A Novel Injection-Locked Oscillator MMIC with Combined Ultrawide-Band Active CombinedDivider and Amplifiers

A subharmonically injection-locked oscillator (ILO) MMIC for local oscillators, synthesizers, and phased-array antennas is proposed. An ultrawide-hand four-port active combineddivider in the oscillator feedback loop provides an FEToriented circuit topology extremely suitable for single-chip integration, and performs subharmonic injection locking at various subharmonic factors, l/n. Two types of ILO MMIC’s were constructed. One of them exhibits a locking range as wide as 1 GHz at n = 1, and the other operates at n from 1 to 16, with an output power larger than 5 dBm. The proposed ILO MMIC is promising for applications such as microwave and millimeter-wave synthesizers, large-aperture phased array antennas, frequency-selective FM-receivers, and so on. I. I N ~ O D U C T I O N OCAL oscillators play an important role in various miL crowave receiver and transmitter components. Using a phase-lock-loop (PLL) is a practical way to stabilize the oscillation frequency and suppress the phase noise. However, many components such as VCO’s, frequency dividers, and phase frequency comparators (PFCl’s) are required, and the phase noise of the VCO has to be thoroughly suppressed beyond the PLL bandwidth. Furthermore, the frequency divider limits the stabilized oscillation frequency range, resulting in the need for additional frequency multipliers and amplifiers for higher frequencies. These requirements result in expensive, complex multichip packaging. In this paper, a novel injection-locked oscillator (ILO) MMIC, which refers to a commercially available (or already developed) lower-frequency synthesizer IC, is proposed as an effective solution for these problems. This novel ILO MMIC is based on a two-port feedback oscillator previously reported [ I ] and contains an active four-port combineddivider, instead of a passive quadrature hybrid, associated with an amplifier. The most significant advantage of the ILO is that it provides an FET-oriented circuit topology extremely suitable for singlechip integration: two in-phase active dividers are connected symmetrically at the high-impedance output ports to provide a nonreciprocal four-port combineddivider 121; and an amplifier is connected between an output port and an input port of the combineddivider. The new [LO MMIC enables single-chip Manuscript received March 7, 1994; revised June 27, 1994. The authors are with NTT Radio Communication Systems Laboratories, Radio Systems Lahoratory, 1-2356 Take, Yokosukashi, Kanagawa 238-03, Japan. IEEE Log Number 9405428. 00 18-9480/94$04 integration with very little increase in size and cost relative to other approaches. In addition, it makes it possible to minimize the length of the line connecting the four-port circuit and amplifier for lower effective 4) of the oscillator, resulting in a wider locking range. Since the active combinerldivider operates in an ultrawide-band frequency range approaching the FET cutoff frequency, f ~ , injection locking to an nth-order subharmonic (n = 1, 2. 3, . . .) can be performed effectively. The organization of this paper is as follows. First, the circuit design is outlined in Section 11, with details provided on the circuit topology, free-running oscillation characteristics, and effective Q. Section I11 describes the injection-locking ability of the proposed ILO MMIC and the characteristics of subharmonically injection-locked oscillators. Finally, possible oscillator applications are presented in Section IV. 11. C I R C U ~ DESIGN Fig. 1 shows the circuit topology for a two-port feedback oscillator, where A is the amplifier gain, and T and C are the transmission and coupling coefficients of a four-port circuit. This type of injection-locked oscillator was developed recently by Birkeland and Itoh [ I ] for space power combining. It was shown to have a wide injection-locking range due to its low effective Q, Qef, , which is represented as where B is the rate of change of phase AC‘ at the freerunning oscillation frequency, wg. The effective 9 of an oscillator is based on its open-loop frequency characteristics [ 3 ] . However, the oscillator designed by Birkeland and Itoh uses a passive quadrature hybrid for the four-port circuit, and thus is applicable only to fundamental-frequency injection signals. Fig. 2 shows an active combineddivider replacement for the passive quadrature hybrid for nth-order subharmonic locking. As the figure shows, it consists of two in-phase dividers, each of which has a pair of symmetrical common-gate-FET’s (CGF’s), connected to each other at the high-impedance output ports to provide a non-reciprocal 4-port circuit. The input ports @ and @ and the output ports @ and @ are isolated from each other, respectively, and every input port-output port path is nonreciprocal due to the unilateral characteristic