Microwave and High Speed Digital Design

Academic Year 2019/20

P30026 – Microwave and High Speed Digital Design

Referral Assessment

Instructions:

Complete Both Parts

Additional Information:

This is an open book coursework.

Type your answers using Word or similar word processing software, then convert to pdf and submit via Moodle Inbox on the unit site by the specified deadline in Moodle.

Part A only: Alternatively, you can write and scan your answers to Task 1. In that case, make sure your submission is clear and readable. Illegible sections of your answer will not be marked. You DO need to show all your working, derivations and calculations where necessary. Correct answers without supporting calculations will earn zero marks without shown calculations, even if correct.

Calculators:

Any calculator or mathematical software

Examiners:

Manish Malik

Rallis Papademetriou

Deadline: 7th August 2020, 23:00 hrs.

2019-20 Page 2 of 5

Part A

1 (a) A clock signal has a swing of 3 V, a frequency of 120 MHz and rise time of 0.5 ns. Find

the approximate 3-dB bandwidth of the signal.

[3 Marks]

(b) (i) Determine how long it takes for a logic transition on a 24 inches, seriesterminated

PCB trace to settle along the entire length of the trace. Assume a

stripline trace with a 𝜀𝑟 of 4.

[4 Marks]

(ii) Which of the following are generally likely to make a PC board trace behave more

like a transmission line and less like a lumped load?

Explain.

A – Increasing the voltage swing of the driver

B – Decreasing the rise time of the driver

C – Increasing the length of the trace

D – Making the trace wider

[6 Marks]

(c) (i) A driver with a 3 V output swing and an output impedance of 10 Ω is connected

to a 50 Ω trace. If the driver transitions from LOW to HIGH, calculate the size of

the initial wavefront that travels down the line.

[3 Marks]

(ii) The circuit shown below represents two power supply rails of a circuit board

fitted with TTL components (rise time = 10 ns). The DC supply current for each

rail is as shown. Measurement of interference on these rails has indicated the

presence of capacitive cross-talk. It is observed that 0.75 V, 10 ns rise time

transients on the 10 V rail are inducing similar rise time impulses of 150 mV on

the 5 V rail. Calculate the value of the coupling capacitance.

[6 Marks]

(iii) Give the definition of skin effect and its effect on the edge rates.

[3 Marks]

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2 (a) Assume that an oscilloscope and a probe are both rated at 300 MHz (specifications are

3-dB bandwidths).

(i) Determine how this combination will affect signals having 2 ns rise times.

[4 Marks]

(ii) If the scope displays a 2.2 ns rising edge, find the actual input rise time.

[2 Marks]

(b) Determine the dimensions of a rectangular FR4 microstrip circuit board fitted with

digital circuitry of minimum tr = 12 ns, at which propagation delays of 60 ps/cm start

becoming significant.

[5 Marks]

(c) A driver with source resistance 25 Ω is connected to a trace terminated with a 50 Ω

resistor. If the initial wavefront that travels down the line is 2.25 V and the steady state

voltage is 2 V, determine the characteristic impedance of the trace.

[6 Marks]

(d) (i) Specify the cause of crosstalk in high speed digital systems.

[3 Marks]

(ii) Specify the level of system hierarchy at which interconnect effects exist.

[2 Marks]

(iii) List the major bottlenecks for today’s high speed designs and give the main

reason for their occurrence.

[3 Marks]

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3 (a) Determine the parameters that the

(i) ripple frequency, and

(ii) ripple amplitude

depend on.

[4 Marks]

(b) (i) Determine the typical method of representing the ‘parasitics’ that govern the

electrical performance of a coupled transmission line system.

[3 Marks]

(ii) Define and comment on the various parameters in these representations.

[3 Marks]

(c) A driver with source resistance 23 Ω and a swing of 0 to 2.9 V is connected to a receiver

of input resistance 20 kΩ via a 7 inch long trace having characteristic impedance 70 Ω

and propagation delay 150 ps/in.

(i) Use a lattice diagram to calculate multiple reflections on the trace.

[11 Marks]

(ii) Sketch the time representations of the reflected signals at the source and at the

load.

[4 Marks]

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Part B

1. Microwave Circuit Design task

For this assessment, you will work on the same block as you had chosen to work on during TB1. For

marking scheme and task details refer to the CW document issues in TB1:

https://moodle.port.ac.uk/pluginfile.php/1635546/mod_resource/content/1/Microwave%20CW%2

0%281%29.pdf

Transform the design you made earlier to new frequencies F1 and F2, both 100 MHz higher than the

frequency you have already worked with.

Please note, there is no need to submit the team tasks, simply rework your design for your block

with the two new frequencies.

What to submit

A report, no more than 1500 words, detailing your work, results and conclusions. Also upload

separately your simulation files used in AWR.