Generators of functions
Perhaps the generators of functions are one of the complex and expensive assemblies but, but nevertheless, is essential to count them in our range of realized projects if they are wanted to analyze the virtues and defects of the majority of the electronic assemblies given the importance that they have for the verification of the bandwidth of the sound amplifiers, analysis of the operation of the digital accountants, etc.
We will study a generator of functions that will count on the generation of sinusoidal, triangular signals, squared and impulses, until a 100 frequency of KHz and tension of 0.05 exit V, 0.5 5 V and V. Also will have the possibility of obtaining a train of impulses with an external signal of firing.
In order to be able to take advantage of the advantages that present/display to us to tell on a generator of functions it is necessary that this one counts on a series of characteristics:
- They must be most versatile possible, with several waveform of exit, frequency and amplitude.
- It is necessary that as much the amplitude as the frequency is but stable the possible thing, even with the temperature.
The sine wave is applied for the analysis of the amplifier bandwidth and to verify the operation of filters (it passes band, it happens low or it passes stops).
The square wave will be used in the study of digital circuits to verify retardations of rise times and slope.
The triangular wave is applied, in certain cases, as a complement to secure sine waves in alineales networks. The linearity of this type of wave must sufficiently be good like so that at first he is not perceivable.
A generator of functions can be considered like a set of independent blocks but with their related parameters. We will study these blocks in separated form.
The main blocks are: power supply, oscillator and amplifier.
Block power supply: It consists normally of a transformer, a rectifier, a filter and a regulating series.
All these components of a tension source or were studied when we saw the tension source, reason why we will not make commentaries exceeds they, we sent to the reader who needs an extra understanding on these to the corresponding section where or they were analyzed (Brief description of the operation of a tension source)
Amplifying block: This block has the function to secure the necessary gain, as much of tension as of power of the signal generated by the oscillator.
Oscillating block: The main set within the generator of functions is this one.
Its principle of operation is, by means of the conversion of continuous power in alternating, to maintain a signal of periodic exit. This is due to the use of a high-gain amplifier, whose exit is red-supply to the entrance.
Generally the oscillating are classified in sine, of square wave and impulses.
Two types of oscillating are distinguished: those of desfasadoras networks and those of oscillating circuits.
Oscillating R-C of been out of phase networks more common are those than they have three simple cells R-C, those of bridge of Vienna and those of bypassed T.
The oscillating of resonant circuits are known like oscillating L-C. Two types are known: the oscillating that have indictive coupling and those that does not have it, as well, within the oscillating with indictive coupling can mention been in tune in drenador for transistors FET or the collector in bipolar transistors and the been in tune ones in door for transistors FET or bases on the bipolar ones. Those that does not have indictive coupling are the Colpitts, Harley, Clapp and those of quartz crystal.
Oscillating R-C:
Three identical cells R-C: Generally they are constructed with a followed amplifier of a network R-C that will make the necessary desfasaje in the exit until fulfilling the condition for being in phase with the entrance. This network has the disadvantage of owning a considerable power loss, reason why it must be recovered with an amplifier. It has the advantage of which inductancias are not used, which would be insastifactorias for the use in audio frequencies.
Bridge of Vienna: In order to obtain a stable operating frequency but a disposition of bridge balanced like the one of the bridge of Vienna is used.
The operation of the circuit is the following one: through a branch of the bridge, made up of two cells RC (a series and the other parallel), a positive refeeding is introduced, the amplitude and the phase of the red-supply signal is function of the frequency, existing a single frequency for which the desfasaje is null. This frequency will be the oscillation frequency. The negative network of refeeding has the mission to cause that the module of the bow gain is equal to the unit.
Circuit in bypassed T: This oscillator is basically equal to the one of the bridge of Vienna, unless the curl of positive refeeding has been replaced by cuadripolo in bypassed T.
Oscillating L-C:
These oscillating use like desfasadora network of refeeding condesadores and inductancias. The study of these oscillating is not easy to realize, therefore, and to facilitate its compression, the operation of the used oscillating will be analyzed but.
Classic oscillating L-C:
Oscillating L-C without indictive coupling more widely used are the Colpitts, Hartley, Clapp and to crystal.
Colpitts oscillator: This oscillator uses a network LC in p formed by C1, C2 and L, as it is seen in figure 1:
figure 1
The oscillation frequency and the condition of oscillation will be:
f (osc) = 1/2p Ö1/L (1/C1 + 1/C2)
TO > C1/C2
The relation for the oscillation frequency is valid for a transistor FET, if however we used a bipolar one:
f (osc) = 1/2p Ö1/L (1/C1 + 1/C2) 1 (C1 C2 Ro Ri)
Hartley oscillator: The circuit tank is formed by two coils, L1 and L2 and a capacitor C with a connection of coefficient M. The diagram of the same can be appreciated in figure 2:
figure 2
If the used transistor is of type FET, the frequency of resonacia will be:
f (osc) = 1/(2p ÖL2 C´)
where:
C´= (C1 C2 C)/(C1 C + C2 C + C1 C2)
Clapp oscillator: The scheme of an oscillator of this type can be observed in figure 3, the same has an oscillating circuit made up of L3, C2, C4 and C6. The one of the figure is an oscillator of 24 MHz and 300 mW of power:
figure 3
In this one, the coils L1 and L2 are circuits abiertos to the oscillation frequency, whereas the capacitores C1 and C3 are short circuits.
