KR100848290B1 - Amplifier with damping resistor in constant current load - Google Patents

Abstract

In this paper, we propose an amplifier with a damping resistor installed at a constant current load to reduce the distortion of the signal and obtain a cleaner signal by reducing the ringing occurring in the rapidly changing signal in the amplifier using the constant current circuit as a load. An amplifier provided with a damping resistor at a given constant current load includes a drive amplifier stage, complementary transistors of the first and second transistors, and an output terminal of which the bases of the first and second transistors are respectively connected to the output side of the drive amplifier stage and the constant current connected to the output side of the drive amplifier stage. And a damping resistor connected in parallel to the load stage and the constant current load stage. By connecting the damping resistors in parallel to the constant current load, the amplification gain is increased and the ringing occurs, resulting in a cleaner output signal.

Description

Amplifier with damping resistor in constant current load

1 is a circuit example of a class A amplifier with a general resistance load.

FIG. 2 is an operation characteristic diagram of the resistance load shown in FIG. 1.

3 is a circuit example of a class A amplifier with a general constant current load.

4 is an operation characteristic diagram of the constant current load shown in FIG.

5 is an example of a conventional negative feedback amplifier configured with a constant current load.

FIG. 6 is a graph illustrating signal waveforms at both ends of the constant current load shown in FIG. 5.

7 is a circuit diagram of an amplifier provided with a damping resistor in a constant current load according to the first embodiment of the present invention.

8 is a signal waveform graph for explaining the effect of the damping resistance shown in FIG.

9 is a circuit diagram of an amplifier installed in a damping resistor under a constant current load according to a second embodiment of the present invention.

10 is a circuit diagram of an amplifier provided with a damping resistor in a constant current load according to a third embodiment of the present invention.

11 is a circuit diagram according to a modification of the present invention.

<Description of Symbols for Major Parts of Drawings>

10: drive amplifier stage 12: constant current load stage

14: differential amplifier 16: feedback stage

18: constant current stage 20: output stage

The present invention relates to an amplifier provided with a damping resistor in a constant current load, and more particularly, to an amplifier provided with a damping resistor in a constant current load for reducing high frequency noise generated from the constant current load.

In a class A amplifier using a transistor, the signal voltage input to the base changes the current flowing through the collector and the emitter, and is converted into a voltage at the load connected to the collector to appear as an amplified signal. The load used at this time is a resistance, a coil, a transformer, a constant current circuit, and the like. When using a coil or a transformer as a load, the operating current is set in DC, and the actual operation is performed as an AC load. At this time, the impedance of the load can be freely designed according to the design of the AC load, but the frequency band by the coil is narrow, the signal is distorted by the core, etc., and it is not used as a load because it is bulky.

For this reason, resistors are commonly used for loads. The resistance load used in class A amplifier is fixed when the operating conditions are determined, the characteristic curve is difficult to adjust, and the voltage gain is low. In particular, there is a disadvantage in that the range of the load resistance value is narrow and gain cannot be obtained according to the operating current.

1 is a circuit example of a class A amplifier with a general resistance load. Normal bias is supplied to the base of the transistor Q31. The capacitor C31 is a coupling capacitor which directly separates the input signal source from the base of the transistor Q31. It is assumed that the collector voltage of the transistor Q31 is set to 1/2 the voltage of the positive polarity power supply VPP3. FIG. 2 is a characteristic curve graph of the resistor R31 of FIG. 1. It is assumed that there is no voltage drop between the collector and emitter of transistor Q31 and no voltage drop across resistor R32.

In FIG. 1, when the input signal is zero to the input terminal IN3, the normal bias is supplied to the transistor Q31 so that the collector voltage of the transistor Q31 becomes 1/2 of the positive polarity power supply VPP3. At this time, the collector current ice_Q31 of the transistor Q31 is

ice_Q31 = VPP3 / 2 / R31

And point B in the graph of FIG. 2.

When the input signal is input to the input terminal IN3, when the lowest signal of the polarity is input, the base current of the transistor Q31 does not flow, so that the collector and the emitter are turned off, so that the current flows through the resistor R31. The voltage across the resistor R31 is 0 (ZERO), and the current flowing through the resistor R31 is 0 (ZERO). (A point in Fig. 2)

On the contrary, when the input signal having the highest signal of "+" polarity is input to the input terminal IN3, the base current of the transistor Q31 flows to the maximum, and the collector and the emitter are turned on to turn on the current to the resistor R31. Will flow to the maximum. The voltage across the resistor R31 is the same as the positive polarity power supply VPP3, and the current flowing through the resistor R31 also becomes the maximum, resulting in VPP3 / R31. (C point of Figure 2)

In the circuit of FIG. 1, the impedance of resistor R31 is obtained from the graph of FIG. 2.

