JPS6210906A - Transistor amplifier - Google Patents

Abstract

PURPOSE:To drive sufficiently a transistor (TR) at an output stage by providing the connection of an emitter resistor and 2 level shift diodes in series to an emitter of an emitter follower TR of the next stage. CONSTITUTION:A TR 1 constitutes an input stage common emitter circuit, a TR 2 constitutes a next stage emitter follower circuit and a TR 3 constitutes a common emitter circuit at the output stage using a choke coil as a collector load. In forming the emitter follower where the series connection of the emitter resistor 9 and the level shift diodes 13, 14 is provided to the emitter of the TR 2, even when the resistance of the resistor 9 is decreased, the emitter current flowing to the TR is unchanged. That is, the resistance of the resistor 9 is decreased without changing the emitter current flowing to the TR 2. Thus, the time required for discharge is reduced and the decrease of the base voltage of the TR 3 is attained sufficiently even at a high frequency so as to prevent the decrease in the output power.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a high-power amplifier in the UHF band.

In particular, the present invention relates to a transistor amplifier device suitable for monolithic IC implementation.

[Conventional technology]

In high-output power amplifiers such as booster amplifiers used in the UHF band, an amplifier circuit in which a choke coil is used as the collector load of the output stage has been considered as a means of improving power supply efficiency.

A conventional example of such an amplifier circuit is shown in FIG.

Referring to FIG. 2, in this circuit, the input stage is a transistor 1.
The output stage consists of a common emitter circuit consisting of a transistor 3 using a choke coil as a collector load. Further, a level shift diode 4 composed of a collector-base diode/diode is provided in series with a resistor 10 on the emitter side of the transistor 3 as a means for securing a DC bias voltage between the collector and emitter of the transistor 1. This level shift diode 4 has a direct connection configuration suitable for monolithic IC.

At high frequencies in the UHF band, the input impedance of the output stage transistor 3 becomes low due to stray capacitance of the base electrode.

In the conventional example shown in FIG. 2, the collector output of the input stage transistor is sufficient to drive the output stage transistor 3 at its output limit.

There is a problem in that a large amount of current is required in the front stage circuit (input stage emitter grounded circuit), and the power supply efficiency of the entire amplifier circuit deteriorates. As a means to solve this problem, a circuit as shown in FIG. 6 has been proposed in which an emitter follower circuit is inserted between the input stage and the output stage in order to drive the output stage with low impedance.

[Problem that the invention seeks to solve]

Referring to FIG. 6, when a high-frequency, high-level input signal is input to the input terminal a, and the output stage transistor 3 is driven at a high signal level by the next stage emitter follower circuit, the l-transistor 2 In the direction in which the emitter voltage, that is, the base voltage of the transistor 3 increases, the stray capacitance seen from the base side of the transistor 3 is charged to a positive voltage. This charge is discharged in the direction in which the base voltage of the l transistor 3 decreases.

The time required for discharging at this time is determined by the stray capacitance seen from the base side of the transistor 3 and the time constant of the emitter resistor 9 of the transistor 2.

Therefore, the larger the value of the resistor 9, the longer it takes to discharge. By the way, if this discharge time is long, the operation of lowering the base voltage of the transistor 3 will be insufficient at high frequencies in the UHF band, and as a result, the collector voltage of the transistor 3 will not rise sufficiently, and the power that can be output at low frequencies will be reduced. The output will be lower than that.

The present invention can sufficiently drive the output stage transistor in a UHF band high output amplifier composed of transistors,
It is an object of the present invention to provide a high-output amplifying device having a drive circuit that can output up to the limit of an output stage transistor.

[Failure to solve the problem]

The amplifier device according to the present invention includes an input stage amplification transistor and one
An amplifier circuit comprising a next-stage emitter follower transistor and an output-stage transistor having a choke coil as a collector load, characterized in that an emitter resistor and two level shift diodes are connected in series to the emitter of the next-stage emitter follower transistor. shall be.

〔Example〕

The present invention will be explained below with reference to an embodiment shown in the drawings.

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

Referring to FIG. 1, transistors constitute an input stage emitter grounded circuit, transistor 2 constitutes a next stage emitter follower circuit, and transistor 3 constitutes an output stage emitter grounded circuit using a choke coil as a collector load. By the way, if the transistor 2 is an emitter follower circuit consisting only of an emitter resistor, as in the conventional amplifier circuit example shown in FIG. 3, the value of the resistor 9 must be made small in order to shorten the above-mentioned discharge time. Must be. As a result, the emitter current flowing through the transistor 2 increases, resulting in poor power supply efficiency. However, if an emitter follower is provided in which an emitter resistor 9 and level shift diodes 13, 1.4 are connected in series to the emitter of the transistor 2 as shown in FIG. The current never changes. That is, the value of the resistor 9 can be reduced without changing the emitter current flowing through the transistor 2. Therefore, the time required for the above-mentioned discharge is shortened, and the operation of lowering the base voltage of the transistor 3 can be carried out sufficiently even at high frequencies, and a decrease in output power can be prevented.

Incidentally, in order to obtain power gain in the output stage emitter grounded circuit, the resistance value of the resistor 10 must be small. Furthermore, considering practical current, the voltage difference across the resistor 100 is small, less than one drop of a level shift diode.

Therefore, the number of level shift diodes provided in series with the resistor 9 is set to two, which corresponds to the base-emitter drop of the transistor 3 and the drop of the level shift diode 4.

The resistance value of resistor 9 can be reduced, and it is a monolift IC.
A direct connection configuration suitable for the collector of input stage transistor 1.
The emitter voltage can also be increased.

〔Effect of the invention〕

Since the transistor amplifier device according to the present invention has a drive circuit that can sufficiently drive the output stage transistor, an amplifier device with high power supply efficiency and high output can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an amplifier device according to the present invention, and FIGS. 2 and 6 are circuit diagrams each showing an example of a conventional transistor amplifier device. 1.2.3...Transistor, 4...Level shift diode, 5,6,7,8,9.10...Resistor,
11... Choke coil, 12... Capacitor, 1
3.14... Level shift Figure 1 Figure 2

Claims (1)

[Claims] 1. In an amplifier device in which a next-stage emitter follower circuit is connected to the output of the input stage transistor amplifier circuit, and an emitter-grounded transistor amplifier circuit using a choke coil as a collector load is connected to the output of the emitter follower circuit, the emitter follower circuit is connected to the output of the input stage transistor amplifier circuit. A transistor amplifier device characterized in that a resistor and two diodes are provided in series between the emitter of a constituent transistor and a ground potential.