JPH0918246A - High frequency amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency amplifier circuit which can suppress the undesired signals and also can ensure its stable operation by adding an attenuator between the amplifier circuit and a filter. SOLUTION: This amplifier circuit consists of a transistor amplifier 11 where one of both resistors is used as a power terminal with the other connected to its collector, an attenuator 30 consisting of a resistor 31 which is connected to the collector output terminal of the amplifier 11, and a filter 20 which is connected to the other terminal of the attenuator 30. The filter 20 uses an LPF where a filter connected to a capacitor having grounded one of its both terminals is connected in multistage to the output terminal of a parallel resonance circuit consisting of a coil and a capacitor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency amplifier circuit having a filter at the output end of the amplifier circuit.

[0002]

2. Description of the Related Art Conventionally, high-frequency amplifier circuits have been used in all high-frequency circuits such as tuners for televisions, and in recent years it has become more and more desirable to improve their performance.

A conventional high frequency amplifier circuit will be described below. FIG. 3 shows a high-frequency amplifier circuit provided with a filter at the output end of a conventional grounded-emitter amplifier circuit. FIG.
In, 11 is a transistor, 12 is a transistor 1
A voltage dividing resistor for applying a bias voltage to the base of 1.
Reference numeral 3 is a collector resistance, 14 is an emitter resistance, 15 is a bypass capacitor for flowing an AC component of the emitter, 19 is an external feedback circuit for canceling internal feedback of a transistor including a resistor 16, an inductor 17 and a capacitor 18. Yes, the amplifier circuit 10 is configured as described above. 2
0 is inductors 21, 25, 28 and capacitors 22, 2
A polar low-pass filter composed of 3, 24, 26, 27, and 29.

The operation of the high-frequency amplifier circuit configured as described above will be described below.

First, a high-frequency signal input from the first input terminal 1 is amplified by a transistor,
Is output to the output terminal 2. By passing this output signal to the low-pass filter 20, unnecessary harmonics generated in the transistor 11 can be removed or the low-pass filter 20 can be removed.
The disturbance generated in the latter stage is prevented from leaking to the input stage through the transistor 11. Then, only the amplified frequency signal is transmitted to the subsequent circuit. In this conventional example, the out-of-band attenuation in the low pass filter 20 is designed to be large. As shown in FIG. 2B, it is -25 dB or more.

Further, when a mixer is provided in the subsequent stage, if the out-of-band attenuation of this low pass filter is small,
A local oscillation signal with a high signal level leaks to the transistor input terminal through the mixer. Therefore, it is necessary to increase the out-of-band attenuation.

[0007]

However, in the above-mentioned conventional configuration, when a low-pass filter having a sharp attenuation characteristic is directly connected to a stage subsequent to the grounded emitter transistor amplifier, the collector terminal of the transistor and the ground are disconnected at a frequency outside the band. At the series resonance frequency of the low-pass filter, there is a problem that the high-frequency amplifier circuit 10 easily oscillates due to the AC low impedance.

The present invention is intended to solve the above problems, and an object thereof is to provide a high-frequency amplifier circuit in which a transistor does not oscillate even if a low-pass filter having a large out-of-band attenuation is provided in the collector output stage of the transistor. To do.

[0009]

In order to solve this object, a high-frequency amplifier circuit of the present invention comprises a resistor having a voltage dividing resistor for determining a base voltage connected to a base terminal and an emitter terminal of which one terminal is grounded and an alternating current. A transistor having a configuration in which the other side of the bypass capacitor is connected, each terminal of the circuit in which a resistor, a capacitor, and an inductor are connected in series is connected to the base and collector, and the other of the resistors having one as a power supply terminal is connected to the collector. An attenuator composed of an amplifier, a resistor connected to the collector output terminal of the transistor amplification circuit, and the attenuator, in which the output terminal of a parallel resonance circuit including a coil and a capacitor is connected to a capacitor whose other terminal is grounded. This is a configuration in which filters are cascade-connected to a low-pass filter having a three-stage configuration.

[0010]

With this configuration, since there is an attenuator composed of a resistor, even if a signal matching the resonance frequency of the low-pass filter is input to the filter with a large out-of-band attenuation, the emitter-grounded transistor's collector and ground are connected. The AC impedance does not become small enough to satisfy the oscillation condition. That is, unnecessary harmonics generated in the transistor and unnecessary signals mixed from the output end of the filter can be removed, and only the desired frequency signal can be output in a stable state.

[0011]

【Example】

(Embodiment 1) A first embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 10 is a grounded-emitter amplifier circuit, 11 is a transistor, 12 is a dividing resistor for applying a bias voltage to the base of the transistor 11, 13 is a collector resistor, 14 is an emitter resistor, and 15 is an AC signal. A capacitor 19 for bypassing is a feedback circuit for canceling internal feedback of the transistor, and is composed of a resistor 16, an inductor 17, and a capacitor 18. Reference numeral 30 denotes an attenuator circuit composed of a resistor 31, 20 is a three-stage low-pass filter composed of a coil and a capacitor, 1 is an input terminal of the amplifier circuit, 2 is an output terminal of the amplifier circuit, 5 is an input terminal of the attenuator circuit, 6 Are output terminals of the attenuator circuit, input terminals of the low-pass filter, 4
Is an output terminal of the low-pass filter circuit.

