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# phase shifting of pulse train

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#### KerimF

I asked if the 400Hz is generated internally because if it is the case then the signal would start as sinusoidal generated for a convenient amplitude. Then it will be shifted as you have suggested. Both sine waves will then be amplified and limited at the desired amplitude.

Note: In general it is hard to give a good/acceptable solution when the input source and the output load are not known clearly, mainly their impedance (along the amplitude of the signal). To you both external sides are clear because you know what you have... for others one can think of many possibilities.

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#### FvM

##### Super Moderator
Staff member
Without asking about the purpose of your circuit, yes you can convert a square wave to a sine of same amplitude by a bandpass filter.

#### ata90

##### Member level 5
Without asking about the purpose of your circuit, yes you can convert a square wave to a sine of same amplitude by a bandpass filter.

Thanks for your post. below you can see parameters of BPF. what are the values of beta and f ?

#### FvM

##### Super Moderator
Staff member
what are the values of beta and f ?
f = 400 Hz, B = 40..200 Hz
B is a compromise between waveform distortion and phase error due to frequency deviation, you should try.

#### permute

There are several ways to phase shift a square wave. A pulse train as well. If only edges are important, there are even more ways. Of these, the transient responses and ability to scale can be affected.

My two suggestions would be:
1.) input waveform into an integrator (with some supporting circuity for biasing) to generate a triangular waveform. The rate of change of voltage is constant and determined by the level of the input square wave*. The amplitude of the waveform scales with frequency (inversely). The delay required for a 90deg phase shift then becomes a A/2. A comparator is used to restore the waveform.
2.) A PLL with XOR phase detector can also provide a 90deg phase shift with a square wave input*.
3.) basically, the same idea as #1, but with a fixed delay. obviously this only gives a 90deg phase shift at one frequency. idea #1 attempts to adjust delay based on an estimate of frequency, thus creating the phase shift.

*modifications need to be made for non-square pulse trains. The above methods ignore some of the biasing issues (and control), which will tend to result in a slightly greater/less than a 90deg phase shift, especially vs input frequency.

#### ata90

##### Member level 5
1.) input waveform into an integrator (with some supporting circuity for biasing) to generate a triangular waveform. The rate of change of voltage is constant and determined by the level of the input square wave*. The amplitude of the waveform scales with frequency (inversely). The delay required for a 90deg phase shift then becomes a A/2. A comparator is used to restore the waveform.

It's nice idea and it will be work correctly for applying 90 deg phase shift. but I'm not sure that the amplitude of output square wave follows the amplitude of input square wave. because after using comparator in last stage, the amplitude of output square wave is constant ( 2VDD in which +VDD and -VDD is supply of comparator ).

2.) A PLL with XOR phase detector can also provide a 90deg phase shift with a square wave input*.

PLL with XOR can apply 90 degree phase shift, however, output signal is logical. ( amplitude of output square wave doesn't follow the amplitude of input square wave.
if it's possible for you, please check post #13 attachment.

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