Friday, August 24, 2012
High speed board design interview questions
1. when board trace starts radiating,
Hint:In relation with wavelenth
2. Propagation delay is more in which topology (stipline or microstrip)
3. How to decide layer stack up
4. What is significance of dielectric constant
5. When you call signal as high speed signals:
Hint: do not give silly answers such as greater than 100MHz
6. what is the difference between FPGA and ASIC
7. What is CLB and its significance in FPGA
8. What is SSTL and its advantages
9 When to use terminations, Series termination when? and parallel termination when?
10. Disadvantage of each termination
11. Propagation delay of 1 inch PCB trace on micro strip
12. What is buried via
13. Draw the near end cross talk shape
14. what is far end cross talk and near end cross talk:
Hint: See black magic for good explanation
15.What is the bandwidth of a signal
16. if you increase width and height of transmission line what is effect on charcterstic impedence (Zo)
17. If we measure a cable impedance(Z0=50 ohm) using multimeter what is impedence
18. what is the min bandwidth of oscilloscope required to measure 100MHz signal.
19.what is skin effect
20.Input impedance of short grounded PCB trace looks like 1.inductive 2.Capacitive 3.Resistive
Ans:Inductive
21.what is ISI
22. Write Setup and hold equations for Source synchronous memory
23. Impact of Frequency on on hold time
24. what is great advance of differnetial signalling
25. Why eye diagram used for evaluation of high speed signals
26. What is bath tub curve
27. what is jitter? its types
28. SATA speeds.
29. HDMI speeds
30. HDMI resolutions
31. USB charterstic impedence
32. How USB determines a slave is connected.
33. DDR3 vs DDR2 ( what as hardware board engineer must know)
Routing topology has chaged, RESET pin introduced.
34.what are advantages of CML(current mode logic)
35.How to measure reflections using TDR
36.what are dielectic losses
37. what is CL in DDR
38. How DDR3 speed has been incresed when compared to DDR4
Hint: Pre-Fetch technology is different.
39. what is eye specifications
40. What is significane of equalizer
41. can pre-emphasis and equlaiser be used at same time
42. what is insertion losses
43. what is ground bounce
44. how many number of decoupling capacitors you place around an ASIC,
hint: I=C*dV/dT
45. what is Vcc sag.
46. Explain how you decrese power consumption if you decrease core voltage
47. what is significance of 2D field solver.
48.common mode noise tolerance for LVDS signalling
49.NEXT near end crosstalk grows at what dB/Decade
50.what is S12 signifies
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9 comments:
"1. When board trace starts radiating"
>I have no idea what you are trying to ask here.
"2. Propagation delay is more in which topology (stipline or microstrip)"
>Stripline has longer propogation delay, since there is high dielectric (i.e. no air as in microstrip)
"3. How to decide layer stack up"
> Highly dependant on number of routes on the board, controlled impedance, etc. Controlled impedance will typically always need some type of plane near it
"4. What is significance of dielectric constant"
>This is basically a measure of capactitance of the insulator material. Higher numbers imply more signal loss.
"5. When you call signal as high speed signals"
>Good rule of thumb: when propagation time is much longer than the rise time, then you have a high speed signal
"6. what is the difference between FPGA and ASIC"
> FPGA is field programmable and ASIC is not
"7. What is CLB and its significance in FPGA"
>Configurable Logic Block, this is the programmable parts in an FPGA, like multiplexer, flip flops, adders, etc.
"8. What is SSTL and its advantages"
Stub-series terminated logic. its main advantage is that the voltage swing is fairly low so it operates quickly, and the driver will sink/source current from/to VTT island.
"9 When to use terminations, Series termination when? and parallel termination when?"
Terminations are used when there is a risk of unwanted reflections or ringing clobbering sender's data stream. Series termination is used when increased rise/fall time is acceptable and when driving one load. Series is most power efficient, too.
Parallel termination typically has less propagation delay, but more power.
"10. Disadvantage of each termination"
See above
"11. Propagation delay of 1 inch PCB trace on micro strip"
typical values are .14 ns/inch
"12. What is buried via "
Via is not exposed to outer layers of board.
"13. Draw the near end cross talk shape"
?
"14. what is far end cross talk and near end cross talk"
Near-end: Interference between two pairs in a cable measured at the same end of the cable as the interfering transmitter.
Far-end:Interference between two pairs of a cable measured at the other end of the cable with respect to the interfering transmitter.
"15.What is the bandwidth of a signal"
Range of signal frequencies that are passed in the signal
"16. if you increase width and height of transmission line what is effect on charcterstic impedence (Zo)"
Wider trace means lower Zo. Increasing height of trace (i assume you mean distance from plane) increases Zo.
"17. If we measure a cable impedance(Z0=50 ohm) using multimeter what is impedence "
DOn't understand the question, be more specific
"18. what is the min bandwidth of oscilloscope required to measure 100MHz signal."
200 MHZ
"19.what is skin effect "
As frequency gets very high, i.e. several hundreds of MHZ or into the GHZ, the current will flow mostly along outsides of the conductor.
Sorry, i got sick of this. Please explain #17
For #17. What will be the multimeter (Resistance mode)reading when you measure 50 ohm(Zo = 50 ohm) cable.?
Ans: The reading will be "OPEN" provided that cable length is defined length. Since, typ. multimeter cannot capture the instantaneous impedance. Need TDR to measure the cable impedance.
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17.measuring the cable with a Multimeter is its resistance and not its impedance(which need special setup or instruments like TDR etc).
Hardware Design Interview Questions and Answers
http://allinterviewquestionsandanswerspdf.blogspot.in/2016/06/top-10-hardware-design-interview.html
1-I think 2 conditions may be possible.
1- When trace length become more than 1/3 of its rise time then radiation started.
2-When loop area become large then radiation started.
Please elaborate question. no. 5 how propagation delay is more than rise time will be called as high speed signal?
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