Graphic method for solving critical working point and output range of amplifying circuit

Abstract

The invention belongs to the technical field of electronics, and provides a graphical method for solving a critical working point and an output range of an amplifying circuit. The method comprises the following steps: firstly, dividing three parameters of a working point into connotation and extension, designing connotation and extension of the working point, designing a concept of an alternating-current load line angular template, designing a key point that the angular template is suitable for passing through an intersection point of a direct-current load line and a current coordinate axis, and designing an intercept concept of the angular template on a voltage coordinate axis and an intercept calculation method; the angle template translates rightwards to line segments on two sides of an intersection point of the angle template and the direct current load line or a position when two projections on a coordinate axis are equal in length is a judgment rule of a critical working point; when the alternating-current load line angular template translates rightwards to a critical position, the collector-emitter critical bias voltage is equal to or converted to be equal to the output range of the amplification circuit, and during implementation, the scheme that the voltage serves as the abscissa axis and the current serves as the ordinate axis or the scheme that the current serves as the abscissa axis and the voltage serves as the ordinate axis can be adopted. The method is suitable for all three-configuration BJT or FET amplification circuits.

Description

Technical Field

[0001] The invention belongs to the technical field of electronics, and in particular is a graphical method for obtaining a critical operating point and an output range of an amplifier circuit. Background Art

[0002] In the field of electronic technology, the design and analysis of amplifier circuits have always been an important research topic. Among them, obtaining the optimal operating point and the maximum undistorted output sinusoidal voltage amplitude of the amplifier circuit is the key to ensuring the performance of the circuit. The graphical method is intuitive and easy to use. However, many defects of the existing graphical method have not been overcome, resulting in the failure to find the optimal operating point and the maximum undistorted output sinusoidal voltage amplitude. This not only seriously affects its application in electronic technology teaching, but also potentially affects the design quality of many related electronic products.

[0003] The obvious defects and shortcomings of the existing graphic method are as follows:

[0004] 1) The existing graphical method for comprehensively seeking the three parameters of the working point is essentially not distinguishing between primary and secondary

[0005] The ordinates of the coordinate system used in the existing graphical method are I b , there is also I c , which shows that the existing graphical method can simultaneously find the three parameters of the working point I b ,I c , U ce The collector bias current I c and base bias current I b , and at the same time seek the three parameters of the working point I b ,I c The practice goes against common sense in many ways:

[0006] (1) Power supply voltage U cc or U bb Is the impact I b The main parameters of the transistor emitter junction bias voltage U be is a minor factor. In many cases, be can be ignored, but the existing graphical method ignores U cc or U bb , and U be As the main factor, the existing diagrammatic method confuses the main contradiction with the secondary contradiction;

[0007] (2) The collector current of the transistor is equal to β times the base current, that is, I c =βI b Therefore, if we use the graphical method to determine I b , we must follow I c =βI b , use calculation method to determine I c , we can no longer use the graphical method to determine Ic ; If the graphical method is used to determine I c , we must follow I b =I c / β, using calculation method to determine I b , we can no longer use the graphical method to determine I b , stabilized I c I cannot stabilize b , stabilized I b I cannot stabilize c . I have determined c You can no longer choose I b , determined I b You can no longer choose I c .

[0008] (3) Existing graphical method to simultaneously find and stabilize the three parameters of Q point I b ,I c , U ce The approach seems to be meticulous, thoughtful, and systematic, but in fact it is not hierarchical. Although the three bias parameter symbols in the prior art solution are specially added with subscripts q, the existing base bias current symbol is I bq , the collector bias current symbol is I cq , the collector-emitter bias voltage symbol is U ceq However, the optimal operating point and the maximum undistorted output sinusoidal voltage amplitude are still difficult to calculate; in fact, the three parameters of the operating point I b ,I c , U ce To stabilize or select all of them at the same time is neither achievable nor necessary, that is, it is neither necessary nor sufficient;

[0009] 2) It is neither necessary nor sufficient to bundle the existing graphical method with the transistor output characteristic curve family

[0010] The main function of the transistor output characteristic curve family is to express the collector-emitter voltage U ce With collector current I c The transistor output characteristic curve family has nothing to do with the operating point of the amplifier circuit, that is, the bias current and bias voltage. The transistor output characteristic curve family and the DC load line that expresses the relationship between the bias current and bias voltage only share the same coordinate system U ce OI c ;

[0011] The three parameters I of the Q point on the transistor output characteristic curve family b ,I c , U ce Complete, draw the transistor output characteristic curve family, Q point three parameters I b ,I c , Uce Together, as the base current I b Starting from zero and gradually increasing, theoretically there are countless curves in the transistor output characteristic curve family, but in fact, in order to prevent the curves from being too dense and affecting the visual effect, only a limited number of curves can be drawn. The working point is determined according to the maximum requirement of the output voltage amplitude without losing the true value. The working point is not necessarily located exactly on a certain existing curve in the transistor output characteristic curve family. Therefore, even if it is necessary to use the transistor output characteristic curve family, the limited number of curves drawn by the existing transistor output characteristic curve family is often not enough;

[0012] The existing transistor output characteristic curve family may not be exactly consistent with the current amplification factor β value of the tube used in the amplifier circuit. In fact, there is also an Early voltage, but it may not meet the requirements. Therefore, even if it is necessary to use the transistor output characteristic curve family, it still needs to be specially drawn in theory. Such a graphical method is difficult to use;

[0013] Although the transistor output characteristic curve family can show the tube current amplification factor β value, this is only an auxiliary characteristic. c =βI b , we can c , β, do a simple division operation I c / β can calculate I b , the calculation can be completed with a simple relationship, so there is no need to draw several curves.

