In this paper, a novel frequency-locked loop (FLL) architecture for phase-noise reduction of wideband voltage-controlled oscillators (VCO) is presented. The circuit makes use of a phase-shifterless frequency discriminator, which completely avoids the use of any control circuitry to keep the loop in its quadrature condition, highly simplifying the loop. The FLL circuit, which can be operated in a completely transparent way, can be easily interchangeable with the original VCO. An FLL prototype, based on a commercial state-of-the-art VCO, has been fabricated and measured exhibiting a phase-noise reduction higher than 9 and 5.5 dB up to 100-kHz and 1-MHz offset from carrier, respectively, in the complete 4.6-9-GHz band. Absolute phase noise results of -106.5 and -124 dBc/Hz at 100-kHz and 1-MHz offset from carrier have been obtained, showing lower phase noise than other wideband FLLs in the literature.
