JPS6264106A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To attain stable operation even for a load including an inductance component by coupling an input side emitter and an output base of two transistors (TR) connected in cascode via a resistor in terms of AC. CONSTITUTION:Since the base and emitter of TRs Q2, Q1 are connected to a DC voltage source B and a resistor R6, a resistor R6 is connected in series with a series resonance circuit comprising a base-collector capacitance of the TR Q2 and the inductance of a load Zl to reduce the feedback quantity of the output voltage to the emitter of the TR Q1. In this case, the effect of stabilization is larger when the resistor R6 is larger than the resistance R3, even then the resistor R6 and the resistor R3 are equal, the circuit applies sufficiently stable operation actually. Since the resistor R6 is inserted to the circuit coupling the emitter and base of the TRs Q1, Q2 in terms of AC and the load including the inductance component as the load Zl is connected, the circuit operation is stabilized while the amplification with low distortion factor and excellent high frequency characteristic is kept.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an amplifier circuit suitable for handling high frequency signals.

[Technical background of the invention]

Generally, in order to attenuate or amplify high frequency signals, a circuit in which transistors are connected in cascode is used. FIG. 1 is a diagram showing an example of this type of circuit in which a cascode connection is made using bipolar transistors. The collector of transistor Q1 and the emitter of transistor Q2 are connected.

The emitter of transistor Ql is grounded via resistor B3, and the collector of transistor Q2 is connected to power supply Vcc via load ZJ. A DC voltage source B is applied to the base of the transistor Q2. Transistor Ql
A DC power supply VCC is applied to the base of the circuit through a resistor 'fLl, and the base is grounded through a resistor R2. Furthermore, input terminal 1 is connected to the same base via capacitor C1.
An input signal is applied from

In the above circuit, the emitter-grounded transistor Ql and the base-grounded transistor Q2 are connected in cascode, and the AC potential at the collector of the transistor Q1 (which is in opposite phase to the input signal applied to the input terminal 1) is widened. The mirror effect caused by the capacitance between the base and collector is eliminated, improving the high-frequency wave characteristics of the circuit. Note that what is shown as DC voltage source B in the figure is often replaced by a connection of a resistor and a capacitor in an actual circuit.

FIG. 5 shows an example of a conventional circuit of this type using a cascode-Putstrap connection in order to improve the nonlinearity of amplifier elements such as transistors when handling high frequency and large signals. In this circuit, a DC voltage source B is connected between the emitter of the base transistor Ql of the transistor Q2 and the emitter of the transistor Ql and the transistor Q2.
The bases of the transistors are set at the same potential in an alternating current manner, and the transistor Q1 is driven with a constant voltage between the collector and emitter, thereby improving the nonlinearity of the vine transistors Ql and Q2 at the time of a large signal.

Incidentally, the DC voltage source B shown in FIG. 5 has a configuration as shown in FIG. 6 or 7 in an actual circuit.

That is, in the 6th @, the cathode side of the Zener diode D is connected to the resistor R4 to which the DC power supply Vcc is applied to one end,
This connection point is connected to the anode side of transiode D to the emitter of transistor Ql, and then to the emitter of transistor Q2.
The base of the transistor Ql and the emitter of the transistor Ql are connected to the capacitor C
Connected with 2. In the circuit shown in FIG. 7, a resistor R5 to which a DC power supply Vcc is applied to one end is connected to a resistor R5 which is grounded, and the connection point of these resistors is connected to a transistor Q2.
Further, the base of the transistor Q2 and the emitter of the transistor Ql are connected by a capacitor C2. Note that the emitters and collectors of the transistors Ql and Q2 are AC-coupled by the capacitor C2 in the circuit shown in FIG. 6.7.

[The juncture of background technology]

This type of amplifier circuit shown in FIGS. 4 and 5 above has the advantage that distortion can be greatly reduced when a high frequency signal is amplified. However, if, for example, a load zl that includes an inductance component such as a magnetic head is connected, the base-collector Ω of the transistor Q2 resonates with the inductance component of the load, and their DC impedance disappears. Therefore, the output voltage is strongly fed back to the emitter of the transistor Q1, making the system unstable. Therefore, conventional circuits of this type have the disadvantage that yA oscillations occur due to external stimulation or temperature changes, and distortion increases. Therefore, if an attempt is made to avoid the above drawback by adding a new active element such as a transistor for impedance conversion, the distortion of the added active element itself will be added, and the distortion reduction effect due to the cascode bootstrap connection will be reduced. The objective of the present invention is to provide an amplifier circuit that can operate stably even with a load including an inductance component while maintaining frequency characteristics and a low distortion factor.

[Summary of the invention]

In the present invention, among the two transistors connected in cascode, the transistor on the input side is The emitter and the base of the output transistor are connected via a resistor in an alternating current manner, and the input transistor is driven with a constant voltage between the collector and emitter, and at the same time, the output voltage of the output transistor is fed back to the emitter of the input transistor. The above objective is achieved by alleviating the

[Embodiments of the invention]

Hereinafter, an embodiment of the present invention will be described with reference to the drawings, in which the same parts as those of the conventional example are denoted by the same reference numerals. FIG. 1 is a circuit diagram showing an embodiment of the amplifier circuit of the present invention. transistor Q
The base of 1 is connected to a resistor hole l whose one end is connected to the DC power supply V (c) and a resistor R2 whose one end is grounded, and further connected to the base of 1.
An input signal is applied from input terminal 1 via capacitor C1. Note that the resistors R1 and R2 constitute a base bias circuit of the transistor Ql.

