{{projectinfo|Tutorial| Investigating RF Transmission of Digital Data |RF176MixTUT6 17.png|In this project, the basic concepts of RF.Spice A/D are demonstrated, and you will transmit various pulse waveforms over a simple voltage divider is modeled long transmission line and examinedinvestigate the signal distortion effects.|
*[[CubeCAD]]Transmission Line*VisualizationAttenuation Constant*[[EM.Tempo#Lumped Sources | Lumped Sources]]Pulse Waveform*[[EM.Tempo#Scattering Parameters and Port Characteristics | S-Parameters]] Exponential Waveform*[[EM.Tempo#Far Field Calculations in FDTD | Far Fields]] Digital Source*[[Advanced Meshing in EM.Tempo]] DAC Conversion Bridge*Pulse Width Modulation*Ramp Generator*Nonlinear Controlled Source|All versions|{{download|http://www.emagtech.com/contentdownloads/projectProjectRepo/SystemLesson1.zip System-file-download-repository|EM.Tempo Level Lesson 1|[[EM.Cube]] 14.8}} }}
=== What You Will Learn ===
In this tutorial you will explore the transient response of long [[Transmission Lines|transmission lines]] with resistive and capacitive loads when they are excited with digital signals. You will define a digital source to perform a mixed-mode digital-RF simulationand will transmit the binary output of a pulse width modulator (PWM) over the long transmission line. You will also learn how to define complex waveforms in [[RF.Spice A/D]].
== RF Signal Transmission Over Long Distances ==
| 100
|}
In RF Tutorial Lesson 2, you analyzed the transient response of a quarter wave transformer that was designed to match a 100Ω load to a 50Ω transmission line connected to the voltage source with a 50Ω source resistance at an operational frequency of 2GHz. For this tutorial you are going to use the same circuit but with a much longer transmission line.
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Run a Transient Test of this circuit with the [[parameters]] specified below:
{| border="0"
|-
! scope="row"| Stop Time
| 20m20n
|-
! scope="row"| Linearize Step
| 1u1p
|-
! scope="row"| Step Ceiling
| 1u1p
|-
! scope="row"| Preset Graph Plots
| v(VIN2), v(VOUT4)
|}
== Exploring a Lossy Transmission line ==
So far you have worked mostly with lossless [[Transmission Lines|transmission lines]] with a zero attenuation constant. In this part, you will use a long lossy transmission line segment. Open the property dialog of the T-Line XTL1 and set the value of the '''Alpha''' parameter to 1dB/m. For your 1.5m line, this means a total attenuation of 1.5dB.
<table>
</table>
Run another transient test with the same parameters s before. The results are shown in the figure below. The line attenuation causes additional distortion of the transmitted signal. Also, in comparison to a steady value of 687mV in the previous lossless case, you can see that the peak amplitude of the load voltage has now dropped to a value of 578mV at t = 5.2ns and continues to decline to a value of 528mV at t = 20ns. You can easily verify your results noting that
<math> \frac{v_L^{lossy}}{v_L^{lossless}} = 20\log \left( \frac{578mV}{687mV} \right) = 20\log(0.841) = -1.5dB </math>
<table>
<tr>
</table>
You also need to add a 1-bit DAC Conversion Bridge between the digital source and the analog/RF part of your circuit. Place a DAC bridge in your circuit and set the values of its '''out_low''' and '''out_high''' [[parameters]] to 0V and 5V, respectively. Also make sure to set the '''t_rise''' and '''t_fall''' [[parameters]] both to 1ps. You can use the circuit of the previous part
<table>
<tr>
<td>
[[File:MixTUT6 1416.png|thumb|640px570px|A digital source connected to a long transmission line segmentSetting the output voltage levels and rise/fall times of the DAC conversion bridge.]]
</td>
</tr>
</table>
During You can use the simulation, [[RF.Spice A/D]] places a digital-to-analog (D/A) converter behind circuit of the scenes to convert the binary bit sequence "0" previous part and "1" values to 0 and +5V simply replace the old analog voltages. The resulting waveform then feeds your RF circuit via pulse source with the new digital source resistorand the DAC bridge as shown below. Also, open the property dialog of the T-Line XTL1 and set its '''Alpha''' parameters to zero to have a lossless line.