[0014] In short, the transistor output characteristic curve family is neither sufficient nor necessary for the graphical method of seeking the operating point and output range of the expansion circuit. The existing graphical method draws the transistor output characteristic curve family together with the DC load line and the AC load line, and bundles them together, which is inappropriate;

[0015] 3) The DC load line has a large bevel angle, which does not leave enough space for drawing the AC load line

[0016] The existing technical solution adopts a rectangular coordinate system with voltage as the horizontal axis and current as the vertical axis. In such a rectangular coordinate system, the slope of the AC load line is larger than that of the DC load line. If the DC load line is drawn with a larger angle, the AC load line is forced to be drawn steeper, increasing the space occupied. Only when the DC load line is drawn flatter can there be enough space for drawing the AC load line.

[0017] When drawing DC load lines using the graphical method in the prior art, the bevel angle is often too large, even up to 45°, leaving insufficient space for drawing AC load lines, causing the AC load lines to be too steep. The bevel angle of some AC load lines even reaches 80°, affecting the next step of thinking and operation.

[0018] The upper end of the AC load line does not intersect the ordinate axis, leaving an opening, which is a typical defect caused by the large bevel angle of the DC load line under the existing technical framework;

[0019] 4) Ignoring that the slope of the load line has a dimension, the effect of drawing the load line using the point slope method is not good

[0020] The slopes of DC load lines and AC load lines both have conductivity dimensions. Their slope values ​​are affected by the conductivity units and are not very objective. The slope angle values ​​have little geometric significance. The prior art does not fully recognize this fact. Many people have not noticed that in order to accurately draw DC load lines and AC load lines with dimensional slopes, they must be drawn using the two-point method.

[0021] 5) There is no concept of AC load line template and no rules for the optimal AC load line after reasonable movement.

[0022] The disproportion of the graph is only a superficial formal problem. The key is that there is no concept of AC load line template, and there is no rule for the best AC load line after reasonable movement. Finally, the best working point and output range are not found. At present, the AC load line is made through the Q point, but there is no translation, so the best working point and output range cannot be found;

[0023] Trying to draw an AC load line template and then translate the angle template is the only way to obtain the best working point and the maximum undistorted output sinusoidal AC voltage amplitude. The best existing technology is the auxiliary line concept, or a certain AC load line concept, but there is no idea of ​​reasonably moving the AC load line to obtain the best working point.

[0024] There are countless AC load lines, but many technicians only draw an AC load line through a certain point, also called an auxiliary line, and the most critical issues, whether the drawn AC load line is optimal, whether the operating point is optimal, and whether the maximum undistorted output sinusoidal AC voltage amplitude is found, are not considered.

[0025] Some technicians pass the Q point when drawing the AC load line and do not follow up. But in fact, if the Q point is already optimal, there is no need to draw the AC load line; if the Q point is not optimal, the drawn AC load line is also not optimal and has no practical use.

[0026] 6) The existing graphical method is subject to many interferences and errors caused by bad habits and wrong concepts during execution, resulting in various serious errors, which result in the failure to show the optimal operating point and the maximum undistorted output sinusoidal voltage amplitude. At the same time, relevant academic papers no longer bundle the transistor input characteristic curve with the graphical method. This is the first existing progress;

[0027] At the same time, some scholars have realized that it is inappropriate to bundle the operating point load line with the transistor output characteristic curve family in the existing technology, so the transistor output characteristic curve family is simplified into one output characteristic curve. This is the second existing progress;

[0028] In the graphical method, the transistor output characteristic curve family is completely abandoned, and most of them even the entire transistor output characteristic curve family is abandoned. This is the third existing progress. Under the framework of the existing technical solution, "taking V' om and V" om The smaller of the two means that the smaller one is taken, and the maximum undistorted output voltage amplitude U om .

[0029] With "U om =min(U ce , R′ L I c )” determines the output range, which is the most similar solution to the present invention among the existing technical solutions. This is the fourth existing progress;

[0030] Picking the smaller one from the two means that the largest one has not been found, and it also proves that the problem has not been solved in the end. Due to the influence of many wrong thinking habits, the existing technology has not been able to find the largest one in the "U om =min(U ce , R′ L I c )”;

[0031] It is necessary but not sufficient to abandon the transistor output characteristic curve family in the graphical method, because this is only a formal and superficial approach, and the error has not been realized in essence. ce , R′ L I c The smaller one is the output range, which is also an improvement, but it is also insufficient, so despite these improvements, the amplifier circuit operating point diagram method still has no results;

[0032] In summary, the existing graphical method has many defects and shortcomings in the analysis and design of amplifier circuits. Therefore, it is necessary to improve and optimize the existing graphical method to more accurately find the optimal operating point and the maximum undistorted output sinusoidal voltage amplitude of the amplifier circuit. To this end, technical personnel in this field have proposed a graphical method for finding the critical operating point and output range of the amplifier circuit to solve the problems raised by the background technology. Summary of the invention

[0033] In order to solve the above technical problems, the present invention provides a graphical method for finding the critical operating point and output range of a release amplifier circuit, so as to solve the defects and legacy tasks existing in the prior art graphical method when finding the optimal operating point and maximum output range of a release amplifier circuit, such as the transistor output characteristic curve family is drawn together with the graphical method, the drawing is very arbitrary, there is a lack of clear thinking and judgment, the AC load line is drawn unscientifically and abandoned halfway, etc., which leads to serious problems such as difficulty in finding the optimal operating point and the maximum undistorted output sinusoidal voltage amplitude (output range) and so on.

[0034] A graphical method for obtaining a critical operating point and an output range of a release amplifier circuit comprises the following steps:

[0035] S1. First determine the DC load line of the amplifier circuit and draw it in the coordinate system using the two-point method;

[0036] S2. Secondly, the intercept of the AC load line angle template on the voltage coordinate axis is calculated to determine the designated intersection point of the angle template and the voltage coordinate axis;

[0037] S3, then through the intersection of the DC load line and the current coordinate axis, and the specified point of the voltage coordinate axis, use the two-point method to draw the AC load line angle template;

[0038] S4, then translate the AC load line angle template to the right in the coordinate system until the projection lengths of the line segments on the left and right sides of the intersection of the template and the DC load line on the voltage axis are equal;

[0039] S5. Finally, the intersection of the shifted AC load line and the DC load line is determined as the critical operating point. The collector-emitter bias voltage value corresponding to the intersection is the output range (maximum undistorted output sinusoidal voltage amplitude), or the output range after conversion.

