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Substrate Noise Coupling in Analog/RF Circuits

Answers to RF Cafe Quiz #26
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All RF Cafe quizzes would make perfect fodder for employment interviews for technicians or engineers - particularly those who are fresh out of school or are relatively new to the work world. Come to think of it, they would make equally excellent study material for the same persons who are going to be interviewed for a job.

Some of these books used in quizzes are available as prizes in the monthly RF Cafe Giveaway.

Note: Many answers contain passages quoted from the text.


Return to RF Cafe Quiz #26



RF Cafe Featured Book - Substrate Noise Coupling in Analog/RF CircuitsThis quiz is based on the information presented in Substrate Noise Coupling in Analog/RF Circuits, by Stephane Bronkers, Geert Van der Plas, Gerd Vandersteen, and Yves Rolain. Published by Artech House.
 Note: Some of these books are available as prizes in the monthly RF Cafe Giveaway.


1.  Which is NOT a class of substrate noise analysis?

RF Cafe - "Substrate Noise Coupling in Analog/RF Circuits" Figure 1.1d)  Transverse

Figure 1.1, on page 3, illustrates generation, propagation, and
impact substrate noise analysis partitioning.






2.  What is the most popular and straightforward method for shielding analog integrated circuits
      against substrate noise?

b)  Guard rings

Per page 39, "Guard rings are passive isolation structures, which prevent substrate noise currents from reaching the analog circuitry."



3. Aggressor and victim refer to what process?

b)  The source of and recipient of substrate noise, respectively

An aggressor is the area of the substrate generating the potential noise source, and the victim is the area to which the noise is coupled. See Figure 3.3 on page 41.



4.  What is the best way to separate substrate coupling noise from other regional noise coupling sources when developing mixed (digital/analog) signal devices?

a)  Dice between the regions to physically separate the digital/analog regions, then wire bond between

During the development/characterization process, a dicing line can be designed into the die that allows physically separating the two (or more) partitions, then wire bonding between regions after mounting to a carrier. Wire bond lengths can usually be kept short enough to not degrade function, but still permit determination of substrate noise sources. See page 145.



5.  At high frequencies, which off-chip noise coupling mechanism typically dominates?

d)  Magnetic coupling between die bond wires

Magnetic coupling between the die bond wires is typically many decibels greater than PCB trace coupling. See page 142.



6.  What is the primary source of FM modulated noise spurs?

c)  Perturbations on the ground interconnect

"To reduce the power of the FM modulated spurs, the impedance of the on-chip ground interconnect has to be small compared to the impedance of the PCB ground network." See page 174.



7.  In a VCO circuit, what is a likely mechanism for AM spur generation and intermediate frequencies?

a)  Capacitive coupling from on-chip inductors to the substrate

Parasitic capacitance permits the AM coupling by altering the reference potential of the substrate. See page 175.



8.  How are digital and analog grounds kept separate on the die?

d)  Separate digital / analog ground metal on the die, with separate off-chip digital / analog
     grounding points

As with PCB design, maintaining isolated digital / analog grounds( and supplies when practical) is the best method for avoiding coupling noise. Inserting a small value resistor (0.5 ohms) between the PCB ground and the IC mounting pad can help reduce ground reference bounce. See page 186.



9.  For what purpose is parasitic extraction used?

c)  Obtaining parasitic RLC values for use in simulation

In order to allow more accurate simulation of devices, it is necessary to construct a robust equivalent circuit model that includes intentional and unintentional R,L, and C values. The model can then be used with high confidence in other designs. See page 200.



10.  What determines to a large extent the efficiency of a P+ guard ring?

a)  Impedance of the ground interconnect

Substrate currents are picked up by the P+ region of the guard ring and are drained toward the PCB ground. See page 65.
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