The operation of the high frequency amplifier circuit configured as described above will be described. First, a frequency signal input from the first input terminal 1 is amplified by the grounded-emitter transistor 10 and output from the output terminal 2 which is a collector. Then, it is input to the low-pass filter via the attenuator 30 composed of a resistor. Even if a signal matching the resonance frequency of the low-pass filter is mixed into the filter, the attenuator 30 prevents the impedance between the collector of the transistor and the ground from being lowered in terms of AC, so that the transistor operates stably in the high frequency band. You can

The characteristics of the S11 Smith chart according to this embodiment and the characteristics of the conventional S11 Smith chart are shown in comparison with FIG.

As is apparent from FIG. 2, the high frequency amplifier circuit according to the present embodiment is excellent in that it stably operates not only for signals within the band up to 600 MHz but also for signals outside the band above that. You can get the effect.

As described above, according to the present embodiment, by providing the attenuator 30 by the resistance between the amplifier circuit 10 and the low-pass filter 20 having a large out-of-band attenuation amount, unnecessary harmonics generated in the transistor 11 are eliminated. It is possible to remove the interfering wave mixed from the output terminal 4 of the low-pass filter and output the frequency signal in the desired high frequency band in a stable state.

In the first embodiment, the attenuator 30 has a resistor arranged in series between the collector output terminal 2 of the transistor and the input terminal 3 of the low-pass filter 20, but the attenuator 30 has the configuration of one terminal. To the other terminal of the first resistor having an input terminal connected to the other terminal of the second resistor having one terminal grounded, and the other terminal of the third resistor having one terminal an output terminal. It goes without saying that it may be a tee type.

In the first embodiment, the attenuator 30 has a resistor arranged in series between the collector output terminal 2 of the transistor and the input terminal 3 of the low pass filter 20. However, the attenuator 30 has one terminal. Is connected to the input terminal of the first resistor having the other terminal as the output terminal and the other terminal of the second resistor whose one terminal is grounded, and the other terminal of the third resistor whose one terminal is grounded. It goes without saying that the other terminal may be connected to the output terminal of the first resistor to be a pie type.

As described above, by using a tee type or a pie type as an attenuator instead of a simple resistor, impedance matching viewed from the side of the amplifier circuit and the low pass filter can be easily obtained.

[0020]

As described above, according to the present invention, the voltage dividing resistor for determining the base voltage is connected to the base terminal, the emitter terminal is connected to the resistor having one terminal grounded, and the other of the AC bypass capacitors is connected to form the resistor. A transistor amplifier having a configuration in which each terminal of a circuit in which a capacitor and an inductor are connected in series is connected to a base and a collector, and the other of the resistors having one as a power supply terminal is connected to the collector, and the collector output of the transistor amplification circuit. Multi-stage connection of an attenuator consisting of a resistor connected to the terminal and a filter in which the other terminal of the attenuator is connected to the output terminal of the parallel resonance circuit consisting of a coil and a capacitor and the other terminal is grounded. By configuring the low-pass filters that are connected in multiple stages, Be provided with a larger low-pass filter of band attenuation to the subsequent register amplifiers, it can realize excellent high-frequency amplifier circuit can be stably operated transistor in a broadband.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a high frequency amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of a high frequency amplifier circuit according to an embodiment of the present invention and a characteristic diagram of a conventional high frequency amplifier circuit.

FIG. 3 is a circuit diagram of a conventional high frequency amplifier circuit.

[Explanation of symbols]

 1 Input terminal of amplifier circuit 2 Output terminal of amplifier circuit 3 Input terminal of filter 4 Output terminal of filter 5 Input terminal of attenuator 6 Output terminal of attenuator 7 Power supply 10 Amplifier circuit 11 Transistor 12 Dividing resistor for bias voltage 13 Collector resistor 14 Emitter Resistor 15 Bypass capacitor 16 Resistor 17 Inductor 18 Capacitor 19 Feedback circuit 20 Filter circuit 21,25,28 Inductor 22,23,24,26,27,29 Capacitor 30 Attenuator 31-37 Resistor

Front page continued (72) Inventor Fumihiro Kameoka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A transistor amplifier circuit for amplifying a high-frequency signal, an attenuator composed of a resistor connected to an output terminal of the transistor amplifier circuit, and a filter connected to the attenuator, the filter being a coil. A high-frequency amplifier circuit characterized in that it is a low-pass filter in which a capacitor in which the other terminal is grounded is connected in multiple stages to the output terminal of a parallel resonance circuit composed of capacitors. 2. An emitter-grounded transistor amplifier circuit for amplifying a high-frequency signal, an attenuator composed of a resistor connected to the collector output terminal of the transistor amplifier circuit, and the other terminal of the attenuator. A high-frequency amplifier circuit composed of a low-pass filter in which a filter in which a capacitor having the other terminal connected to the ground is connected in multiple stages is connected to the output terminal of a parallel resonance circuit composed of a coil and a capacitor. 3. A transistor amplifier circuit, wherein a voltage dividing resistor for determining a base voltage is connected to a base terminal, and a resistor having one terminal grounded to the emitter terminal of the transistor and the other of an AC bypass capacitor are connected to the resistor. The respective terminals of a circuit in which the capacitor and the inductor are connected in series are connected to the base and collector of the transistor, and the other of the resistors having one as a power supply terminal is connected to the collector of the transistor. The high frequency amplifier circuit according to claim 2.