Feedback and Oscillators in Electronics - Lab Report Example

Feedback and Oscillators in Electronics Task and Question Types of feedback Introduction In an oscillator, a fraction of the amplifier signal is often feed back onto the amplifier’s input (Ellinger 45). Following this, the amplification of signal is then resent to the input where it undergoes amplification once more. This process takes place repeatedly, thereby producing an amplified sound from a speaker (Ellinger 78). Feedback entails this process of sending a section of the output of an amplifier back to the amplifier input. Feedback is one of the powerful tools that provide an allowance for designing high-performance circuit with the use of components that have uncertain parameter values (Ellinger 89). The two types of amplifier are the positive and the negative feedback. The two differ in terms of whether the signal is described as being in phase or out of phase with the input signal. The two types of feedback can also be referred to as regenerative or direct feedbacks. Regenerative feedback or negative feedback occurs whenever a signal is said to be 180 degrees out of phase to the input signal (Musrt 89). A widely cited, negative feedback is appropriate since it helps in creating a practical circuit given that it can create rates and gains. It can also be used in making circuits stable, as well as self-creating and it has an output that can characteristically create equilibrium condition. In an op-amp, a negative feedback is used for purposes of creating a corrective mechanism (Musrt 67). Moreover, it limits the amplifier’s input signal hence improving the fidelity of an amplifier. By and large, it increases the frequency response of any given amplifier through preventing the decreasing in the gain of an amplifier. During the application of an amplifier, the feedback signal reduces with the increasing input signal (Musrt 76). On the other hand, in the positive feedback, the voltage or current feedback is often applied for purposes of increasing the input voltage (Musrt 47). When a positive feedback is applied in an inverting signal circuit, a portion of an output signal is fed back to the input. It is worth noting lacking a positive feedback in any circuit causes a slowdown in the detectors of the open loop. Positive feedback can lead to an increase in the amplifier gain. More often than not, feedback is used in electronic circuits for various reasons. First, circuit characteristics can be controlled and made independent of wide variations in most of the active device parameters (Musrt 34). Second, using feedback, it is possible to make circuit characteristics relatively independent of some operating condition. Third, with the use of feedbacks, it is possible to come up with a signal distortion occurring due to the none-linear nature of certain active devices, which can become reduced significantly. Last but not least, frequency responses, as well as the bandwidth or gain trade-off can easily be controlled (Musrt 75). A circuit with a negative feedback. Figure 1.1: The Negative feedback The circuit below indicates that with the feedback voltage applied, the input signal is somewhat weakened in particularly in a negative feedback. It is clear that in feedback network, there is a combination of section of the output signal with the input signal. Noting that in the case of a negative feedback, the output signal is always 180o out of phase with an output signal leading to the negative feedback shown above. Response to Task 1 Question 3. There are a number of factors that are considered when building a Wien-Bridge oscillator. First, frequency control need to be assured with a varied number of frequency decades maintained for purposes of constructing a Wien-bridge oscillator. On most cases, at least three frequency decades are often used. It is proper to ensure that frequency decades cover a certain audible spectrum, which ranges between 20 Hz to about 20 KHz. Moreover, a two-gang variable capacitor along with two section variable capacitor is required to serve the purpose of adjusting of the circuit frequency. By and large, in order to build a Wien-Bridge oscillator, there is need for a differential amplifier alongside a large open-loop gain. An R-c network is also required for the determination of frequency and a non-linear resistive network that helps in amplitude stabilization. The Effect of applying the feedback to the single and multi-stage circuits. It is worth noting that feedback amplifiers are the kind of amplifies whose output energy gets fed back to the same circuit’s input. In making sure a positive feedback takes place, there is a positive feedback must always made such that the feedback signal is in phase with an input signal making it regarded as additive. For a case where the feedback signal is at 180o out of phase with the input signal, it becomes a negative feedback. There are many applications of negative feedback. First, a negative feedback has a significant effect when used in multi-stage circuits. In this case, it serves to reduce on the high gain to a lower and usable amount. The application of