# Ultra Low Power BioelectronicsAnswers to RF Cafe Quiz #24

All RF Cafe quizzes would make perfect fodder in 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.

Note: Some material based on books have quoted passages.

This quiz is based on the information presented in Ultra Low Power Bioelectronics: Fundamentals, Biomedical Applications, and Bio-Inspired Systems, by Rahul Sarpeshkar, published by Cambridge University Press.
Note: Some of these books are available as prizes in the monthly RF Cafe Giveaway.

1.  Which formula represents what is known as "1/f" noise?

b)  1/fn

Noise has many sources, including thermal. flicker, 1/f, etc. The 1/f component dominates in the region from DC to the point where 1/f noise is equal to white noise power (fc).
An explanation, along with the chart to the right, is from page 170.

2.  What is Return Ratio Analysis?

b)  A method for analyzing circuit robustness in response to changes in gain or impedance

Return ratio is a quantity analogous to the robustness of a transmission feedback loop, in that its analysis quantifies the robustness of a circuit in response to a change in gain or impedance.
An explanation is given in chapter 10 (p 240).

3.  What is the name of the process used to simplify
analysis of a complex system when an additional
passive element is added in parallel?

c)  Middlebrook's extra-element theorem

This approach defines how to simplify analyzing a complex system (for which a transfer function is known) when a passive element is added in parallel or in series to it.
An explanation is given on page 261.

4.  What function does a gyrator circuit perform?

a)  Inverts impedance (changes L to C, or C to L)

This is an Electronics 101 circuit that uses a one or more active elements to basically switch the sign of the imaginary part of a complex impedance.
An explanation is given on page 333.

5.  What is a key feature of a neuron-inspired analog-to-digital converter?

a)  Brain-like logic
b)  Small size comparable to neurons
c)  A concept though of while using the inventor's brain's neurons
d)  Energy efficiency

Just as the biological brain is an extremely efficient processor of information, a properly configured ADC circuit can gain enhanced efficiency.
An explanation is given on page 395.

6.  What does the Bode-Fano criterion state?

d)  For passive loads (series or parallel RC or RL), there is an inverse relationship between good
impedance matching at a single frequency and good matching across the entire band

This is intuitive to anyone who has struggled to find a good impedance match across a wide bandwidth using a minimum number of elements.
An explanation is given on page 471.

7.  Which type of biomedical implant is not likely to employ a wireless link to an external transceiver?

c)  Hair plug

Many kinds of medical implants exploit the availability of micro-scale wireless electronics to both retrieve data from implants and to send programming data to them.
An explanation is given on page 395.

8.  Which curve in the graph to the right represents
skin depth in biological tissue?

b)  A

To the left is a transmission line model of biological tissue that helps predict how an RF plane wave propagates through tissues.

Component values vary with frequency and tissue type.

An explanation is given on page 526.

9.  What is the approximate power consumed by the average
human male brain, consisting of 22 billion neuronal cells?

b)  15 W

Oh, the jokes that can come from this question! It has been estimated that the human brain performs the equivalent of at least 6x1016 FLOPS (floating-point operations per second) while consuming a mere 15 W of power.
An explanation is given on page 395.

10.  Name the three regions of current-dependent battery polarization as a function of voltage

a)  Active, ohmic, concentration

An explanation, along with the chart to the right, is from page 801.