R31 = voltage change value / current change value

R31 = (VPP3-0) / (VPP3 / R31-0) ------------------------- Equation 1

Becomes

In Figure 1 the voltage amplification degree A3

A3 = R31 / R32 --------------------------------------------- Equation 2

Becomes

In order to obtain the maximum signal by the input signal in the amplifier of FIG. 1, the collector current of transistor Q31 must vary from 0 to VPP3 / R31 to the maximum. Operating the collector current of the transistor Q31 in the entire range from 0 to 100% causes the operation of the transistor Q31 to be unstable at around 0% and 100%, and the amplified output signal becomes severely distorted. (Description 1)

In the transistor class A amplifier, the voltage gain is calculated by the above equation (2).

The resistor R32 connected to the emitter of the transistor Q31 cannot be too low because it is related to the stability of the transistor class A amplifier. Therefore, the amplification degree can be increased only by increasing the resistance value of the resistor R31. (Description 2)

In the case of the same load resistance, narrowing the operating range of the collector current in Description 1 can stabilize the operation of the amplifier and reduce the distortion of the output waveform, but the output voltage becomes small. (Description 3)

In addition, increasing the load resistance of Description 2 can increase the amplification degree, but increasing the load resistance at the same power supply voltage (that is, increasing the resistance value of the resistor R31) causes the collector operating current of the transistor Q31 to decrease. As a result, the load driving force drops. (Description 4)

Therefore, in order to increase the load resistance, the power supply voltage can only be increased. (Description 5) However, if the power supply voltage is set and designed, it is difficult to substantially increase the power supply voltage afterwards. Even if the power supply voltage is increased, a problem arises because the impedance of the circuit becomes high.

According to the above descriptions 3, 4, and 5, it is not free to increase the load resistance while increasing the degree of amplification while the distortion of the amplified signal is small. That is, it is not easy to steeply adjust the load resistance characteristic curve as shown in the thick dotted line in the graph of FIG.

In general, a method of increasing the amplification degree is as follows.

As shown in FIG. 3, there is a method of using a constant current circuit for a load. 3 is a circuit example of a class A amplifier with a constant current load CC4. A normal bias is supplied to the base of the transistor Q42, and the capacitor C41 is a coupling capacitor which directly separates the input signal source from the base of the transistor Q42. It is assumed that the collector voltage of transistor Q42 is set to 1/2 the voltage of positive polarity power supply VPP4.

The constant voltage across the zener diode Z41 is supplied to the base of the transistor Q41 by the resistor R41. The current flowing through the emitter and the collector of the transistor Q41 is always controlled constantly by the resistor R42 connected to the emitter of the transistor Q41.

FIG. 4 is a characteristic curve graph of the constant current load CC4 of FIG. 3. It is assumed that there is no voltage drop between the collector and emitter of transistor Q42 and no voltage drop across resistor R43.

In FIG. 3, when the input signal is zero to the input terminal IN4, the normal bias is supplied to the transistor Q42, so that the collector voltage of the transistor Q42 becomes 1/2 of the positive polarity power supply VPP4. (B point in Fig. 4)

At this time, the collector current ice_Q42 is equal to the collector current of the transistor Q41.

The current ice_Q41 of the constant current load (CC4)

ice_Q41 = (V_Z41-Vbe_Q41) / R42

Becomes

If the polarity of the signal input to the input terminal IN4 is "-" polarity, the base current of the transistor Q42 decreases, the impedance between the collector and emitter of the transistor Q42 increases, and the current of the constant current load CC4 is constant. Try to flow. As a result, the voltage between the collector and the emitter of the transistor Q41 of the constant current load CC4 is minimized. (A point in Fig. 4)

On the contrary, if the polarity of the signal input to the input terminal IN4 is "+" polarity, the base current of the transistor Q42 is increased to decrease the impedance between the collector and the emitter of the transistor Q42 and the constant current load CC4. The current of tries to flow constantly. As a result, the voltage between the collector and the emitter of the transistor Q41 of the constant current load CC4 is maximized. (C point in Figure 4)

As described above, it is known that the load characteristic curve of the amplifier of FIG. 3 appears as a characteristic that changes rapidly around the constant current as shown in FIG. 4. In other words, the constant current load in the amplifier acts as if a high resistance was connected. At this time, the collector current of the transistor Q41 may be freely set by adjusting the resistor R42. As the problem of the above description 4 is solved, there is no need to increase the power supply voltage of the description 5. However, the operating range of the collector current in the explanation 3 is too narrow as a steep slope as shown in Fig. 4, so that the normal amplification operation cannot be performed.

Amplification degree A4 in the amplifier of FIG.

A4 = Impedance of CC4 / R43

A4 = infinity / R43

A4 = infinity

The output signal is turned on and off with respect to the input signal.

In this way, the A class amplifier using the constant current load for analog signal amplification is not used alone, but is used inside the negative feedback amplifier as an amplifier stabilized by negative feedback. Another application is the emitter load of a collector ground amplifier (emitter follower).

Using a constant current load inside the negative feedback amplifier results in high voltage gain with a small number of amplifier stages and simplifies the circuit. In addition, there is an advantage that the voltage gain can be freely adjusted by adjusting the negative feedback amount from the outside.

