Constantly low‐phase‐noise differential VCO based on balanced tunable quasi‐elliptic and constant‐ABW BPF

Abstract

In this article, a parallel-feedback differential voltagecontrolled oscillator (VCO) with constantly low-phase noise and frequency tuning range (FTR) of 1.72-2.12 GHz (20.8%) is presented. The presented differential VCO with differential outputs and low-phase noise is achieved using a four-pole tunable balanced bandpass filter (BAL-BPF) with quasi-elliptic frequency response as a frequency stabilization element. The low-phase noise is obtained and maintained because of the high in-band group delay and the constant absolute bandwidth (CABW) of the used tunable BAL-BPF. For demonstration, an example is designed, fabricated, and measured. The measured oscillation frequency of the differential VCO can be tuned from 1.72-2.12 GHz (20.8%) and the phase noises keep better than −99 dBc/Hz @100 kHz and − 129.1 dBc/Hz @1 MHz over the FTR. In the meantime, the differential oscillating signals are generated at two outputs.

A modified Jerusalem microstrip filter and its complementary for low phase noise X-band oscillator

“…By changing the active device and selecting SiGe HBT on the same substrate, in [48], the LPN elliptic oscillator operates at about 8.06 GHz and shows a PN of −122.5 and −143.5 dBc/Hz at 100-kHz and 1-MHz offset frequency and an FOM of −207 dBc/Hz. The transistor of [19, 20, 23, 24] is Si BJT. The resonators of them are MF, stepped impedance resonator filter, quasi-elliptic filter, and stubs-loaded nested split ring resonator, respectively.…”

“…In the category of these Si BJT oscillators, the oscillator based on a stepped impedance resonator filter shows the best PN and FOM. In [19], the structure operates at about 1.77 GHz and shows a PN of −135 dBc/Hz at 1-MHz offset frequency and an FOM of −185 dBc/Hz. Also, the second harmonic suppression is nearly 37 dBc.…”

“…Therefore, the PNs of [20] and [24] are not good as Scheme 1 and Scheme 2. The features of active devices of [19] and [23] are not suitable for X-band oscillator application.…”

“…The other technique for designing LPN MPOs is based on microstrip filters (MFs) [13][14][15][16], the example of which are microstrip elliptic oscillators [17,18] and microstrip voltagecontrolled oscillators (VCOs) [19]. These microstrip oscillators (MOs) possess some advantages in designing including high Q-factor, mass production, low fabrication cost, miniaturized, and ease-of-integration in MMICs and RFICs structures [20][21][22].…”