JPS60134505A - Transistor amplifier circuit - Google Patents

Abstract

PURPOSE:To realize a broad band and a low distortion factor at large amplification by applying a prescribed current to a collector of a transistor (TR) of the 1st stage of the inverted Darlington circuit comprising two TRs. CONSTITUTION:A base of a TR7 is connected to a signal source 3, a collector and a base of the TR1 are connected respectively to a constant current source 11, an emitter of the TR7 and the collector of the TR1 are connected and grounded via a resistor 4. The emitter of the TR1 is connected to a power supply 6 via a resistor 5, the power supply 6 is connected to a current source 11 and an output signal is extracted from the collector of the TR1. Since the collector current of the TR7 is the constant current in this way, the emitter current of the TR7 is unchanged, then the change in the equivalent emitter resistance (hib) due to the emitter current change of the TR7 is not caused, the distortion due to the change in the (hib) is not produced so as to amplify a signal with a low distortion factor, thereby realizing the broad band and low distortion factor at large amplification.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a transistor amplifier circuit suitable for use in a video signal circuit of a video tape recorder or the like.

[Technical background of the invention and its problems]

Video signal circuits and the like require wideband, large amplitude, and low distortion transistor amplifier circuits. FIG. 1 is a circuit diagram showing an example of a conventional transistor amplifier circuit. The transistor 1 constitutes a common emitter amplifier circuit, its base is connected to a signal source 3 having an internal resistor 2, and its emitter is grounded via a resistor 4. Furthermore, transistor 1
The collector of is connected to a power source 6 via a load resistor 5. However, the base bias circuit is omitted.

The circuit as described above is a current feedback amplifier circuit of one transistor, and the emitter current ie of the transistor 1 changes depending on the signal from the signal source 3. In other words, since such a circuit has an equivalent emitter resistance hib that is approximately inversely proportional to the emitter current of transistor 1, the emitter voltage does not accurately follow the signal waveform when the amplitude is large, and as a result, the collector output voltage is distorted. There were drawbacks. This drawback is
The same applies to the emitter follower shown in FIG. 2, in which the power source 6 is directly connected to the collector of the transistor 1 and the output is output from the emitter.

3 and 4 show examples of circuits using a Darlington circuit and an inverted Darlington circuit in which two transistors are combined in order to correct the above-mentioned problems even to some extent. In FIG. 3, the emitter of transistor 7 is connected to the base of transistor 1, and is also grounded via resistor 8.

The emitter of the transistor 7 is grounded to a signal source 3 having an internal resistor 2, and its collector, together with the collector of the transistor 1, is connected to a power source 6 via a resistor 5. The emitter of transistor 1 is grounded via resistor 4. In FIG. 4, the collector of transistor 7 is connected to the base of transistor 1 and is also connected to power supply 6 via resistor 9. In FIG. The base of the transistor 7 is connected to a signal source 3 having an internal resistor 2, and its emitter, together with the collector of the transistor 1, is grounded via a resistor 4. The emitter of the transistor 1 is connected to the C power supply 6 through a resistor 5. In these circuits, a transistor with relatively good linearity, such as a small signal transistor, is used as the first stage transistor 7. This is an attempt to reduce the total distortion.However, even though the transistor has good linearity, the equivalent emitter resistance hi increases due to the emitter current.
There is no change in the essential operation of the transistor in that b changes, and the distortion cannot be reduced below a certain value. That is,
In the Darlington circuit of FIG. 3, the current flowing through resistor 8 and resistor 4 causes the equivalent emitter resistance h of transistor 7 to
ib and the equivalent emitter resistance hib of transistor l will change, resulting in a distorted output. In the inverted Darlington circuit shown in Figure 4, the current flowing through the resistor 9 changes depending on the signal, which causes the collector current of the transistor 7 to change, which in turn causes a change in the equivalent emitter resistance hib of the transistor 7, which also distorts the output. It turns out.

Here, the pace emitter voltage of transistor 1 is ■y
When sm is the emitter current, Ic is the base-emitter reverse saturation current, Is is the Boltzmann constant, q is the electron charge, and T is the absolute temperature, the following relationship exists.