In addition, by using it for the emitter load of the collector ground amplifier (emitter follower), a large operating current and a high input impedance can be obtained, which faithfully follows the change of the input signal, and is characterized by low distortion.

FIG. 5 uses the constant current load stage 12 including the transistor Q25 and the resistor R26 as the load of the transistor Q24 of the drive amplifier stage 10. Since a constant voltage is always supplied to the base of the transistor Q25 by the zener diode ZD21, the transistor Q25 operates to maintain a constant voltage across the resistor R26 provided at the emitter of the transistor Q25. .

Assume that the voltage across the zener diode ZD21 is V_ZD21, the voltage between the base and emitter of the transistor Q25 is Vbe_Q25, and the voltage across the resistor R26 is V_R26.

V_R26 = V_ZD21-Vbe_Q25,

The current I_R26 flowing through the resistor R26 is I_R26 = V_R26 / R26.

It operates so that a constant current I_R26 always flows between the collector and the emitter of the transistor Q25. The voltage between the collector and the emitter of the transistor Q24 of the drive amplifier stage 10 changes in accordance with the amplified signal with the same characteristics as the solid line of FIG. 4. Since the voltage gain of the drive amplifier stage 10 is considerably high by using a constant current load, the output of the output by the differential amplifier stage 14 including the transistors Q21 and Q22 and the feedback stage 16 by the negative feedback resistors Rf21 and Rf22. The signal is fed back to reduce the voltage gain. In FIG. 5, reference numeral 18 denotes a constant current stage for the differential amplifier stage 14 to supply a constant voltage to the differential amplifier stage 14, and 20 denotes an output stage for outputting a signal output from the drive amplifier stage 10.

Current constant current loads are widely used in many amplifiers.

However, when using a constant current circuit as a load, there are the following problems. It demonstrates with reference to the circuit diagram of FIG.

First, FIG. 5 shows that the collector of the transistor Q24 and the collector of the transistor Q25 are connected (the bias power source BV21, which is a bias voltage source, is a constant voltage source and can be omitted in an alternating description). It is a terrestrial amplifier. The emitter grounding amplifier of FIG. 5 is characterized in that only a constant current flows through the collector of transistor Q24 and the collector of transistor Q25 at all times. Therefore, in response to a signal change input to the base of transistor Q24, the collector of transistor Q24 operates in which the current is constant and the impedance between the collector and emitter of transistor Q24 changes. For example, the lower the impedance between the collector and emitter of transistor Q24, the higher the impedance between the collector and emitter of transistor Q25. As the impedance between the collector and emitter of transistor Q24 increases, the impedance between the collector and emitter of transistor Q25 decreases.

That is, the impedance change of the transistors Q24 and Q25 is converted into a voltage based on the input signal and output. The voltage signal generated by the impedance change is faster than the voltage signal generated by the current change. Because the current in the base and the emitter must change in order for the collector current to change. In order for the base current to change, the charge accumulated in the capacitance between the base and the emitter must change, and since the charge takes time to change, the time is delayed until the collector current changes. Therefore, since the drive amplifier stage 10 of FIG. 5 is a voltage signal generated by a change in impedance, the output signal generation time is fast. Therefore, the following phenomenon occurs at point B where the drive amplifier stage 10 and the constant current load stage 12 are connected.

In FIG. 5, when the signal voltage of the input terminal IN2 is changed, the primary amplification is performed in the differential amplifier stage 14 correspondingly, and the output terminal of the output terminal 20 after the secondary amplification is performed in the drive amplifier stage 10. Output via (OUT2). In this way, the output terminal 20 outputs the changed signal voltage based on the change of the signal voltage of the input terminal IN2. (Operation 1)

The output voltage of the output terminal OUT2 is fed back to the base of the transistor Q22 of the differential amplifier stage 14 via the feedback stage 16. The differential amplifier stage 14 operates to correct the feedback voltage and the voltage input to the input terminal IN2. (Operation 2)

The operation 1 and 2 described above are repeated again, and the operation is repeated until the voltage inputted to the input terminal IN2 and the feedback voltage are the same. (Operation 3)

Subsequently, if the voltage of the output terminal OUT2 is stabilized, the voltage V_OUT output through the output terminal OUT2 is

V_OUT = V_IN * (1 + Rf21 / Rf22)

Will be

Voltage Amplitude A2

A2 = 1 + Rf21 / Rf22

In FIG. 5, the input / output delay time is T_IO from when the signal voltage of the input terminal IN2 changes to the output voltage of the output terminal OUT2 as in operation 1, and T_IO. It is assumed that the feedback delay time from the time when the voltage at the output terminal OUT2 changes to the compensation operation by comparing the input voltage of the input terminal IN2 with the feedback voltage in the differential amplifier stage 14 is T_fb.

