# Transmission lines bounce diagram

• likephysics
In summary, the reflected wave at the load is 1 and the reflected wave at the source is 0, resulting in a pulse waveform that starts and ends at -1.65V and has a peak of 3.3V. This is due to the matched impedance of the transmission line and the source, causing a voltage division and resulting in a full positive reflected wave.
likephysics

## Homework Statement

This is not a HW problem. Just refreshing Tx line theory(reflections).
I have a pulse of 3.3v, period 36nsecs. (Ton=18ns, Toff=18ns) with a source impedance of 50 ohms, connected to a tx line of impedance 50 ohms. The load is high impedance or infinity.
So reflection at load is 1 and reflection at source is 0.
I drew the pulse waveform, but the pulse ends up at -1.65v. This does not agree with my Signal integrity simulation. So I wanted to double check if my work is right. Pls see attachment.

## Homework Equations

To draw bounce digram for a pulse, I made 2 sources. One with +3.3v and the other with -3.3v.
Also, when should I stop drawing the bounce diagram. In my case $$\Gamma$$g is 0. so, after 3ns : ($$\Gamma$$L * $$\Gamma$$g* V1+) will be zero.

L is load and g is for generator.

## The Attempt at a Solution

#### Attachments

• Hithesh.pdf
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likephysics said:

## Homework Statement

This is not a HW problem. Just refreshing Tx line theory(reflections).
I have a pulse of 3.3v, period 36nsecs. (Ton=18ns, Toff=18ns) with a source impedance of 50 ohms, connected to a tx line of impedance 50 ohms. The load is high impedance or infinity.
So reflection at load is 1 and reflection at source is 0.
I drew the pulse waveform, but the pulse ends up at -1.65v. This does not agree with my Signal integrity simulation. So I wanted to double check if my work is right. Pls see attachment.

## Homework Equations

To draw bounce digram for a pulse, I made 2 sources. One with +3.3v and the other with -3.3v.
Also, when should I stop drawing the bounce diagram. In my case $$\Gamma$$g is 0. so, after 3ns : ($$\Gamma$$L * $$\Gamma$$g* V1+) will be zero.

L is load and g is for generator.

## The Attempt at a Solution

It depends on whether your square wave driven is 0V to +3.3V, or -3.3V to +3.3V as you have drawn.

If it is +/-3.3V as you have drawn, then your bounce diagram is correct. Just keep on extending the timeline of the v(t) waveform, and you'll see it is correct.

Since the Zo of the TL is matched to the Zout of the source, there is a voltage division, and the initial wave headed down the TL is 1.65V. When it reflects off the far end, you get a full positive reflected wave, and as it propagates back up the TL, it raises the voltage along the TL to the full 3.3V output of the source. When that reflected wave hits the source, there are no further reflections, so the TL stays charged up to the DC 3.3V.

When the source transitions down to -3.3V, you again get the voltage division against Zo of the TL, so you get -1.65V, until the full (same direction) reflection from the far end of the TL can push the voltage down all the way to -3.3V.

## 1. What is a transmission line bounce diagram?

A transmission line bounce diagram is a graphical representation of the voltage and current behavior in a transmission line that is terminated with an open or short circuit at one end. It helps to visualize the reflections and standing waves that occur in the line due to impedance mismatches.

## 2. How is a transmission line bounce diagram useful?

A transmission line bounce diagram is useful for analyzing the behavior of transmission lines and predicting the effects of impedance mismatches. It can also be used to design and optimize transmission line circuits for maximum power transfer.

## 3. What factors affect the shape of a transmission line bounce diagram?

The shape of a transmission line bounce diagram is affected by the length and characteristic impedance of the transmission line, the frequency of the signal, and the type of termination (open or short circuit).

## 4. How do you interpret a transmission line bounce diagram?

The peaks and valleys on a transmission line bounce diagram represent voltage and current reflections, respectively. The amplitude of these reflections can be used to calculate the standing wave ratio (SWR) and the magnitude of the reflected power. A flat line indicates no reflections and maximum power transfer.

## 5. Can a transmission line bounce diagram be used for any type of transmission line?

Yes, a transmission line bounce diagram can be used for any type of transmission line, including coaxial cables, microstrip lines, and waveguides. However, the shape and behavior may vary depending on the characteristics of the specific type of transmission line being used.

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