Vlll # ” In (--12';' In
'■! (°, °h>x kTIs kTIs...(su+Z hib=d7;m q tense...(2) Figure 5 shows the relationship between VBI and Ie of equation (0). As is clear from the figure, <VBK and C have a nonlinear relationship, and the relationship between the emitter voltage and base voltage (input voltage) of transistor 1 in the circuit of Figure 1 is as shown in Figure 6, and the nonlinear relationship is It can be seen that distortion is occurring.The broken line in Figure 6 shows the characteristics when no distortion occurs for comparison.The principle of distortion generation as described above is shown in Figure 3. The inverted Darlington circuit shown in FIG. The AC voltage becomes approximately equal to the voltage across the output resistor 5, and the emitter current of the transistor 7 changes approximately equal to the output voltage.Therefore,
The voltage change across the resistor 5 has the same distortion as in the case of the common emitter amplifier circuit shown in FIG.'gTJ1. Note that equation (2) indicates that the equivalent emitter resistance hlb changes in inverse proportion to the change in the emitter current Ie.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above drawbacks, an object of the present invention is to provide a transistor amplifier circuit that achieves low distortion even in a wide band and large amplitude.

[Summary of the invention]

In the present invention, the collector of the first transistor is connected to the base of the second transistor having the opposite polarity, and the emitter of the first transistor and the collector of the second transistor are commonly grounded through a resistor. In an inverted Darlington circuit, a constant current source is provided to supply a constant current to the collector of the first transistor, a collector voltage is applied to the collector of the second transistor, and a signal is applied to the base of the first transistor. The above object is achieved by taking out the output from the collector or emitter of the second transistor.

The principle of the present invention will now be explained. The distortion generation process in the inverted Darlington circuit shown in FIG. 4 will be analyzed more strictly. That is, the inverted Darlington circuit shown in FIG. 4 is a modification of the C-E negative feedback two-stage transistor amplifier circuit, and can be said to be a 100-chi negative feedback circuit. However, it is known that distortion in a negative feedback amplifier circuit occurs mostly in the first stage when the loop gain is large. That is,
In the inverted Darlington circuit, distortion in the transistor 7 is the most important factor. As mentioned above, in a transistor, the equivalent emitter resistance ht due to the emitter current
b changes and the burr causes distortion. In FIG. 4, the emitter current of the transistor 7 becomes equal to the collector current when the input impedance hfe of the transistor 7 is large. The collector current of the transistor 7 is the sum of the current flowing through the resistor 9 and the pace current of the transistor 1, but if the input impedance hfe of the transistor 1 is sufficiently large, it will almost always match the current flowing through the resistor 9.

That is, if the current flowing through the resistor 9 is kept unchanged,
The emitter current of the transistor 7 can be kept unchanged, and therefore the emitter equivalent resistance hib does not change due to a change in the emitter current, making it possible to realize low distortion. The voltage across the resistor 9 is approximately equal to the voltage across the load resistor 5 in terms of alternating current, and varies depending on the signal from the signal source 3. Therefore, by using a constant current source instead of the resistor 9 to keep the collector current of the transistor 7 constant, the above-mentioned low distortion can be achieved.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings, in which the same parts as those of the conventional example are denoted by the same reference numerals. FIG. 7 is a circuit diagram showing an embodiment of the transistor amplifier circuit of the present invention. The base of the transistor 70 is connected to a signal source 3 having an internal resistance 2, and the collector thereof, together with the base of the transistor 1, is connected to a constant current source 11. The emitter of transistor 7 and the collector of transistor 1 are commonly connected and grounded via resistor 4. The emitter of the transistor 1 is connected through a resistor 5 to a °C power supply 6, which is connected to a constant current source 11. The 'output signal is taken out from the collector of transistor 1.

In this embodiment, since the collector current of the transistor 7 is a constant current supplied from the constant current source 11, it hardly changes (therefore, the emitter current of the transistor 7 also hardly changes. , transistor 7
There is no change in the equivalent emitter resistance hib of the transistor 7 due to a change in the emitter current, and distortion caused by this change in hib is almost eliminated. In the inverted Darlington circuit shown in Fig. 7, the distortion of transistor 7 controls the overall distortion, so the distortion of transistor 7 becomes extremely small, making it possible for this transistor amplifier circuit to achieve a low distortion rate. can. In particular, distortion due to changes in the equivalent emitter resistance hib becomes noticeable when the circuit has a wide band and large amplitude, so the embodiment shown in FIG. 7 can achieve a low distortion rate when the circuit has a wide band and large amplitude. It is ideal for use in video signal circuits such as video tape recorders.

