ECE342 EMC Lab #5. Transmission Line TransientsName:_____________________________ Box:__________( Individual work! Each student must turn in this lab worksheet with the three requested PSPICE simulation attachments. Each student is expected to bring to this lab session their laptop with Cadence Orcad Lite Version 9.2 PSPICE installed!)1. “LC” Analog Delay Line (Distributed Transmission Line Model)Consider the “LC” analog delay line, or “synthetic transmission line”, shown in Figure 1. It consists of10 LC sections, where each section is Δz in length. The entire line length is therefore 10Δz. This circuit only approximates the behavior of a real transmission line, since Δz has not been shrunk down to an infinitesimal length (which would require an infinite number of L and C components for a finite length of line!) Note that the inductance per unit length is L = L/Δz, and the capacitance per unit length is C = C/Δz, where in this example, L = 4.6 mH and C = 0.33 μF. Figure 1. Analog “LC” delay line (approximate distributed transmission line model)C 40 . 3 3 U Fd e l zL 54 . 6 m HL 74 . 6 m HC 70 . 3 3 U FL 24 . 6 m H1 0 d e l zR L5 0L 44 . 6 m HVC 20 . 3 3 U FC 60 . 3 3 U Fv o ( t )C 80 . 3 3 U FL 94 . 6 m H++C 10 . 3 3 U F0V gT D = 0T F = 0P W = 3 0 0 U SP E R = 2 m sV 1 = 0 VT R = 0V 2 = 1 VC 30 . 3 3 U F-L 64 . 6 m HL 34 . 6 m HR g5 0-L 14 . 6 m Hv i n ( t )C 1 00 . 3 3 U FC 50 . 3 3 U FV+-C 90 . 3 3 U FL 1 04 . 6 m HL 84 . 6 m HThus the approximate characteristic impedance and velocity of propagation of this line are approximately given by CLzCzLZo // LCzzCzLvp)/)(/(1 The propagation delay time Td, or the travel time from the input to the output terminals of the line, is given by Td = Line_Length / vp = 10Δz / vpAdjust the Agilent function generator (with an output resistance of Rg = 50 Ω) to deliver a “short” Vg = 0 V to 1 V step train with a duration of 300 μs and a period of 2 ms. (We shall define a “short pulse” as a pulse whose duration is less than twice the propagation delay of the line, thus the short pulse ends BEFORE the first reflection from the receiving end arrives back at the sending end.) With RL set to about 50 Ω, determine the delay time (Td) using the Agilent oscilloscope with its probes placed at both the sending and receiving ends. Then vary RL until no echo is received back at the 1sending end. The value of RL that results in no echo must be equal to the characteristic impedance of the line, and the line is said to be “matched”. Record your measured values of Td and Zo, and calculate % error between the measured and predicted results. Fill in the blanks below: Td(pred) = ____________ Td(meas) = ____________ % error = _________Zo(pred) = ___________ Zo(meas) = ___________ % error = _________In the space below, sketch the observed vin(t) and vo(t) for RL set to 0 (short-circuit termination), for RL = Zo (matched termination), and for RL set to infinity (open-circuit termination). Note that the wave shape of the pulse becomes increasingly distorted as the pulse travels back and forth on the line, since this circuit is only an approximation to a true lossless transmission line. Sketch of vin(t) and vo(t) for RL = infinitySketch of vin(t) and vo(t) for RL = Zo Sketch of vin(t) and vo(t) for RL = 0Now simulate this circuit using ORCAD PSPICE. Use the VPULSE source (V1 = “down” voltage, V2= “up” voltage, TD = delay before pulse rises, TR = rise time, TF = fall time, PW = width of pulse, PER = period of pulse train) and a time-domain (transient) simulation. Note that this source generates a train of pulses, but we will focus only on the response to the first pulse out of the generator. Include as Attachment A your PSPICE schematic and your PROBE plots of vi(t) and vo(t) for the same three observed cases: RL = 0, RL = Zo, and RL = infinity. Your PSPICE simulation plots should closely resemble the observed plots sketched above. Note: PSPICE does not like 0 ohm resistors, so the first case must be simulated using a very small resistor, say RL = 0.001 ohms. Also, remember that PSPICE simulations require that a ground symbol with a “0” be used. Next, simulate this circuit using ORCAD PSPICE using an ideal lossless transmission line component, which is designated “T” in the PSPICE library. Your circuit should look like Figure 2. Once you have drawn this circuit, single left click on the transmission line symbol to select it (it should be surrounded 2by a pink dotted box), then single right click on this box and choose “Edit Properties”. Scroll to the right to the Zo and Td entry boxes in the Properties Window, and enter the desired values of Zo and Td that you calculated earlier. Include as Attachment B your schematic diagram (for just one of the cases) and the three resulting PROBE plots of the sending and receiving end voltages, vi(t) and vo(t) for the three cases considered above (RL = 0, RL = Zo, and RL = infinity). Use the ORCAD “Toggle Cursor” button and “Mark Label” button to label the relevant vin(t) and vo(t) voltage levels directly onyour PROBE plot. Figure 2. Precise transmission line modeling in PSPICE using the “T” (lossless transmission line) component V gVT D = 0T F = 0P W = 3 0 0 U SP E R = 2 m sV 1 = 0 VT R = 0V 2 = 1 Vv i n ( t )0+T 1-F u n c t i o n G e n e r a t o rT d = 3 8 9 . 6 u SVv o ( t )Z o = 1 1 8 . 1 o h m sR g5 0+-+R L-2. Transients on a Real Transmission LineIn this section of the lab demo, we will be working with a rolled up coaxial cable that was acquired as military surplus. It was used to provide a precise analog delay in a radar system. This “Mystery Line” is somewhat cryptically labeled “Short Delay Coil 25 m”. Let us assume that this coaxial cable uses polystyrene dielectric, as do most coaxial cables. Polystyrene has a relative permittivity of εR = 2.25, and thus vp = 1/sqrt(με) = 3 x 108 / sqrt(2.25) = 200 m/μs. We shall adjust the Agilent function generator to deliver a Vg = 0 V to 1 V “short pulse” (PW < 2Td) with a width of 0.1 μs, and a period of10 μs, using the circuit of …