Stable phase locked states" are found amongst the equiliblia of the phasor model known as a generalized Hopfield model having complex-valued local states on the unit circle with centre at the origin. The asynchronous updating rule is assumed, and the energy decreasing characteristic is used to investigate a property of the equilibrium states. Some of the equilibria are shown to be fragile" in the sense that the energy is not locally convex. It is also shown that the local convexity of the energy is assured by a sort of consistency between the equilibrium and the connection weights.

A 3.2 GHz, 50 mW, 1 V, GaAs clock pulse generator (CG) based on a phase-locked loop (PLL) circuit has been designed for use as an on-chip clock generator in future high speed processor LSIs. 0.5 µm GaAs MESFET and DCFL circuit technologies have been used for the CG, which consists of 224 MESFETs. An "enhanced charge-up current" inverter has been specially designed for a low power and high speed voltage controlled oscillator (VCO). In this new inverter, a voltage controlled dMESFET is combined in parallel with the load dMESFET of a conventional DCFL inverter. This voltage controlled dMESFET produces an additional charge-up current resulting in the new VCO obtaining a much higher oscillation frequency than that of a ring oscillator produced with a conventional inverter. With a single 1 V power supply (Vdd), SPICE calculation results showed that the VCO tuning range was 2.25 GHz to 3.65 GHz and that the average VCO gain was approximately 1.4 GHz/V in the range of a control voltage (Vc) from 0 to 1 V. Simulation also indicated that at a Vdd of 1 V the CG locked on a 50 MHz external clock and generated a 3.2 GHz internal clock (=50 MHz64). The jitter and power dissipation of the CG at 3.2 GHz oscillation and a Vdd of 1 V were less than 8.75 psec and 50 mW, respectively. The typical lock range was 2.90 GHz to 3.59 GHz which corresponded to a pull-in range of 45.3 MHz to 56.2 MHz.