Amplifying circuit for an integrated circuit with low-noise char

Details Amplifying circuit for an integrated circuit with low-noise char Amplifying circuit for an integrated circuit with low-noise char

1995-02-16

1997-07-15

Mottola, Steven J.

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330311, H03F 345

Patent

active

056487436

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an amplifying circuit. More particularly, it relates to an amplifying circuit, which is suitable for an integrated circuit with the low-noise, high gain and low power consumption characteristics.
2. Description of the Prior Art
In recent years, movable communication terminals, such as a portable telephone, are spreading extensively. According to this fact, there is a demand for making a circuit of high frequency characteristic used for movable communication terminals, such as a portable telephone, micro-miniaturized. Moreover, there is also a demand for making an amplifying circuit, which has been composed of individual parts integrated.
Further, most of the movable communication terminals, such as a portable telephone, are driven with batteries. Accordingly, it is required to reduce current consumption for lengthening the period of life of a battery.
FIG. 19 is one structural example of a conventional transistor amplifying circuit.
In the diagram, a constant-current source I.sub.0 and a condenser C.sub.E connected to the constant-current source in parallel are connected to the emitter of a first transistor Q.sub.1. Also, a voltage source V.sub.CC is connected to the collector of the transistor Q.sub.1, via a load-resistor R.sub.C. A bias voltage V.sub.BB is supplied to the base of the transistor Q.sub.1.
Further, the conventional transistor amplifying circuit includes a second transistor Q.sub.2, of which the collector is connected to the voltage V.sub.CC and the emitter is connected to a resistor R.sub.E. Furthermore, an output from the collector of the first transistor Q.sub.1 is connected to the base of the second transistor Q.sub.2.
Moreover, the base of the transistor Q.sub.1 is used as an input terminal of a high-frequency signal, and the emitter of the transistor Q.sub.2 is used as an output terminal of the high-frequency signal. In this circuit, the transistor Q.sub.1 is an amplifying circuit of an emitter grounded type, and the transistor Q.sub.2 forms an emitter follower circuit for matching impedance with the circuit arranged behind the emitter follower circuit.
FIG. 20 further illustrates a structural example of the conventional transistor amplifying circuit including a bias circuit section 21. As is apparent from FIG. 20, the transistor amplifying circuit is composed of the amplifying circuit section 20 and the bias circuit section 21 for supplying a bias voltage required to each portion of the amplifying circuit.
In FIG. 20, the amplifying circuit section 20 corresponds to the transistor amplifying circuit shown in FIG. 19. The amplifying circuit section has a transistor Q.sub.3 and a resistor R.sub.E1, instead of the current source I.sub.0 shown in FIG. 19 and a transistor Q.sub.1 and a resistor R.sub.E2, instead of the resistor R.sub.E shown in FIG. 19.
The bias circuit section 21 shown in FIG. 20 supplies bias current source, that is, base potential of the transistors Q.sub.1, Q.sub.2, Q.sub.3, and Q.sub.4, required for the amplifying circuit section 20 positioned on the right side of the circuit of FIG. 20. The bias circuit section 21 is composed of a 2-line structured constant current circuit which has three transistors Q.sub.B1 to Q.sub.B3, and three transistors Q.sub.B4 to Q.sub.B6 laid lengthwise, respectively. Further, the transistors Q.sub.B2 to Q.sub.B3 and Q.sub.B5 to Q.sub.B6 function as diodes by connecting the bases and the collectors in common.
Meanwhile, in the transistor amplifying circuit of an emitter grounded type shown in FIGS. 19 and 20, noise amount (NF) of the circuit is generally proportional to the resistance of base resistor R.sub.b of a transistor used. Further, it is generally known that noise amount (NF) is inversely proportional to the second power of f.sub.t (cutoff frequency) of a transistor.
In FIGS. 19 and 20, a resistor R.sub.C is a collector load resistor of transistor Q.sub.1, which is an amplifying element. At the same time, the resistor R.sub.C also has a function

REFERENCES:
patent: 4940949 (1990-07-01), Landi

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