The Function Generator and the Oscilloscope

Dr. Len Trombetta

1

ECE 2100

Sinusoid Basics

2

General form of the sinusoid:

v(t) = Vm sin(2pf t + f) [V]

• Vm is the amplitude• f is the frequency• f is the phase• 2Vm = Vpp (peak-to-peak)

t

We usually write w = 2pf, and w is the angular frequency. But note that what you set on the function generator is f, not w.

v(t)

Vm Vpp

Sinusoid Basics

3

A sinusoid may also have a dc offset.

v(t) = Vm sin(2pf t) [V] + Vdc

v(t)

tVdc0

Function Generator

4

Power

Let’s explore basic function generator properties...

Displays and Output

5

The default setting is1 [kHz], displayed here…

…and 100 [mV] peak-peak amplitude, displayed by pressing this button.

Next, connect Output to the oscilloscope using a BNC-to-BNC cable.

scope

You won’t get an output until you press “Output”.

BNC to BNC

Oscilloscope

6

From Function GeneratorPower

The oscilloscope displays input signal as voltage vs. time.V

olta

ge

time

(You don’t have these inputs.)

Scale Factors

7

Vertical scale factor (in Volts/Div)

Horizontal scale factor (in sec/Div)

Convince yourself that the signal frequency and amplitude are what is stated on the function generator display.

Change the scale factors to see how the display is changed on the ‘scope.

f = 1/T T

20 mV/ 500 uS/

Vpp

scale factor adjustments

Waveform (Function)

8

Step through the functions to observe each one.

A ramp with a 50% asmmetry is a triangle wave…

Amplitude

9

Use the keypad and the Vpp* button…

…or…

…the wheel and the “ten’s place” buttons.

To adjust the amplitude:v(t)

Vm

t

v(t) = Vm sin(2pf t) [V]

* Note that this button generally sets the “0 – peak” amplitude, not the “peak-peak” amplitude. It selects “peak-peak” only if the load is 50 W.

Frequency

10

Use the keypad and the Hz, kHz, or MHz button…

…or…

…the wheel and the “ten’s place” buttons.

To adjust the frequency:v(t)

t

T

v(t) = Vm sin(2pf t) [V]

T = 1/f

dc Offset

11

Use the keypad and the Vpp* button…

…or…

…the wheel and the “ten’s place” buttons.

To adjust the offset:v(t)

t

v(t) = Vm sin(2pf t) [V] + Vdc

Vdc

* This procedure will give you twice the offset you key in, unless the load is 50 W.

0

Coupling

12

Whether or not you observe the dc component on the scope depends on the coupling.

1. Select whichever channel your signal is connected to.

2. Toggle through the coupling options:

dc: dc AND ac components are displayed.

ac: only the ac component is displayed.

The “T” Connector

13

output connected to BNC “T”

The three BNC connectors are in parallel, effectively providing two FGEN outputs. Typically one will go to the scope and the other will be your circuit input.

scopecircuit input

RMS Measurements

14

Another way to characterize the amplitude of a periodic waveform is the rms (root-mean-square) amplitude:

When set to measure ac voltage or current, the Agilent automatically displays rms.

0

0

21( ) .

t T

rms tV v t dt

T

If v(t) is a sine or cosine (sinusoid), then

.2m

rms

VV

Fun With Speakers!

15

Play with the speakers by connecting one output to the speaker and one to the ‘scope. Observe the effects of amplitude and frequency.

speaker

oscilloscopeWhat happens to the sound if you change the wave-form (sine/triangle/square)?

Triggering

16

When the oscilloscope is properly triggered, the image is “stable” because it is displayed the same way each time it sweeps across the screen. If the triggering is not correct, the image looks garbled , like it is “running” across the screen.

Trigger Menu

Trigger Level

External Trigger connection

For more info: www.egr.uh.edu/courses/ece/ece2100/Trigger_Controls.pdf

External Triggering

17

An external trigger signal is provided by the SYNC output of the function generator. This provides a square wave of 1Vpp amplitude at the frequency of the MAIN waveform. So as long as your signal is coming from MAIN, the scope knows exactly when to trigger!