JPS61103307A - High frequency amplifier circuit - Google Patents

Abstract

PURPOSE:To keep the distortion characteristic with maximum gain excellent by providing a diode whose anode is connected to an AGC input gate between the gate and source of a dual gate FET. CONSTITUTION:The output of the FET to the 1st gate G1 of which an output of an input tuning circuit is impressed and to the 2nd gate G2 of which an AGC voltage is impressed, the amplified output is impressed to the circuit of next stage via a connected between the 2nd gate G2 and the source. Further, the FET and the diode 21 are formed as an integrated circuit. Thus, the AGC voltage input gate voltage is set to an optimum value, 0V independently of the individual difference of circuit elements and an amplifier with an excellent characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to AGC (Auto++
Regarding high frequency amplification circuits with control (automatic gain control) circuits, in detail, dual gate FET (Fiel
This invention relates to the improvement of AGC circuits in high-frequency amplifiers using field-effect transistors (field-effect transistors) and their implementation into semiconductor integrated circuits.

(Conventional Structure and Problems Therein) In recent years, attempts have been made to integrate high-frequency amplifier circuits (hereinafter referred to as RF amplifiers) using GaAs (gallium arsenide) FETs into semiconductors.

RF amplifiers for TV tuners are an example of this.As is well known, TV radio waves use the VHF and UHF frequency bands, and there are two types of RF amplifiers for TV tuners, but in any case, The RF amplifier has
Because the electric field fluctuation of the received radio waves is large, AGC
Since a circuit is added, the distortion characteristics are required to be extremely excellent, and FETs that satisfy these characteristics have recently been increasingly used. In particular, GaAsFETs are used in RF amplifiers in the UHF band due to their various characteristics.

FIG. 1 is an explanatory diagram of a conventional example of a television tuner using the above-mentioned FET as an RF amplifier, particularly showing a bias circuit. Reference numeral Q indicates a dual gate FE7.1 is an input tuning circuit, 2 is an output tuning circuit, and the output (out) thereof is guided to the next stage circuit, for example, a frequency mixing circuit. Further, 3 to 8 are bias resistors, and 9. 10 is a bypass capacitor, 11.12 is a DC blocking capacitor, and 13 is a choke coil. In such a circuit, GaAs is used in the FET.
When an FET is used, the voltage between the second gate G2 and the source 5 of the FET, v, 28, is usually set to approximately +1 to +3 V at maximum gain.

Incidentally, in such a circuit, when a change occurs in the current between the drain and source of the FET Q, the voltage drop across the resistor 7 fluctuates. Therefore, the voltage V between the second gate and the source at maximum gain without AGC. , changes, resulting in overall changes in circuit gain and instability in distortion characteristics. In conventional circuits in which one circuit is formed from individual elements, it is possible to overcome such problems in high-frequency amplification circuits through adjustment or other methods, but when converting open circuits into semiconductor integrated circuits, it is necessary to use a monolithic circuit, especially around the FET. Gathered in'
If an attempt is made to simplify the assembly by increasing the t %+ product, a big problem arises.

Additionally, as mentioned above, the voltage VO2M between the second gate and source of fET is usually set to the maximum gain, that is, in the range of approximately +1 to +3 V when no AGC voltage is applied, but it is possible to maintain the gain. In this case, it has been experimentally confirmed that the distortion characteristics are better when the value is set near Ov.

(Objective of the Invention) The present invention solves the above-mentioned problems that hinder monolithic integration of the main parts of high-frequency amplifier circuits, and also maintains good distortion characteristics even at maximum gain based on new experimental results. The present invention provides a high frequency amplifier circuit whose main parts are integrated circuits.

(Structure of the Invention) In order to achieve the above object, the present invention uses a dual gate FET as a transistor for applying an AGC voltage in a high frequency amplifier circuit with an AGC circuit, and selects, for example, a second gate as a gate for applying an AGC voltage. , a diode j is connected between this second gate and the source,
provided so as to connect the anode to the second gate side, and
These FET and diode parts are constructed as a semiconductor integrated circuit.

