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Hi everyone.. I've a question here. I have a square wave of high-level 3.5V and low-level 0.1V. I need to do a phase shift of 90 degrees to this signal. I read in the internet that it is possible to do it by using op-amp triangle wave generator. Here is the link: http://www.ecircuitcenter.com/Circuits/op_tri_gen/op_tri_gen.htm But it's only work on a symmetrical square wave(eg HL=5V and LL=-5V). So, do anyone know how to do a phase shift for my signal? I hope you can share your knowledge with me:) Thank you.

thanks for your suggestion. I'll tried it. I'll be using EXOR Gate for the phase comparator. And the signal from EXOR will be low pass filtered and be input to the control voltage pin of the 555. I'll try to simulate it first to see whether its work or not. But right now I'm quite busy with my school works. Maybe it will takes time. Hope it will working right.

I only allowed to use the 555 timer. But I think your suggestion of using inverting amplifier is a very good idea. Thanks for that. I'll tried. :)

Thanks for the recommendation. But it's my lecturer's idea at the first place. My project is to construct a DPLL by using 555 timer as vco. The duty cycle is not a big deal because I can use a D-FF to make it 50%.

I tried to do a DPLL which the signal is a square-pulse.

Is it suitable to use in PLL? Usually in PLL, when there is phase error(reference input leading vco signal output) the PD develops a signal Ud which increase with time. This cause the VCO to increase its frequency. With timer 555 when Ud increases the output frequency will be decreases. In this case, can Timer 555 be used in PLL? I just don't get the idea. Hope you can help me.

Hi, currently I tried to design a DPLL that use timer 555 as the vco. From what I read usually VCO will have a positive linearity(f(U)). But in my case(using timer 555) I got a negative linearity. What I mean here, when the voltage of control voltage increase the frequency output will be decreased. So I want to ask: Is it still possible to use timer 555 as a VCO?