Amplifiers – With semiconductor amplifying device – Including plural stages cascaded
Reexamination Certificate
2000-03-06
2001-04-17
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including plural stages cascaded
C330S290000
Reexamination Certificate
active
06218906
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to an amplifier circuit having a first transistor of a first conductivity type, into whose control input an input signal is coupled and whose controlled path is connected at one end to a first supply potential. A second transistor of the first conductivity type is provided, to whose control input a bias potential is applied and whose controlled path is connected at one end to the other end of the controlled path of the first transistor and which outputs an output signal at its other end. The circuit has a first resistor, which is connected between the other end of the second transistor and a second supply potential.
One such amplifier circuit is generally designated as a cascode amplifier circuit and is known for instance from the publication by U. Tietze, Ch. Schenk, titled “Electronic Circuits”, 1991, pages 439 and 440. Cascode amplifier circuits are distinguished by a high input resistance and by the elimination of the Miller effect. However, they are vulnerable to component parameter fluctuations, temperature fluctuations, and voltage fluctuations.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an amplifier circuit which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which component, temperature and voltage fluctuations exert less of an influence.
With the foregoing and other objects in view there is provided, in accordance with the invention, an amplifier circuit, containing:
a first transistor of a first conductivity type having a control input receiving an input signal and a controlled path having a first end to be connected to a first supply potential and a second end;
a second transistor of the first conductivity type having a control input receiving a bias potential and a controlled path with a first end connected to the second end of the controlled path of the first transistor and a second end outputting an output signal; and
a first resistor having a first terminal connected to the second end of the controlled path of the second transistor and a second terminal to be connected to a second supply potential;
a capacitor having a first terminal connected to the control input of the first transistor and a second terminal;
a third transistor of a second conductivity type having a control input connected to the second end of the controlled path of the second transistor and a controlled path with a first end to be connected to the second supply potential and a second end;
a fourth transistor of the second conductivity type having a control input connected to the second end of the controlled path of the third transistor and a controlled path with a first end connected to the control input of the third transistor and a second end;
a second resistor connected between the control input of the fourth transistor and the second terminal of the capacitor; and
a third resistor connected between the second end of the controlled path of the fourth transistor and the first terminal of the capacitor.
The third and fourth transistors, together with the second and third resistors form a stabilizing stage to regulate the operating point of the cascode stage. The voltage in the input circuit of the third transistor, that is, the voltage across the first resistor, is used as an input variable, and the current through the first resistor is regulated by the stabilizing circuit. In this way, fluctuations in component parameters, in the temperature, and in the supply voltage are leveled.
Preferably, the control input of the fourth transistor is coupled via a second capacitor to the first supply potential, and/or the other end of the controlled path of the fourth transistor is coupled to the first supply potential via a third capacitor. The second and third capacitors serve in particular to block off high-frequency alternating signals.
Preferably, the bias potential for the control input of the second transistor is generated by a fourth resistor connected between the control input and the other end of the controlled path of the second transistor. To suppress high-frequency alternating components, a fourth capacitor can be connected between the control input of the second transistor and the first supply potential.
On the basis of the stabilizing stage, the operating range of the amplifier circuit of the invention can be varied arbitrarily. On the one hand, it is possible in a simple way to turn the entire amplifier circuit on and off. To do so, the first or second supply potential is simply applied to the node point between the second resistor and the first capacitor via a fifth resistor. If the second supply potential is applied, then the stabilizing circuit is deactivated, and the cascode stage is made currentless via the stabilizing stage. The entire amplifier circuit is thus turned off. If the first supply potential is applied, the stabilizing circuit functions normally. The fifth resistor then serves to decouple the high-frequency signals at the input and is preferably embodied with high impedance.
Along with turning the circuit on and off, the operating point can also be shifted arbitrarily. This is done by varying the resistance of the first resistor. To vary the resistance, preferably a sixth resistor is connected in parallel with the first resistor via a controlled switch. Accordingly, a switchover can be made between two operating points. The operating points can be defined such that with the resistors connected in parallel, the amplifier circuit functions in the normal mode, while if only one resistor is used a state of repose with a predefined resting current is maintained.
The amplifier circuit of the invention is suitable particularly for high-frequency applications. Preferably, the transistors used are of the bipolar type. In this case, one end of the applicable controlled path is formed by the emitter and the other end of the applicable controlled path is formed by the collector, and the control input is formed by the base.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an amplifier circuit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
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patent: 3493882 (1970-02-01), Seader et al.
patent: 4237414 (1980-12-01), Stein
patent: 4940949 (1990-07-01), Landi
patent: 5404585 (1995-04-01), Vimpari et al.
patent: 5986509 (1999-11-01), Lohninger
patent: 0718965A1 (1996-06-01), None
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Japanese Patent Abstract No. 52060047 (Mitsutoshi), dated May 18, 1977.
“Investigation of the Temperature Stability of a Broadband”, A.V. Baranov et al., Telecommunications and Radio Engineering 43, Jul. 1988, No. 7, New York, pp. 148-150.
“Electronic Circuits—Design and Applications”, U. Tietze et al., Springer-Verlag, pp. 439-440.
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Nguyen Khanh Van
Pascal Robert
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