Also, the collector of transistor Ql is connected to transistor Q2.
The collector of transistor Q2 is connected to the DC power supply VC via a load ZI (in this case, a magnetic head, etc.).
Connected to C. The base of the transistor Q2 and the emitter of the transistor Ql are connected in an alternating current manner via a direct current voltage source B and a resistor R6.

FIG. 2 is a circuit diagram showing a detailed example of the DC voltage source B and resistor R6 shown in FIG. 1. DC voltage source B is resistor R4
and a Zener diode D are connected in series, and a capacitor C2 is further connected in parallel to the Zener diode D. One end of resistor R4 is connected to DC power supply Vc
The connection point between the resistor R4, the Zener diode D and the capacitor C2 is connected to the base of the transistor Q2, and the connection point between the capacitor C2 and the Zener diode D is connected to the resistance hole 6.

FIG. 3 is a circuit diagram showing another detailed example of the DC voltage source B and resistor R6 shown in FIG. 1. DC voltage source B consists of a circuit in which resistor R4 and resistor R5 are directly connected and capacitor C.
One end of the resistor R4 is connected to the DC power supply VCC, the connection point of the other end C2 of the resistor hole 5 is connected to the base of the transistor Q2, and the other end of the capacitor C2 is connected to the resistor hole 6.

Next, the operation of this embodiment will be explained. Since the base and emitter of transistors Q2 and Ql in FIG. 1 are connected to DC voltage source B through resistor hole 6, transistor Q
2 base, collector capacitance and Z! The resistor hole 6 is added in series to the series resonant circuit with the inductance component of the transistor Q1 to reduce the amount of feedback of the output voltage to the emitter of the transistor Q1. Moreover, in the detailed circuits shown in FIGS. 2 and 3, if the resistance value of each resistor hole 6 is selected to be sufficiently lower than that of the resistors R4 and R5, the emitter potential of the transistor Ql is almost the same as that of the transistor Q2. It appears at the base, and can perform amplification operation with low distortion and good high frequency characteristics, similar to normal cascode, boot, and one-suit-lap connections. In this case, the stabilizing effect will be greater if the value of the resistor R6 is larger than that of the resistor hole 3, but in reality the resistor R
It has been confirmed that the circuit operates in a sufficiently stable manner even if the value of the resistor R3 is approximately the same as that of the resistor R3.

According to this embodiment, transistor Q1 and transistor Q
A resistor R is added to the circuit that connects the emitter and base of 2 in an alternating current manner.
6 in series, even if a load containing an inductance component such as a magnetic head is connected as the load Zl, the amplification operation with low distortion and good high frequency characteristics can be maintained.
Highly reliable operation can be obtained by applying the circuit operation to an inexpensive recording head driving amplifier or the like.

In the above embodiment, the case where a magnetic head is connected as the load Zl has been described, but the same effect can be obtained even if a resistor is connected as the load. Similar effects can be obtained even when the present invention is applied to a differential amplifier circuit in which two sets of differential amplifier circuits are connected. Also, is the amplifier element connected in cascode connected to pi? -'t L 4'/S
7 h l--fEr 7 W L l碍f
A similar effect can be obtained in h/T;'T;'

〔Effect of the invention〕

As described above, according to the amplifier circuit of the present invention, the emitter of the input side transistor and the base of the output side transistor of two cascode-connected transistors are coupled in an alternating current manner through a resistor. A circuit diagram that maintains high frequency characteristics and low distortion, and is also safe for loads containing inductance components. Figure 2 is a circuit diagram showing a detailed example of the circuit shown in Figure 1, and Figure 3 is the circuit diagram shown in Figure 1. 4 is a circuit diagram showing an example of a conventional cascode connection amplifier circuit, and FIG. 5 is a circuit diagram showing an example of a conventional cascode bootstrap connection amplifier circuit. 6 is a circuit diagram showing a detailed example of FIG. 5, and FIG. 7 is a circuit diagram showing another detailed example of FIG. 5.

B...DC chamber WMC2...Capacitor D...Zener diode qxt Q2...Transistor R4
,I(,5,n+6-resistance Z l -...load agent patent attorney rule
HaruhiroFigure 1Figure 2Figure 3Figure 4Figure 6Figure 5Figure 7

Claims (1)

[Claims] A first transistor whose base is connected to an input signal through a bias circuit, whose emitter is connected to a reference potential through an impedance element such as a resistor, whose emitter is connected to the collector of the first transistor, and whose collector is connected to a DC potential through a load. In a cascode-connected amplifier circuit consisting of a second transistor connected to a different reference potential, the emitter of the first transistor and the base of the second transistor are AC-coupled via a resistor. Characteristic amplifier circuit.