In FIG. 5, when the rising signal is input to the input terminal IN2 as shown in FIG. 6, the voltage change according to the operation 1 is generated at the point B of FIG. 5 after the input / output delay time T_IO. At this time, the voltage of the point B is the same as the rising direction and the direction of the point A, but because the voltage size is not yet corrected by the feedback is changed higher than the amplification ratio. That is, the voltage change at point B rises in the direction in which the input signal rises and rises higher than the amplification ratio voltage. Compared to the input voltage at the differential amplifier stage 14 by the feedback signal after the feedback delay time T_fb as in the operation 2, the differential amplifier stage 14 outputs the feedback signal higher than the input signal of the input terminal IN2. Lower the operation. (Action 4)

At this time, the voltage of the point B changes in the opposite direction to the rising direction of the point A, and the voltage size is lower than the amplification ratio because it is not yet corrected by the feedback. That is, the voltage change at the point B drops in the opposite direction to the input signal and falls below the amplification ratio voltage. Compared to the input voltage at the differential amplifier stage 14 by the feedback signal after the feedback delay time T_fb as in operation 2, the differential amplifier stage 14 is reversed because the feedback signal is lower than the input signal of the input terminal IN2. Raise the output. (Operation 5)

While repeating the operations 4 and 5 several times, the ringing phenomenon as shown in FIG. 6 is repeated such that the rising and falling is repeated by a certain period until the voltage of the amplification ratio is stabilized.

The frequency of ringing thus generated is higher as the collector capacity Cob_Q24 of the transistor Q24 and the collector capacity Cob_Q25 of the transistor Q25 are smaller, and the amplitude becomes larger as the feedback delay time T_fb is longer.

Second, the ringing occurring at the portion where the input signal described above is rapidly changed appears at a high frequency of several MHz and the amplitude is not negligible so that the amplified signal is mixed with noise and output. In particular, in the audio device, the reproducing sound is irritating, and if you listen long, you will feel tired.

The present invention has been proposed to solve the above-mentioned conventional problems, and the constant current load to reduce the distortion of the signal and obtain a cleaner signal by reducing the ringing generated in the rapidly changing signal in the amplifier using the constant current circuit as a load The purpose is to provide an amplifier with a damping resistor installed in the circuit.

In order to achieve the above object, an amplifier provided with a damping resistor in a constant current load according to a preferred embodiment of the present invention includes a constant current load stage; And a damping resistor connected in parallel to the constant current load stage.

According to another embodiment of the present invention, an amplifier in which a damping resistor is installed at a constant current load includes: a plurality of drive amplifier stages; A plurality of constant current load stages configured in the same number as the drive amplifier stages and connected one to one to each of the drive amplifier stages; And a plurality of damping resistors configured to be smaller than the number of the plurality of constant current load stages, and connected in parallel to each of the plurality of constant current load stages.

An amplifier provided with a damping resistor in a constant current load according to another embodiment of the present invention, a drive amplifier stage; An output stage including complementary transistors of the first and second transistors, the bases of the first and second transistors being respectively connected to the output side of the drive amplifier stage; A constant current load stage connected to the output side of the drive amplifier stage; And a damping resistor connected in parallel to the constant current load stage.

Here, the constant current load stage includes a third transistor having one end connected to the output side of the drive amplifier stage, and the damping resistor is connected to one end of the third transistor and the other end thereof to the other end of the third transistor.

Alternatively, the drive amplifier stage includes a fourth transistor, one end of which is connected to the bases of the first and second transistors, and the constant current load stage includes a fifth transistor, one end of which is connected to one end of the fourth transistor, and the damping resistor has one end. It is connected to one end of the fourth transistor and the other end is connected to the other end of the fifth transistor.

Hereinafter, an amplifier installed with a damping resistor in a constant current load according to an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 7 is a circuit diagram of an amplifier provided with a damping resistor in a constant current load according to the first embodiment of the present invention, and FIG. 8 is a signal waveform graph for explaining the effect of the damping resistor shown in FIG. The amplifier shown in FIG. 7 is a negative feedback amplifier. The circuit shown in Fig. 7 is almost similar to the circuit shown in Fig. 5 described above, and differs in that the damping resistor is connected in parallel to the constant current load. In FIG. 7, the reference numerals of the elements may be the same as the reference numerals of the corresponding elements in FIG. 5, but are different in the specification of the present invention for convenience.

The first embodiment includes an input terminal IN1; A differential amplifier stage 14 including a transistor Q11 and a transistor Q12; A drive amplifier stage 10 including a transistor Q14 and a resistor R15; A constant current load stage 12 consisting of a zener diode ZD11, resistors R14 and R16, and a transistor Q15; A feedback stage 16 composed of a negative feedback resistor Rf11 and a negative feedback resistor Rf12; An output stage 20 for driving a load including a transistor Q16 and a complementary transistor of transistor Q17; A bias voltage source BV11 for supplying a bias voltage to the transistor Q16 and the base of the transistor Q17 of the output terminal 20; And a damping resistor R19 connected in parallel with the constant current load end 12.

Here, the bias voltage source BV11 may be referred to as a bias stage.

