Project 3 Ee087732

SEMESTER 3, 2011/12 EEEB141: ELECTRONIC DESIGN LABORATORY PROJECT 2 (REPORT)

NAME ID

: PHUA MEI GUAN : EE087732

NAME ID

: WONG YINWEN : EP088143

SECTION : 03 DATE DEMO : 2nd MAY 2012 LECTURER : SYED SULAIMAN BIN KAJA MOHIDEEN

Problem Statement:

We are the design engineer of a multinational electronic company. Recently, our company was developing a new type of hand held radio receiver. The radio set required a special type of filter that amplify low frequency signal and attenuate high frequency noise. We were tasked to design the amplifier and filter circuit for the radio sets. The specifications of the input waveform, input frequency and output waveforms: Input waveform

: 1Vp-p sine wave

LPF cutoff frequency : 2kHz Input Frequency

100Hz

1kHz

2kHz

20kHz

200kHz

Output Amplitude

10VP-P

< 10Vp-p

5Vp-p

≤ 1Vp-p

≤ 0.1Vp-p

Objective:  

To apply the knowledge gained from the previous labs To use creativity in problem solving

Materials: 

BJT

:

1 x Q2N3904



Resistors

:

1 x 160, 1 x 470k, 1 x 36k, 1 x 6.8k, 1 x 400, 1 x 11.5k



Capacitors

:

3 x 1µF

Equipment:    

Protoboard Fluke 45 Dual Display Multimeter Tektronix CFG 253 3MHz Function Generator Hewlett Packard Oscilloscope 100MHz 54600B

Methodology: The whole experiment was carried out by both software which is LTspice and also hardware. Knowledge and creativity were applied to design and construct the circuit to get the desired output. After some research we did

on the internet, we manage to design a new circuit which works as same as the problem statement in this project. By using the LTspice simulation software, we found out that we design the circuit correctly because we got the correct output waveform. Since our group presentation will also count points, so besides using the LTspice to do the stimulation, we construct the same circuit experimentally in the electronic design lab. After that, the device was demonstrated and presented to prove that the expected output is obtained. Other than that, the report shows all the calculations, simulations, and discussion to give more details explanation. The simulation tool is used and the results were attaching together with the full report.

Theoretical Background: We have used a low-pass passive filter in order to allow low frequency input signal to pass through the circuit while effectively attenuate high frequency input signal and noise. The low-pass filter is designed such that its cut-off frequency is 2kHz. Besides that, we have implemented a BJT amplifier into the circuit in order to amplify the signal into desired value. The amplifier we have implemented it by using one BJT transistor. Therefore, we might expect an inverting waveform on the output. A DC voltage is use to amplify the amplifier part of BJT transistor to gives out a high gain output. It’s mainly the contributor to the BJT transistor. By using the LTspice simulation software, we have found out the resistor value needed and designation of the circuit under nominal conditions. The BJT, capacitors, and resistors we use in the simulation software are ideal. So we might expect some changes to the result after the circuit is being constructed.

Procedure: 1. The values of the resistors were measured and recorded.

2. The circuit was constructed as below.

3. The function generator was set to 1Vp-p sine wave with frequency 100Hz. 4. The function generator was then being connected into the circuit. 5. The Vin and Vout are being connected to probe 1 and 2 of the oscilloscope respectively. (Vout is the voltage across 11.5kΩ resistor) 6. The value for DC supply was set to 30V and connected to the circuit. 7. The function generator and oscilloscope were switched on. The results were taken and graph was obtained. 8. The input frequency was then changed to 1kHz, 2kHz, 20kHz, and 200kHz respectively with the input voltage of 1Vp-p sine wave. The results were taken and the graphs were obtained.

Theoretical Result: The circuit used to simulate using LTspice is as shown in figure below.

The graphs we obtain by using LTspice simulation software are as shown in figure below. Input waveform from LTspice simulation:

Input and output waveform from LTspice simulation: 100Hz

1kHz

2kHz

20kHz

200kHz

Resistors values from the LTspice which are ideal values: R1 = 160Ω R2 = 470kΩ R3 = 36kΩ R4 = 6.8kΩ R5 = 400Ω R6 = 11.5kΩ

Input Frequency:

100Hz

1kHz

2kHz

20kHz

200kHz

Output Amplitude:

10.01 Vp-p

7.554Vp-p

5.028Vp-p

549.53m Vp-p

99.9m Vp-p

Experimental results:

Resistors values from the experiment: R1 = 158.33Ω R2 = 471.56kΩ R3 = 35.86kΩ R4 = 6.842kΩ R5 = 399.82Ω R6 = 11.688kΩ Input Frequency:

100Hz

1kHz

2kHz

20kHz

200kHz

Output Amplitude:

10.31 Vp-p

7.013 Vp-p

4.888 Vp-p

537.5m Vp-p

100mVp-p

Input and output waveform from the experiment:

100Hz

1kHz

2kHz

20kHz

200kHz

Calculation:

Percentage error of resistors: % error of R1 = × 100%= 1.04375% % error of R2 = × 100%= 0.3319% % error of R3 = × 100% = 0.3889% % error of R4 = × 100% = 0.6176% % error of R5 = × 100% = 0.045% % error of R6 = × 100% = 1.6348%

Percentage error of output voltages: 100Hz: % error = × 100%= 2.997% 1kHz: % error = × 100%= 7.162% 2kHz: % error = × 100% = 4.296% 20kHz: % error = × 100% = 2.189% 200kHz: % error = × 100% = 0.1%

Discussion: In this experiment we are able to construct an active noise control circuit using bipolar junction transistor (BJT). Actually this project we got it from the project 2, in project 2 we use 2 transistors because the first transistor was inverting the output waveform by 180, and for project 2 we need the output waveform not inverting 0, that is why we use the second transistor to get 0. So, for this project we remove the second transistor and used only one transistor.

A low-pass filter passes low frequencies fairly well, but attenuates 'high' frequencies. Therefore it is better called a high-cut filter or treble cut filter. Low-pass filters are used to block unwanted high-frequency signals, whilst passing the lower frequencies. The low frequencies to be filtered out are relative to the unwanted higher frequencies and therefore do not have a definitive range. The frequencies that are cut vary from filter to filter. A low-pass filter is the opposite of a high-pass filter. A physical barrier acts as a low-pass filter for waves. When music is playing in another room, the low notes are easily heard, while the high notes are largely filtered out. Similarly, very loud music played in one car is heard as a low throbbing by occupants of other cars, because the closed vehicles (and air gap) function as a very low-pass filter. Low-pass filters are also used to drive subwoofers and other types of loudspeakers, to block high pitches that they can't efficiently broadcast. Our circuit has been constructed as in the figure in procedure part. In addition to that, a passive filter, low-pass filter is used to strengthen the low frequency signal and attenuate high frequency noise in a cut-off frequency of 2 kHz. In computer simulation, we get the almost exact value of outputs that we want shown in Objective part. However, we got some slightly difference in value of output during lab experiment. This is because there is a difference between ideal component and experimental component. The difference in results occurred because of some external factors such as effect of temperature when building up components, surrounding environment, type of materials used and etc. We had made sure all legs of the laboratory materials such as BJTs, capacitors and resistors are inserted properly into the breadboard (Protoboard). The legs must touch each other with the plate inside the breadboard to ensure circuits are connected in properly manner. Filter is a circuit that is designed to pass signals with desired frequency and block

unwanted frequency. Based on the formula (Xc =

1 RC ), as the frequency goes higher,

the capacitor will discharge lesser and lesser. The frequency is directly proportional to the capacitor. Diagram of transfer function of ideal passive low-pass filter will have a value of

‘1’ when the input frequency is below cut-off frequency (2kHz) and a value of ‘0’ when the input frequency is above the cut-off frequency. The BJT amplifying portion is a common-emitter circuit. Therefore, the voltage gain, Av will be more than 1 and that the output voltage will be inverted (180o phase shift).The characteristics of combination of passive low-pass filter and an inverting BJT amplifier is almost the same as an active lowpass filter, where the BJT amplifying portion behaves as an op-amp. The result which we obtained was good, and the percentage error was small only 2.997% of output voltage for 100Hz, 7.162% of output voltage for 1kHz, 4.296% of output voltage for 2KHz, 2.189% of output voltage for 20KHz, and 0.15 of output voltage for 200KHz. This error due to an accurate reading, the transistor is not ideal, and also the non ideal resistors.

Conclusion: Following the project, we have further our understanding towards the function of BJT transistor. We get to know how the BJT transistor can be used to amplify an input waveform into desired output waveform. Lastly, we know how to design amplifier with low pass filter (LPF) circuit. The LPF cut-off frequency just allow the frequency below 2kHz and we can get over 1Vp-p. When the frequency above 2kHz, the output Vp-p we get is below 1Vp-p and make noise. The low-pass passive filter can be used to filter out high frequency input waveform and noise while remains the low frequency input waveform. By combining this two parts (amplifier + low-pass filter), we are able to create a filter that effectively amplify low frequency input waveform and attenuate high frequency input waveform.