<table><tr><td>[[File:MixTUT6 14.png|thumb|680px|A digital source connected to a long transmission line segment.]]</td></tr></table> Run a Transient Test of your this circuit with the start and stop times set to parameters specified below: {| border="0 and 5ns, respectively, and a "|-| valign="top"||-{| class="wikitable"|-! scope="row"| Start Time| 0|-! scope="row"| Stop Time| 20n|-! scope="row"| Linearize Step| 1p|-! scope="row"| Step Ceiling of 1ps. | 1p|-! scope="row"| Preset Graph Plots| v(2), v(4), dig_source|} The following figure shows the results for are shown in the source, figure below. The yellow binary input pulse train has a total duration of 8ns, and output voltages. Note that the source input voltage does not jump between 0 and 5V instantaneouslyv(2) drops to zero after t = 8ns. The transmitted pulse train reaches the load at t = 5.125ns. The reflected signal from the load reaches Node 2 at t = 10.25ns, but it has nonzero when you see v(2) rise once again, and fall timesit continues until t = 18. The graph also shows 25ns. Also note the input binary bit sequence sizable distortion of the digital source on a separate digital axis because you just performed a mixed-mode simulationtransmitted signal at the load.
<table>
<tr>
<td>
[[File:RF179MixTUT6 17.png|thumb|900px750px|The graph graphs of the source, input voltage v(2), output voltage v(4) and the binary output voltages in of the quarter-wave transformer circuit with a digital source.]]
</td>
</tr>
</table>
== Exploring Pulse Width Modulation ==
The following is a list of parts needed for this part of the tutorial lesson:
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|-
! scope="col"| Part Name
! scope="col"| Part Type
! scope="col"| Part Value
|-
! scope="row"| VS
| Voltage Source
| Waveform: TBD
|-
! scope="row"| R1
| Resistor
| 50
|-
! scope="row"| X1
| Pulse Width Modulation Block
| Defaults
|-
! scope="row"| X2
| Ramp Generator
| Defaults
|}
A pulse width modulator (PWM) generates the binary data from an analog signal. It has a analog signal input (v<sub>s</sub>) and another input for a ramp generator (v<sub>ramp</sub>). The PWM basically consists of a voltage comparator that compares the ramp and input signals. The binary output is given by:
<math> v_{out} = \begin{array}{ll} V_{high}, & v_s > v_{ramp} \\
V_{low}, & v_s < v_{ramp} \end{array} </math>
Place and connect the parts as shown in the figure below. You can access the Ramp Generator from the menu item '''Menu > Parts > Waveform Generation Blocks > Basic Waveforms > Ramp Generator'''. Open its property dialog and set its '''Period''' to 1ns. Set the '''out_high''' and '''out_low''' voltage levels to +2V and 0V, respectively. You can access the PWM modulator from the menu item '''Menu > Parts > Modulation Blocks > Pulse Width Modulation (PWM) Block'''. Open its property dialog and set its '''T_rmp''' (ramp period) to 1ns. Set the values of '''rmp_high''' and '''rmp_low''' parameters (input ramp min and max levels) to +2V and 0V, respectively. You have to make sure that these parameters are consistent. Keep all the other default parameter values.
<table>
<tr>
<td>
[[File:MixTUT6 19.png|thumb|550px|The property dialog of a PWM modulator.]]
</td>
</tr>
</table>
<table>
<tr>
<td>
[[File:MixTUT6 20.png|thumb|550px|The property dialog of a ramp generator.]]
</td>
</tr>
</table>
Define a sinusoidal waveform for your voltage source according to the table below:
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|+ VS
|-
! scope="row"| Offset Voltage
| 1
|-
! scope="row"| Peak Amplitude
| 1
|-
! scope="row"| Frequency
| 100Meg
|-
! scope="row"| Delay Time
| 0
|-
! scope="row"| Damping Factor
| 0
|}
<table>
<tr>
<td>
[[File:MixTUT6 25.png|thumb|450px|A basic circuit to test a PWM modulator.]]
</td>
</tr>
</table>
Run a Transient Test of this circuit with the parameters specified below:
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|-
! scope="row"| Start Time
| 0
|-
! scope="row"| Stop Time
| 30n
|-
! scope="row"| Linearize Step
| 1p
|-
! scope="row"| Step Ceiling
| 1p
|-
! scope="row"| Preset Graph Plots
| v(1), v(2), v(3)
|}
The results are shown in the figure below. Note that even though the output voltage has a binary nature, switching between the low and high levels, the output of the PWM block is an analog signal.