[0040] Preferably, in step S1, the coordinate system is a UceOIc coordinate system with voltage as the horizontal axis and current as the vertical axis or an IcoUce coordinate system with current as the horizontal axis and voltage as the vertical axis.

[0041] Preferably, it also includes adjusting the equivalent DC load resistance and AC load resistance according to the specific type of the amplifier circuit (such as a basic common-emitter amplifier circuit, an emitter-biased common-emitter amplifier circuit, a common-collector amplifier circuit, and a common-base amplifier circuit), and substituting them into the formula for calculation; that is, the calculation formula for the intercept of the AC load line on the voltage coordinate axis is related to the specific type of the amplifier circuit (such as a basic common-emitter amplifier circuit, an emitter-biased common-emitter amplifier circuit, a common-collector amplifier circuit, and a common-base amplifier circuit), and substituting them into the formula for calculation.

[0042] Preferably, in step S1, when drawing the DC load line and the AC load line, a two-point method is used to ensure that the straight line with a dimensional slope is drawn accurately and the size of the bevel angle can minimize the space used by the graphical method.

[0043] Preferably, in step S4, the criterion for the rightward translation of the AC load line template is that the line segments on the left and right sides of the intersection of the template and the DC load line are of equal length, or the projections on the voltage axis are of equal length.

[0044] Preferably, when using a coordinate system with voltage as the horizontal axis and current as the vertical axis, the DC load line should be drawn flatter to prevent the AC load line from being too steep and occupying too much space vertically; or when using a coordinate system with current as the horizontal axis and voltage as the vertical axis, the DC load line should be drawn steeper to prevent the AC load line from being too flat and occupying too much space horizontally.

[0045] Preferably, in order to reflect the theory that the three parameters of the working point are divided into connotation and extension, and the connotation should be considered first and then the extension when determining the working point, the transistor output characteristic curve family is separated from the graphical method, which straightens out the thinking and avoids interference.

[0046] Preferably, first determine the working point connotation I c , and then perform the division operation I c / β to get epitaxial I b , then determine the base bias resistor R b , complete the entire working point design.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The present invention provides a clear criterion for determining whether the working point reaches the optimal state by translating the AC load line template and judging the intersection point with the DC load line; at the same time, the load line is drawn by using the two-point method, which ensures that the straight line with a dimensional slope is drawn accurately, improves the calculation accuracy, and separates the transistor output characteristic curve family from the graphic method, avoids interference, and simplifies the operation process;

[0049] This method is not only applicable to basic common-emitter amplifier circuits, but also to various types of amplifier circuits such as emitter-biased common-emitter amplifier circuits, common-collector amplifier circuits and common-base amplifier circuits. It has wide applicability and can intuitively display the working status and output range of the amplifier circuit through graphical methods, which is convenient for engineers to quickly adjust and optimize circuit parameters and improve design efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic diagram of the connotation and extension of the working point Q of the transistor amplifier circuit of the present invention;

[0051] Figure 2A schematic diagram of a DC load line of a basic common-emitter amplifier of the present invention;

[0052] Figure 3 It is a schematic diagram of an AC load line angle template of the present invention;

[0053] Figure 4 It is a schematic diagram of the AC load line angle template of the present invention starting to shift right;

[0054] Figure 5 It is a schematic diagram of the present invention being translated to the right to a critical position (optimal position);

[0055] Figure 6 An example diagram of the graphical method of the present invention for finding the critical operating point and output range of a basic common-emitter amplifier;

[0056] Figure 7 A schematic diagram of a DC load line of a basic common-emitter amplifier of the present invention;

[0057] Figure 8 It is a schematic diagram of an AC load line angle template of the present invention;

[0058] Fig. 9 It is a schematic diagram of the AC load line angle template of the present invention starting to shift right;

[0059] Fig.10 It is a schematic diagram of the present invention moving rightward to a critical position;

[0060] Fig.11 A schematic diagram of the critical operating point and output range of a basic common-emitter amplifier obtained by the graphical method of the present invention;

[0061] Fig.12 It is a schematic diagram of an emitter biased common-emitter amplifier circuit (voltage-dividing biased common-emitter amplifier circuit) of the present invention;

[0062] Fig.13 It is a schematic diagram of a common collector amplifier circuit (emitter follower) of the present invention;

[0063] Fig.14 It is a schematic diagram of the common base amplifier circuit of the present invention;

[0064] Fig.15 This is a schematic diagram of the basic common-emitter amplifier circuit of the present invention. DETAILED DESCRIPTION

[0065] The following embodiments of the present invention are described in detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0066] The present invention provides a graphical method for obtaining a critical operating point and an output range of a release amplifier circuit, comprising the following steps:

[0067] S1. First, determine the DC load line of the amplifier circuit and draw it in a coordinate system; the coordinate system is a UceOI c coordinate system with voltage as the horizontal axis and current as the vertical axis or an I cOUce coordinate system with current as the horizontal axis and voltage as the vertical axis; when drawing the DC load line and the AC load line, a two-point method is used to ensure that the straight line with a dimensional slope is drawn accurately;

[0068] S2. Then draw an AC load line angle template, which passes through the intersection of the DC load line and the coordinate axis;

[0069] S3, then translate the AC load line template to the right in the coordinate system until the projection lengths of the line segments on the left and right sides of the intersection of the template and the DC load line on the voltage axis are equal; the criterion for the translation of the AC load line template to the right is: the projection lengths of the line segments on the left and right sides of the intersection of the template and the DC load line on the voltage axis are equal;

[0070] S4. Finally, the intersection of the translated AC load line and the DC load line is determined as the critical operating point. The voltage value corresponding to the intersection is the maximum undistorted output sinusoidal voltage amplitude.

