JPS63153902A - Amplifier with low noise - Google Patents

Abstract

PURPOSE:To take matching with an input impedance and to obtain a characteristic with a superior noise factor, by inserting a varactor diode between the source electrode of a FET and the earth, and controlling the bias current of the varactor diode. CONSTITUTION:The FET3 is inserted and connected between input/output matching circuits 1 and 2, and the impedance 4 is connected in series to the varactor diode 5, and the source electrode of the FET3 is arranged through those parts. And a control part 6 to control the bias voltage of the diode 5 is provided, and controls reactance electrically between the source and the earth from the outside. In such a way, the input impedance of the FET3 and a source impedance in which the noise factor is minimized are set so as to form almost complex conjugate. Therefore, the matching between an amplifier and the input impedance can be taken, and also, it is possible to easily control a low noise amplifier with the superior noise factor with electrical control from the outside.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low-frequency amplifier, and more particularly to a low-noise FF amplifier using a field effect transistor as a dynamic element.

[Prior Art] Conventionally, this type of low-noise amplifier has the following characteristics, as shown in FIG.
A field effect transistor 3 is inserted and connected between the input and output matching circuits 1 and 2, and the source impedance 4 of the field effect transistor 3 is controlled by controlling the length of the bonding wire on which the source electrode is installed. The human input impedance of the effect transistor 3 was set to be 81 element conjugate with the source impedance that minimizes the noise finger fiNF, and was configured to match the input impedance and have good noise figure NF characteristics.

[Problems to be solved] In the conventional low noise amplifier described above, in order to control the impedance 4 of the source, it is safe to adjust the length of the bonding wire to fllm, but there is a 1-1 variation in practical use and control is difficult. The drawback was that it was not easy.

Therefore, an object of the present invention is to provide a low-noise amplifier whose input impedances are matched and whose noise figure NF is good.
The purpose is to easily realize this by using 1jlll.

[Solving Problems] In order to achieve the above-mentioned object, the present invention provides a low-noise amplifier in which a field-effect transistor is inserted and connected between an input impedance circuit and an output impedance circuit. A varactor diode is inserted and connected between the electrode and the ground terminal, and the bias voltage of this varactor diode is controlled to make the input impedance of the field effect transistor and the source impedance that minimizes the noise figure NF approximately a complex conjugate. This configuration includes a control unit that sets the following.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a high frequency equivalent circuit of a low noise amplifier according to an embodiment of the present invention. The difference between the low noise amplifier shown in the figure and the conventional configuration shown in FIG. 2 is that the impedance 4 and the varactor diode 5 are connected in series, and the source electrode of the field effect transistor 3 is connected through these. In addition, a control section 6 for controlling the bias voltage of the varactor diode 5 is provided, and the actance between the source and the ground is electrically controlled from the outside.

By controlling the bias voltage of the varactor diode 5 by the control unit 6, the input impedance of the field effect transistor 3 and the source impedance are set to be approximately complex conjugate so that the noise wt number NF is minimized. ing.

Figure 3 shows the human impedance a of a field effect transistor over 2GH3 to 180H3.

The source impedance b at which the noise figure NFi is small is expressed on a Smith chart. As shown in FIG. 3, by changing the bias voltage of the varactor diode 5, it is easily possible to make the input impedance of the field effect transistor 3 almost complex j Become.

As described above, according to this embodiment, by external electrical control, the input impedance of the field effect transistor 3 and the source impedance that minimizes the noise figure NF can be set in a substantially complex conjugate relationship. Unlike conventional methods, the complicated operation of managing the length of the bonding wire for installing the source electrode is not required, and the control can be easily and accurately performed.

Note that the present invention is not limited to the first embodiment,
Various modified implementations are possible within the scope of the invention.

[Effects of the Invention] As explained above, the present invention provides a low-noise amplifier using a field-effect transistor, in which the source electrode is installed with an appropriate impedance and a varactor diode in series, thereby reducing the human impedance of the field-effect transistor. , the source impedance that makes the noise finger fiNFl small can be made electrically approximately complex conjugate from the external fi.

Therefore, a low-noise amplifier with matching input impedance and good noise finger @NF can be easily realized by external electrical control.

[Brief explanation of the drawing]

Figure 1 is a high frequency equivalent circuit diagram of an embodiment of the present invention, Figure 2 is a high frequency equivalent circuit diagram of a conventional low sweat amplifier, and Figure 3 is
It is a Smith chart of the input impedance of a field effect transistor and the source impedance which becomes the NF minimum. l: input matching circuit 2, output matching circuit 3, near 1 (field effect transistor 4: source impedance 5: varactor diode 6: control section

Claims (1)

[Claims] A low noise amplifier including a field effect transistor inserted and connected between an input impedance circuit and an output impedance circuit, a varactor diode inserted and connected between a source electrode of the field effect transistor and a ground terminal;
The present invention is characterized by comprising a control unit that controls the bias voltage of the varactor diode so that the input impedance of the field effect transistor and the source impedance at which the noise figure is minimized are approximately complex conjugate. low noise amplifier.