说明：  任意波形源的pwm信号生成电路控制桥式结构 其中上面是双极式调制pwm考虑了上下桥臂不能同时开通（加了延迟）；下面是受限单极式调制pwm信号发生器
(Pwm arbitrary waveform signal generating circuit bridge structure wherein the control source is a bipolar modulator pwm at the upper and lower arms can be considered simultaneously opened (with delay) following is limited single modulator pwm signal generator)