JPS61285807A - Frequency converter - Google Patents

Abstract

PURPOSE:To simplify the constitution of a matching circuit by connecting a source of an FET to common, applying an intermediate frequency signal to a gate, applying a local oscillation signal to a drain and outputting a frequency conversion output signal from the drain. CONSTITUTION:An intermediate frequency signal is inputted to a gate G of a microwave FET 1, a source S is connected to common, a local oscillation signal is inputted to a drain D and signal subjected to frequency conversion is led out of the drain D. The intermediate frequency signal is fed to the gate G via a matching circuit 2 and a prescribed gate bias voltage Vg is fed to the gate G. Further, the local oscillation signal is fed to the drain D via a circulator 4 and the matching circuit 3, and the signal subjected to frequency conversion by the FET 1 is outputted via matching circuit 3 and the circulator 4.

Description

[Detailed Description of the Invention] [Summary] A microwave field effect transistor is used as a frequency conversion element, a relatively low frequency signal is input to the gate, a high frequency local oscillation signal is input to the drain, and from the drain. It outputs frequency-converted signals in ultra-high frequency bands such as microwaves and quasi-millimeter wave bands, improves isolation, and simplifies input/output matching circuits.

[Industrial application field]

The present invention relates to a frequency converter for microwave and sub-millimeter wave bands using microwave field effect transistors.

Advances in semiconductor technology have led to GaAs field-effect transistors (
FET (hereinafter abbreviated as FET) was developed, and Schottky-barrier diode (Schottky-barrier diode) was developed.
It has become possible to use it as a frequency conversion element in the microwave band instead of a diode, a varactor, etc.

[Conventional technology]

Conventionally, microwave diodes such as Schottky barrier diodes and varactors have been commonly used as frequency conversion elements in the microwave band. However, as mentioned above, microwave band FETs have been developed and are now used in microwave band amplifiers, etc., and these FETs can be used instead of microwave diodes in frequency converters. was considered. In that case, considering the Sirotchi barrier diode as a frequency conversion element, Ga
It has been proposed to use an AsFET Schottky barrier gate. FIG. 7 shows a conventional frequency converter using FETs, 31 is a QaAsFET, 32 is a hybrid circuit, 33 is an input terminal for a local oscillation signal of frequency fL (for example, 12 GHz), and 34 is an input terminal for a local oscillation signal of frequency f□ (for example, I
35 is an output terminal for the intermediate frequency signal (GHz),
36 is an input terminal for gate bias voltage Vg, 37 is an input terminal for input bias voltage Vd, and 38.39 is a choke coil.

The GaAsFET 31 has a Schottky barrier gate, and has a local oscillation signal of frequency f and a frequency f
The intermediate frequency signal of □ is connected to G via the hybrid circuit 32.
aAs Input to gate G of FET31, frequency fL
An output signal of ±f4 is output from the drain D to the output terminal 35. In this case, a conversion gain can be obtained by appropriately selecting the gate bias voltage Vg and drain bias voltage Vd.

FIG. 8 shows a conventional example using a diode as a frequency conversion element, where 41 and 42 are microwave diodes such as varactors, 43 is a rough trace type hybrid circuit, 44 is an in-phase hybrid circuit, and 45 is a microwave diode such as a varactor.
is an input terminal for intermediate frequency signals, 46 is an input terminal for local oscillation signals, 47 is an output terminal for frequency-converted signals, 48-
50 is a capacitor, 51.52 is a short stub for high frequency grounding, 53 to 55 are choke coils, 56
．． 57 is a terminal for applying bias voltages +V and -V.

The intermediate frequency signal is applied to the hybrid circuit 44 from the input terminal 45 via the capacitor 48, divided in phase, and applied to the diodes 41 and 42. Further, the local oscillation signal is applied to the terminal (2) of the rough trace type hybrid circuit 43 via the capacitor 50.

This rough trace type hybrid circuit 43 distributes a signal from terminal ■ to terminals ■ and ■, and terminal ■ serves as an isolation terminal for terminal ■. Therefore, the local oscillation signal is transmitted from terminal ■ to terminal ■ ,■ divided into diode 41
．． 42 and connected to the output terminal 47, no local oscillation signal is output. Also, since there is a 180° phase difference between the propagation from terminal ■ to terminal ■ and the propagation from terminal ■ to terminal ■, diodes 41 and 42 are connected in opposite directions to each other, and the propagation is converted by diodes 41 and 42. The configuration is such that the signals are combined in phase at terminal (2). A frequency-converted signal is output from this terminal 4 to an output terminal 47 via a capacitor 49.

In addition, bias voltages -V and +V are applied from terminals 56 and 57 to diodes 41 and 42 through choke coils 53 and 54 to flow a weak current, thereby improving conversion efficiency.