FIG. 8 is a circuit diagram showing another embodiment of the present invention. This circuit uses the circuit shown in FIG. 7 as an emitter follower. That is, the output signal is taken out from the connection point between the emitter of the transistor 7 and the collector of the transistor 1, and the power supply 6 is directly connected to the emitter of the transistor 1. Similarly to the circuit shown in FIG. 7, this circuit also always supplies a constant current to the collector of the transistor 7 from the constant current source 11. Therefore, this embodiment is similar to the previous embodiment, and can achieve low distortion in a wide band and large amplitude.

FIG. 9 is a circuit diagram showing still another embodiment of the present invention. This circuit is a circuit diagram in which the inverted Darlington circuit shown in FIG. 7 is connected in a complementary manner. That is, the collector of the transistor 7 is connected to the base of the transistor 1, and its emitter, together with the collector of the transistor 1, is connected to the power supply 6 via the resistor 4. The collector of transistor 7' is connected to the base of transistor 1', and its emitter, together with the collector of transistor 1', is connected to power supply 6' via resistor 4'. The leads of the transistors 1.1' are connected via a resistor 13, and their emitters are connected together and grounded via a resistor 5. The bases of the transistors 7.7' are each connected to a signal source 3 with a resistor 2 via a bias voltage 12.12'.

The output is taken from the connection point between the two emitters of transistor 1.1'. This circuit uses complementary connection and applies signals of the same phase to the bases of transistors 7 and 7', so the AC voltages across the resistor 13 are approximately equal, and almost no AC current flows through this resistor 13. . Therefore, this resistor 13 performs the same operation as a constant current source.

Therefore, the collector current of the transistor 7.7' becomes approximately constant, and as mentioned above (distortion caused by the equivalent emitter resistance bib of the transistor 7.7' is almost eliminated), and this circuit also has low distortion in a wide band and large 4-channel width. In addition, since a constant current source is not used and only the resistor 13 is required, the circuit can be simplified.

〔Effect of the invention〕

As described above, according to the transistor amplifier circuit of the present invention, a constant current is supplied from a constant current source to the collector of the first stage transistor of an inverted Darlington circuit composed of two transistors, and the emitter of this transistor is supplied with a constant current to the collector of the first stage transistor. By minimizing the change in current and eliminating most of the distortion in the first-stage transistor caused by changes in the equivalent emitter resistance, it is possible to achieve a low distortion rate over a wide band and large amplitude.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a conventional emitter common transistor amplifier circuit, Fig. 2 is a circuit diagram showing an example of a conventional emitter follower transistor amplifier circuit, and Fig. 3 is a circuit diagram showing an example of a conventional emitter follower transistor amplifier circuit. A circuit diagram showing an example of a common emitter amplifier circuit. Figure 4 is a circuit diagram showing an example of an equal constraint common emitter amplifier circuit using a conventional inverted Darlington connection. Figure 5 is an example of the circuit shown in Figure 1. FIG. 6 is a characteristic diagram showing the relationship between the base emitter voltage and emitter current of the transistor in the circuit example of FIG. FIG. 8 is a circuit diagram showing another embodiment of the transistor amplifier circuit of the invention. FIG. 9 is a circuit diagram showing another embodiment of the transistor amplifier circuit of the invention. FIG. 2 is a circuit diagram showing an example. 1.1', 7.7' -- Transistor 3... Power source 4.4', 5.5', 13... Resistor 6... Electric fishing 11... Current source agent Patent attorney Shi Nori Chika (and 1 other person) Figure 1 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] The emitter of the first transistor and the collector of a second transistor of opposite polarity to this transistor are commonly connected to the first point via a resistor, and the collector of the first transistor is connected to the base of the second transistor. and is connected to a second point via a constant current means, the emitter of the second transistor is connected via a resistor or directly to a point with a ratio of 2, and a power source is connected between the first point and the second point. Connected and 4th
A transistor amplifier circuit characterized in that a signal is applied to the base of a second transistor and an output is taken out from the collector or emitter of a second transistor.