[0071] Specifically, it also includes adjusting the equivalent DC load resistance and AC load resistance according to the specific type of the amplifier circuit (such as a basic common-emitter amplifier circuit, an emitter-biased common-emitter amplifier circuit, a common-collector amplifier circuit, and a common-base amplifier circuit), and substituting them into the formula for calculation.

[0072] From the above, it can be seen that this method provides a clear criterion for whether the working point reaches the optimal state by translating the AC load line template and judging its intersection with the DC load line; at the same time, the two-point method is used to draw the load line, which ensures that the straight line with a dimensional slope is drawn accurately, improves the calculation accuracy, and separates the transistor output characteristic curve family from the graphical method, avoiding interference and simplifying the operation process.

[0073] This method is not only applicable to basic common-emitter amplifier circuits, but also to various types of amplifier circuits such as emitter-biased common-emitter amplifier circuits, common-collector amplifier circuits and common-base amplifier circuits. It has wide applicability and can intuitively display the working status and output range of the amplifier circuit through graphical methods, which is convenient for engineers to quickly adjust and optimize circuit parameters and improve design efficiency.

[0074] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and examples.

[0075] In order to find the best operating point and the maximum true-undistorted sinusoidal output voltage amplitude of the amplifier circuit in the best way or process, the following points should be noted first:

[0076] 1) Set Q point I b ,Ic , U ce The three parameters are divided into connotation and extension. It is clear that the connotation parameter I is what we want to find. c , U ce ;

[0077] The three parameters of the operating point are the base bias current I b , collector bias current I c , collector-emitter bias voltage U ce ;I b ,I c , U ce Among the three parameters, I c , U ce Belong to the interrelated connotations, I b It is just the extension of the connotation of the working point, such as Figure 1 As shown;

[0078] The three parameters of Q point in the prior art b ,I c , U ce There is no distinction between connotation and extension; there is no distinction between connotation and extension, that is, no distinction between primary and secondary; this gives people the illusion that finding the working point is the Q point three parameters I b ,I c , U ce Let's find it together. The stable working point is the Q point. Three parameters I b ,I c , U ce Stabilize together;

[0079] 2) Theoretically explain why the transistor output characteristic curve family is irrelevant to the graphical method;

[0080] The family of transistor output characteristic curves is not relevant to the graphical method for two reasons:

[0081] ①Use a simple division operation I c / β can calculate I b , so there is no need to draw a lot of curve families;

[0082] ② The purpose of a coordinate system is generally not unique, and a coordinate system should not accommodate both the transistor output characteristic curve family and the graphical method of the amplifier circuit;

[0083] 3) Leave space for the AC load line when drawing the DC load line;

[0084] in U ce OI c In the coordinate system, be careful to draw the DC load line flatter to avoid drawing the AC load line too steep;

[0085] in I c OUce In the coordinate system, be careful to draw the DC load line steeper to avoid drawing the AC load line too flat;

[0086] 4) Both DC load lines and AC load lines are drawn using the two-point method;

[0087] The slope angle of a straight line with a dimensioned slope, such as a DC load line and an AC load line, has little geometric significance and lacks objectivity; however, when drawing a DC load line and an AC load line, their slope angle can be adjusted manually to obtain the best drawing effect;

[0088] 5) The size of the graphic should be within the range of approximately 10cm×10cm;

[0089] The AC load line angle template is drawn through the intersection of the DC load line and the current ordinate axis, which can minimize the vertical size of the graph so that the entire graph is distributed within a square area of ​​approximately 10cm×10cm;

[0090] 6) Shift the AC load line sample to the right to obtain the optimal working point and output range;

[0091] After the AC load line template is drawn, it is shifted to the right to obtain the intersection of the AC and DC load lines, i.e., point Q, and the AC load line is divided into two sections on the left and right. The AC load line is shifted to the right, and its final position, i.e., the optimal operating point, is determined according to the principle that the left and right sections of the AC load line are equal in length, i.e., the two projections of the AC load line on the voltage coordinate axis are equal. Finally, it is natural to obtain the maximum undistorted output sinusoidal voltage amplitude (output range, or dynamic range).

[0092] The existing graphical method uses voltage as the horizontal axis and current as the vertical axis to establish the U ce OI c Coordinate system, and this graphical method can use the voltage as the horizontal axis and the current as the vertical axis to establish the U ce OI c Coordinate system, you can also use I with current as the horizontal axis and voltage as the vertical axis c OU ce Coordinate system; in comparison, the current is the horizontal axis and the voltage is the vertical axis. c OU ce The coordinate system is more advantageous.

[0093] The present invention first adopts the U ce OI c coordinate system, discuss the implementation of the graphical method, and then switch to I c OU ce Coordinate system, discuss the implementation process of the graphical method, and compare the advantages and disadvantages of the two coordinate systems based on these two implementation processes:

[0094] 1) The new graphical method uses the voltage as the horizontal axis and the current as the vertical axis to calculate the U ce OI c Implementation process in the coordinate system:

[0095] (1) DC load line

[0096] Fig.15 The basic common-emitter amplifier circuit shown in the figure has a collector-emitter bias voltage drop U ce and collector bias current I c The relationship is U ce =U cc -R c I c ; In the case of U with voltage as the horizontal axis and current as the vertical axis ce OI c The standard straight line equation in the coordinate system is:

[0097] I c =U cc / R c -U ce / R c (1)

[0098] Formula (1) expresses the bias current I c With bias voltage U ce The relationship is a straight line, such as Figure 2 As shown; because the bias current flows entirely through R c , R c Also called DC load resistance, and the straight line is called the DC load line; ce OI c In the coordinate system, the slope of the DC load line is -1 / Rc; R′ L =R c / / R L It is called AC load resistance, and the slope of the AC load line is -1 / R′L; since R′L≤Rc, 1 / R′L≥1 / Rc; that is, the slope of the AC load line is greater than the slope of the DC load line, and the AC load line is steeper than the DC load line;