(Explanation of Examples) The present invention will be explained below by way of an example.

FIG. 2 shows a main circuit of an embodiment of the present invention, which is a bias circuit of a high frequency amplifier circuit, and the portion surrounded by a dotted line is monolithically integrated with a semiconductor, and includes a dual gate FET and a diode 21, which is a feature of the present invention. The anode is connected to the second gate G2 side of the Q FET. Other resistors, capacitors, etc. have large element shapes and are difficult to make monolithic.

It is attached separately. The output of the input tuning circuit is applied to the first gate G8 as before, and the output of the input tuning circuit is applied to the first gate G8.

The amplified output is controlled by the AGC voltage applied to.

The voltage is applied to the next stage circuit via the capacitor 22 as in the conventional circuit.

In this way, between the AGC input gate G2 and the source.

In the circuit of the present invention provided with the diode 21 whose anode is connected to the 62 side, the voltage VO2 between the second gate G8 and the source is
The value of g is clamped to the built-in voltage of diode 21. However, at this time, it is necessary to set the value of the resistor 23 to a sufficiently large value, otherwise the second gate and source S
The leakage current between the two increases, which becomes a problem. Note that the capacitor 24 is used as a bypass for the second gate G2.

FIG. 3 shows an example in which the present invention is implemented in a television tuner. UHF and VHF television waves are
After passing through the respective input tuning circuits 31 and 32, the signals are added to high frequency amplifier circuits 33 and 34, which are formed by monolithically integrating GaAs FETs, surrounded by a dotted line.

Note that the selection of the high frequency amplifier circuits 33 and 34 is performed by controlling the switching diodes 35 and 35'.

36 and 37 are diodes for keeping the AGC voltage application d gate in each FET of the UHF and VHF high frequency amplification circuits 33 and 34 at approximately O potential at maximum gain, and this also serves as gate protection. It is formed by a p+-n junction. The present invention can be achieved even if the diodes 36 and 37 are configured with Schottky diodes, similar to the switching diodes 35 and 35' for selecting the UHF and V) IF high frequency amplifier circuits.

Further, resistors 38 and 39 of the AGC circuit are the second gates of each FET.

In this example, in order to prevent an increase in leakage current between the sources, 100 and 100 Ω were selected, respectively.

This example achieved excellent distortion characteristics with an interference signal level of 90 dB or more in the maximum gain state.

(Effects of the Invention) As is clear from the detailed explanation above, the present invention provides a high frequency amplifier circuit using a dual gate FET.
A diode is connected between the second gate, which is the AGC voltage input gate of the ET, and the source so that the second gate side becomes the anode side, and these FET and diode parts are monolithically integrated into a semiconductor circuit. Since the AGC voltage input gate voltage can be set to the optimal Ov regardless of individual differences in circuit elements, it is not only possible to obtain an amplifier with good characteristics, but also to reduce the number of parts and simplify the peripheral circuitry. For example, it can be used in a television tuner to great advantage.

[Brief explanation of drawings]

! 11. FIG. 1 is a high frequency amplification circuit diagram of a television tuner explaining a conventional example, FIG. 2 is an AGC circuit diagram of a high frequency amplification circuit according to the present invention, and FIG. 3 is a circuit diagram in which the present invention is applied to a television tuner. Q...Dual gate FET, 1...Input tuning circuit, 2...Output tuning circuit, 21, 36, 37.
...Diode, 23...Second gate AGC resistance, 3
1...UHF input circuit, 32..., VHF input circuit. Patent applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) In a high-frequency amplifier circuit that uses a dual-gate FET and applies an AGC voltage to one gate, a diode is connected between the one gate to which the AGC voltage is applied and the source so that the anode is on the gate side. A high frequency amplification circuit characterized by: (2) The circuit of the dual gate FET and diode portion is formed by a semiconductor integrated circuit,
A high frequency amplifier circuit according to claim (1).