# bipolar waveforms VS SUM waveforms

#### relicmarks

Joined Oct 13, 2006
355
Bipolar waveforms - are not summed but are mixed with DC offset i guess

Dual waveforms- Are two seperate waveforms

AC waveforms- are alternating in polarity from positive to negative

In video electronics they use Bipolar waveforms

On the RED color channel they sum the RED color with the vertical sync, so when you look at the RED channel on the oscilloscope you will see a "bipolar waveform" it will be a red channel video waveform + the vertical sync riding ontop or DC offset to superimpose the vertical sync

They do the same with the BLUe color channel but they sum the hortizonal sync, so when you look at the Blue channel on the oscilloscope you will see a "bipolar waveform" its the blue channel video waveform + the hortizontal sync

Another Bipolar waveform example is

The sum/bipolar the RED color channel with the LEFT audio channel and the BLUE channel they sum/bipolar RIGHT audio channel

Bipolar waveforms VS summing waveforms are difference because Summing would take 2 different waveforms and merge them together into One.

Bipolar waveforms examples:
1.) analog video signal + digital vertical or horizontal sync waveforms on ONE channel or single ended channel
2.) Analog Video signals + audio left or right channels onto a single ended channel or ONE channel

THey use differential Op-amps in differential MODE to Input pin#1 will be the analog video signal RED and Input pin#2 will be the vertical sync signal

They use these Video driver op-amp chips that do this so you can mix video signals with digital vertical and horizontal sync signals

**DOn't ever SUMM or Bipolar audio with Digital signals this will create buzzing and noises**

Why is it a "bipolar" waveform and not a summed waveform#1::
is because on the oscilloscope display on ONE channel you can see 2 difference waveforms, you can see the RED channel + the vertical sync seperated by DC offset it seems, even when the oscillscope is on the AC coupled the bipolar signals are still riding/superimposed or seperated from one another

Why is it a "Bipolar" waveform and not a summed waveform#2::
is because the op-amp is in differential mode using the input pin positive (+) and input pin negative (-)

Bipolar waveform#1 example:
Video RED channel is on input pin (+)
Vertical sync is on input pin ( - )
Output is Bipolar = Video red channel with the Vertical sync

Bipolar waveform#2 example:
Video RED channel is on input pin ( + )
Audio LEFT channel is on input pin ( - )
Output is Bipolar = Video Red channel with the Audio Left channel

Bipolar waveform#3 example:
Video BLUE channel is on input pin ( + )
*Digital logic* , clocks signals , data lines , control lines on input pin (-)
Output is Bipolar= Video Blue channel with digital signals etc.

Summing would need summing resistors and its a single ended input and single ended output

I think with summing you can't SUM or mix analog signals with digital signals

I'm not sure with summing you can sum/mix video signals with digital signals

#### Søren

Joined Sep 2, 2006
472
Hi,

Bipolar waveforms - are not summed but are mixed with DC offset i guess
[Snip]

Bipolar waveforms VS summing waveforms are difference because Summing would take 2 different waveforms and merge them together into One.
[Snip]

Summing would need summing resistors and its a single ended input and single ended output
Mixing IS summing, whether there's a DC offset or not.
A difference signal... Do you mean summing with one signal inverted or are you perhaps "mixing in" some info about frequency mixing (or do you mean the kind where you use difference resistors )?

I am not really sure what your question is?

#### beenthere

Joined Apr 20, 2004
15,808
Bipolar means having both positive going and negative going components. That's also the definition of AC. With enough offset, a bipolar waveform can be made to be unipolar. There is no need or reason to have a DC component in a bipolar waveform. If there is an offset, use a coupling capacitor to remove it, as in AC amplifiers

It's fairly easy to convert from single-ended to differential and back.

If the frequencies are far enough apart, mixing digital and analog is no biggie - that's how DSL functions. Even analog signals can mix with different frequencies and be used separately. FM broadcast radio has space for subcarrier channels for things like dentist office background music.

#### relicmarks

Joined Oct 13, 2006
355
HOw do you mix digital and analog signals?

What is the theory behind it please? and what modes or techniques are they called and used ?

Whats the difference between a unipolar Vs a Bipolar waveform then?

#### beenthere

Joined Apr 20, 2004
15,808
The digital bitstream is not mixed in with the audio as a continuous string of 1's and 0's. A high frequency carrier is modulated by the state of each byte of data. I don't recall if it's PSK or FSK. The important part is that the frequency of the audio and the digital data are so different that it's easy to use filters to eliminate the digital out of the audio, and vice versa.

There is no theory in particular - dissimilar signals have been mixed together since tv standards got set in 1927.

A signal is unipolar if it always stays on the same side of ground, or circuit common. It becomes AC (bipolar) if it ever crosses to the opposite polarity during any portion of the waveform. A sine wave that is negative for 99.99% of the envelope is considered AC when that remaining .01% goes positive. This is elementary. You could do yourself a favor and at least read through the first two chapters of the Ebook.

#### relicmarks

Joined Oct 13, 2006
355
unipolar signal
1.) A rectified waveform
2.) a digital signal staying at ground to positive or ground to negative

bipolar
1.) AC alternating polarities or AC component + Digital DC component or DC toggling levels

----------------------------------------------

Bipolar MIXING and summing lesson:

74HC74 chip ( its a flip flop )
1.) D input
Clock input
Q output

Bipolar mixing stage/chip:
2.) Put the Audio waveform in the D input
3.) Put the Digital waveform signal in the Clock input

Bipolar output stage/chip:
4.) Q output of the 74HC74 is going to have Audio signal + the Digital signal how so ??

EL5370 video chip:

Bipolar mixing stage:
1.) Red,green,blue colour " analog" inputs goes to the EL5370 video chip inputs
2.) 74HC86 Vertical sync and horizontal sync "digital" signal goes to the EL5370 video chip inputs

Bipolar output stage:
3.) EL5370 video chip outputs Bipolar waveforms
a.) RED channel is analog + vertical sync is digital signal
b.) BLUE channel is analog + horizontal sync is digital signal

4.) On the oscilloscope viewing the RED channel you will see a "bipolar waveform" because you will see the RED channel that is analog AC and the vertical sync which is a digital signal, you see a AC component and a DC component at the same time on the single ended channel #1 on the oscilloscope this is a True bipolar signal

#### thingmaker3

Joined May 16, 2005
5,073

#### Audioguru

Joined Dec 20, 2007
11,251
Relicmarks (AKA Walters),
What type of video signals are you talking about??

NTSC composite video on an analog TV has black and white video (luminance), vertical and horizontal sync, color sidebands (chrominance) and color burst all combined. The FM sound for TV is on its own carrier frequency 4.5MHz above the video carrier frequency.
The sound is multiplexed into stereo.

The signals are not "mixed". When it is time for a sync pulse then the luminance and chrominance signals are cutoff and the sync pulse occurs with its proper voltage levels.
During color burst the luminance and chrominance signals are also cutoff and the color burst has the proper voltage level. The luminance and chrominance signals are not mixed but are combined together so that their frequencies interleave with each other.

Chrominance has the 3 colors combined to make two signals in quadrature phase and modulated in double sideband suppressed carrier. One of the two signals (flesh-tone colors) has a wider bandwidth than the other.

The colors are not transmitted separately and they do not have sync nor audio mixed with them.

#### relicmarks

Joined Oct 13, 2006
355
When it is time for a sync pulse then the luminance and chrominance signals are cutoff

What you mean by this Cutoff?

The luminance and chrominance signals are not mixed but are combined together so that their frequencies interleave with each other.

How is interleave done?

How is interleave different that mixing?