Wideband Frequency Synthesizer at X/Ku Band by Mixing and Phase Locking of Half Frequency Output of VCO
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Wideband Frequency Synthesizer at X/Ku Band by Mixing and Phase Locking of Half Frequency Output of VCO Mo Chen & Jinping Xu
Received: 21 June 2009 / Accepted: 5 August 2009 / Published online: 17 September 2009 # Springer Science + Business Media, LLC 2009
Abstract A wideband low phase noise frequency synthesizer at X/Ku band has been developed by using phase locking and mixing technique at half frequency of voltage controlled oscillator (VCO). The half frequency output signal of the VCO is down converted by a balanced mixer at C band to obtain an intermediate frequency (IF) signal used for phase locking of the VCO. An ultra low phase noise local signal source at 6 GHz is developed with a frequency multiplying chain driven by a 100 MHz oven controlled crystal oscillator (OCXO). Coupling circuit outside the VCO chip to the mixer does not need to be specially designed, which is beneficial to simplify the circuit scheme and improve the phase noise performance. Measurement results show that the phase noise of the output signal at 10.6 GHz to 11.8 GHz and 12.3 GHz to 13.0 GHz is better than −102 dBc/Hz at 10 kHz away form the carrier center. This frequency synthesizer can be used as local signal source or driving source for the development of wideband millimeter-wave frequency synthesizer systems. Keywords Frequency synthesizer . Phase locking and mixing . Phase noise
1 Introduction Frequency synthesizer is one of the key modules in advanced microwave and millimeterwave application systems, such as radar, communication and electronic countermeasures. Phase locked loop (PLL) is commonly applied to develop high performance frequency synthesizers with good long-time and short-time stability. In a digital phase locking synthesizer, the frequency division ratio in phase and frequency detector (PFD) module is a critical parameter which determines the phase noise performance of the output signals. If the output signal of a VCO at microwave or millimeter-wave band is directly coupled to RF input port of a digital PFD in PLL circuit, the value of the frequency division ratio would be enormous in the case of small comparison frequency in PFD for high frequency resolution. M. Chen (*) : J. Xu State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China e-mail: [email protected]
J Infrared Milli Terahz Waves (2010) 31:100–110
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That would lead to an awful degradation of phase noise in output signals. One of the most effective solutions to this problem is to combine the PLL with frequency mixing technique. The microwave or millimeter-wave signals are firstly mixed with a LO signal or its harmonics and down converted to an IF signals with much lower frequency. Then the IF signal will be divided and compared with a properly divided reference signal in the PFD to produce an error control signal fed back into the VCO [1–3]. In this way, the frequency division ratio can be greatly reduced, and the phase noise of the output signal in locked state can be greatly improved when the loop filter is well designed
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