<table>
<tr>
<td>
[[File:MixTUT6 26.png|thumb|750px|The binary output of a PWM modulator.]]
</td>
</tr>
</table>
== Transmitting a PWM Signal Over a Long Distance ==
The following is a list of parts needed for this part of the tutorial lesson:
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|-
! scope="col"| Part Name
! scope="col"| Part Type
! scope="col"| Part Value
|-
! scope="row"| VS
| Voltage Source
| Waveform: TBD
|-
! scope="row"| XTL1
| Generic T-Line
| Defaults: Z0 = 50, eeff = 1, len = 1500
|-
! scope="row"| XTL2
| Generic T-Line
| Defaults: Z0 = 70.71, eeff = 1, len = 37.5
|-
! scope="row"| RS
| Resistor
| 50
|-
! scope="row"| RL
| Resistor
| 100
|-
! scope="row"| X1
| T_rmp = 1n, rmp_low = 0, rmp_high = 2
| Defaults
|-
! scope="row"| X2
| Ramp Generator
| period = 1n, out_low = 0, out_high = 2
|}
In this part of the tutorial lesson, you will use the PWM modulator of the previous part to feed a binary input signal to the transmission line circuit of the first part. place and connect all the parts as shown in the figure below:
<table>
<tr>
<td>
[[File:MixTUT6 18.png|thumb|750px|Transmitting the binary output of a PWM modulator through a long transmission line segment.]]
</td>
</tr>
</table>
Use the same sinusoidal waveform definition for the voltage source VS:
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|+ VS
|-
! scope="row"| Offset Voltage
| 1
|-
! scope="row"| Peak Amplitude
| 1
|-
! scope="row"| Frequency
| 100Meg
|-
! scope="row"| Delay Time
| 0
|-
! scope="row"| Damping Factor
| 0
|}
Run a Transient Test of this circuit with the parameters specified below:
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|-
! scope="row"| Start Time
| 0
|-
! scope="row"| Stop Time
| 30n
|-
! scope="row"| Linearize Step
| 1p
|-
! scope="row"| Step Ceiling
| 1p
|-
! scope="row"| Preset Graph Plots
| v(1), v(2), v(4)
|}
The results are shown in the figure below. All the three graphs are initially plotted together on a single chart. You can separate the graphs by activating the graph window first and selecting the menu item '''Menu > Edit> Separate Plots With Vertical Tiling'''. The voltage v(1) is the output of the PWM modulator and the same as you saw before in the previous part. You can see from the figure that the output voltage v(4) at the load is visibly distorted. But it still preserves the transmitted data reasonably well.
<table>
<tr>
<td>
[[File:MixTUT6 28.png|thumb|750px|Three separate plots for v(1), v(2) and v(4) with a periodic sinusoidal input signal.]]
</td>
</tr>
</table>
== Defining Complex Input Waveforms ==
The following is a list of the <u>additional</u> parts needed for this part of the tutorial lesson:
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|-
! scope="col"| Part Name
! scope="col"| Part Type
! scope="col"| Part Value
|-
! scope="row"| VP
| Voltage Source
| Waveform: TBD
|-
! scope="row"| B1
| Nonlinear Controlled Voltage Source
| Definition: TBD
|}
So far you have mostly used SPICE's standard voltage sources with a few waveforms like constant, sinusoidal and pulse. In the last part of this tutorial lesson, you will use RF.Spice's "'''Nonlinear Controlled Source'''" to synthesize more complex waveforms. For example, your input signal to the PWM modulator in the previous part was a periodic sinusoid. In this part, you will use a time-limited sinusoid with a finite duration of 8ns. You can make this waveform by multiplying the original sinusoid by a one-shot pulse of the same duration. The latter can be defined as a pulse waveform with an extremely large period. Place the new voltage source VP and define its waveform as specified in the table below:
<table>
<tr>
<td>
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|+ VS: Sinusoid
|-
! scope="row"| Offset Voltage
| 1
|-
! scope="row"| Peak Amplitude
| 1
|-
! scope="row"| Frequency
| 100Meg
|-
! scope="row"| Delay Time
| 0
|-
! scope="row"| Damping Factor
| 0
|}
</td>
<td>
<p> </p>
</td>
<td>
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|+ VP: Pulse
|-
! scope="row"| Initial Voltage
| 0
|-
! scope="row"| Peak Voltage
| 1
|-
! scope="row"| Delay Time
| 0
|-
! scope="row"| Rise Time
| 0
|-
! scope="row"| Fall Time
| 0
|-
! scope="row"| Pulse Width
| 8n
|-
! scope="row"| Pulse Period
| 1e3
|}
</td>
</tr>
</table>
You can place the nonlinear source using the keyboard shortcut {{key|B}}. Define its voltage as the product of the voltages of VS and VP as shown in the figure below:
<table>
<tr>
<td>
[[File:MixTUT6 31.png|thumb|500px|The property dialog of the Nonlinear Controlled Voltage Source.]]
