占空比不同的方波 变成高电平或者低电平

beyond某人

求解答：如何通过analog电路将占空比大于30%的方波变成高电平，而将占空比小于30%的电路变成低电平？            我们事先不知道所给的信号是占空比大于还是小于30%。应该如何将电路调整到正常工作状态？
            电路不想太复杂。哪位大神能解答一下呢？


           方案提供：用一个积分电路，然后是一个三极管放大电路，

beyond某人

自己先顶一下

beyond某人

继续再顶啊 {哭}

ulsi123

Lots of options. It depends on signal speed, accuracy requirement and etc.

beyond某人

回复 4# ulsi123


   20khz （50u）方波信号 ，accuracy在2u以内。我采用的是npn集电极输出经过两级的RC在经过npn，得到最终输出out

ulsi123

As I said earlier, there are lots of options for this design. Your clock speed is very slow, and I believe you can use an integrator approach. Here are some hints for you:

1. Let's assume your clock cycle is T;
2. You wanna check if the duty cycle is great than 30%;
3. So tH=0.3T, tL=0.7T;
4. Now let's build a circuitry that is similar to PLL charge pump with a source current isource, and a sink current isink;
5. If we use this charge pump to charge/discharge a capacitor, the charge difference is Qdiff = isource * tH - isink * tL;
6. OK, let's tweak isource and isink, and make isource = 7i and isink = 3i;
7. Then Qdiff = 7i * 0.3T - 3i * 0.7T = 0 if duty cycle is exactly 30%;
8. So if you monitor Vout at the capacitor (Qdiff = Vdiff * C) for some periods, for example, 20, 30 or 100 cycles, you'll be able to get a very accurate result.

Of course, you need to design the circuit carefully, such as minimizing the mismatch between isource & isink. And be aware of clock feedthrough, charge injection and etc.

beyond某人

回复 6# ulsi123


   太感谢先生您了!说的这么详细，万分感谢。我的英文实在有些丢人，只能用中文回复你了，很是佩服你！ 这是我采用的电路结构，我不能明白电路的原理，不知道电阻电容是如何确定的？所以就发帖求助了。

ulsi123

I don't know if your circuit can achieve 2u (4%) accuracy. Here's my idea.