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1. Basic Design Concepts

1. Basic Design Concepts. 1.1 Introduction to Electronics System Design 1.2 Checking Gains and Impedances 1.3 Open-ended and Trade-off 1.4 Principles of Design. 1.1 Introduction to Electronics System Design. Design Example: Public Address (PA) amplifier.

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1. Basic Design Concepts

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  1. 1. Basic Design Concepts 1.1 Introduction to Electronics System Design 1.2 Checking Gains and Impedances 1.3 Open-ended and Trade-off 1.4 Principles of Design

  2. 1.1 Introduction to Electronics System Design Design Example: Public Address (PA) amplifier

  3. FAQ . What kind of stages are there inside the amplifier ? May be I have no idea about the inside the amplifier…What should I do? Answer: Better study the circuit diagrams of any amplifier within your reach..

  4. Microphone Pre-amplifier Volume Control Driver amplifier Power amplifier Bass Treble Speaker Stages are shown by block diagrams Tone amplifier

  5. 2. How will you start the system design ?

  6. Microphone Pre-amplifier Volume Control Tone amplifier Driver amplifier Power amplifier Bass Treble Speaker 300W cable Ri=300W 1 mV,300W AV=200 AV=1 Vi=1mV VO=200mV AV=10 AV=10 AV=1 RO<4W Vi=200mV Vi=2V VO=20V VL=20V • In/Out voltages (yellow) • Voltage gain of the stages (cyan) • In/Out impedances (red) RL=4W,100W

  7. 3. What kind of circuits are there inside each block ?

  8. Microphone Microphone is a transducer which converts sound pressure energy into electrical energy. It is a low output impedance and low output voltage (a few mV) device.

  9. Microphone Pre-amplifier Microphone cable is connected to the preamplifier. The cable may be long and should be considered as a transmission line, and therefore impedance matching ( RO = RL ) is needed between (1) microphone, (2) cable and (3) preamplifier input impedance Ri Preamplifier needs to amplify the input mV to hundreds of mV. So this should be a high voltage gain amplifier ( AV > 100 Common Emitter Amplifier)

  10. Common Emitter Amplifier High AV and low Ri Voltage amplification applications Microphone and the cable Input Zi of following stage or volume control Circuit of the preamplifier

  11. Microphone Pre-amplifier Volume Control

  12. Circuit of the volume control Volume control is a voltage divider circuit connected at the output of the preamplifier Adjustable voltage divider can adjust the loudness of the output sound from the amplifier. It should be changed manually from mute( VV = 0V ) to full loudness (VV = VO of preamplifier)

  13. Microphone Pre-amplifier Volume Control Bass Treble Tone amplifier

  14. Circuit of the tone amplifier CE with RE Amplifier Low AV and high Ri Simple Tone control circuit is a Low-pass filter. The higher cutoff frequency fH (tone) can be changed by varying RF (part of RF isselected by the variable resistor) fH will be high at Treble position and it will be low at Bass position. It is given by fH = 1/(2pRFCF)

  15. Microphone Pre-amplifier Volume Control Driver amplifier Bass Treble Tone amplifier

  16. Circuit of the driver amplifier Driver amplifier should have a undistorted high output voltage (tens of volts) required by the input of the power amplifier. This is a CE with RE Amplifier having Low AV and high Ri but can produce undistorted high output voltage

  17. Microphone Pre-amplifier Volume Control Driver amplifier Power amplifier Bass Treble Speaker Tone amplifier

  18. Output Transformer-Less (OTL) Emitter Follower Amplifier Both Emitters are connected to the speaker load Circuit of the power amplifier Power amplifier should be able to drive the speaker having very low load resistance (4 to 16 ohms) This is a EF with RO very low but the voltage gain is one (AV = 1) and should produce undistorted high voltage, high current (high power) output to the speaker.

  19. 4. What is the schematic diagram of the amplifier ?

  20. CE pre-amplifier CE with RE tone amplifier CE with RE driver amplifier EF- OTL power amplifier

  21. 5. Conclusion To make the design, we should have the knowledge of: 5.1 Specifications of the devices, such as, microphones, speakers, BJT, transmission cable.

  22. 5.2 Standard circuits and knowing the properties of each circuit such as, optimum biasing for undistorted output, voltage gains and in/out impedance of the circuits.

