Amplifiers more stages

1) Distortion of amplitude:

It is a linear distortion in which the amplitude of marks them of escape is function of the frequency of marks them in income, an amplifier that does not introduce amplitude distortion is characterized from A(w) = constant.

 

2) Distortion of phase:

It is a linear distortion in which the phase of marks them of escape is function of the frequency of marks them in income, an amplifier that does not introduce phase distortion is characterized from q(w) = Kw .

 

3) Distortion not linearity:

It is had that it marks them of escape from the amplifier introduces of the harmonic members who were not present in mark them of income, is a type of distortion that interests the power amplifiers mostly.

 

4) Amplifier RC and its study:

Two connected amplifiers to common emettitore in cascade are had separate to you in continuous from one condenser C_b .

An amplifier of the sort comes studied differently to second of the frequencies, in particular to the vlves the abilities to connection C _b andthe abilities to bypass C are considered only_z while to vhf the abilities introduced from the transistor that is abilities C _and between baseare considered only and emettitore and C_B between base and collector. The cut frequencies are determined in such a way and consequently the gain to all the frequencies expressed in function of the gain to the MFS.

 

5) direct Method in order to estimate the passing band:

It is necessary to find the frequencies for which the equation is verified, that 8 abilities involve in the case of an amplifier RC the resolution of an equation of 8° degree in how much are present, 2 of connection, 2 of by-pass and others 2 for every transistor.

 

6) interacting Abilities:

Two abilities are considered interacting when there is a current distance that it joins to them and therefore the stiffness seen to the heads of one is function of the reattanza of the other.

 

7) Method of the poles in order to estimate the band passing in the case of multiple poles coinciding:

Neglecting the zeroes a G(w)relativeto the frequency of advanced cut is written and a relative one to the frequency of inferior cut, obtains e being n the number of the coinciding poles.

They are two important formulas a lot in how much from they deduces that if we put in cascade two having amplifiers the same band, the total band is reduced, that it is logical in how much is to the frequency of inferior cut that to that advanced one instead of having â?"3dB is had â?"6dB and therefore the frequency for which is had â?"3dB more towards the inside is moved.

 

8) Method of the poles in order to estimate the band passing in the case of distinguished multiple poles:

The module of the G(j is equaledw) to , squaring, adding and inverting an expression is obtained from which neglecting the mixed terms the two pulsations of cut e are obtained , the made approximation leads but to it turns out you optimistic in how much too much obtains a frequency of inferior cut that is inferior to that real one and a frequency of advanced cut that is advanced to that real one.Naturally the method is applicable only in the case that is possible to write the denominator in fattorizzata shape and that the abilities are not interacting.

 

9) Method of the constants of time in short circuit and to open circuit in order to estimate the passing band:

To difference of the method of the poles, they do not come neglects the mixed terms to you and two frequencies of cut are obtained therefore which gives to a pessimistic approximation that is the frequency of inferior cut is higher of the frequency of real cut while the frequency of advanced cut is lower than that real one, has e , but the great advantage of this method is that the second members of the two previous ones can be gained easy in how much are demonstrated that they are worth the relations e where t_js the other abilities are the constant of time of the ability j-esima in the circuit of calculate vlf cortocircuitando all while t_l0 the other abilities replaced from an open circuit are the constant of time of l-esima the ability in the circuit calculated with all.

 

10) Answer in vlf of an amplifier to two stages:

In vlf the circuit of Giacoletto is not necessary but the hybrid circuit is sufficient simplified equivalent, with it the first stage is taken an examination in which abilities C_b and C_z are interacting therefore in how much the relative constant of timet _zs to the ability to by-pass C_z can be rendered much large one using a electrolytic one. In the analysis of the two-stage they consider therefore the relative sun constant of time to ability C_b and must be had Remembering that in the calculation of the f the other condensers must be cortocircuitare, has e from which if R_S= R_C has t₁=t₂ and therefore the relative formula to the case of the coinciding poles can be used. The answer in vlf obtains dalla where To₀ it is the answer to the MFS.

