JPH0218609B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in amplifier circuits.

Conventionally, cascode amplifier circuits having wideband and low noise characteristics have been widely used.

However, in such a conventional cascode amplifier circuit, a high DC voltage is generated at the output terminal, so
It has drawbacks such as not being able to freely connect directly to the next stage. The present applicant has proposed an amplifier as shown in Fig. 1, which can easily be directly connected to the next stage without impairing the excellent wide-band low-noise characteristics of the cascode amplification circuit as described above, and which eliminates the above-mentioned drawbacks. No. 56-80912 was proposed as "Amplifier".

In FIG. 1, an input signal is applied from an input terminal 1 grounded through a resistor 2 to the control electrode of the first transistor, that is, the gate of FET 3, and the drain is connected to the positive power supply +B via a constant current source 10. and is connected to the emitter of a second transistor, that is, transistor 12, which is a common base input type,
The source is grounded via a resistor 5. A predetermined DC voltage is applied to the control electrode, that is, the base of the transistor 12 by the DC power supply 6, and the collector is connected to the resistor 1.
4 to the negative power supply -B and to the output terminal 15.

In the above configuration, compared to a conventional cascode amplifier, the polarity of FET 3 and transistor 12 are different, and the resistor 14 connected to transistor 12 is connected to negative power supply -B instead of positive power supply. The difference is that a constant current source 9 is connected to the positive power supply +B from the common connection point of the FET 3 and the transistor 12, but the alternating current performs a cascode operation equivalent to the conventional one.

That is, if a positive signal is applied to the input terminal 1, the current of the FET 3 increases. Therefore, the current in transistor 12 decreases by this increase, and the level at output terminal 15 becomes negative. In this way, the AC operation is the same as the conventional cascode operation inverting amplifier, and it has the broadband low noise characteristics of the cascode amplifier circuit.

Next, DC operation will be explained. The operating current of the FET 3 is supplied by a constant current source 10, and a current value obtained by subtracting the operating current of the FET 3 from the current value of the constant current source 10 is supplied to the transistor 12. Since a DC voltage is applied to the base of the transistor 12 by the DC power supply 6, the above-mentioned
The drain voltage of FET 3 is maintained at a voltage approximately equal to the voltage value of DC power supply 6, and the DC operation of FET 3 is equivalent to that of a conventional cascode amplifier. Also FET
The operating current of FET 3 is determined by the characteristics of FET 3 and the resistance value of resistor 5. Since the collector of the transistor 12 is connected to the negative power supply -B via the resistor 14, even if the resistance value of the resistor 14 is restricted due to restrictions on the degree of amplification, the current value of the constant current source 10 or the negative power supply - Output terminal 15 depending on the setting of the voltage value of B.
Since the DC potential of can be set to any voltage value, and of course it can also be set to ground potential, direct connection to the next stage is easy.

Figure 2 shows the other ends of the power supplies (constant voltage elements) 6 and 7 connected to the bases of transistors 12 and 13 in order to make the above-mentioned amplifiers push-pull connected and to make cascode bootstrap connections.
It is connected to the sources of FETs 3 and 4, and has the same features as a normal cascode bootstrap circuit, and in addition, the DC potential of the output terminal 15 can be set to the ground potential.

However, as shown in FIG. 2, there is a drawback that two power supplies are required. Furthermore, the power supplies 16 and 17 shown in the figure are not actually ideal DC power supplies, and as shown in the figure, the power supply 16 is an ideal DC power supply _E1 and a power supply e that includes ripple components, noise components, etc. ₁ , the power supply 17 is divided into an ideal DC power supply _E2 and a power supply _e2 containing ripple components, noise components, etc. Here, the current flowing from the power source e ₁ is as follows: power source e ₁ → resistor 8 → constant voltage element 6 →
It flows through the following path: resistor 5 → ground → power supply e ₁ . On the other hand, the current flowing from power supply e ₂ is power supply e ₂ → ground → resistor 5
→ Constant voltage element 7 → Resistor 9 → Power supply e It flows through the following path _{: 2} . Therefore, if the voltage values of the power supplies e ₁ and e ₂ have the same amplitude and opposite phase, no ripple component or noise component will occur at both ends of the resistor 5, and therefore no ripple component or noise component will occur at the output terminal 15. No special effects occur. However, in reality, the voltage values of the power supplies e ₁ and e ₂ cannot have the same amplitude and opposite phase, so ripple components and noise components are generated at both ends of the resistor 5, and therefore, ripple components and noise components are generated at the output terminal 15. There were some drawbacks such as:

The present invention has been made to eliminate the above-mentioned drawbacks, and even if the power supply has a simple amplification circuit or the power supply contains ripple components or noise components, the output will still contain ripple components or noise components. The purpose of this invention is to provide an amplifier circuit that does not cause such problems.

Hereinafter, the present invention will be explained in detail according to examples.

FIG. 3 is a circuit diagram showing one embodiment of the present invention. Parts corresponding to those in FIG. 2 are given the same reference numerals and explanations are omitted. The power supplies 16 and 17 shown are replaced by floating power supplies 18. Other parts are the same as in FIG. 2.

Even in this case, the floating power supply 18 is not an ideal DC power supply, but is divided into an ideal DC power supply E ₃ and a power supply e ₃ containing ripple components, noise components, etc., as shown in FIG. Here, the current flowing from power supply e ₃ is: power supply e ₃ → resistor 8 → constant voltage element 6 →
The current flows through the constant voltage element 7→resistor 9→power supply _e3 , and no ripple or noise components are generated at both ends of the resistor 5, and therefore no ripple or noise components are generated at the output terminal 15 either.

Next, when the input signal ei is input to the input terminal 1, the output signal e ₀ appearing at the output terminal 15 is determined. When the input signal ei is input to the gates of FETs 3 and 4, the current flowing through FETs 3 and 4 is
The current value is determined by the resistance value of . or,
The current I ₁ flowing through the FET3 flows through a path of FET3→transistor 12→resistor 14→resistor 5→FET3. On the other hand, the current I ₂ flowing through FET4 is
It flows through the path FET4→Resistor 5→Resistor 14→Transistor 13→FET4. That is, all of the current flowing through the resistor 5 will flow through the resistor 14. (Here, we ignore the gate leakage currents of FETs 3 and 7, the base currents of transistors 12 and 13, etc.) Therefore, let the resistance values of resistors 5 and 14 be R ₅ and R ₁₄ , respectively, and Ignoring transconductance, the output signal e ₀ becomes e ₀ =−R ₁₄ /R ₅ ei.

Furthermore, the same effect can be obtained by connecting the common connection point of constant voltage elements 6 and 7 to the gates of FETs 3 and 4 in FIG. Furthermore, if the common connection point is grounded, characteristics similar to those of a cascode amplifier circuit can be obtained, and only one power supply is required.

Furthermore, it goes without saying that the FET used in the present invention may be a bipolar transistor, and the transistor may also be a FET.

As explained above, according to the present invention, even if the power supply contains ripple components, noise components, etc., it is possible to obtain the excellent effect that the output is not affected by the ripple components or noise components.

[Brief explanation of drawings]

Figures 1 and 2 were filed by the applicant in a patent application published in 1983.
A circuit diagram showing an amplifier proposed as "Amplifier" in No. 80912, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. In the figure, 3 and 4 are FETs, 6 and 7 are constant voltage elements, 2, 5, 8, 9 and 14 are resistors, 18 is a floating power supply, and 10 and 11 are constant current sources.

Claims (1)

[Claims] 1. A first series circuit of transistors of different conductivity types, whose sources or emitters are connected together to form a first common connection point, and whose gates or bases are connected to form an input terminal; A second series circuit of transistors of different conductivity types which are used as a common connection point and an output terminal of the two transistors, and a bias voltage is applied from the first common connection point to the gate or base of each transistor in the second series circuit. a bias voltage applying means for applying a bias voltage, a first resistor for providing the first common connection point, a second resistor for providing the second common connection point, and a bias voltage applying means for applying the first and second It is characterized by having floating power supplies supplied via constant current sources to both ends of a parallel circuit made up of a series circuit, and preventing ripples and noise contained in the supplied power from being output to the output terminals. Amplification circuit.