In addition, the resistor R14 of the constant current load stage 12 may not be a component of the constant current load stage. This also applies to other embodiments.

The amplifier in which the damping resistor is installed in the constant current load according to the first embodiment described above is a negative feedback amplifier in which the damping resistor R19 is provided in parallel with the constant current load stage 12 in the drive amplifier stage 10. Since the bias bias voltage source BV11 is a constant voltage source and can be omitted in an alternating description, the collector of the transistor Q14 of the drive amplifier stage 10 and the collector of the transistor Q15 of the constant current load stage 12 are connected. can see.

In FIG. 7, one end of the damping resistor R19 is connected to the collector of the transistor Q15 to connect the damping resistor R19 in parallel with the constant current load stage 12, but the transistor Q14 of the drive amplifier stage 10 is connected. It may be connected to the collector.

The operation of the first embodiment described above will be described below. In the first embodiment, the collector of transistor Q14 and the collector of transistor Q15 are connected to each other and can be referred to as an emitter grounding amplifier composed of a constant current load. The collector of the transistor Q14 and the collector of the transistor Q15 operate so that only a constant current flows at all times. Therefore, the collector current of transistor Q14 is constant and the impedance between the collector and emitter of transistor Q14 changes according to the signal change input to the base of transistor Q14. For example, when the impedance between the collector and emitter of transistor Q14 is lowered, the impedance between the collector and emitter of transistor Q15 becomes higher. As the impedance between the collector and emitter of transistor Q14 increases, the impedance between the collector and emitter of transistor Q15 decreases.

That is, the impedance change of the transistors Q14 and Q15 is converted into a voltage and output according to the input signal. The voltage signal generated by this impedance change (an amplifier operating with a change in collector impedance) is faster than the voltage signal (an amplifier operating with a change in collector current) generated by a change in current. Because the current in the base and the emitter must change in order for the collector current to change. In order for the base current to change, the charge accumulated in the capacitance between the base and the emitter must change, and since the charge takes time to change, it takes time for the collector current to change. (Theorem 11)

Therefore, since the drive amplifier stage 10 using the constant current load stage 12 of FIG. 7 is an amplifier that operates with impedance change, the rise and fall time of the output signal is fast. Thus, the damping resistor R19 is provided in parallel with the constant current load stage 12. A portion of the current flowing through the collector of transistor Q14 of drive amplifier stage 10 flows to damping resistor R19 to operate transistor Q14 as an amplifier operating with a collector current change. As a result, in amplifying the signal input to the base of the transistor Q14, the rise and fall time of the signal output to the collector of the transistor Q14 is delayed to reduce the occurrence of ringing.

Referring to the operation of Figure 7 in more detail as follows.

When the signal voltage of the input terminal IN1 changes, the first amplification is performed in the differential amplifier stage 14, and after the second amplification is performed in the drive amplifier stage 10, the output terminal OUT1 of the output terminal 20 is changed. Is output via In this way, the output terminal 20 outputs the changed signal voltage based on the change of the signal voltage of the input terminal IN1. (Operation 11)

The voltage at the output terminal OUT1 is fed back to the base of the transistor Q12 of the differential amplifier 14 via the feedback terminal 16, and the differential amplifier 14 is equal to the voltage input to the input terminal IN1. The operation of correcting the feedback voltage is the same. (Action 12)

The above operations 11 and 12 are repeated, and the operation is repeated until the voltage inputted to the input terminal IN1 and the feedback voltage are the same. (Operation 13)

In Fig. 7, the input / output delay time from when the signal voltage is changed to the input terminal IN1 to the output voltage of the output terminal OUT1 is changed to T_IO1 as in the operation 11, and the operation 12 and Likewise, it is assumed that the feedback delay time from the time when the voltage at the output terminal OUT1 changes to the correction operation compared with the input voltage and the feedback voltage of the input terminal IN1 at the differential amplifier stage 14 is T_fb1.

In FIG. 7, the following phenomenon occurs at the connection point B between the drive amplifier stage 10 and the constant current load stage 12.

In FIG. 7, when the rising signal is input to the input terminal IN1 as shown in A of FIG. 8, the voltage change by the operation 11 is generated at the point B of FIG. 7 after the input / output delay time T_IO1. At this time, the voltage of the point B is the same as the rising direction and the direction of the point A, but the voltage size has not yet been corrected by the feedback, and tries to change higher than the amplification ratio. However, the damping resistor (R19) is connected in parallel with the constant current load stage 12, the current flowing through the damping resistor (R19) is changed by the voltage change at the point B. This changing current changes the collector current of the transistor Q14 of the drive amplifier stage 10, and it takes time as shown in Theorem 11 to change the collector current.

Therefore, the transistor Q14 operates from the amplifier operating with the collector impedance change to the amplifier operating with the collector current change, and it takes some time for the current flowing through the damping resistor R19 to change, so that the voltage at the point B increases. It will take longer. If the time increases as the voltage rises, the overshoot voltage becomes smaller due to the lower voltage change per unit time.

