Circuit Design: Automatic Gain Control (AGC) circuits Theory and design
Posted by: Chloe
On: 25 Nop, 2018
Viewed:120 times - 2 day, 1 minute, 48 second ago
Downloaded: 0 times -
Rated 4 / 5 based on 431 reviews
Many attempts have been made to fully describe an AGC system in terms of control system theory, from pseudo linear approximations to multivariable systems. Each model has its advantages and disadvantages, first order models are easy to analyze and...
Many attempts have been made to fully describe an AGC system in terms of control system theory, from pseudo linear approximations to multivariable systems. Each model has its advantages and disadvantages, first order models are easy to analyze and understand but sometimes the final results show a high degree of inaccuracy when they are compared with practical results. On the other hand, non-linear and multivariable systems show a relative high degree of accuracy but the theory and physical implementation of the system can become really tedious. From a practical point of view, the most general description of an AGC system is presented in figure 1. The input signal is amplified by a variable gain amplifier (VGA), whose gain is controlled by an external signal V C . The output from the VGA can be further amplified by a second stage to generate and adequate level of V O . Some the output signal’s parameters, such as amplitude, carrier frequency, index of modulation or frequency, are sensed by the detector; any undesired component is filtered out and the remaining signal is compared with a reference signal. The result of the comparison is used to generate the control voltage (V C ) and adjust the gain of the VGA.
Since an AGC is essentially a negative feedback system, the system can be described in terms of its transfer function. The idealized transfer function for an AGC system is illustrated in figure 2. For low input signals the AGC is disabled and the output is a linear function of the input, when the output reaches a threshold value (V1) the AGC becomes operative and maintains a constant output level until it reaches a second threshold value (V2). At this point, the AGC becomes inoperative again; this is usually done in order to prevent stability problems at high levels of gain.
Many of the parameters of the AGC loop depend on the type of modulation used inside the system. If any kind of amplitude modulation (AM) is present, the AGC should not respond to any change in amplitude modulation or distortion will occur. Thus the bandwidth of the AGC must be limited to a value lower than the lowest modulating frequency. For systems where frequency or pulse modulation is used, the system requirements are not that stringent.
As mentioned before, an AGC system is considered a nonlinear systems and it is very hard to find solutions for the nonlinear equation that arise during the analysis. Nevertheless, there are two models that describe the system’s behaviour with a good degree of accuracy and are relatively easy to implement when the small signal transfer equations of the main blocks are known (which is usually the case).
Pressure measurement in liquids or gases is common, particularly in process control. Pressure is defined as the force per unit area. To measure a pres-
sure, it is either compared with a known...
A bimetal is a sensor formed by two metals having different thermal expansion coefficients that are firmly joined, for example, by welding and that are
exposed to the same temperature. Wheneve...
A sensor is of second order when it contains two energy-storing elements and one energy-dissipating element. Its input x(r) and output y(t) are related by a second-order linear differential equatio...
In a first-order sensor there is an element that stores energy and another one that dissipates it. The relation between the input r(r) and the output y(l) is described by a differential equation th...
The sensor response to variable input signals is different from that exhibited when input signals are constant, described by means of static characteristics. The reason is the piesence of energy-st...
The effects of interfering and modifying inputs can be reduced by changing the system design or by adding new elements to it. The best approach is to
design systems with an insensitivity to in...
As the fastest growing demand of circuit and wiring diagram for automotive and electronics on internet based on different uses such as electronic hobbyists, students, technicians and engineers than we decided to provide free circuit and wiring diagram base on your needed.
To find circuit and wiring diagram now a day its easy. E-learning through internet as a right place to search an exact circuit and wiring diagram of your choice and it's much fun and knowledgable. On internet you will find thousands of electronic circuit diagrams some are very good designed and some are not. So you have to modify them to make them according to your needs but some circuits are ready to make and require no changes.
There are many categories of circuit and wiring diagrams like automotive, audio circuits, radio & RF circuits, power supply circuits, light circuits, telephone circuits, timer circuits, battery charger circuits etc. There are many types of circuit and wiring diagrams some are very easy to build and some are very complicated, some are so small and some contain huge list of parts.
We provides free best quality and good designed schematic diagrams our diagrams are free to use for all electronic hobbyists, students, technicians and engineers. We also provides a full educational system to students new to electronics. If you are new to electronics you are a student or a electronic hobbyist and want to increase your knowledge in electronics or want to understand electronics in a very easy way so this is the right place for you we provide electronics beginner guide tutorials to easily understand complicated electronic theory. Our mission is to help students and professionals in their field.