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RAIL TO RAIL OP AMP AMPLIFIER WITH UNIPOLAR SUPPLY I. OBJECTIVES a) Understanding the functioning of a rail-to-rail OP AMP amplifier. b) Understanding the use of a rail-to-rail OP AMP amplifier with unipolar supply for input signals with a 0 DC voltage component. c) Developing a general method for solving the unipolar rail-to-rail OP AMP amplifier problem regarding a 0 DC voltage component input signal. II. COMPONENTS AND DEVICES We will use the experimental circuit equipped with an AD820 OP AMP rail-to-rail amplifier, resistances and capacitors. The circuit will be supplied using a double voltage source, the input voltage will be generated using the signal generator and the waveforms and voltage transfer characteristics will be visualized using a 2 channel oscilloscope. III. PREPARATION P.1. Noninverting rail-to-rail amplifier P.1.1. Noninverting amplifer with differential voltage supply (±VAl) For the circuit in Fig. 1: Determine the value of the voltage gain Av= vO/vI. Draw the vO(t) waveform for vI(t) – triangular signal with 0.4V amplitude, frequency of 1kHz and a 0V DC component value. Draw vO(t) for vI(t) - triangular signal with 1.5V amplitude, frequency of 1kHz and a 0V DC component value. VTC vO(vI) for vI(t) of amplitude 1.5V. P.1.2. Noninverting amplifier with unipolar voltage supply (+VAl) a) For the circuit in Fig. 2: Draw the vO(t) waveform for vI(t) – triangular signal with 0.4V amplitude, frequency of 1kHz and a 0V DC component value. Which part of the input voltage does the circuit amplify? Explain. Draw vO(t) for vI(t) - triangular signal with 1.5V amplitude, frequency of 1kHz and a 0V DC component value. Draw the VTC vO(vI) for vI(t) of amplitude 1.5V. b) For the circuit in Fig.3., draw: Input voltage waveforms at the noninverting input of the OP AMP and vO(t) for vI(t)- triangular voltage of amplitude 0.4V at 1kHz and a 0V DC component. Explain the shape of the output voltage. c) For the circuit in Fig.4: Draw the waveforms for the input voltage at the noninverting OP AMP input, the C2 capacitor voltage and vO(t) for vI(t) - triangular voltage of 0.4V amplitude at 1kHz with a 0V DC component. What part of the input signal does the circuit amplify? Explain. Determine the AC gain value.-vo/vi. Determine the DC gain value – the DC component value of vO/ the DC component value of vI. Draw vO(t) and the VTC vO(vI) for vI(t) = 1.5Vsinωt [Hz]. P.2. Inverting amplifier with unipolar voltage supply (+VAl) a) For the circuit in Fig. 5: Draw the vO(t) waveform for vI(t) – triangular signal with 0.4V amplitude, frequency of 1kHz and a 0V DC component value. Which part of the input voltage does the circuit amplify? Explain. Draw vO(t) for vI(t) - triangular signal with 1.5V amplitude, frequency of 1kHz and a 0V DC component value. Draw the VTC vO(vI) for vI(t) of amplitude 1.5V. b) For the circuit in Fig. 6: Draw the waveforms for the input voltage at the noninverting OP AMP input, the C2 capacitor voltage and vO(t) for vI(t)- triangular voltage of 0.4V amplitude at 1kHz with a 0V DC component. What part of the input signal does the circuit amplify? Explain. Determine the AC gain value.-vo/vi. Determine the DC gain value – the DC component value of vO/ the DC component value of vI. Draw vO(t) and the VTC vO(vI) for vI(t) = 1.5Vsinωt [Hz]. IV. EXPLORATION AND RESULTS 1. Noninverting rail-to-rail amplifier 1.1. Noninverting amplifier with differential voltage supply (±VAl) Exploration Build the circuit in Fig. 1, for ±12V supply voltage, applying a triangular input voltage of 0.4V amplitude at 1kHz, 0V DC voltage component applied at IN+ having point D connected to GND – Fig. 5. 7 +12V + 6 vO R1 2 vI 4,7K 4 -12V R2 47K Fig.1. Non inverting amplifier with differential supply Results Visualize on the oscilloscope, in Y-t mode, the input and output voltages. Draw the vI(t) and vO(t) waveforms, writing down the output voltage amplitude and determine the value of the voltage gain vO/vI. Raise the input voltage amplitude up to 1.5V whilst visualising on the oscilloscope and drawing the input and output waveforms (Y-t mode). With the oscilloscope in X-Y mode, visualise and draw the VTC vO(vI). Waveforms for vI(t) and vO(t) as show on the oscilloscope and their amplitudes for vI(t) of 0.4V amplitude. The voltage gain sign and value as shown from the oscilloscope. vI(t) and vO(t) with their amplitudes; vI(t) of amplitude 1.5V. VTC vO(vI) with the point coordinates that determine the active region for vI(t) of amplitude 1.5V. The maximum value of the output voltage vO(t). Explain. 1.2. Noninverting amplifier with unipolar voltage supply (+VAl) Exploration a) Build the circuit in Fig. 2 supplied with +12V (–VAl is connected to GND). Apply at the input (IN+ from Fig. 7.) a triangular voltage of amplitude 0.4V at 1KHz and 0V DC component. 7 +12V + 6 vO R1 2 - 4,7K vI 4 R2 47K Fig. 2. Non inverting amplifier with unipolar supply Visualize on the oscilloscope the input and output voltages and draw their waveforms. Raise the input amplitude up to 1.5 V, observe it on the oscilloscope and draw the waveforms for the input and output signals (Y-t mode). With the oscilloscope in X-Y mode, observe and draw the VTC vO(vI). b) In order to amplify the whole input signal (and not just half of it) build the circuit in Fig 3 by applying at point A a triangular input voltage of 0.4V amplitude at 1kHz and 0V DC component and connecting point B to IN+ -- Fig. 7. 