Thereafter, the feedback signal is higher than the signal of the input terminal IN1 due to the feedback signal after the feedback delay time T_fb1 after the feedback delay time T_fb1, so that the differential amplifier stage 14 is reversed. The action is to lower the output. (Action 14)

At this time, the voltage of point B is opposite to the rising direction of the point A, and the voltage size is not yet corrected by the feedback, so it tries to change lower than the amplification ratio. However, the damping resistor R19 is connected in parallel with the constant current load stage 12, so that the current flowing through the damping resistor R19 is changed by the voltage change at the point B. This changing current changes the collector current of the transistor Q14 of the drive amplifier stage 10, and it takes time as shown in Theorem 11 to change the collector current.

Therefore, the transistor Q14 operates from an amplifier operating at a collector impedance change to an amplifier operating at a collector current change, and it takes some time for the current flowing through the damping resistor R19 to change, so that the voltage at point B drops. It will take longer. If the time goes down while the voltage falls, the voltage change per unit time is lowered, thereby making the overshoot voltage small.

Subsequently, since the feedback signal is lower than the signal of the input terminal IN1 by the feedback signal after the feedback delay time T_fb1 as in operation 12 described above, the differential amplifier stage 14 On the contrary, it raises the output. (Operation 15)

While repeating operations 14 and 15 several times, a ringing phenomenon occurs in which the rising and falling is repeated by a predetermined period until the voltage of the amplification ratio is stabilized. However, as shown in FIG. Compared with, it is significantly smaller.

That is, by providing the damping resistor R19 in parallel with the constant current load stage 12, a part of the collector current of the amplifier operating the transistor Q14 of the drive amplifier stage 10 with the impedance change is operated by the change of the output signal. By prolonging the rise and fall times of, it is possible to reduce the ringing occurring in the output signal.

9 is a circuit diagram of an amplifier installed in a damping resistor under a constant current load according to a second embodiment of the present invention.

The amplifier of the second embodiment is a collector ground amplifier (emitter follower). The amplifier of the second embodiment includes a drive amplifier stage 30 composed of a transistor Q51 having an input signal input to a base at an input terminal IN5 and a buffered signal output at an emitter; A constant current load stage 32 connected to the emitter of the transistor Q51 and composed of a zener diode ZD51, resistors R51 and R52, and a transistor Q52; And a damping resistor R53 connected in parallel with the constant current load end 32.

The operation of the amplifier of the second embodiment is as follows.

In the amplifier of the second embodiment, basically, the collector in which the signal input to the input terminal IN5 is input to the base of the transistor Q51, and the buffered output signal is output from the emitter of the transistor Q51 to the output terminal OUT5. Ground amplifier (emitter follower).

When the signal voltage changes at the input terminal IN5, the voltage between the base and emitter of transistor Q51 is 0.6V (indicated by the voltage of base and emitter of transistor Q51, and is expressed as 0.6V for convenience). The transistor Q51 is operated so as to be effective. By the operation of the transistor Q51, the emitter voltage of the transistor Q51 is changed and output to the output terminal OUT5. (Operation 51)

Then, the transistor Q51 checks that the voltage change of the output terminal OUT5 is 0.6V between the base and the emitter of the transistor Q51 (this is used as feedback acting inside the transistor). Local feedback). That is, an operation of correcting the voltage between the base and the emitter of the transistor Q51 to be 0.6V is performed. (Action 52)

The operation 51 and 52 are repeated again until the voltage between the base of the transistor Q51 and the emitter becomes 0.6V. (Operation 53)

In Fig. 9, the input / output delay time is T_IO5 from when the signal voltage is changed to the input terminal IN5 to when the output voltage of the output terminal OUT5 is changed as in operation 51 above. It is assumed that the feedback delay time is T_fb5 from the time when the voltage is changed at the output terminal OUT5 until the correction operation is performed such that the voltage between the base of the transistor Q51 and the emitter is 0.6V.

The second embodiment is a collector ground amplifier in which the emitter of transistor Q51 and the collector of transistor Q52 are connected to constitute a constant current load. The emitter of transistor Q51 and the collector of transistor Q52 always operate to flow a constant current. Therefore, the emitter current of transistor Q51 is constant and the impedance between the collector and emitter of transistor Q51 changes according to the signal change input to the base of transistor Q51. For example, if the impedance between the collector and emitter of transistor Q51 is low, the impedance between the collector and emitter of transistor Q52 is high, and the impedance between the collector and emitter of transistor Q51 is high. Conversely, the impedance between the collector and emitter of transistor Q52 is lowered.

