JPH0294908A - Fet mixer - Google Patents

Abstract

PURPOSE:To miniaturize a circuit and to heighten the performance of a mixer characteristic at the same time by making the threshold voltage of an FET(field effect transistor) into a specific value and operating a gate bias and a drain bias under a grounded state. CONSTITUTION:In the FET mixer to input a high frequency RF signal to a gate, input a local oscillating LO signal to a drain, and take out an intermediate frequency IF signal from the drain, for an FET 10, its threshold voltage is set to 0 to -0.3V, preferably -0.1 to -0.3V, and the RF signal is inputted through an RF band matching circuit 2 to the gate of the FET 10. At this time, the RF band matching circuit 2 is connected to a grounding line 11 and gives 0V to the FET 10 as gate voltage. Further, the circuit is composed by setting the drain bias to 0V. Consequently, since both the gate and the drain are DC-grounded and operated with no power source, a power source and a bias circuit accompanying the power source can be omitted. Thus, the performance of the mixer can be heightened, and the circuit can be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency mixer that uses FETs (field effect transistors) as mixing elements and handles signals in the microwave band, for example.

Conventional Blood DistortionIn recent years, mixers have been developed that use FETs, which have advantages such as amplification, instead of diodes, which have been traditionally used as frequency conversion elements for microwave band receivers such as satellite communications. ing.

The circuit configuration of the FET mixer is RF (high frequency), L
There are several formats depending on which terminal of the FET the O (local oscillation) and IF (intermediate frequency) signals are input and output from.

For example, there is a drain mixer type (hereinafter, this type of FET mixer is simply referred to as an rFET mixer) that inputs an RF signal from the gate of the FET, inputs an LO signal from the drain, and extracts an IF multiplied signal from the drain. In the FET mixer, the drain bias at which mixer characteristics such as noise figure and conversion gain are best is near Ov. In this bias state, the FET is in the non-saturation region, so the output impedance of the FET at the drain end becomes small. This has the advantage of making it easy to match the input and output of the LO and IF multiplier signals, making it a promising mixer circuit type in the future. 1
It is one.

FIGS. 3(a) and 3(b) show the circuit configuration of a conventional FET mixer and the bias state B' of the FET during mixer operation. In FIG. 3(a), 1 is a mixing FET, 2 is an RF band matching circuit composed of strip lines, 3 is a choke coil for applying gate bias Vg, and 4 is a mixing FET.
is an IF band low-pass or band-pass filter, and 5 is an I
F band matching circuit, 6 is LO band band pass filter, 7 is L
In the O-band matching circuit, 8 is a choke coil for applying drain bias.

This conventional example shows a case where the drain bias is set to Ov, which provides good mixer characteristics.

FIG. 3(b) shows the drain current vs. LO voltage VtO! The change in d is shown using the gate voltage Vg as a parameter, and is shown by a solid line in FIG. 3(b).

Mixer characteristics such as noise figure and conversion gain are best near V g = V th + 0.2V. Here, vth
represents the threshold voltage of the FET.

However, as a mixer FET, there are the following problems.In other words, FETs for small signal and low noise are used for -a, and these FETs are usually gate biased. Since it is designed to be used by applying a negative voltage as
There are few that have a shallow dark value voltage such as h>-0.3V, so as can be seen from Figure 3 (a) and (b),
In order to obtain the best mixer characteristics, in the conventional example shown in Fig. 3, it is necessary to apply a negative gate bias from the outside.
There is a problem in that a bias source and a bias circuit are newly required, and the circuit becomes larger in size.

The present invention has been made in view of the above points, and an object of the present invention is to provide a novel FET mixer that eliminates the above conventional problems.

Means for Accomplishing the Problems In order to achieve the above object, the present invention provides an FET mixer that inputs the LO signal from the RF multiplication signal gate and the LO signal from the drain, and takes out the IF multiplication signal from the drain.
The threshold voltage of T is O ~ -0,39, preferably -0,1 ~
-0.3v, and the drain and gate biases of the FETs are set to a direct current grounding state to perform a mixing operation.