</td>
</tr>
</table>
Your new circuit should like this:
<table>
<tr>
<td>
[[File:MixTUT6 29.png|thumb|750px|The PWM modulator with a long transmission line and a nonlinear controlled signal source.]]
</td>
</tr>
</table>
Run a Transient Test of this circuit with the parameters specified below:
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|-
! scope="row"| Start Time
| 0
|-
! scope="row"| Stop Time
| 20n
|-
! scope="row"| Linearize Step
| 1p
|-
! scope="row"| Step Ceiling
| 1p
|-
! scope="row"| Preset Graph Plots
| v(1), v(2), v(4), v(8)
|}
The results are shown in the figure below. Note that there is no source input to the transmission line after t = 8ns. The size of the reflected signal returning to Node 2 is significant.
<table>
<tr>
<td>
[[File:MixTUT6 30.png|thumb|750px|Three separate plots for v(1), v(2) and v(4) with a time-limited sinusoidal input signal.]]
</td>
</tr>
</table>
Finally, change the waveform of VP to exponential and change the sinusoidal waveform of VS according to the table below:
<table>
<tr>
<td>
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|+ VS: Sinusoid
|-
! scope="row"| Offset Voltage
| 1
|-
! scope="row"| Peak Amplitude
| 1
|-
! scope="row"| Frequency
| 200Meg
|-
! scope="row"| Delay Time
| 0
|-
! scope="row"| Damping Factor
| 0
|}
</td>
<td>
<p> </p>
</td>
<td>
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|+ VP: Exponential
|-
! scope="row"| Initial Voltage
| 0
|-
! scope="row"| Peak Voltage
| 1
|-
! scope="row"| Rise Time Delay (Td1)
| 0
|-
! scope="row"| Rise Time Constant (Tau1)
| 1n
|-
! scope="row"| Fall Time Delay (Td2)
| 12n
|-
! scope="row"| Fall Time Constant (Tau2)
| 0.1n
|}
</td>
</tr>
</table>
<table>
<tr>
<td>
[[File:MixTUT6 32.png|thumb|500px|The property dialog of the voltage source VP with an exponential waveform.]]
</td>
</tr>
</table>
Run a Transient Test of this circuit with the parameters specified below:
{| border="0"
|-
| valign="top"|
|-
{| class="wikitable"
|-
! scope="row"| Start Time
| 0
|-
! scope="row"| Stop Time
| 25n
|-
! scope="row"| Linearize Step
| 1p
|-
! scope="row"| Step Ceiling
| 1p
|-
! scope="row"| Preset Graph Plots
| v(1), v(2), v(4), v(8)
|}
The results are shown in the figure below. Note that the output of the PWM modulator has completely changed from the previous cases due to an entirely different waveform. While highly distorted, the output signal at the load still maintains the digital data. The input signal at Node 2 is identical to the input PWM signal until t = 10.25ns, when the reflected signal from the load strikes. The figure also shows the input analog signal at Node 8. After t = 12.18ns, both v(8) and v(1) drop to zero.
<table>
<tr>
<td>
[[File:MixTUT6 33.png|thumb|750px|Four separate plots for v(1), v(2), v(4) and v(8) with a complex input signal.]]
</td>
</tr>
</table>
<p> </p>
[[Image:Back_icon.png|40px]] '''[[RF.Spice_A/D#RF.Spice_A.2FD_Tutorial 2FD_Tutorials | Back to RF.Spice A/D Tutorial Gateway]]'''