That is, the impedance changes of the transistors Q51 and Q52 are converted into voltages and output according to the input signals. The voltage signal generated by this impedance change (an amplifier operating with a change in collector impedance) is faster than the voltage signal (an amplifier operating with a change in collector current) generated by a change in current. Because the current in the base and the emitter must change in order for the collector current to change. In order for the base current to change, the charge accumulated in the capacitance between the base and the emitter must change, and since the charge takes time to change, it takes time for the collector current to change. (Theorem 51)

Therefore, since the transistor Q51 of Fig. 9 is an amplifier which operates with an impedance change, the rise and fall time of the output signal is fast. Thus, the damping resistor R53 is provided in parallel with the constant current load stage 32. A portion of the current flowing in the emitter of the transistor Q51 of the drive amplifier stage 30 flows to the damping resistor R53 to operate the transistor Q51 as an amplifier operating with a collector current change, thereby increasing the rise and fall time of the amplified signal. Delay to reduce the occurrence of ringing.

In FIG. 9, the following phenomenon occurs at the connection point B between the emitter of the transistor Q51 and the collector of the transistor Q52.

When a rising signal is input to the input terminal IN5 as shown in A of FIG. 8, the voltage change by the operation 51 described above occurs at the point B of FIG. 9 after the input / output delay time T_IO5. At this time, the voltage of point B is the same as the rising direction and the direction of the point A, but the voltage is not yet corrected by the feedback, so the voltage between the base and the emitter of the transistor Q51 is about to decrease than 0.6V. However, the damping resistor R53 is connected in parallel with the constant current load stage 32, so that the current flowing through the damping resistor R53 changes due to the voltage change at the B point. The emitter current of transistor Q51 is changed. It takes time for the emitter current to change as shown in Theorem 51.

Therefore, the transistor Q51 operates from the amplifier operating at the collector impedance change to the amplifier operating at the collector current change, and it takes some time for the current flowing through the damping resistor R53 to change, so that the voltage at the point B increases. It will take longer. If the time increases as the voltage rises, the overshoot voltage becomes smaller due to the lower voltage change per unit time.

Subsequently, after the feedback delay time T_fb5, the voltage between the base and the emitter of the transistor Q51 decreases by less than 0.6V after the feedback delay time T_fb5 as in operation 52, so that the transistor Q51 reverses the voltage between the base and the emitter. To increase the operation. (Operation 54)

At this time, the voltage of point B is opposite to the rising direction of the point A, and the voltage size is not yet corrected by the feedback, so it tries to increase more than 0.6V. However, the damping resistor R53 is connected in parallel with the constant current load stage 32, so that the current flowing through the damping resistor R53 changes due to the voltage change at the B point. The emitter current of transistor Q51 is changed. It takes time for the emitter current to change as shown in Theorem 51.

Therefore, the transistor Q51 operates from the amplifier operating at the collector impedance change to the amplifier operating at the collector current change, and it takes some time for the current flowing through the damping resistor R53 to change, so that the voltage at the point B decreases. It will take longer. If the time goes down while the voltage falls, the voltage change per unit time is lowered, thereby making the overshoot voltage small.

Subsequently, since the voltage between the base of the transistor Q51 and the emitter increased by more than 0.6 V due to the feedback signal after the feedback delay time T_fb5 as in operation 52, the transistor Q51 reverses the base of the transistor Q51. Try to reduce the voltage between and emitter. (The potential at point B increases.) (Operation 55)

While repeating the operations 54 and 55 several times, a ringing phenomenon occurs in which the rising and falling is repeated by a predetermined period until the voltage between the base and the emitter of the transistor Q51 becomes 0.6 V, but FIG. 8 As shown above, the overshooting amplitude of ringing is small. That is, by installing the damping resistor R53 in parallel with the constant current load stage 32, a part of the emitter current of the amplifier which operates the transistor Q51 with the impedance change is operated by the change of current, so that the rise and fall time of the output signal. By lengthening, the effect of reducing ringing occurring in the output signal can be obtained.

10 is a circuit diagram of an amplifier provided with a damping resistor in a constant current load according to a third embodiment of the present invention.

The amplifier of the third embodiment is an emitter ground amplifier. The amplifier of the third embodiment includes a drive amplifier stage 40 consisting of a transistor Q61 in which an input signal is input to a base at an input terminal IN6 and an amplified signal is output from a collector; A constant current load stage 42 connected to a collector of the transistor Q61 and composed of a zener diode ZD61, resistors R61 and R62, and a transistor Q62; And a damping resistor R63 connected in parallel with the constant current load end 42.

The operation of the amplifier of the third embodiment is as follows.

In the amplifier of the third embodiment, an emitter, in which a signal input to the input terminal IN6 is basically input to the base of the transistor Q61, and the amplified output signal is output from the collector of the transistor Q61 to the output terminal OUT6. Ground amplifier.

The collector of the transistor Q61 and the collector of the transistor Q62 always operate so that only a constant current flows. Therefore, in response to the signal change input to the base of the transistor Q61, the collector of the transistor Q61 has a constant current and operates to change the impedance between the collector and the emitter of the transistor Q61. For example, if the impedance between the collector and emitter of transistor Q61 is low, the impedance between the collector and emitter of transistor Q62 is high, and the impedance between the collector and emitter of transistor Q61 is high. On the contrary, the impedance between the collector and the emitter of transistor Q62 becomes low.