  23. 5.3 The following chapters of this course will describe how to design those components.

  24. 1.2 Checking Gains and Impedances

  25. 1.2 Checking Gains and Impedances Checking 1-Voltage gain Av 2-Current gain Ai 3-Input impedance Zi and 4-Output impedance Zo of each stage is also important in the design process.

  26. Caution !! To avoid amplifier distortion which will produce error on the measurements, all voltage levels should be adjusted approximately to actual signal voltages. Example: Preamplifier input voltage should be adjusted nearly 1mV so that the out put is not more than 200mV avoiding the distortion.

  27. AV=200 Ri=300W Ro= Rc VO=200mV Vi=1mV CE pre-amplifier circuit for checking specifications

  28. Oscilloscope Ch-1 Vi = 1mV (pp) Adjust generator Oscilloscope Ch-2 Vo = ? Read assume 220 mV (pp) 1- Check Voltage gain Av CE pre-amplifier Circuit Then Voltage gain Av = Vo / Vi= 220mV(pp) / 1mV(pp) = 220

  29. Select RX approx 300W = 330W (Since Zi=300W) Oscilloscope Ch-1 Vi = 2mV (pp) Adjust generator Oscilloscope Ch-2 Vi = ? Read assume 0.8 mV (pp) 2- Check Input Impedance Zi CE pre-amplifier Circuit

  30. (a) Assume that after the design, Rc=RL 4.7kW (b) With RL=4.7kW connected at the output, set 1mV to the sine generator and measure Vo (assume reading is 100mV) (c) Remove RL=4.7kW from the output, with the same input, measure no load output voltage Vo(NL) (assume reading is 180mV) 3- Check Output Impedance Zo Continue….

  31. (d) Substitute Vo(NL), Vo, RL in the simple formula below and find Zo

  32. 4- Check Current Gain Ai Use previously checked Av=220, Ri =220W values in the above formula and put RL value. Then Ai is found.

  33. 1.3 Open-ended and Trade-off Open-ended design Once you have designed the circuit other possible circuit is discussed for other designers. To leave your circuit with discussions for further modifications is called “open-ended” so that another design engineer may come up with totally different way to get the same design specifications or design requirements.

  34. Trade off The circuit is designed in such a way that the cost, accuracy, size, durability, attractiveness are well balanced. An accurate circuit may need a lot of components and will cost a lot, but a circuit with small percentage of tolerance may cost less and more light weight, attractive etc. This is the trade off between accuracy and cost. Today, electronic systems work with both hardware (IC,BJT,Gates etc.) and software (programs, languages). Software will command the hardware and the hardware will feed back the results to the software. Cost. complexity of the system should be balanced making a trade off between the software and hardware. Read 1.7.3 page 11-Text for other informations

  35. 1.4 Principles of Design

  36. 1.Define the problem and Divide into small parts 2.Write initial documents 3. Build prototype 4. Test the prototype and if not, make Changes in prototype Define the problem Y Divide into small parts Finalize documents Test OK Test the prototype and if OK, N Finalize documents Changes in prototype Write initial documents Build prototype

  37. 1. State the required performance of the product and set the specification for the design. Write initial documents Build prototype 2.The whole product should be designed by combinations of small parts or circuits. The input-output links should be taken care to reconstruct the whole product. Define the problem Y Divide into small parts Finalize documents Test OK N Change prototype

  38. 3. Drawing of the system (electronic circuits and mechanical parts) are to be made. It will help to design and to maintain the product. Modifications of the product starts from the original drawing. Write initial documents Build prototype 4. Using the design theory (circuits and equation), or by using computer simulation software, calculate the components and connect them to become a basic stage under test. Here specifications should be observed. This stage is called a prototype stage. Define the problem Y Divide into small parts Finalize documents Test OK N Change prototype

  39. Write initial documents Build prototype 5. Test the prototype and if the performance of the circuit does not meet the required specifications, modifications are made on the basic stage and test again. Both physical and electronic performance should be satisfied as a final basic stage. Define the problem Y Divide into small parts Finalize documents Test OK N Change prototype

  40. Write initial documents Build prototype 6. The satisfied basic stage is recorded. This stage is then documented as the original drawings for the production and marketing. Define the problem Y Divide into small parts Finalize documents Test OK N Change prototype

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