与具有奇数增益级的差分环形振荡器不同，偶数级振荡器除了具有能够起振的非稳定平衡态，还有可能在起振前处于一种稳定平衡状态从而使电路锁定不能起振。该文主要分析了这种稳定平衡状态存在的原理，同时为了避免振荡器设计中的这种风险，提出了一种振荡器起振电路，使得电路在起振前处于接近非稳定平衡态的状态，从而能够快速起振。在0.13 m 1P8M 标准CMOS工艺下流片实现的4级差分环形压控振荡器(VCO)及其改进版本很好地验证了该文提出的理论和解决方法。经测试发现，第1款不带起振电路的4级VCO芯片锁定于稳定平衡态，不能起振；两种改进版本3级VCO和带起振电路的4级VCO都能够正常输出振荡信号。
The start-up conditions for differential oscillator with an even number of stages are analyzed in this paper. Compared with those that have an odd number of stages, such oscillators may have two stable equilibrium states besides an astable equilibrium state in which the circuits can start to oscillate. To avoid the risk of possible latching up into the stable states, an additional start-up circuit technique is proposed. The proposed circuit should also reduce the start-up time. The theory is further confirmed with the design and fabrication of three kinds of differential ring Voltage-Controlled Oscillator (VCO), a 3-stage one, 4-stage ones with and without the start-up circuit based on a 0.13 m standard CMOS process. The measurement results show that the 3-stage one and the 4-stage one with the start-up circuit have the correct output oscillation signals, but the 4-stage without the start-up circuit has nothing to output.