That is, the impedance change of the transistors Q61 and Q62 is converted into a voltage and output according to the input signal. The voltage signal generated by this impedance change (an amplifier operating with a change in collector impedance) is faster than the voltage signal (an amplifier operating with a change in collector current) generated by a change in current. Because the current in the base and the emitter must change in order for the collector current to change. In order for the base current to change, the charge accumulated in the capacitance between the base and the emitter must change, and since the charge takes time to change, it takes time for the collector current to change.

The operation description of FIG. 10 is the same as the operation description of the drive amplifier stage and the constant current load stage of the first embodiment described above, and thus further detailed description thereof will be omitted. Omitting this detailed description can be sufficiently understood by those skilled in the art as the operation description of the drive amplifier stage and the constant current load stage of the first embodiment described above.

In the third embodiment, the damping resistor R63 is provided in parallel with the constant current load stage 42 so that a part of the collector current of the amplifier operating the transistor Q61 with the impedance change is operated with the current change, thereby raising the output signal. By prolonging the fall time, it is possible to reduce the ringing occurring in the output signal.

FIG. 11 is a circuit diagram according to a modified example of the present invention and is an embodiment of a collector ground amplifier to which another constant current circuit is applied. The collector and the base of the transistor Q73 are connected to each other, and the base of the transistor Q72 is connected to this connection point. One end of the resistor R71 is connected to the connection point between the transistors Q72 and Q73, and the other end of the resistor R71 is connected to the power supply terminal VCC7.

A circuit having the same connection relationship as the transistors Q72 and Q73 in FIG. 11 is called a current mirror circuit. That is, when the current Ice_Q73 flows through the resistor R71 to the connection point of the transistors Q72 and Q73, the current Ice_Q72 flowing through the collector of the transistor Q72 is the same as the current Ice_Q73 flowing through the collector of the transistor Q73.

Here, the constant current circuit composed of the transistor Q72, the transistor Q73, and the resistor R71 may be referred to as a constant current load end. By providing a damping resistor R72 in parallel with this constant current load end, it has the same function as the collector ground amplifier of the second embodiment described above. A more detailed description of the operation of FIG. 11 is fully understood by those skilled in the art as described in the above-described second embodiment.

On the other hand, although not shown in the drawings, a constant current load may be used as a load in each drive amplifier stage in configuring a negative feedback amplifier or an amplifier that does not apply negative feedback. In this case, it is obvious that the damping resistor can be selectively installed to reduce the ringing at the constant current load of each drive amplifier stage. In other words, in an amplifier using multiple drive amplifier stages, constant current loads may be connected one-to-one for each drive amplifier stage, and damping resistors may be connected in parallel one-to-one to each constant current load, or ringing may be required to further optimize circuit configuration. The damping resistance may be connected in parallel only to the constant current load considered to be. As described above, a resistor installed in parallel with a constant current load is called a damping resistor. In the amplifier using the constant current load described above, by installing a damping resistor in parallel with the constant current load, it is possible to reduce the ringing voltage at the portion where the input signal changes rapidly.

The present invention is not limited only to the above-described embodiments, but may be modified and modified without departing from the scope of the present invention, and the technical spirit to which such modifications and variations are applied should also be regarded as belonging to the following claims. .

As described in detail above, according to the present invention, by connecting the damping resistors in parallel to the constant current load, the amplification gain is increased and the ringing occurs, thereby obtaining a cleaner output signal.

Since the ratio of harmonics included in the output signal is low, there is no need to install a separate filter.

In addition, when the present invention is applied to an acoustic device, it is possible to reproduce clean sound quality that is not irritating.

Claims (6)

Constant current load stage; And And a damping resistor connected to the constant current load stage in parallel. Multiple drive amplifiers; A plurality of constant current load stages configured in the same number as the drive amplifier stages and connected one to one to each of the drive amplifier stages; And A damping resistor is installed in the constant current load, wherein the damping resistor is configured to be smaller than the number of the constant current load stages, and includes a plurality of damping resistors connected in parallel to each of the plurality of constant current load stages. amplifier. Drive amplifier stage; An output stage comprising complementary transistors of first and second transistors, the bases of the first and second transistors being respectively connected to an output side of the drive amplifier stage; A constant current load stage coupled to the output side of the drive amplifier stage; And And a damping resistor connected to the constant current load stage in parallel. The method according to claim 3, The constant current load stage includes a third transistor having one end connected to an output side of the drive amplifier stage, The damping resistor is provided with a damping resistor in a constant current load, characterized in that one end is connected to one end of the third transistor and the other end is connected to the other end of the third transistor. The method according to claim 3, The drive amplifier stage includes a fourth transistor having one end connected to a base of the first and second transistors, The constant current load end includes a fifth transistor having one end connected to one end of the fourth transistor, The damping resistor is provided with a damping resistor in a constant current load, characterized in that one end is connected to one end of the fourth transistor and the other end is connected to the other end of the fifth transistor. A negative feedback amplifier comprising the amplifier according to any one of claims 1 to 5.

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