the feedback in a multi-stage circuit reduces distortion, as well as increases response in the upper frequency. By and large, negative feedback increases the input impedance. It also causes an increase in the input impedance. Applying a feedback in a multi-stage circuit has also been found to cause a reduction of the output impedance. Types of Oscillators Wave generators are vital elements as far as electronics is concerned. Notably, generators make use of various circuits that generate varied outputs. These include saw tooth, trapezoidal, sinusoidal, squire among other wave shapes. An oscillator is an example of a generator. Fundamentally, an oscillator is a kind of amplifier that characteristically generates its own signal. Oscillators are either classified according to the wave produced or the requirements or conditions based upon their production of such oscillations. Oscillators are often characterized by frequency accuracy, frequency stability, and the purity associated with the output waveform. Frequency stability entails the oscillator’s ability to remain where it was formerly set and avoid drifting its frequency. Frequency accuracy, on the other hand, entails how close a desired frequency an oscillator becomes. Basically, two types of oscillators exist. These are the none-sinusoidal and the sinusoidal oscillators. Sinusoidal oscillators give a sine wave output signal, whose amplitude is constant and with no variations in the frequency. In order to achieve an ideal sine wave, factors such as the stability of amplitude, frequency stability, as well as the amplifier properties need to be taken into consideration. As widely cited, generators that produce sine wave signals have their output signal ranging from a somewhat low audio frequency to the level of a microwave frequency, which is often considered as being ultrahigh. A significant number of generators make use of resistors, as well as capacitors for purposes of establishing their own frequency networks. These types of generators are regarded as RC oscillators. The other sine-wave generators utilizing capacitors and inductors for determining their frequency are called the LC oscillators. Most of them make use of circuit tanks for the radio frequencies. However, one thing to content with is that these type of generators are limited such that they cannot be used a pure oscillators of somewhat low frequencies given that if used, the capacitors and inductors would be much costly owing to their large size. Crystal generators are the crystal controlled oscillators also forming part of oscillators. They are known for their characteristic frequency that is somewhat excellent commonly applied in the radio range and middle audio range. The second category of oscillators is often referred to as the Nonsinuisoidal Oscillators. These are often known for producing waveforms, in the shape of a rectangular, trapezoidal, trigger, saw-tooth, and square. The outputs of Nonsinuisoidal Oscillators are often characterized by an abrupt change and a relaxation. Because of this, they are commonly referred to as relaxation oscillators. Their signal frequency is more often than not, governed by either a discharge or charge time of a resistor alongside a capacitor in series. Notably, there are those types that possess conductors in them, which do significantly influence in their output. Unlike the sinusoidal oscillators, the LC and RC networks are used in the determination of oscillator frequencies. In this regard, the non-sinusoidal oscillators can either be regarded as saw-tooth, trapezoidal, multivibrators, or blocking generators. As noted above an oscillator is just but a form of an amplifier, which gives out a feedback signal. Oscillators are generally none rotating and produce current in an alternating form. Oscillators produce waveforms, whose peak are constant and with a specifically maintained frequency of a certain limits of waveforms and amplitude. Oscillators are made such that they can produce amplification. Given that in an oscillator, an output signal is often fed back onto the sustained input, most of the power is required to be fed to the input for purposes of making sure it is self driving. Methods for achieving a sinusoidal oscillation and the circuit conditions and the methods There are basically three fundamental rules that need be met in order for the circuit to serve as an oscillator circuit. These are: first, the circuit need to have a tank circuit for purposes of producing the necessary damped oscillations. Then second, there is need for the circuit to posse a gain and for the amplifier and the gain to be greater than unity. Last the circuit has to be able to provide the positive feedback, as well as the feedback circuit. The figure shows an example of the oscillator circuit. a) Given a Wien-Bridge Oscillator, the formula for the Resonance frequency can be found from Fr = 1/2RCπ From this, if C is made the subject, then in order to find the value of the capacitor, the formula becomes C= 1/2RFrπ = 1/188495.56= 5.30516*10-3F Hence it is certain that capacity value required = 5.30516*10-3F b) For the Close loop gain, as well