[0099] The graphical method requires that the AC load line and the DC load line be drawn in the same coordinate system; a straight line that is too flat or too steep will affect the drawing and reading effect; in order to make the AC load line not too steep, the DC load line should be drawn flatter; the DC load line should be at an angle of about 30°;

[0100] The coordinate axes of DC and AC load lines are voltage and current respectively. The slope has dimensions. The slope of a straight line with a dimensional slope is related to the units of voltage and current, is not unique, and has little practical value. Therefore, a straight line with a dimensional slope is best made using the two-point method:

[0101] Assume that the intercepts of the DC load line on the current axis and voltage axis are U cc / R c , U cc ; Line segment |OA| represents U cc / R c , |OB| represents U cc ; Taking the length of line segment |OB| equal to twice |OA|, that is, |OB|=2|OA|, can make the DC load line angle approximately 30°; at this time, the AC load line angle is around 45°, which takes up the least space, is more decent, and conforms to the aesthetic view;

[0102] Connection point A (0V, U cc / R c ) and B(U cc , 0mA), that is, draw a DC load line, such as Figure 2 As shown; U cc With R c They are all certain, so the DC load line is unique;

[0103] (2) AC load line and its angle template

[0104] The straight line whose slope is determined by the equivalent AC load resistance R′L is called the AC load line; the intersection of the AC load line and the DC load line is the working point; the key to the graphical method is how to draw the AC load line; although there are many AC load lines, they are all parallel to each other; try to draw an AC load line angle template, and then translate the two line segments on the left and right of the intersection of the two straight lines according to the rule of equal length, you can get the critical AC load line and the maximum undistorted output voltage amplitude;

[0105] To reduce the difficulty and workload of drawing, the AC load line angle template should pass through a known special point on the coordinate axis, that is, or pass through point A on the current axis (0V, U cc / R c ), or point B on the overvoltage axis (U cc , 0A);

[0106] Make an AC load line angle sample through point A, such as Figure 3 As shown; such an angle template does not take up any additional space; when the angle template is translated to the right, the AC load line is divided into two sections, left and right, by the DC load line; the projections of the left and right sections on the voltage axis are respectively the maximum true-undistorted sinusoidal output voltage amplitude U limited by the transistor saturation om(sat) =U ce The maximum true-undistorted sinusoidal output voltage amplitude U limited by the transistor cutoff om(off) =R' L I c ; when U om(sat) =U om(off)When the working point reaches the optimal position or critical position, U om(sat) =U om(off) =U om(max) It is the maximum undistorted output sinusoidal voltage amplitude;

[0107] After setting the AC load line angle template through point A, U cc / R c That is the intercept of the AC load line angle template on the vertical axis. The only problem left is how to find the intercept of the voltage on the horizontal axis.

[0108] Assume the AC load line angle sample voltage horizontal axis intercept is U int(sam) , int is the abbreviation of intercept, sam is the abbreviation of sample; the AC load line angle sample equation is U ce =U int(sam) -R' L I c ; In the UceOIc coordinate system, the standard straight line equation is:

[0109] I c =U int(sam) / R' L -U ce / R' L (2)

[0110] There are two methods to determine the intercept of the AC load line angle template on the voltage axis;

[0111] ① Set the coordinates of point A (0V, U cc / R c ) into the AC load line angle template equation, we have U int(sam) -(U cc / R c )R′ L =0, from which we can find the intercept of the AC load line angle sample on the voltage axis:

[0112]

[0113] ② According to the principle that the ratio of the current axis intercept and the voltage axis intercept of the AC load line should be equal to the absolute value of the slope of the AC load line, the equation U is listed: int(sam) / (U cc / R c ) = R′ L , to calculate the horizontal intercept of the AC load line angle template:

[0114]

[0115] The intercepts of the voltage axis on the horizontal axis calculated by the two methods are the same; here the DC load line is drawn at approximately 30°, as shown in Figure 2 As shown, take R c =R L , the AC load line angle sample is about 45°, such as Figure 3 As shown;

[0116] (3) Angle sample translation to obtain the best AC load line, critical operating point and output range:

[0117] The AC load line template is shifted to the right, and its intersection point Q with the DC load line is the working point. The intersection points with the vertical and horizontal axes are set as C and D. Figure 4 , the projections of CQ and QD on the voltage axis are U ce , R′ L I c ; When the template starts to move right, U ce <R′ L I c ; When translated to the critical position, U ce =R′ L I c ; When exceeding the critical position, U ce >R′ L I c ; Generally, when the working point is non-critical, U ce ≠R′ L I c ;if U ce <R′ L I c , then as the input signal voltage amplitude increases, the transistor saturates first, and the output range is limited by the transistor saturation; if R′ L I c ce , then as the input signal voltage amplitude increases, the transistor is cut off first, and the output range is limited by the transistor cutoff; therefore, U ce and R′ L I c The smaller of the two is the output range, U om =min(U ce , R′ L I c );

[0118] If U ce =R′ L I c , then as the input signal voltage amplitude increases, the transistor is cut off at the bottom of the signal voltage and saturated at the peak of the signal voltage. The operating point at this time is the optimal operating point, and the output range reaches the maximum value.

[0119] ​In short, the AC load line is translated to the appropriate position until the lengths of line segments CQ and QD are equal, or the projection lengths of line segments CQ and QD on the voltage coordinate axis are equal, that is, U ce =R′ L I c When Figure 5 As shown, the intersection of it and the DC load line is the critical operating point, U ce =R′ L I c It is the maximum undistorted output voltage amplitude U om ;

[0120] Example 1 Basic common emitter amplifier circuit U cc =12V, R c =R L =1kΩ, transistor β=100; then use the graphical method to find its critical operating point and output range, and explain how to achieve the critical operating point and output range.