 

11) Answer in vhf of an amplifier to two stages:

A single stage is considered before and the model of Giacoletto in vhf is replaced to the transistor, on it ability C_c can be brought back in parallel is to the income that to the escape through Miller with the difference that the constant of time associated to the ability that filler in income is the much largest one regarding that due to the ability that filler in escape, in how much the R_L never does not exceed 2Kthe W in the typical circuits therefore this last one can be neglected.

The f_s of the two-stage it is estimated replacing in it the circuit equivalent of the transistor for vhf, neglecting r₁//r₂ , r_cb' and r_ce applying Miller to ability C_C and neglecting also the ability that derives some in parallel to the escape, a circuit with two interacting abilities C _T1and C _t2therefore is obtained . The answer in vhf is obtained from

where To₀ it is the answer to the MFS.

 

12) Answer in MF of an amplifier to two stages:

The condensers of block C must be considered cortocircuita you_b and of bypass C_z while they are considered opened i condensers C_C and C_and relati you to the transistor for which it uses the representation to p- hybrid, analyzing the circuit backwards and being let alone the amplification to the MFS is obtained therefore has obtained the result classic according to which the amplification in tension total is given from the product of the amplifications in current for the cargo resistance of the last stage uniform for the resistance of income of the first stage.

 

13) Compensation to the vlves of an amplifier RC:

Reference to a FET in the configuration to source common modified placing to mount of the resistance R _Done condenser C towards₃ mass and a resistance R ₃is made towards V_DD, supposing to find to the vlves is considered opened the inner abilities to the FET and supposing them much large they are considered cortocircuita the condenser of block in income (that one…in escape not) and the condenser to you of bypass, therefore replacing the outline equivalent for small it marks them of the FET is estimated To_v that under the conditions and turns out equal to the amplification to the MFS calculate sonsiderando absent all the condensers therefore after all the cut frequency has moved towards one lower frequency.

 

14) Compensation to vhf of an amplifier RC:

Reference to a FET in the configuration to source common is made modified placing one L inductance between the resistance of drain R_C and the drain same. The analysis is carried out replacing the FET with its equivalent circuit and grouping in C_t it is the escape ability that the ability of income of the following stage determines To_v and it is divided for_{to 0} imposing that the module of this relationship is worth 1 obtains while imposing that the module of the relationship is worth 0,707 obtains the new pulsation of advanced cut .

 

15) Cascode Amplifier:

Nello study della amplifier RC has been looked at like the frequency of advanced cut is determined mostly gives it ability C_C that comes brought back in income for Miller effect with value, data that to an amplifier comes demanded to amplify it is much high one and therefore it reduces the frequency of advanced cut, in theory the maximum band short has in conditions circuit in how much v_out = 0 and therefore but also with a cargo resistance much lowland obtains an optimal result therefore loads the common emettitore with a common base that income stiffness has one much lowland. Moreover I use it of the common base is determining in how much from the relation we have inasmuch as it has a greater band 100 times regarding the common emettitore and therefore if the two stages are puttinges in cascade the customary effect of reduction of the band total verification in modest way and therefore it comes to coincide with the band of the common emettitore. Moreover the resistance of escape of the common base is highest between the 3 possible configurations, is worth approximately 300kW that it wants to say that the high current in income is the same one that is had in escape but multiplied here for a high resistance it gives one high tension to me of escape. The calculation of the frequency of advanced cut for the previous reasonings is carried out considering the relative constant of time to condenser C_and , is found while the amplification in tension of MF simply obtains like product of the amplifications in current of the others stages for the resistance of escape of the last divided stage the resistance of income of the first one, has where the amplification to = does not appear1 of the common base.

 

16) integrated Cascode Amplifier:

An amplifier is used differentiates integrated them in which one of the BJT it comes used like variable resistance in function of the current that slides in the emettitore controlled from v_{the AGC} which concurs to change the frequency of advanced cut of the Cascode. According to transistor of it differentiates them comes used like common base while the third transistor rather than to be used like generator of constant current comes used as emettitore common whose point of job is stabilized through a diode valve. The amplification To_v of the circuit comes determined replacing to the common emettitore the circuit of Giacoletto and to the common base the relative hybrid circuit moreover joins of parasitic abilities C_S between the collector of every transistor and the substrate, obtains that To_v it is function of the AGC tension.