JPH04334104A - Amplifier - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution and to realize an inexpensive amplifier without need for inserting a band pass filter by dividing a band for a gain into a low frequency and a broad frequency. CONSTITUTION:Desired band split is realized by providing a resonance circuit 21 to a base of a transistor (TR) Q2 of a common base amplifier circuit 2 being a component of the amplifier. A broad band gain frequency characteristic covering low and high frequencies of a band is shown as shown in a curve B through the application of current series feedback and voltage parallel feedback. A resonance circuit 21 whose resonance frequency is set to an intermediate frequency f0 of a band is inserted to the base of the TR Q2. Since the impedance of the resonance circuit 21 is increased in the vicinity of the resonance frequency f0, a gain of the common base amplifier circuit 2 is reduced. On the other hand, since the impedance of the resonance circuit 21 is sufficiently reduced at a low frequency or a high frequency apart from the resonance frequency f0, the gain of the common base amplifier circuit 2 is restored to the substantial gain. Thus, the desired low and high frequency is split into two bands.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier, and more particularly to an amplifier for high frequency broadband amplification.

0002

2. Description of the Related Art High frequency loop feedback type broadband amplifiers are well known as this type of amplifier.

[0003] A conventional high frequency loop feedback type wideband amplifier has an inductive load such as a high frequency transformer, in which a first stage common emitter common amplifier circuit and a final stage common base amplifier circuit are connected in cascade. It was something.

In this conventional amplifier, when the gain band is divided into two bands, low and high, and the middle band is cut off, a bandpass filter is installed before or after the amplifier. The desired characteristics were obtained by inserting .

[0005]

[Problems to be Solved by the Invention] In the conventional amplifier described above, when dividing the gain band into a low band side and a high band side,
Since it is necessary to insert a bandpass filter, the circuit configuration becomes complicated and therefore expensive.

An object of the present invention is to eliminate the above-mentioned drawbacks, to provide an amplifier that can divide the gain band into a low band side and a wide band side, eliminates the need to insert a bandpass filter for this purpose, has a simple circuit configuration, and is inexpensive. Our goal is to provide the following.

[0007]

[Means for Solving the Problems] The amplifier of the present invention includes a common emitter amplifier circuit and a common base amplifier circuit connected in cascade and is loaded with an inductive load. It is constructed with a resonant circuit connected between it and ground.

[0008]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the amplifier of the present invention.

The amplifier of this embodiment, as shown in FIG.
A common emitter amplifier circuit 1 consisting of a transistor Q1 and a resistor R1, a common base amplifier circuit 2 connected in cascade to the common emitter amplifier circuit 1 and consisting of a transistor Q2, a resonant circuit 21, and an inductance L2, a resistor R2 and a capacitor C2. The loop feedback circuit 3 is configured to include a loop feedback circuit 3.

In the common emitter amplifier circuit 1, a feedback resistor R1 is connected between the emitter of the transistor Q1 and ground.

The common base amplifier circuit 2 includes a transistor Q
A resonant circuit 21 in which an inductance L1 and a capacitor C1 are connected in parallel to each other is connected between the base of 2 and the ground. An inductance L2 is connected to the collector of the transistor Q2 as an inductive load such as a high frequency transformer.

Next, the operation of this embodiment will be explained.

The amplifier of this embodiment basically has a common emitter amplifier circuit 1 and a common base amplifier circuit 2 connected in cascade, and a current series feedback circuit with a resistor R1 on the emitter side of the transistor Q1, and a resistor R2. This is a high frequency wide band amplifier configured with a voltage parallel feedback circuit formed by a loop feedback circuit 3 consisting of a DC blocking capacitor C2. Desired band division is achieved by providing a resonant circuit 21 at the base of the transistor Q2 of the common base amplifier circuit 2 constituting this amplifier.

FIG. 2 is a diagram showing an example of the gain band characteristics of the amplifier of this embodiment shown in FIG. In FIG. 2, curve A shows the gain frequency characteristic when there is no current series feedback and voltage parallel feedback, that is, when there is no feedback. When current series feedback and voltage parallel feedback are applied, a wide band gain frequency characteristic is shown as shown by curve B that covers the band from the low range to the high range. Here, a resonant circuit 21 whose resonant frequency is set to a frequency f0 in the middle of the band is inserted into the base of the transistor Q2. Then, since the impedance of the resonant circuit 21 increases near the resonant frequency f0, the gain of the common base amplifier circuit 2 decreases. On the other hand, in a low or high frequency range away from the resonant frequency f0, the impedance of the oscillation circuit 21 is sufficiently reduced, so that the gain of the common base amplifier circuit 2 is restored to its original gain. Therefore, as shown by curves C and D in FIG. 2, it is possible to divide the signal into two desired low and high frequency bands.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified in various ways. For example, it is possible to expand the gain frequency band by connecting a capacitor in parallel to a resistor for current series feedback and inserting an inductance in series in the loop feedback circuit for peaking, as long as it does not depart from the spirit of the present invention. Of course.

[0017]

As explained above, the amplifier of the present invention has a resonant circuit connected between the base of the transistor of the common base amplifier circuit and the ground, thereby changing the gain band to the low frequency side and the wide frequency side. There is no need to insert a bandpass filter for this purpose, and an inexpensive amplifier with a simple circuit configuration can be provided.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of an amplifier of the present invention.

FIG. 2 is a diagram showing an example of gain band characteristics in the amplifier of this embodiment.

[Explanation of symbols]

1 Common emitter amplifier circuit 2　　　　　Base grounded amplifier circuit 3 Loop feedback circuit 21 Resonant circuit C1, C2 Capacitor L1, L2 Inductance Q1, Q2 Transistor R1, R2 Resistance

Claims (2)

[Claims] Claim 1: In an amplifier having a common emitter amplifier circuit and a common base transistor amplifier circuit connected in cascade and serving as an inductive load, a resonator connected between the base of the transistor of the common base amplifier circuit and the ground. An amplifier characterized by comprising a circuit. 2. An amplifier characterized in that the resonant circuit includes an inductive element and a capacitive element connected in parallel.