[0121] Solution: The horizontal intercept of the DC load line is U cc =12V, vertical axis intercept U cc / R c =12V / 1kΩ=12mA, first draw the DC load line, such as Figure 6 As shown; the AC load line angle sample passes through point A, that is, the vertical axis intercept is taken as 12mA, and its horizontal axis intercept is calculated as:

[0122]

[0123] Connecting points A (0V, 12mA) and F (6V, 0mA) will give you the AC load line angle template, such as Figure 6 ;

[0124] The AC load line angle template moves parallel to the right, and the AC load line and the DC load line intersect. Line segment CQ is U ce Variable length, QD is R' L I c becomes shorter, and at a certain position, QD and QC are equal in length, U ce =R' L I c , at this time, the parallel line of the sample line is the critical AC load line; the intersection Q of the critical AC load line and the DC load line is the critical operating point; it can be measured that the bias voltage of the critical operating point should be U ce(cr) =4V, the bias current should be I c(cr) =8mA, can obtain the maximum undistorted output sinusoidal voltage amplitude (output range, dynamic range) U om(max) =4V;

[0125] According to β=100 and I c(cr) =8mA can be calculated Ib =I c(cr) / β=8mA / 100=0.08mA; then calculate the required base bias resistance approximately according to Ohm's law:

[0126] R b =U cc I b =12V / 0.08mA=150kΩ

[0127] If the transistor β value is accurate, then connect R b = 150kΩ base bias resistor, the above critical operating point and output range can be achieved; in fact, due to various factors, the transistor β value is difficult to be so accurate; therefore, in fact, the base bias resistor R b It can be composed of a 100kΩ fixed resistor and a 100kΩ potentiometer in series; in practice, according to U ce(cr) =4V can be achieved by adjusting the potentiometer.

[0128] From the load line coordinates, it can be seen that the Q point is high, U ce Small, prone to saturation distortion, low Q point, R' L I c Small, easy to produce cutoff distortion;

[0129] 2) The new graphical method uses the current as the horizontal axis and the voltage as the vertical axis. c OU ce Implementation process in the coordinate system:

[0130] In the U ce OI c The curve drawn in the coordinate system is called the ampere-volt characteristic curve. c OU ce The curve drawn in the coordinate system is called the volt-ampere characteristic curve; the volt-ampere characteristic curve is the most familiar to people; the most important thing is that in the U with voltage as the horizontal axis and current as the vertical axis ce OI c In the coordinate system, the slope of the DC load line is -1 / R c , the slope of the AC load line is -1 / R′ L ; In I with current as the horizontal axis and voltage as the vertical axis c OU ce In the coordinate system, the slope of the DC load line is -R c , the slope of the AC load line is -R′ L ;

[0131] In contrast, in I with current as the horizontal axis and voltage as the vertical axis c OU ceIn the coordinate system, the DC load line, AC load line slope and equation are simpler; therefore, in the I with current as the horizontal axis and voltage as the vertical axis c OU ce Coordinate system, graphical method is easier to understand and use.

[0132] (1) DC load line

[0133] With current as the horizontal axis and voltage as the vertical axis, I c OU ce In the coordinate system, the DC load line equation of the basic common-emitter amplifier circuit is:

[0134] U ce =U cc -R c I c (5)

[0135] Comparing formula (5) with formula (1), it can be seen that formula (5) is more concise and more practical than formula (1);

[0136] DC load line slope - R c It has dimensions, so the DC load line should be made using the two-point method;

[0137] The slope of the DC load line is -R c , the slope of the AC load line is -R′ L ; Because R′ L <=R c , so the AC load line is flatter than the DC load line; to avoid the AC load line being too flat and affecting the drawing effect, the DC load line should be drawn steeper;

[0138] The vertical and horizontal intercepts of the DC load line are U cc , U cc / R c ; Connecting point A(0,U cc ) and B(U cc / R c , 0), that is, draw the DC load line, such as Figure 7 As shown, the DC load line is drawn at an angle of 45°; U cc With R c They are all certain, so the DC load line is unique and will not be detailed.

[0139] (2) AC load line and its angle template

[0140] If the AC load line angle template exceeds point A on the voltage axis, it will inevitably take up a lot of space; therefore, in I c OU ceIn the coordinate system, the AC load line angle template should be drawn at point B of the current coordinate system:

[0141] Assume the AC load line angle sample voltage axis intercept is U x , then the AC load line angle model equation is:

[0142] U ce =U int(sam) -R' L I c (6)

[0143] There are two methods to determine the voltage axis intercept of the AC load line angle template;

[0144] ① Set the coordinates of point B (U cc / R c , 0V) into the AC load line angle template equation, we have U int(sam) -R′ L (U cc / R c )=0, from which we can find the intercept on the voltage axis:

[0145]

[0146] ② According to the principle that the ratio of the voltage axis intercept and the current axis intercept of the AC load line should be equal to the absolute value of the slope of the AC load line, the equation U is listed: int(sam) / (U cc / R c ) = R′ L , to calculate the horizontal intercept of the AC load line angle template:

[0147]

[0148] Comparing equations (7) and (8) with equations (3) and (4), we can see that the dimension of the intercept of the AC load line angle template is always voltage, regardless of the coordinate system. Here, the DC load line is drawn at approximately 45°, see Figure 7 , take R c =R L , the AC load line angle sample is about 30°, see Figure 8 ;

[0149] (3) Angle sample translation to obtain the best AC load line, critical operating point and output range

[0150] The AC load line angle template is shifted to the right, and its intersection point Q with the DC load line is the working point, and the intersection points with the vertical and horizontal axes are set as C and D, such as Fig. 9 As shown, the projections of CQ and QD on the voltage axis are R′ L I c , U ce; When the template starts to move right, U ce <R′ L I c ; When translated to the critical position, U ce =R′ L I c ; When exceeding the critical position, U ce >R′ L I c ; When the working point is non-critical, U ce ≠R′ L I c ; The smaller one is the output range, U om =min(U ce , R′ L I c );

[0151] In short, the AC load line moves parallel to the appropriate position until the lengths of line segments CQ and QD are equal, that is, U ce =R′ L I c When U ce =R′ L I c It is the maximum undistorted output voltage amplitude U om(max) ;