Figure 2 shows the results of measuring the noise figure and conversion gain by changing the gate voltage when the FET mixer is optimized using a tuner. (d)
represents the conversion gain. vth=-0,17V,
V th = -0,77V (7) Each FET! , 1m vs. city, both around V g = V th + 0.2V,
The mixer characteristics are the best. Also, approximately V g = V
It can be seen that within the range of th+0.1 to V Lh 10.3 V, good characteristics are maintained in both the noise figure and the conversion gain. Also, in terms of noise figure, V g = V Lh - V
The fluctuation in the range of Lh +0.3V remains at about 0.5dll, and low noise is maintained. Moreover, the gate voltage Vg
It has a positive conversion gain even if the region of is expanded to the threshold voltage vth, and maintains its superiority over the diode mixer which cannot obtain a positive conversion gain. Therefore, the FET is operated with the gate bias Vg set to Ov, and this FET
If the threshold voltage vth of is set to θ~-〇, 3v, the noise figure.

Good characteristics such as conversion gain can be obtained. Further, it is possible to create a circuit configuration that does not require a power supply for bias, and it is possible to achieve high performance of the mixer and miniaturization of the circuit at the same time.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1(a) shows a circuit configuration diagram of a FET mixer in an embodiment of the present invention. The numerals assigned to each element in FIG. 1(a) indicate the same operations as those in FIG. 3(a).

Items with the same function are indicated with the same reference numerals.

In FIG. 1(a), FETl0 has a dark value voltage vth of θ to 0.3ν from the measurement results of the mixer characteristics shown in FIG.
, preferably -0,1 to -0,3V. The above FET via the RF double signal RF band matching circuit 2
It is input to the gate of l0. Here, RF band matching circuit 2
is connected to the ground line 11 and applies Ov as the gate voltage Vg to the FET10, unlike the conventional circuit. Regarding the drain, the circuit is configured with the drain bias set to Ov, similar to the conventional drain mixer type.

As mentioned above, in this example, both the gate and drain are DC grounded to operate without power supply.
A power supply and an associated bias circuit can be omitted, and the circuit can be miniaturized.

FIG. 1(b) shows the LO of FET10 constituting this embodiment.
The change in drain current 1d with respect to lightning voltage is expressed as gate voltage Vg
is shown as a parameter.

As mentioned above, in the circuit of this example, the threshold voltage vth of FETl0 is around O~-0.3v, and as shown in FIG.
The mixer operates under a gate bias Ov (drain bias also OV) shown by a solid line. As is clear from FIG. 2, in this embodiment, the bias state is optimal for the mixer characteristics, so the mixer can achieve high performance even when operated without a power source as shown in FIG. 1(a).

This example is an example of a DC grounding method for a gate when an RF band matching circuit is configured with a strip line.
As long as matching in the F band is achieved, any method may be used for grounding the gate, and it goes without saying that the matching circuit is not limited to one using a strip line.

As described above, according to the present invention, F is used as a mixing element.
Using an ET, in the mixer that inputs the RF multiplied signal from the gate of the 3i FET, inputs the LO multiplied signal from the drain, and takes out the IF multiplied signal from the drain, select the dark value voltage of the FET, and set the gate bias and drain bias to the grounded state. By operating the mixer as a controller, good mixing characteristics can be obtained, making it possible to reduce the size of the circuit due to power-free operation and improve the performance of the mixer characteristics at the same time, simplifying the configuration of equipment such as microwave band receivers. can be converted into

[Brief explanation of drawings]

FIG. 1(a) is a circuit configuration diagram of an FET mixer in an embodiment of the present invention, and FIG. 1(b) is a circuit diagram of a FET mixer in an embodiment of the present invention.
Figure 2 shows the relationship between LO lightning voltage and drain current.
Figure 3(a) is a diagram of the relationship between the noise figure and conversion gain of the mixer and the gate voltage. Figure 3(a) is a circuit diagram of the FET mixer in the conventional example. Figure 3(b) is the LO lightning voltage drain current of the FET in the conventional example. It is a relationship diagram. 2-.-RF band matching circuit. 4.-IF band collo-pass filter is a band-pass filter. 1F band matching circuit LO band bandpass filter. LO band matching circuit. Choke coil for applying drain bias. Mixing FET, 11-/Ground line. Figure 11(a)

Claims (1)

[Claims] (1) In a FET mixer that inputs a high frequency signal to the gate, inputs a local oscillation signal to the drain, and takes out an intermediate frequency signal from the drain, the threshold voltage of the FET is set from 0 to -
A FET mixer characterized in that the mixer is operated by setting the voltage to 0.3V and connecting the drain bias and gate bias to a DC ground state.