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Guideline 0.3 Management: Using a non-inverting amplifier circuit, train following things to student, and have discussions with students Show how to use oscilloscope (how to read voltage, frequency etc) Show how to use oscillator (different input wave, frequency, and amplitude) Show how to read resister using different colors (4 bands, 5 bands) Show how the wire is configured in the board How to avoid damaging circuit? o Don’t put any power line to oscillator o Don’t put wrong power line to chip o Turn off power first before you insert the chip to the circuit, or before you take out the chip from the circuit. How to build a safe circuit o Test the chip first before putting it into board o Don’t turn on the power of the circuit board until you build the circuit o Take advantage of four vertical lanes in the circuit diagram. (ex, ground line, input line Vin etc) o Take advantage of different colors of wire. (ex, ground line for brown color, green line for input, red line for output etc). This will save a lots of time for you when students ask you to check his/her circuit. o Connect input oscillator at the end after you make sure there is no current moving to the input oscillator. How to check, if it doesn’t work o If you see something unexpected output, Vout Check the power of the circuit: many students forget to turn on the power of the board. Check the input, Vin signal is correct and reasonable (suitable frequency, and suitable amplitude not to be saturated) against expected gain. Check the oscilloscope is in the proper mode for operation (not in DC mode, timing etc) Check the +/-15 V power lines are connected. Especially, +15 V to pin #7 tends to be connected to pin #8 by accident. Check other resisters/capacitors are properly connected. If it still doesn’t work, it may not be easy to find the problem. You can look at few other things. If virtual ground exist, check the voltage is zero Suspect the chip Suspect wrong resister/capacitor Suspect broken line in the circuit board No luck so far: call other demonstrator or Un-ki o Once you find the solution, don’t provide the solution immediately, but lead student to come to that solution. 2.3 Inverting amplifier and summer Inverting amplifier: Expected gain: G = - R2/R1 with 180 phase difference Summer: Vout = V1 + V2 Tips: Don’t use too small value of the gain. Remember the expected gain comes, assuming beta (=R1/R2)*G(intrinsic) is very large. Don’t use too large value of the gain. Output will be saturated. Output signal cannot be larger than the power supplier voltage, 15 V. So suitable choice will be 0.5 – 100 for gain. Resisters: 1K – 1M ohm. Gain should be constant at low frequency, but gain drops and output shape is changed as the frequency is increased, depending on the gain. If output is in phase with input signal, check that +15V is connected pin 7 (not pin 8) 2.4 Integrator circuit diagram: replace R2 with capacitor Gain (=Vout/Vin) = -Z2/Z1 = -1/jwC/R1 = -1/jwRC Vout = V0 exp (jwt) = - (1/RC) integral (Vin) Tips Use the simplest input wave (square wave). Output should be the triangle wave. You may not see the clean triangle wave, without adding a large resister (1M ohm) in parallel across the capacitor. This resister will spit the current, not saturating capacitor. Use R1=200K, C=10nF Don’t use too small value of the gain. Remember the expected gain only depends on external circuit components, assuming beta (=R1/R2)*G(intrinsic) is very large. Don’t use too large value of the gain. Output will be saturated. Output signal cannot be larger than the power supplier voltage, 15 V. So suitable choice will be 0.5 – 100 for gain. Resisters: 1K – 1M ohm. 2.5 Phase shifter ZC VIN R2 ZC VIN V V VOUT V (VIN VOUT ) / 2 R1 R1 V V according to Golden rule V V VOUT VIN ZC VIN (VIN VOUT ) / 2 R2 ZC Z R2 C , where Z C 1 / jwC Z C R2 VOUT 1 jwR2C 1 (wR2C)2 2 jwR2C VIN 1 jwR2C 1 (wR2C)2 tan 1 2wR2C / {(wR2C)2 1} 1.732 For 1kHz frequency, 1 1 1.732 2 RC 1.732 / (w 6.28 *1.000) 2.758 10 4 1.732w 2.6 In the real world: gain limitation A realistic OP amplifier don’t have an infinite gain, and it’s gain drops at high frequency, and output response is not instantaneous. Slew rate: the rate at which the output voltage can change: V/t, typically, 106V/s QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Gain: Large bandwidth with lower gain: Don’t saturate output voltage using higher input voltage and higher gain Go QuickTime™ and a F (Uncompressed) decompressor re needed to see this picture. G Bandwidth - 2.7 Output impedance Output impedance is very small, ~100 ohm. With external resister r, Vout will drop by r/(r+R). Use a small resister. It would be very hard to see any chance with large value of the resister (>1k ohm). 3.2 Schmitt trigger Make sure that student draw output very carefully in their logbook, especially threshold region. If there is any student, you can guide them to use two oscillators plus summer circuit (two sine waves with small and large amplitudes). This will produce a noisy signal. +15 V(H) QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. V(L) -15V t t1 t2 3.3 Astable multivibrator Vout: oscillating square wave Vout signal goes to V+ via a positive feedback, and Vout signal also goes to V- via a negative feedback. Vout depends on the comparison of V+ (=Vref) and V- (Vramp). If V+ > V-, Vout will have a saturated output, +15V. Then, V+ has a positive voltage (=4.7/(47+4.7)Vout=0.9*15V=1.36V) and the capacitor will be positively charged up. Once V- exceeds V+, then Vout will be immediately -15V, then the capacitor will start to discharge until V- is below V+. This will produce an oscillation. Oscillation frequency will be determined by the capacitor and 10Kohm. (positive feedback is immediate, whereas QuickTime™ and a decompressor negative feedbackTIFF is (Uncompressed) delayed by ~RC amount) are needed to see this picture. 3.4 Wien bridege oscillator R2 Z2 VOUT , V VOUT R1 R2 Z1 Z 2 R / jwC 1 jwCR Z2 , Z1 R 1 / jwC jwC V jwCR 2 V VOUT V , 2 1 (wCR) 3 jwCR Thus, imaginary component of V+ should be zero So, w=1/RC And, V =0.33RVOUT , V- will be set to V+ using a light bulb. 4.3 Flash ADC LM311 CHIP WILL BE USED, NOT 741 CHIP: EMPHASIZE TO STUDENTS THAT THIS CHIP HAS DIFFENT PIN ASSIGNMENTS FOR POWER AND OUTPUT. See how we setup a voltage divider to make 3V, 2V, and 1V for C3, C2, and C1 respectively. +Vcc should be +15 V, and –Vcc should be -15V In this circuit, there is a high risk to burn the oscillator or circuit, based on last year’s experience, because there are so many wire connections and power lines for this chip are changed, compared to the previous experiment. Absolutely necessary to check Vin wire line using oscilloscope, because they connect Vin wire to the oscillator. How to setup above encoder? A C2, B C3 C2 C1 : XOR gate (chip #7486) or A C2, B C3 C2 C1 : XNOR gate Once students setup their ADC, demonstrator needs to confirm their circuit design and output. Because output is LED signal, practically it is not possible whether they have built ADC properly or not. It is also good to ask them draw Vin and A channel together using oscilloscope for a triangle wave (with 4V amplitude). Vin and B channel too.