[0152] Example 2 Basic common emitter amplifier circuit U cc =12V, R c =R L =1kΩ, transistor β=100; use the graphical method to find its critical operating point and output range, and explain how to achieve the critical operating point and output range;

[0153] The solution is based on the horizontal intercept U cc =12V, vertical axis intercept U cc / R c =12V / 1kΩ=12mA Draw the DC load line, such as Fig.11 As shown; the horizontal axis intercept of the AC load line angle sample is also taken as 12mA, and its vertical axis intercept is:

[0154]

[0155] Connecting points B (12mA, 0V) and F (0mA, 6V) gives the AC load line angle template, such as Fig.11 As shown;

[0156] The AC load line angle template moves parallel to the right, the line segment CQ shortens, and QD lengthens; at a certain position, QD and QC are equal in length, and the parallel line at this time is the critical AC load line; the intersection Q of the critical AC load line and the DC load line is the critical operating point; the critical operating point bias voltage can be measured to be U ce(cr) =4V, the bias current should be I c(cr) =8mA, can obtain the maximum undistorted output sinusoidal voltage amplitude (output range, dynamic range) U om(max) =4V; the implementation method is the same as Example 1;

[0157] (4) Use the graphical method to derive the analytical formula:

[0158] Figure 5 The projection of the line segments CQ and QD on the AC load line on the voltage axis is U ce , R′ L I c ; Fig.10 The projections of the line segments CQ and QD on the AC load line on the voltage axis are R' L I c , U ce ; The projections of the two line segments on the AC load line on the voltage axis are equal, which is actually the critical condition of the operating point R′ L I c =U ce Substituting formula (1) into R′ L I c =U cc -R c I c ; The I obtained from it c and U ce is the critical bias current I c(cr) , critical bias voltage U ce(cr) And the maximum undistorted output sinusoidal voltage amplitude U om(max) :

[0159]

[0160] The subscript cr means critical, which is taken from the first two letters of the English word critical;

[0161] This is exactly the same result as obtained analytically;

[0162] Therefore, the critical analytical conditions of the working point can also be derived by the graphical method; the graphical method and the analytical method are unified;

[0163] 3) The graphical method can be used for the design of operating points and output range calculation of all amplifier circuits in three configurations;

[0164] (1) Graphical method is used for designing the operating point and calculating the output range of emitter biased common emitter amplifier circuit;

[0165] Emitter biased common emitter amplifier circuit, also known as voltage divider biased common emitter amplifier circuit, such as Fig.12 As shown;

[0166] The equivalent DC load resistance of the emitter biased common emitter amplifier circuit is R c +R e1 +R e2 , the equivalent AC load resistance is R e1 +R' L ; Substitute the equivalent DC load resistance into equations (9), (10), and (11) to replace R c , substitute the equivalent AC load resistance into equations (9), (10), and (11) to replace R' L , respectively obtain the collector critical bias current, collector-emitter critical bias voltage, and the output range obtained on the equivalent AC load resistance;

[0167]

[0168] The output range obtained by the real AC load resistance is obtained by converting the voltage divided by R'L and Re1 in series:

[0169]

[0170] This is exactly the same result as obtained analytically;

[0171] Example 3: The power supply and component parameters of the emitter biased common emitter amplifier circuit are as follows Fig.13 As shown; the critical operating point and output range are obtained by graphical method, and how to achieve the critical operating point and output range is explained;

[0172] Solve the problem using the final results of the graphical method (12), (13), (14):

[0173] R' L =R c / / R' L =2.4kΩ / / 2.4kΩ=1.2kΩ;

[0174]

[0175] R b1 , R b2 The design and calculation method is relatively complicated and will not be discussed here;

[0176] (4) Graphical method for designing the operating point and calculating the output range of common collector amplifier circuit (emitter follower)

[0177] The output side circuit of the emitter follower is the same as that of the basic common-emitter amplifier, and the operating points and output range diagrams and calculations of the two are exactly the same;

[0178] Replace the subscript c in equation (9) with e, and equations (9), (10), and (11) are applicable to the emitter follower:

[0179]

[0180] (3) Graphical method for common base amplifier circuit operating point design and output range calculation

[0181] Common base amplifier circuit Fig.14 As shown, it is similar to the emitter biased common emitter amplifier circuit; the emitter is connected to an external resistor R e Equivalent to R in the emitter biased common emitter amplifier circuit e2 Similar; therefore, in the calculation formula of the emitter biased common emitter amplifier circuit, let R e1 =0, R e2 =R e , we can get the calculation formula for the collector critical bias current, collector-emitter critical bias voltage, and output range design of the common base amplifier circuit:

[0182]

[0183]

[0184] 4) The analysis and calculation of the operating point and output range of the amplifier circuit does not need to consider factors such as transistor saturation voltage drop

[0185] Working point three parameters I b ,I c , U ce The calculation accuracy requirements for the output range are not high, and are usually just estimates; when considering the saturation voltage drop of the transistor, the influence of the tiny current when entering the amplification area from the cut-off area should be considered at the same time, and both factors should be considered; the above shows that factors such as the saturation voltage drop of the transistor do not need to be considered; the actual value of the final maximum undistorted output sinusoidal AC voltage amplitude is only a few percent lower than the theoretical value; such calculation accuracy can usually meet engineering technical needs.

[0186] The method first divides the three parameters of the working point into connotation and extension, designs the working point first with connotation and then with extension, the concept of the AC load line angle template, the key point that the angle template should pass through the intersection of the DC load line and the current coordinate axis, the concept of the intercept of the angle template on the voltage coordinate axis and the intercept calculation method, and the position when the angle template is translated to the right to the line segments on both sides of the intersection with the DC load line or the two projections on the coordinate axis are equal in length is the judgment rule of the critical working point; when the AC load line angle template is translated to the right to the critical position, the collector-emitter critical bias voltage is equal to or equal to the output range of the amplifier circuit after conversion. When implemented, the scheme of voltage as the horizontal axis and current as the vertical axis can be adopted, or the scheme of current as the horizontal axis and voltage as the vertical axis can be adopted. This method is applicable to all three-configuration BJT or FET amplifier circuits.

