today for any type of circuit we need, it is likely that we can find a model of an integrated circuit that performs the same function or part of it. Thus, we have seen that we can find oscillators, multivibrators and voltage regulators, such as 723, as part of integrated electronics.
Different models of integrated circuits are numerous and, therefore, it is somewhat difficult to know exactly which of the that there will fit best to our design. There are many catalogs from different manufacturers, in which applications are often specified for each chip. But one of the most important factors, which rarely is reflected in these catalogs, is the type and amount of external devices that we need to perform the function we want with the integrated circuit. Despite all this, with a little experience in handling these catalogs will be able to get find the integrated circuit is going to be more useful, either to the specific application we need or to provide, by some of the functions want.
As we know, the number of different types of integrated circuits is immense and very difficult to know everyone. We will try to learn a little more depth some of them. With so many types of integrated circuits classifications can be made from them are also numerous. One of these classifications ci divides into three types: linear analog or digital and high consumption ci (radio, TV, etc.).. Linear integrated circuits are those that allow for input signal range within which valid may take infinite values, as happens in the output. Digital integrated circuits, as discussed below, support only a finite set of input values, being typically "two" elements of the set. Linear circuits must meet many conditions, it is sometimes necessary to design one of these circuits knowing in advance the role that will play, although this type of construction is very expensive and, as we saw, to make a lot of the price series circuits becomes cheaper much. For this reason, usually manufactured from highly versatile integrated circuits that a single IC can be used to make different types of functions.
The VCO
An integrated circuit is widely used VCO. This is a precision function generator. VCO stands, in English, of the integrated circuit, mean: oscilator controlled voltage. An integrated circuit ICL8038 is a function generator with which we can generate signals with high accuracy and forms can be sine, square, triangular, sawtooth and pulse. For all this you only need the integrated circuit named above and very few external components. A very important application of the VCO is its use in synthesizers. The VCO is the core of a synthesizer. The stability of the entire instrument will depend on the performance of the VCO. Among the main characteristics of a VCO is able to select the frequency externally in which we work, being able to obtain a wide range of useful frequencies between 0.001 Hz and 300 Hz This selection can be performed using resistors and capacitors.
ICL8038 connected for minimal distortion
We can also modulate the frequency and the sweep with an external stress. The VCO has a wide temperature range for which stable output is achieved. If we connect with a PLL can still further reduce drift in temperature. Another important feature is that we can obtain a VCO output signals simultaneously on the sine, triangular and cosine. If the output is sinusoidal distortion is low and the voltage normally obtained at the output is high. Besides all these qualities, its handling is quite easy and we can get it to work perfectly with a few external components.
The XR2206 is also an integrated function generator. With it we can get a signal output sine, square, triangular, sawtooth type or a pulse train. It is quite stable against temperature variations and has great accuracy. In these circuits, as in the VCO, we have a wide range of valid frequencies, ranging from 0.01 Hz to over 1 MHz and can be adjusted externally. You may also modulate the output signal amplitude and frequency using an external voltage. This integrated circuit is widely used for communications and instrumentation, and, when needed sinusoidal tone modulated FM or AM, is also used. We can shift the oscillation frequency using external control voltage. By doing this we will introduce a small distortion factor but it will be so small that we are worth this small disadvantage compared to the benefits it produces. These integrated circuits are made up of four parts: a VCO (voltage controlled oscillator), an analog multiplier and wave configurator, a gain amplifier and a set of circuit breakers. The main features of the ci are the low signal distortion and excellent stability. As we have seen, they also have a large displacement frequency, low sensitivity to variations in supply and high supply voltage range. Generators are often used as sine waves, square, triangular, etc. AM and FM generators, tone generators, frequency converters, voltage, etc..
We know that with an operational amplifier coupled with some external device, mostly resistance, we could build a voltage comparator. We also have a series of integrated circuits, LM710, voltage comparators that are high speed. They are designed to be used in precision digital sensors and to replace operational amplifiers which function to compare stress when we need a high speed response. This family has an input difference and is well beyond levels that are compatible with the vast majority of logic families. It is a fairly integrated circuit stable against temperature changes. It consists of a silicon chip doped with gold and this type of doping which makes these circuits are much faster than operational amplifiers. In addition, you can not compare the great advantages that integrated circuits due to their minimum size and capacity of the wiring with discreet circuits that perform the same function. Among the applications of the LM710 include the following: can be used as pulse width modulators, voltage comparators, A / D and high-speed sensors operating in automated measuring equipment. There are also some applications for these integrated circuits within digital systems. Because of its low cost are often quite used.
PLL's name comes from the initials of its name in English Phase Locked Loop. Speaking of a PLL we are referring to a feedback circuit. When discussing the PLL loop we think that it behaves like any servo system or closed loop feedback. The loop consists of a filter, a phase detector and a VCO. In a PLL we also find two dividers, which are often very necessary. For example, we use the PLL in a data communication system for a stable clock and free of fluctuations from a fluctuating input. If we have a variation whose amplitude is very large, it will be necessary to divide the input clock to reduce the amplitude of this variation and it is less than a time interval.
diagram of a PLL
Another example might be to use the PLL as frequency synthesizer. But the dividers can bring some problems, because if you introduce a big dividing factor in the feedback loop can greatly reduce the loop gain, and this will lead to a decline in the response to any changes that occur in input. Therefore, the great dividers should be avoided in feedback loop. Many of these circuits do not have a linear behavior because the phase detector output is not proportional to the phase error and the VCO output frequency does not keep a linear relationship with voltage control. But, in most cases, the PLL behave as a linear circuit and thus we will see.
