说明：  分频电路的研究 主要包括：偶数分频（二分频、偶数分频占空比50 ）、奇数分频（占空比50 、占空比非50 ）、半整数分频（不要求占空比）、小数分频（不要求占空比）。
(Frequency of the circuit includes: an even frequency (half frequency, frequency 50 duty cycle even), odd-frequency (50 duty cycle, duty cycle of non-50 ), half-integer frequency division (not required duty cycle), fractional (not required duty cycle).)