Microelectronic circuits problem with transistors

Thread Starter

johndoo

Joined Dec 5, 2015
3
Overview (fictional): NASA has put you in charge of designing the electronic circuits for a next generation asteroid mining robot. It will land, extract platinum and other raw materials, and eject the
materials towards a space station which will execute further processing. The main challenges are landing,
harvesting available sunlight for energy, not getting pushed out of the asteroid surface into space during
operation, and aiming and relaunching of the raw materials towards the space station for collection.
Specifications: There are control pins on the avionics module which trigger various functions of the robot.
These pins are edge triggered meaning that when the pin goes from low to high voltage, the function is
triggered, and when the pin goes from high to low voltage, the function is quit. The pins are bidirectional
in that if a function has completed, it will pull the pin voltage low (output impedance = 50 Ω). The
following is the pinout of this functionality:
C1 (land) – tells the robot to go in to land on the asteroid
Functions: drives thrusters, deploys lander, ensures safe landing
Power draw: 3 W, 5 V
C2 (search) – tells the robot to search the asteroid
o Functions: drives wheel motors, uses internal mapping system to build layout of asteroid
so it does not retrace steps, can be used for finding sunlight or finding material
o Power draw: 5 W, 12 V
C3 (mine) – tells the robot to drill and fill mining bucket
Functions: drives drill, modulates speed for optimal drilling, extracts ore, and empties
each load into its launch bucket.
Power draw: 10 W, 12 V
C4 (launch) – tells the robot to launch a bucket of mined material and load a new bucket
o Functions: seals current mining bucket, aims towards space station, launches the material,
reloads another bucket for future mining.
o Power draw: 15 W, 20 V
There are also various onboard sensors with the following pinout:
A – boolean reading from robot accelerometers indicating (1 mW at 5 V)
1 (+Vdd) – robot firmly on asteroid
0 – robot not on asteroid
B – boolean reading from bucket that it is full of mined material (5 mW at 5 V)
1 – full
0 – not full
S – boolean reading from robot that sunlight is present (1 mW at 5 V)
1 – sunlight present
0 – no sunlight
M – boolean reading from sensors indicating (1 W at 5 V)
1 – drillable material present underneath drill
0 – no drillable material present
Q – analog reading indicating the percentage charge (10 mW at 5 V)
Analog - % of Vdd indicates % charge
The robot is equipped with a panel that outputs 20 W at 20 V and battery that stores 60 Wh at 20 V.
For all problems: calculate and report any characteristics you feel important, show the relevant
parameters of each of the BJTs/MOSFETS/capacitors/resistors/inductors/diodes used (and ensure they are
reasonable), and ensure each schematic contains all operating parameters (voltages of supply, etc). Be
sure to label all parts and assumptions. You will be graded on completeness, correctness, and neatness.
Hint: You may want to start with typical values for BJTs/MOSFETs and see if those need adjusting to
support your circuit. Many of these component values are listed in data sheets online.
Problem 1: Memory and logic
The onboard brains of the robot requires hard-baked logic so that it is resistant to solar electron radiation.
Build a state model representing the state the robot is in. Boolean logic is used to transition between
states. Implement the transistor-level circuitry for your sketched system. Try to minimize transistors. Size
your transistors to maintain a propagation delay of at most 1 microsecond.
Hint 1: You will need to use memory elements to store the state of the satellite. What memory element
might you choose and why?
Hint 2: You may need to use a comparator for the charging signal Q so you know it has enough charge to
operate the function correctly.
Problem 2: DC power distribution
Treating each of the functions C1-4 and sensor modules ABSMQ as black boxes, implement the
powering for each of the stages and the current steering which provides sufficient power. Show the
circuitry for integrating the battery and solar panel with the system. Additionally, in the case of failure, a
function may begin to pull current in excess of its rating. At the transistor level, implement a failure
detection system that would detect such a fault and reset the function and reroute power.
Hint 1: Calculate the input impedance of each function and input of the robot.
Problem 3: Metal detection
Typical metal detection works by sending an AC electromagnetic wave into a material. The changing
magnetic field produces eddy currents in the material. This process effectively dissipates energy and
reflects energy back towards the sensing element. The frequency of the EM emitted field is typically
200 kHz (you do not need to design the emitter). The sensing element for this radiation is picked up by
two receiver coils on two sides of the emitter coil which use a differential amplifier to difference the
signals. Note: The receiver coils produce a current based on the returned AC field. This current needs to
be converted to a voltage which is supplied to the differential amplifier. Assume the differenced signal is
1/1000th of the common mode signal. You need to achieve a bandwidth 100 kHz about a peak frequency
of 200 kHz (Hint: use feedback). Design a circuit that goes from the coils (inductors) through the
multistage amplifier to a voltage output (which will go into an ADC). Write down the frequency response
and draw a Bode plot of your response. At this bandwidth write down your gain for the given
specifications. Also report the CMRR, input and output impedance.
Hint 1: Note, the inputs to the amplification stage may be fed with a voltage (assuming you supply a
current-to-voltage converting circuit).

I'm not asking for someone to solve everything because its against the rules
but I'm asking for hints to start its very overwhelming to me and I don't know what to do or how to start
 

WBahn

Joined Mar 31, 2012
25,907
Break the problem down into small pieces (the description actually does a pretty good job of steering you that direction) and consider what is important for each piece.

This problem sounds like it is integrating material from a number of courses, which would imply that you are pretty far along in your program. That should mean that you should be able to at least make some kind of a start of some of this.
 

Thread Starter

johndoo

Joined Dec 5, 2015
3
the only material should be used is from Microelectronic circuits by sedra
we never had a similar problem or even remotely similar
:(
 

WBahn

Joined Mar 31, 2012
25,907
Have you learned the material in Sedra and Smith?

I don't have a recent edition, but as I recall it focusses on devices and simple circuits. It doesn't get into designing logic systems and such.

What is the context for this problem? Is it for a specific course? What level are you at?
 

Thread Starter

johndoo

Joined Dec 5, 2015
3
this course is EE326 and I'm a junior electric engineer
and this problem has 50% of the exam score I already got the other %50
the instructor said we can get the full points for trying as he doesn't expect us to finish everything
its due in 5 days from now
I'm going over SR flip flops right now to do the memory part
 

WBahn

Joined Mar 31, 2012
25,907
Okay, since this is an exam, it is improper for you to even be asking for help on it or for us to be offering assistance. That defeats the purpose of an exam. Just do the best you can, knowing that the instructor is looking for quality of effort and not correctness of results.
 
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