[0187] First determine the working point connotation I c , and then perform the division operation I c / β to get epitaxial I b , then determine the base bias resistor R b , complete the entire working point design.

[0188] In summary: the technical solution used in the new graphic method has the following beneficial effects:

[0189] 1) Set the working point three parameters I b ,I c , U ce Divided into connotation and denotation;

[0190] The working point three parameters I b ,I c , U ce Divided into connotation and extension, I c , U ce Belongs to the associated connotation, I b It is only the extension; what is stable is the connotation, and what is directly sought in the design work point is also the connotation;

[0191] 2) Make it clear and emphasize that the load line should be drawn using the two-point method based on the dimension of the load line slope;

[0192] 3) The concept of AC load line angle template was established; the concept of AC load line angle template and the concept of parallel movement of angle template were established;

[0193] 4) The criterion for moving the AC load line angle template to the optimal working point is proposed; the intersection of the AC load line angle template and the DC load line, i.e., the intersection of the working point Q, is equal in length to the left and right straight lines, or the projections to the voltage coordinate axis are equal in length, which is the criterion for moving the angle template to the optimal working point;

[0194] 5) It is clarified that the output range reaches the maximum when the AC load line angle sample moves to the optimal working point;

[0195] 6) When drawing the AC load line angle template, pay attention to the intersection of the DC load line and the current coordinate axis: Draw the AC load line angle template through the intersection of the DC load line and the current coordinate axis, which does not take up extra space, is the most feasible, and conforms to the aesthetic view;

[0196] 7) Make it clear that the transistor output characteristic curve family has nothing to do with the working point to eliminate interference; Make it clear that the transistor output characteristic curve family has nothing to do with the working point. When drawing, the transistor output characteristic curve family must be thrown away, and the optimal working point and the maximum undistorted output sinusoidal voltage amplitude must be planned wholeheartedly;

[0197] 8) It is proposed to use current as the horizontal axis and voltage as the vertical axis. c OU ce Coordinate system scheme;

[0198] 9) The versatility and value of the graphical method for three-configuration amplifier circuits have been demonstrated; it has been demonstrated that the graphical method derived from the basic common-emitter amplifier circuit can also solve the operating point design and output range calculation problems of all three-configuration amplifier circuits, such as emitter-biased common-emitter amplifier circuits, common-collector amplifier circuits (emitter followers) and common-base amplifier circuits, that is, the versatility and value of the graphical method.

[0199] The embodiments of the present invention are provided for the purpose of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A graphical method for obtaining the critical operating point and output range of a release amplifier circuit, characterized in that: The following steps are involved: S1. First determine the DC load line of the amplifier circuit and draw it in the coordinate system using the two-point method; S2. Secondly, the intercept of the AC load line angle template on the voltage coordinate axis is calculated to determine the designated intersection point of the angle template and the voltage coordinate axis; S3, then through the intersection of the DC load line and the current coordinate axis, and the specified point of the voltage coordinate axis, use the two-point method to draw the AC load line angle template; S4, then translate the AC load line angle template to the right in the coordinate system until the projection lengths of the line segments on the left and right sides of the intersection of the template and the DC load line on the voltage axis are equal; S5. Finally, the intersection of the shifted AC load line and the DC load line is determined as the critical operating point. The collector-emitter bias voltage value corresponding to the intersection is the output range (maximum undistorted output sinusoidal voltage amplitude), or the output range after conversion.

2. A graphical method for obtaining a critical operating point and an output range of a release amplifier circuit as claimed in claim 1, characterized in that: In step S1, the coordinate system is a UceOIc coordinate system with voltage as the horizontal axis and current as the vertical axis or an IcOUce coordinate system with current as the horizontal axis and voltage as the vertical axis.

3. A graphical method for obtaining a critical operating point and an output range of a release amplifier circuit as claimed in claim 1, characterized in that: The calculation formula for the intercept of the AC load line on the voltage coordinate axis is related to the specific type of amplifier circuit (such as basic common-emitter amplifier circuit, emitter-biased common-emitter amplifier circuit, common-collector amplifier circuit, common-base amplifier circuit). Adjust the equivalent DC load resistance and AC load resistance, and substitute them into the formula for calculation.

4. A graphical method for obtaining a critical operating point and an output range of a release amplifier circuit as claimed in claim 1, characterized in that: In step S1, when drawing the DC load line and the AC load line, the two-point method is used to ensure that the straight line with a dimensional slope is drawn accurately and the size of the slope angle can minimize the space used by the graphical method.

5. A graphical method for obtaining a critical operating point and an output range of a release amplifier circuit as claimed in claim 1, characterized in that: In step S4, the criterion for the rightward translation of the AC load line template is that the line segments on the left and right sides of the intersection of the template and the DC load line are equal in length, or the projections on the voltage axis are equal in length.

6. A graphical method for obtaining a critical operating point and an output range of a release amplifier circuit as claimed in claim 1, characterized in that: When using a coordinate system with voltage as the horizontal axis and current as the vertical axis, the DC load line should be drawn flatter to prevent the AC load line from being too steep and occupying too much space vertically; or when using a coordinate system with current as the horizontal axis and voltage as the vertical axis, the DC load line should be drawn steeper to prevent the AC load line from being too flat and occupying too much space horizontally.

7. A graphical method for obtaining a critical operating point and an output range of a release amplifier circuit as claimed in claim 1, characterized in that: In order to reflect the theory that the three parameters of the working point are divided into connotation and extension, and that the connotation should be considered first and then the extension when determining the working point, the transistor output characteristic curve family is separated from the graphical method, which straightens out the thinking and avoids interference.

8. A graphical method for obtaining a critical operating point and an output range of a release amplifier circuit as claimed in claim 1, characterized in that: First determine the working point connotation I c , and then perform the division operation I c / β to get epitaxial I b , then determine the base bias resistor R b , complete the entire working point design.

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