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=∞