design tradeoffs are analyzed and complemented with a review of fractional-N, direct digital synthesizers (DDSs), frequency offset, multiloop, and other schemes. The current state and development trends of microwave frequency synthesizers will be reviewed.

Frequency synthesizer – as a main module for modern communication systems, test-and-measurement equipment and other electronic devices – should meet certain requirements. The most important requirements include spectral purity of generated signal (low phase noise and spurs), fast switching speed and high frequency resolution (low step size). Other important characteristics include low power consumption, small size and low cost. Thus, the main design goal is selecting proper solutions to support these requirements. This article describes various architectures used to design frequency synthesizers based on phase locked loop.

Dr. Alexander Chenakin shares his views on the anatomy of the fractional-N synthesis and discusses some new ways to address the limitations of the existing technology. There are many techniques to reduce fractional-N spurs, which can be accomplished by adding or subtracting a voltage at the phase detector output during the frequency division change. Another method is based on using a multi-modulus divider that allows a larger number of division coefficients. The mixer inputs are generated internally within the same PLL, eliminating the need for separate offset frequency source. Two frequency dividers divide the VCO output frequency to generate the required mixer inputs.

Some of the latest technological innovations in Russia in the field of RF/microwave signal generation are discussed. Morion has recently developed a new family of low phase noise OCXOs (MV317 and MV318) offering a noise floor down to 178 dBc/Hz and excellent aging characteristics. These parameters are achieved using in-house proprietary technologies for the design and production of precision blanks in combination with advanced filtering methods incorporated into the OCXO design. Magic Xtal develops and manufactures OCXOs utilizing the unique internally heated resonator (IHR) technology. The IHR design incorporates the whole oven-controlled system integrated with the crystal plate inside a miniature TO-8 vacuum holder. Spectran has developed a low-cost 20 GHz synthesizer module. This is a phase-lock-loop (PLL) design that integrates a DDS for fine frequency resolution. The module provides 9 kHz to 20 GHz frequency coverage with fast switching speed and a resolution of 0.01 Hz.

This paper presents two local oscillator modules developed for PXI instrumentation. The modules are based on a novel, patented PLL design that combines fast switching speed, low phase noise, and low spurious characteristics. The modules cover 3-10 and 2-20 GHz frequency ranges respectively. The step size is 0.1 Hz for both modules. The measured phase noise at 10 kHz offset is about -121 dBc/Hz at 10 GHz and -115 dBc/Hz at 20 GHz respectively. The switching time is less than 500 microseconds to be within ±50 kHz from the final frequency for any frequency step within the entire operating range. Spurs do not exceed the -70 dBc level. Both developed modules occupy two standard 3-U PXI slots and can be used in a variety of synthetic instruments based on the PXI platform.

A novel PLL frequency synthesizer architecture is presented. The proposed architecture offers improved phase noise characteristics by removing frequency division from the PLL feedback path. This minimizes the impact of the phase detector residual noise floor. Moreover, phase noise can be further improved by inserting a frequency multiplier into the feedback path. A 5 MHz to 26.5 GHz synthesizer module based on the proposed architecture has been developed. Phase noise at 26.5 GHz output and 10 kHz offset is measured at −110 dBc/Hz. The measured spurs do not exceed −60 dB level. The switching time is less than 100 microseconds for any frequency step within the entire operating range.

The key principles that are considered while designing low-noise microwave oscillators includes reducing the oscillator half band width frequency, reducing the flicker-corner frequency, increasing the oscillator signal-to-thermal noise ratio and preventing the active device noise elevation. The use of the various resonator technologies based on electromagnetic, electro-acoustic and electro-optical principles results in improving the oscillator phase-noise and tuning characteristics. Electromagnetic fixed frequency resonators like dielectric resonators, sapphire resonators have the excellent power handling capabilities and Q-factor. The other type of resonators used are electromagnetic tunable resonators like yttrium iron garnet (YIG) resonators that offers the high-Q factors and wideband tuning. The techniques employed for noise reduction are active device linearization that is used to suppress amplifier intermodulation distortion products. The other method used is based on the use of a transponded-gain amplifier achieved by converting the signal in the frequency mixers.

This paper presents a compact, broadband frequency synthesizer module, which covers 0.1 to 10 GHz frequency range with a 0.001 Hz step size. The synthesizer combines fast switching speed, low phase noise, and low spurious characteristics. The measured phase noise at an output frequency of 10 GHz and 10 kHz offset is -122 dBc/Hz. For an output frequency of 0.1 GHz and 10 kHz offset the phase noise is -150 dBc/Hz. Spurs do not exceed the -70 dBc level and the switching time of the main PLL is less than 10 uSec. This module can be used as a broadband, agile, high-fidelity signal source in a variety of test-and-measurement, communication, and surveillance systems.

PXI synthetic instrumentation is an emerging technology that offers a cost-effective modular approach for building complex test and measurement equipment. The performance of synthetic instruments primarily depends on technical characteristics of their core modules such as a downconverter and LO oscillator. This paper presents a fast switching frequency synthesizer module, which covers 3 to 9 GHz frequency band with a 0.1 Hz step size. The developed module occupies two standard 3-U PXI slots and is used as an LO source for a 26.5 GHz harmonic downconverter. The module construction and test results are discussed.