One of the components used in the feedback loops are phase detectors. Phase detectors, as its name suggests, are able to determine the gap between two signals. There are a variety of them, of which we highlight the following: sampling phase detectors and retention type phase detector discriminator, phase detector multiplier type digital phase detectors. Depending on the application for which we will use the PLL will have to put a phase detector or another, since there is no one that's better, it depends on what we give to the circuit. To choose a detector or the other must take into account two main factors: the type of input signal and the error range of input phase in which the output is linear. Depending on the type of input signal that we will implement the PLL will be using a type of phase detector or another since, for example, a cosine input and digital input sensors require different phase. On the other hand, as the interval phase error of the entry in which the output is linear we will also use a phase detector or another. The broader the range most useful will be the phase detector to control the loop and also the noise will affect fewer. Phase detectors and digital multiplier type are the most commonly used. The former are useful when the input signal is cosine and the second type, as its name suggests, are used for input signals of the digital type.
Voltage Controlled Oscillator
Within the feedback loop of a PLL than a filter and a phase detector is a VCO. As we know, the VCO is voltage-controlled oscillators. There are several types of VCO that can be used in the PLL, crystal oscillators, multivibrators LC and RC oscillators. As with the detection phase we use a VCO or the other depending on the type of application that we will give the PLL. The two factors we have analyzed to choose the most suitable type of VCO is the phase stability and range of control. The frequency of the VCO is subject to the input signal, but phase relationship oscillator output to the input will depend on the natural frequency of the oscillator. Therefore, it will greatly influence the type of VCO say. The natural frequency of oscillation will vary with temperature, time and input noise, producing a change in the output stage if very large may be lost grip. Therefore, for good stability, the frequency of the VCO must be as variable as possible against the temperature, time and noise. On the other hand, it is desirable for the VCO is related in a frequency range as large as possible, because the larger the range of control is easier to maintain the control loop.
PLL with a phase detector and frequency detector
These two factors can not be achieved at once, ie we must have a commitment to see that we need more in each application because if the control range is very large, the phase stability against noise and temperature changes will be pretty bad, and, conversely, if we have a very good stability control interval will be small. Crystal oscillators are more stable but its control range is quite small. Are used in frequency synthesizers and clock synchronizers. However RC multivibrators in a range much greater control but its stability against the possible changes is not so good. They are used as FM demodulators and decoders tone.
As noted above, the input noise of a PLL is a factor that along with temperature and aging of the devices, can destabilize the circuit. Speaking of noise we are referring to unwanted signals that are mixed with the input signal and may even get we do not know what type of input signal or the duration. A very important feature in the PLL is the bandwidth of the noise. According to the application for which we will use the PLL we have to decide the bandwidth of noise.
modulation Follower designed with a PLL
Normally we have two kinds of PLL, a carrier tracking and other monitoring of modulation. With the first we recover, for example, the clock input signal. This clock must have a frequency modulation or phase or a considerable amount of noise and because of this must have a pass band as narrow as possible. The other types are tracking PLL Modulation working as discriminators, the output of the filter should reproduce the spectrum of the baseband and the frequency modulation or phase. In the latter case, the bandwidth of the loop should be wider than the highest modulating frequency. An important factor in treatment of noise is the noise threshold in the PLL. We have assumed that, despite having input noise, the loop is "subject" and this is not true at all. If the noise exceeds a certain value, called threshold of noise, the loop will start losing cycles and may lose the "subject" and will no more linear. The noise threshold of a PLL depends on the structure of the loop, more precisely the phase detector and filter. Another factor that we must also take into account the proper functioning of the loop in the presence of input noise is the frequency spectrum. If we stay within a appropriate frequency range, the loop noise quite well tolerated, but if we get out of that range will have many more problems.
An example of an integrated circuit is the LM565 PLL. The feedback loop of the PLL comprises a VCO, an operational amplifier having a resistor connected to the output and a phase detector, which is of type multiplier, as in most monolithic integrated circuit PLL. By using this type of phase detector we must ensure that the substantial changes in input frequency will not cause large changes in the output of the detector. This PLL can have several applications, among which is its use as a follower of modulation.
internal block diagram of a LM565
The PLL are widely used in electronic analog and digital. Applications include most common are frequency synthesizers, phase and frequency demodulators, coherent amplitude modulators, tone decoders, bit synchronizers, etc.. The PLL is used as frequency synthesizers in communication systems that require carrier frequencies in discrete intervals for a fixed space between channels, for example, the UHF channel band. The PLL that we will use in these applications has a programmable counter in the feedback loop. Another application of the PLL are tone decoders that use the principle that if the bandwidth of a PLL loop is small you can only have an indication of restraint if the input frequency is very near the center of the natural frequency of the VCO. Therefore, to detect a tone center frequency of the VCO must be adjusted to the pitch, so we're going to need a PLL for each of the tones we want to detect. Another application is to obtain a demodulated signal based on a modulated.
CRF
Lenny Z. Perez M
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