+5V
MENG4210/ELEC6210 Electronics Design
10nF
Assignment One, 2024
1.
[1] Draw the small-signal equivalent circuit and determine the model
parameters.
2.
[1] Determine the frequency response, 𝐻 𝑠 =
𝐿1
10nF
50Ω
𝑉𝑂 𝑠
3.
4.
𝑠
𝑉 (𝑠)
Derive 𝑂
•
•
Neglect components that have a small effect.
Use Millers theorem to simplify the small signal model. Approximate
the Miller gain as the maximum voltage gain, i.e. no frequency
dependence.
𝑉𝜋 (𝑠)
, then 𝜋
𝑉𝑖 (𝑠)
𝑍𝑖𝑛
, then combine.
[1] Determine the approximate bandwidth (-3dB cut-off frequency) and
gain. Plot the approximate magnitude frequency response. How could you
increase the bandwidth?
[1] Simulate the frequency response and compare the gain and cut-off
frequencies to what you determined in Question 3.
𝑉𝑂
𝑅𝐿
Q1
Hint:
𝑉
10nF
𝑉𝑖 𝑠
•
𝑍𝑜𝑢𝑡
1𝑘Ω
𝑉𝑖
1V
𝑅𝐸
10nF
Q1 = BFS17, 𝑅𝐿 = 1kΩ, 𝑅𝐸 = 160Ω, 𝐶𝐿 = 1pF , 𝐿1 = 1 uH
For Q1, 𝐶𝜇 =0.8 pF, 𝐶𝜋 = 18 pF, 𝐹𝑇 = 1 GHz, 𝑉𝐴 = 90 V, 𝛽 = 93
Assume 𝑉𝑖 is small enough so that the circuit is operating linearly
𝐶𝐿
5.
[1] Calculate the input impedance at 100 MHz.
6.
[1] Simulate the frequency response of the input impedance, i.e. 𝑍𝑖𝑛 (𝑗𝜔). Compare the
calculated and simulated values at 100 MHz.
7.
[1] At 100 MHz, what kind of network would represent the calculated input impedance?
8.
[1] Simulate and plot the noise spectral density of 𝑉𝑂 . What is the RMS noise voltage? Which
component is the biggest contributor to output voltage noise?
*ZETEX BFS17 Spice model Last revision 9/3/93
*
.MODEL BFS17 NPN IS =4.9E-16 NF =.993 BF =93 VAF=90 IKF=.055
+ ISE=1E-14 NE =1.800 BR =25 VAR=6 NR =1.005 IKR=.01
+ ISC=4.5E-15 NC =1.2 RB =7 RBM=.5 IRB=5E-4 RE =.5
+ RC =2.0 TF =5E-11 XTF=100 ITF=2.3 TR =2.4E-8
+ CJE=1.18E-12 CJC=1.54E-12 VJC=.559 MJC=.25 VJE=1.12
+ MJE=.4
𝑉𝑖𝑛
Protection
Circuit
10. [3] Design a protection circuit for a system that normally operates at +15V and 1A. The
protection circuit should prevent damage to the PCB when the input voltage is:
•
Negative, i.e. when 𝑉𝑖𝑛 is between -1V and -50V
•
Too low, i.e. when 𝑉𝑖𝑛 < 12 V
•
Too high, i.e. when 𝑉𝑖𝑛 > 17 V. The maximum fault voltage is 50V
𝑉𝑜𝑢𝑡
17
You may use discrete components, comparators, and opamps if necessary. Keep the circuit as
simple as possible.
11. [2] Demonstrate that your circuit meets the requirements by plotting the output voltage versus
input voltage, when the input is swept from -50V to +50V. Also plot the output voltage versus
load current. The results should match the plots on the right.
11. [3] Choose components and draw the schematic in Altium (or other software) and provide a bill
of materials, following the tips provided on the following page. Use a 2.5mm ID barrel connector
and screw terminals on the input and output. For important components like opamps and
transistors, ensure the reasons for your selection are described. This is important in commercial
designs since it allows other engineers to follow your process to find replacement parts.
12. [3] Design a 2-Layer PCB for your circuit design. Create a PDF of the Schematic and PCB and
include this in your assignment document. Also submit the SchDoc and PcbDoc files in Canvas.
Your schematic will be assessed for readability and layout. Your PCB will be assessed for: layout
size, routing design, and manufacturability.
12
17
12
−50
50
𝑉𝑖𝑛
𝑉𝑜𝑢𝑡
17
12
1
𝐼𝐿
BOM Tips
• You can export a BOM from Altium Designer
• I recommend using www.partsbox.io to manage your BOM. You don’t really need this for small projects, but it’s a
useful too to manage larger projects. Pick parts which are readily available in Digikey.
• A good BOM includes the info below. You can find a standard “description” on Digikey or www.octopart.com. If
you use PartsBox, all of this information is obtained automatically.
• In the “Notes” section, you can list things like possible part substitutions, or important specifications for active
components. For example, for a 50V and 1A application, you would want components that are rated at 100V and
2A.
Designator
Description
Package
Manufacturer
Part Number
Notes / Required Specs
Q1
MOSFET P-Channel
150V 0.29Ohm 13Amp
D2PAK
Infineon
IRF6215STRLPBF
Vds > 100V, Rds < 1r,
Pd > 1W, Id > 2A.
R1, R2
10K 1% 0.25W
±100ppm/C
1206
Yageo
RC1206FR-0710KL