Pulse and sine signal

[Ipanema]

Hi,

I got a very fundamental question to ask. What is the difference between pulse and sine wave? When I applied both signal to a high pass filter(series connected capacitor), pulse DC level does not goes to zero, while sine signal DC level goes to zero. Pls advise.

Thanks,

 

[simonkuo]

Does your circuit have plus and minus power supply?
If it is true, the sin wave average value will be zero, and pulse not.
Maybe it is the reason.

 

[cetc1525]

pulse has hamonics.

 

[hrkhari]

Hi Guys:

This is b'coz in frquency domain pulse wave is observed to have odd order harmonics whereas a sine wave has only one harmonic at the desired frequency. Hope this helps

Rgds

 

[echo47]

DC level does not goes to zero??

Your input signal goes through a capacitor, through a resistor, into ground, and you are measuring the voltage across the resistor. Correct?

What type of pulses? How are you measuring the DC voltage? Maybe your measuring instrument has some surprising behavior.

 

[Ipanema]

Hi all,

thanks for replying. I didn't connect the series capacitor to an output load. When I connect the series cap (2pF) to an output load of 10Kohms (-3dB at 7.95MHz) with input pulse signal at 15Ghz, the pulse DC level goes to zero. But I don't understand why wth sine wave, the dc will go to zero even if no output load is connected. maybe this is HSPICE bugs?

Thanks

 

[echo47]

If you don't connect the series capacitor to any output load, then no current flows, so you don't have a high pass filter.

The average DC value of a sinewave is zero.

I must be missing something. Can you show us your schematic or Spice code, and explain better what you mean by "the DC level goes to zero"?

 

[layes2]

pulse is a square wave
and sine is sine wave

 

[radigital]

Usually high pass circuits which have a series
capacitor will act as DC blockers. For example,
all discrete transistor amplifiers which use BJTs will
usually have a capacitor in series with the input signal before
the amplifier. This capacitor will block the DC component
in your input signal so that it will not change the base bias
of your amplifying BJT device.
So all circuits having capacitors in series path between
their output and input block DC components of the
signals passing between them.
You can imagine you sine wave as having two components:
an AC component of some frequency and a DC component.
What your high pass circuit does is to pass the AC
component but block the DC component, which is why
your output signal will always have zero DC.

Hope this helps.