Questions and Answers

Test your understanding of Signal Integrity with the questions.

Q1. A high speed digital signal has a 10% to 90% rise time of about 175 psec. What is the approximate bandwidth of the signal?

A. 10 MHz
B. 500 MHz
C. 2 GHz
D. 5 GHz


Q2. An Oscilloscope has rated bandwidth of 10 GHz. Using this oscilloscope the 10%to 90% rise time of this signal is observed to be 60 ps. What is the approximate actual rise time of the signal.

A. 30ps
B. 48ps
C. 56ps
D. 74ps


Q3. Consider the following two capacitors

C = 10uF, Effective Series Inductance = 2 nH
C = 4.7uF, Effective Series Inductance = 0.5 nH


Which of the following two capacitors is more effective for power supply filtering at 10 MHz

A. The Capacitor with 10uF capacitance and 2nH inductance
B. The Capacitor with 4.7uF capacitance and 0.5nH inductance


Q4. An SMD test pad is added on a signal path of a microstrip PCB trace for probing. The width of the test pad is wider than the trace. What is the effect of the test pad on the trace impedance.

A. Trace impedance decreases at the test pad.
B. Trace impedance increases at the test pad.
C. There is no effect on the trace impedance due to the test pad.


Q5. Which of the following is best for very high frequency ( 1 GHz or more) power supply noise filtering

A. Electrolytic Capacitors
B. Ceramic Capacitors
C. Ceramic capacitors with low ESR.
D. Capacitance formed by power planes


Q6. Consider the approach where source series termination as well as the end parallel termination is used. Which of the following is not true about this termination scheme.

A. This reduces the signal amplitude at the receiver.
B. This scheme has better chance of reducing the reflection as compared to source series termination alone or the end parallel termination.
C. This termination scheme increase the signal reflections.


Q7. Consider a transmission line with characteristic impedance Zo. A driver of source resistance x drives the transmission line. What should be the value of the series resistance to in the series termination scheme to minimize reflection:

A. Zo-x
B. Zo/2 –x
C. (Zo-x)/2
D. Zo+x


Q8. The electric signal travels fastest in

A. Stripline
B. Microstrip with soldermask
C. Microstrip without soldermask


Q9. Which of the following is not a reason for using adjacent ground and power plane scheme.

A. It provides power supply filtering at very high frequency.
B. They provide decoupling for low frequency noise.
C. Adjacent power and ground planes have high inductance between them required for high speed signals.
D. It reduces EMI.


Q10. Which of the following is NOT a preferred reason for choosing a BGA package over a QFN package.

A. A BGA package has lower lead inductance
B. BGA package are easier for assembly house and are better for board level testability.
C. A BGA package will have lower SSN noise.


Q11. Consider the 6 Layer stack ups with following two possible arrangements

Stackup A

Layer1
GND
Layer2
Layer3
VCC
Layer4


Stackup B

Layer1
Layer2
GND
VCC
Layer3
Layer4


Which of the following statements is NOT true.

A. In stackup B, the separation between GND and VCC is kept minimum for more power plane capacitance.
B. In stackup B, high speed signals are routed mostly on Layer2 and Layer3.
C. In stackup A, high speed signals can be routed on all four signal layers.
D. Stackup A is better from the power plane capacitance perspective, as it has more capacitance per unit area than that of stackup B.


Q12. Which of the following packages have highest pin inductance

A. DIP
B. QFP
C. PLCC
D. BGA

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