E80 Lecture 4.1: Basic Electrical Measurements
-Basic Electrical Measurements
-Intro to OpAmp Characteristics
E80 Spring 2014
E80 Lecture 4.2: Basic Electrical Measurements
Example: first order system RC circuit
Vin
R
1kΩ
C
1µF
+
Vc
-
o How to present
measurement
results? (E59)
o What instruments to
use?
o How to set up test?
o Any limit?
E80 Lecture 4.3: Basic Electrical Measurements
Example: first order system RC circuit
Vin
R
1kΩ
C
1µF
+
Vc
-
input System output
Breadboard Power supplies
Function generators
Multimeters
Oscilloscope
DAQ
E80 Lecture 4.4: Basic Electrical Measurements
How to present measurement results?
Time-Domain Plots
Vo
ut (V
)
Time (sec)
Vin (
V)
Time (sec)
E80 Lecture 4.5: Basic Electrical Measurements
How to present measurement results?
Frequency-Domain (Bode) Plots Lm
(d
B)
Ph
ase
(d
eg
)
Frequency (rad/sec)
Lm = 20 log10
Vout
Vin
phase =Dt
To
(360 )
E80 Lecture 4.6: Basic Electrical Measurements
Instrumentation
o Instruments that GENERATE signals
– Signal generator (AC or DC)
– Power supply (DC)
o Instruments that MEASURE signals
– Multimeter (AC/DC voltage/current, resistance)
– Oscilloscope (AC)
– DAQ
o Wires and cables that CONNECT the instruments
o BREADBOARD
E80 Lecture 4.7: Basic Electrical Measurements
Function Generator
• Waveforms: Sine, square, triangle, sawtooth • AC signal
• Parameters: Amplitude (Vpp), Frequency (Hz), Out Term (High-Z or 50 Ω)
E80 Lecture 4.8: Basic Electrical Measurements
Power Supply
• DC
• COM = common reference node of circuit
• = chassis/earth ground
E80 Lecture 4.9: Basic Electrical Measurements
Multimeter- Voltage
+
- VM R2
Measuring V:
Vin
R1
• Connect in parallel with C.U.T
• Internal resistance of VM should be
large, 10M for Elenco
• DC vs. AC (RMS for sinusoid)
• Range
Reading VR2
E80 Lecture 4.10: Basic Electrical Measurements
Multimeter- Current
+
-
AM
Measuring I:
I Vin
R
• Connect in series with the C.U.T.
• Internal resistance of AM must be
very small, can be ignored.
• DC vs. AC (RMS for sinusoid)
• Range
E80 Lecture 4.11: Basic Electrical Measurements
Multimeter -Resistance
ΩM
Measuring R:
R
• Connect across R (isolated from
other circuits)
• M has internal battery, so should
not connect to active circuits such
as power supply
E80 Lecture 4.12: Basic Electrical Measurements
Multimeter –Digital vs. Analog
• Analog meter (less precision in VM due to lower
input resistance)
• Digits vs. needle position
• Higher performance: precision, true RMS reading
Simpson 260
HP34401A
(in E80/VLSI lab)
E80 Lecture 4.13: Basic Electrical Measurements
Oscilloscope: Voltage Measurement (Time domain)
Move
up/down
Turn on
cursors
Select
ΔV or Δt
Move
cursors
Toggle
b/w cursors Move
left/right
POSITION POSITION VERTICAL
CH 1
VOLTS/DIV
CH 2
VOLTS/DIV
CH 2 CH 1
SEC/DIV
HORIZONTAL POSITION
ON POSITION CURSOR
ON/OFF
Change
y-axis (voltage) scale
Change
x-axis (time) scale
Inputs
(Channels 1 and 2)
BNC
Connector
E80 Lecture 4.14: Basic Electrical Measurements
Oscilloscope Probe
BNC-BNC connector
Circuit To Be Built
10x probe
E80 Lecture 4.15: Basic Electrical Measurements
Oscilloscope Probe
10x probe
o Oscilloscope: 1M input resistance, 20pF capacitance
o Coax cable capacitance typically ~ 100pF
o 10x probe: 9M, 1/9*(120pF). Improved input impedance
by a factor of 10 not only for low frequency but also for
high frequency
o Oscilloscope bandwidth 60MHz
o Tuning of 10x probe (instruction see BEM guide)
C.U.T
E80 Lecture 4.16: Basic Electrical Measurements
Bre
ad
bo
ard
(Pro
tob
oa
rd)
Use long busses for power
and ground: Don’t use them for signals
Color-code wires: Red = V+ power
Black = V– power
Green = ground
White or Blue = signal
Keep components close to
the board: Trim resistors, capacitors, wires
Check individual component before constructing the whole
circuit
E80 Lecture 4.17: Basic Electrical Measurements
Pay Attention to Details and
Practice
http://makezine.com/2010/03/22/improving-breadboard-layout-through/
E80 Lecture 4.18: Basic Electrical Measurements
Data Organization V
ou
t (V
)
Time (sec)
Vin (
V)
Time (sec)
Lm (
dB
)
Lm = 20 log10
Vout
Vin
phase =Dt
To
(360 )
How many data points to take?
Useful data analysis tool?
DAQ and LabVIEW (automation)?
E80 Lecture 4.19: Basic Electrical Measurements
Introduction to Opamp
o Characteristics
o Simple analysis procedure
o Construct unity-gain amplifier or buffer
E80 Lecture 4.20: Basic Electrical Measurements
Introduction to Opamp
o Active components
provide power gain,
requires power supply
V+ and V-
o Dual polarity vs.
single polarity power
supply
o Vout=A(V+-V-) V-
V+
V+
V-
E80 Lecture 4.21: Basic Electrical Measurements
Characteristics of Opamp
System response: Vout=A(V+-V-)
o Typical A=105 V+≅V- (since Vout
is some finite value <power supply)
o Typical Rin=few M current into
opamp = 𝑖− = 𝑖+ ≅0
V-
V+
V+
V-
E80 Lecture 4.22: Basic Electrical Measurements
Unity Gain Amplifier
V+≅V-
𝑖− = 𝑖+ ≅0
V+
V- 𝑖−
𝑖+
What is the purpose of this buffer? 𝒗𝟎 =?
E80 Lecture 4.23: Basic Electrical Measurements
Non-inverting amplifier
𝒗𝟎𝒗𝒊
= 𝟏 +𝑹𝒇
𝑹𝟏
Rf=0 R1=∞