as the feedback factor It is prudent to let the voltage for the amplifier voltage gain to be A with the feedback attenuation as B Now that the closed loop gain (X) is is often found by the formula A / [ 1 + (A x B )] and with the feedback factor being Y = A / X C) in finding the output voltage, there is need to make use of the formula Vout = Vin (1 + R2/R1)= 150mV/45O. This implies, after substituting (Output voltage) Vout = (1+ 200/200)* 150mV/45O= 2*150mV/45O= 300mv/45O. From this, the output voltage for the oscillating circuit considering the input voltage is 150mV/45 is 300mv/45O Advantages of the crystal-controlled oscillator circuits A crystal oscillator is one of the simplest oscillators that make use of the characteristics of some mineral quartz often referred to as piezoelectric effect. As widely cited, quartz has the ability of bending when subjected to any electric field. This implies that mechanically bending quartz causes an electric field to appear. Cutting and polishing quartz crystal and attaching it to the electrodes might cause them to resonate mechanically at a specific frequency. Applying an alternating voltage on a quartz electrode causes it to bend at a resonance frequency. Using a circuitry point of view, a crystal is similar to a high Q tuned circuit. This implies that a quartz crystal can be used in oscillator circuits as feedbacks. In this case, the quartz crystal frequency is always constant in respect to the variations in temperature. This property makes crystal oscillators to be very highly stable. When considering crystal oscillators, it is worth noting that in circuits of parallel circuits, an additional capacitance is often connected in parallel with the crystal because of the external circuit (Musrt 42). For parallel resonance crystals, it has a specified load capacitor often determined during manufacturing and it has to be present in order for a crystal to work at a marked frequency. On the other hand, series resonance frequency as used in circuits, have outputs that an integer times the frequency of a crystal (Musrt 92). Such forms of crystals are meant for purposes of the final output frequency. They are not fundamental and in case, they are used in fundamental circuits, they may fail to be exactly on a marked frequency (Musrt 43). The figure below shows crystal oscillators. The figure is a diagrammatic representation of a crystal oscillator often referred to as piece oscillator. Identification of the properties of an oscillator is that crystal location is found between the output elements, and the control elements of an active device (Musrt 32). If taken in the context of a FET, it implies that a crystal is connected in between the drain and the gate. For a bipolar transistor a crystal is located between the collector and the base. Ignoring the crystal makes the circuit in the figure shown above to be similar to that of a source amplifier that has an inductor that forms its load. In this case, capacitor C1 needs to be as small as possible in ensuring that during the next stage the load resistance the resonance frequency is affected by the impedance. If the circuit ceases to oscillate accordingly, the random fluctuations that occur because of the thermal effects, and supply voltage can lead to slight flexing of the crystal. In this case, a small voltage is build up across the drain or gate junction and not in phase with the gate. It can be noted that this is one of the key conditions for the positive feedback. The crystal forces of the high Q causes a feedback signal that is coupled with an input via a capacitive coupling to be at a resonance frequency of a crystal. Therefore, a stable output is formed. This implies that in ensuring that an oscillator starts reliably, the overall circuit gain has to be about a unit. In crystal oscillators, frequency helps in keeping track of the time and provides a somewhat stable clock signal for the digital integrated circuit. It also helps in the stabilization of frequencies in radio transmitters, as well as in receivers. Unlike other oscillators’ circuits, the mechanical resonance characterized by a crystal oscillator makes it to be able to create to be able to create an electric signal that has a precise frequency. Moreover, proper cutting of quartz crystal alongside mounting it properly can help in the distortion of an electric field. In summary, the crystal oscillator has the following advantages. Very high stability, relatively low component count, relatively low noise content due to a very high Q, and has a very accurate frequency, which is often determined by the manufacturer (Borst 56). However, it has its limitations. First, its differential frequency does need a new crystal. Second, its crystal seems relatively expensive (Borst 42). Works Cited Borst, Bosco. “The Behavior Experimental Analysis.” American Scientist 45.4 (1999): 343- 371. Ellinger, Fartus. The Circuit Technology and the Radio Frequency Integrated Circuit. New York: John Wiley and Sons, 2008. Print. Musrt, Humphrey. The Fifth Discipline: The Art and Practice of the Learning Organization. New York: Doubleday, 2009. Print. Read More