*Ramp Generator
*Nonlinear Controlled Source
|All versions|{{download|http://www.emagtech.com/contentdownloads/project-file-download-repository|ProjectRepo/SystemLesson1.zip System-Level Tutorial Lesson 1|[[RF.Spice A/D]] R15}} }}
=== What You Will Learn ===
In this tutorial you will explore the transient response of long [[Transmission Lines|transmission lines]] when excited with digital signals. You will define a digital source to perform a mixed-mode digital-RF simulation and 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 ==
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Run a Transient Test of this circuit with the [[parameters]] specified below:
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== 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.
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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>
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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.
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You can use the circuit of the previous part and simply replace the old analog pulse source with the new digital source and 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.
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Run a Transient Test of this circuit with the [[parameters]] specified below:
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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.
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Run a Transient Test of this circuit with the [[parameters]] specified below:
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Run a Transient Test of this circuit with the [[parameters]] specified below:
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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:
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Run a Transient Test of this circuit with the [[parameters]] specified below:
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! scope="row"| Preset Graph Plots
| v(1), v(2), v(4), v(8)
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Run a Transient Test of this circuit with the [[parameters]] specified below:
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