Digital Storage Oscilloscope Setting Computer Science Essay

Published Date: 02 Nov 2017

introduction

In this lab

EQUIPMENT

GW Instek GDS820S Digital Storage Oscilloscope (DSO), connected to a PC via a USB cable

1 PC with 'Free View' software installed for the GDS820S DSO

1 TIMS 301 System Unit with the following plug-in modules:

Audio Oscillator, Sequence Generator

'Patch' cables with 4 mm plugs as required

2 BNC to 4 mm plug cables

Communication Channel box with BNC sockets for RFT50 experiment.

procedure.

1.1 DIGITAL STORAGE OSCILLOSCOPE (DSO) SETTINGS

G:\praticals\Figure2_1_1 Baseband data transmission via a band limited channel.jpg

Pressing the blue 'Auto Set' button

Press the blue Trigger Menu button and set the triggering controls,

F1 Trigger type, select Edge. Set Slope/Coupling to the rising edge or falling edge symbols as required.

Select F2 Source ( select Ch1 or Ch2 as required. )

F3 Mode to select Auto initially.

rotary Trigger Level up 1.5V control on the DSO .

2.1 Displaying the whole data sequence.

part A

Connect the TIMS modules and the communication channel box as shown in Fig. 2.1.1.

Set the gate time on the frequency counter to 0.1 second.

Set the audio oscillator frequency to 3 kHz initially.

Set the DSO time base to 500αs/div and set the triggering source to External.

Adjust the Trigger Level control on the DSO to approx. 1.5 V.

Set both the TIMS 'scope selector switches to A.

Set the DSO to display Channel 1 and Channel 2 and set the volts/div controls to a suitable value.

You should see the bit rate clock and the complete transmitted data sequence.

Part B

Change Channel 2 to B on the TIMS 'scope selector

adjust the frequency of the oscillator until you reach the highest frequency that would allow data to be recovered using a comparator set half way between the logic '0' and '1' levels.

2.1.2 Displaying an 'Eye' Diagram

Change the oscilloscope settings so that the trigger source is Channel 1 (bit rate clock) and the time base setting is100αs/div.

press the "display" in order to see the eye diagram on channel 2.

press F2 on DSO to select Accumulate.

Start with the oscillator frequency at about 1 kHz then gradually increase the frequency using frequency control turning in to clockwise.

As you adjust the oscillator frequency, press F3 Refresh

Continue to adjust the oscillator frequency until you reach the highest frequency until eye is fully close.

2.2 Finding the bandwidth of the communication channel

G:\praticals\Figure2_2_2 Setup for measuring the bandwidth of the cmmunication channel.jpg

Disconnect the communication channel input from the sequence generator and connect the communication channel input to the sine wave output of the audio oscillator.

Select the B input on channel 2 of the TIMS 'scope selector.

Press the Display button on the DSO then press F2 to turn off the Accumulate function.

Set the trigger source to Channel 2.

Turn the audio oscillator frequency down to approximately 0.3 kHz.

change the setting of the 'scope Channel 2' 0.5 volts/div.

It can be assumed that a frequency of 0.3 kHz is well within the pass band of the communication channel and is well below the cut-off frequency of the communication channel.

Increase the frequency of the audio oscillator gradually to find the -3dB point of the filter.

make additional measurements at the -6dB, -10 dB and -20 dB points

then plot the frequency response of the filter on graph paper.

Results.

2.2. :position A 2.2. : position B

2.2. :3 kHz 2.2. : 5kHz

2.2. : 7kHz 2.2. : 7.89kHz

Discussion.

In the above

2.1.2 Displaying an 'Eye' Diagram

theory.

Analyzing EYE Pattern

An EYE diagram is a useful tool for understanding signal impairments in the physical layer of high-speed digital data systems, verifying transmitter outputs in manufacturing, and clarifying the amplitude and time distortion elements that degrade the Bit Error Ratio (BER). A broadband sampling oscilloscope samples high-speed digital signals by taking a high-speed digital data stream of random 0s and 1s, superimposing them, and synchronizing the rise and fall times of the data transitions. The result is the "EYE" of the EYE diagram (Fig 2.1). For easy viewing, the time axis in Figure is normalized for 2 bits, with the 1-bit EYE opening in the centre of the display and 1 bit to the left and right of the centre for capturing rise/fall transitions.

figure 2.1: Eye diagram.

Although the EYE pattern in above diagram shows some noise and jitter, more examples below show waveforms with considerably more noise and a significantly closed centre EYE. Generally speaking, the more open the EYE (arrows in diagram), the less chance that the receiver will mistake a logical 1 bit for a logical 0 bit, and vice versa. Noise, both amplitude and time jitter, reduces that margin as closure of the EYE. The percentage of bits with errors compared to total bits is called BER. A lower BER is always better. The EYE diagram does not show protocol or logic problems. However, it does help engineers to more easily view signal impairments in the physical layer in terms of amplitude and time distortion. To analyze the data stream, a Bit Error Rate Tester is used to measure BER in the circuit. Using this integrated error detector supports simultaneous testing and analysis of both BER and EYE pattern.

Results.

C:\Users\kasun\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\2.12 _1KHZ.PNG

2. 1. : eye diagram 1KHz.

C:\Users\kasun\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\2.2-1 2khz.png

2. 1. : eye diagram 2KHz.

C:\Users\kasun\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\2.2-1 3khz.png

2. 1. :eye diagram 3KHz.

C:\Users\kasun\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\2.2-1 4khz.png

2. 1. : eye diagram 4KHz.

C:\Users\kasun\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\2.2-1 5khz.png

2. 1. : eye diagram 5KHz.

C:\Users\kasun\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\2.2-1 5.5khz.png

2. 1. :eye diagram 5.5 KHz.

C:\Users\kasun\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\2.2-1 6khz.png

2. 1. :eye diagram 6 KHz.

C:\Users\kasun\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\2.12 _7.3Khz.png

2. 1. : eye diagram 7.3KHz.

discussion.

In the above diagram shows how the signal and noise relate with the eye. In figure 2.1.1 shows eye diagram initially in 1 KHz. When starts the increase the frequency then the eye starts closing. According to the above figure 2.1.1 to figure 2.1.4 shows a better eye that signal can be receive properly. In figure 2.1.5 shows the amount of distortion is nearly equal to the signal strength because the upper part of the eye diagram width is relatively bigger. Then rapidly starts to increase the frequency. In frequency 7.3 KHz the eye is disappear.

2.2 Finding the bandwidth of the communication channel

Amplitude

dB

Cut-off frequency (KHz)

Comments.

1.74

0

0.01

1.74

0

0.3

1.22

-3

1.25

0.86

-6

2.06

0.54

-12

3.39

0.18

-20

8.84