12V 4 R3 10k C1 10u vI 3 R4 10k + 6 2 vO - R1 R2 4,7k 47k Fig. 3. Noninverting amplifier after applying a polarization voltage Visualise on the oscilloscope (DC button switched ON) in Y-t mode the input voltages and from point B (vB – Fig.7), and then draw the input and output voltages. c) By different values of the AC and DC gains, the limiting of the output voltage is avoided. The circuit is modified with respect to b) by introducing the C2 capacitor between point C and D (point D is disconnected from GND but, in return, point C is connected to GND – Fig. 7), thus resulting the circuit in Fig. 4. The input is a triangular voltage of amplitude 0.4V at 1kHz and 0V DC component. 12V C1 R3 10k 3 4 10u vI C 10u R4 10k + 6 2 vO - R1 R2 4,7k 47k Fig. 4. Noninverting amplifier final circuit Visualise on the oscilloscope (DC button switched ON) in Y-t mode and draw the waveforms for: o Input and point B (vB) voltages; o Point B voltage(vB) and point D voltage(vD); o In and Out voltages. Raise the input voltage amplitude up to 1.5V, visualise the waveforms for the input and output (Y-t mode) on the oscilloscope, the VTC vO(vI) (X-Y mode) and draw them. Results a) vI(t), vO(t) waveforms as shown on the oscilloscope and pointing out their amplitudes; vI(t) of amplitude 0.4V. Explain why we obtain only positive values for the output voltage. Can the voltage gain value be determined? Why? vI(t) and vO(t) with their amplitudes; vI(t) of amplitude 1.5V. VTC vO(vI) with point coordinates that determine the active region. ASSIGNMENT: modify the circuit in order to obtain a half-wave rectifier. Hint: for the half-wave rectifier, the values for the input and output voltages are the same. b) vI(t), vB(t) waveforms drawn as they appear on the oscilloscope and write down the amplitudes. vI(t), vO(t) waveforms drawn as they appear on the oscilloscope and write down the amplitudes. How can you explain the fact that the output of the amplifier is always limited? c) vI(t), vB(t) waveforms drawn as they appear on the oscilloscope and write down the amplitudes. vB(t), vD(t) waveforms drawn as they appear on the oscilloscope and write down the amplitudes. vI(t), vO(t) waveforms drawn as they appear on the oscilloscope and write down the amplitudes. AC gain sign and value determined from the oscilloscope. DC gain sign and value determined from the oscilloscope. vI(t), vO(t) and VTC vO(vI) for vI(t) of amplitude 1,5V. 2. Inverting amplifier with unipolar voltage supply (+VAl) Exploration a) Build the circuit in Fig. 5, supplied with +12V, by applying at the input (point D) a triangular voltage of amplitude 0.4V at 1KHz, 0V DC component and connecting point IN+ to GND – Fig.7. 7 3 +12V + R1 2 vO 6 0 - 4,7k 4 vI 0 R2 47k 0 Fig. 5. Inverting amplifier with unipolar supply Visualise on the oscilloscope, in Y-t mode, the input and output voltages and draw them. Raise the value of the input up to 1.5V, visualise on the oscilloscope and then draw the waveforms for the input and output voltages. With the oscilloscope in X-Y mode, visualise and draw the VTC vO(vI). b) Apply a triangular input voltage of 0.4V amplitude at 1kHz and 0V DC component at point C and connect points B and IN+ (what purpose do these connections serve?) – Fig. 7, resulting the circuit from Fig. 6. +12V 7 R3 10k 3 + 6 vI R4 10k C2 R1 10u 2 vO - 4,7k R2 47k Fig. 6. Final circuit for the inverting amplifier Visualise on the oscilloscope (DC button is pushed), in Y-t mode, and draw the following voltage waveforms: o Input and point D(vD); o point D(vD) and point B(vB); o input and output; Raise the input amplitude up to 1.5V, visualise the input and output voltage waveforms (Y-t mode) and the VTC. Results a) vI(t), vO(t) waveforms drawn from the oscilloscope with their values written down for vI(t) of 0.4V amplitude. Explain why the output voltage has only positive values. Can the voltage gain be determined? Why? vI(t) and vO(t) with their amplitudes written down for vI(t) of amplitude 1.5V. VTC vO(vI) with the point coordinates that determine the active region. b) vI(t), vD(t) waveforms as they appear on the oscilloscope with their amplitudes written down. vD(t), vB(t) waveforms as they appear on the oscilloscope with their amplitudes written down. vI(t), vO(t) waveforms as they appear on the oscilloscope with their amplitudes written down. AC gain sign and value determined from the oscilloscope. DC gain sign and value determined from the oscilloscope. vI(t), vO(t) and CSTV vO(vI) for vI(t) of amplitude 1.5V. Bibliography 1. Oltean, G., Sipos, Emilia, Oltean, Ioana – A New Approach of Op-Amp Amplifier Biasing, Buletinul Ştinţific al Universităţii Politehnica din Timişoara, Simpozionul de Electronică şi telecomunicaţii - ETc, 2004, Octombrie 22-23, Timişoara, Romania, ISBN – 1583-3380, Tom 49, Fascicola 2, pag. 328-331 2. Oltean, G., ş.a. - Electronic devices and circuits, Electronic devices, Laboratory manual, UT Pres, Cluj-Napoca, 2004. 3. Oltean, G. - Dispozitive şi circuite electronice, Ed. Risoprint, Cluj-Napoca, 2003. 4. http://www.bel.utcluj.ro/dce/didactic/fec/fec.htm Fig. 7. Experimental assembly