[Problem that the invention seeks to solve]

The conventional frequency converter using diodes shown in FIG. 8 described above has the following drawbacks. That is, (1) since the diodes 41 and 42 are two-terminal elements, input/output isolation is poor, and when trying to reduce conversion loss, the operating band becomes narrow; (2) intermediate frequency side and local oscillation and It is difficult to optimize the matching circuit with the conversion output side.

(3) When an external bias is applied and used, the bias circuit becomes somewhat complicated and it is necessary to provide a high impedance choke coil for direct current circulation in the propagation path of the ultra-high frequency signal. (4) In very high frequency bands, especially above the Ku band, mixer diodes are very expensive, which makes frequency converters expensive.

Furthermore, in the frequency converter using FETs shown in FIG. 7, a Schottky barrier gate is simply used instead of a Schottky barrier diode, as described above. When this FET is used as a frequency conversion element of a frequency converter using a rough trace type hybrid circuit shown in FIG. Since the distributed local oscillation signals are combined and input to the gate of the FET, a combining means must be added.

An object of the present invention is to provide a frequency converter that uses a microwave FET as a frequency conversion element and has a relatively simple configuration and excellent frequency conversion characteristics.

[Means for solving problems]

The frequency converter of the present invention will be described with reference to FIG. A frequency-converted signal is derived from D, and the intermediate frequency signal is applied to a gate G via a matching circuit 2, and a predetermined gate bias voltage Vg is applied to the gate G. Further, the local oscillation signal is applied to the drain D via the circulator 4 etc. and the matching circuit 3, and the signal frequency-converted by the FETI is output via the matching circuit 3 and the circulator 4.

[Effect]

Since the drain conductance of the FET changes depending on the gate voltage, the drain conductance changes depending on the intermediate frequency signal input to the gate G of the FET, and by applying a local oscillation signal with a higher frequency than the intermediate frequency signal to the drain D, approximately The local oscillation signal is amplitude-modulated, includes a frequency conversion component, and is output from the drain D. Therefore, it is sufficient to separate the local oscillation signal and the frequency conversion output signal using the circulator 4 or the like. Furthermore, since the matching circuit 2, which serves as a circuit for inputting an intermediate frequency signal, only needs to match the intermediate frequency signal, the configuration becomes simple. In addition, since the local oscillation signal and the frequency conversion output signal are generally relatively close in frequency, the matching circuit 3
The configuration is also relatively simple.

〔Example〕

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

FIG. 1 is a block diagram of an embodiment of the present invention, in which the FETI
The source S of is grounded, and the gate G is applied with a gate bias voltage V.
g via the chiller coil, and the matching circuit 2
An intermediate frequency signal of frequency flF is applied via the . Further, a matching circuit 3 is connected to the drain D, and a local oscillation signal of frequency fL is applied to the drain D via the circulator 4 and the matching circuit 3. A frequency-converted signal is output from the drain D, and an output signal having a frequency of fL±flF is derived to the output terminal via the matching circuit 3 and the circulator 4.

The matching circuit 2 on the input side has a simple configuration because it only needs to match the intermediate frequency signal, and the local oscillation signal has a higher frequency than the intermediate frequency signal, so the frequency of the frequency-converted signal , the configuration of the matching circuit 3 on the output side is also relatively simple. Even if the drain bias voltage is set to Ov, the frequency conversion operation can be performed, which simplifies the configuration. Note that it is also possible to improve the conversion efficiency by appropriately setting the drain bias voltage.

Figure 2 is a drain current characteristic curve diagram, where the vertical axis is the drain current I d (mA) and the horizontal axis is the drain voltage Vd.
(V), with gate bias voltage Vg as a parameter. As you can see from this second figure,
The drain conductance (ΔId/ΔVd) changes depending on the gate bias voltage Vg. Therefore, as shown in FIG. 3, when the drain bias voltage is set to 0 and a local oscillation signal is input to the drain D, the drain current 1d changes depending on the gate voltage. When this drain current 1d is converted into a voltage, .about.v3, and the signal waveform at the drain D is shown in FIG. That is, the drain conductance of the FETI changes in accordance with the amplitude of the intermediate frequency signal applied to the gate G, and the local oscillation signal applied to the drain D becomes approximately amplitude modulated, so that f
A frequency converted output signal of ttf+r is obtained.

FIG. 5 shows a balanced modulation type frequency converter according to an embodiment of the present invention, 11.12 is an FET, 13 is a rough trace type hybrid circuit, 14 is a 180° hybrid circuit, and 15
1 is an input terminal for an intermediate frequency signal, 16 is an input terminal for a local oscillation signal, 17 is a frequency conversion output terminal, 18 to 21 are capacitors, and 22 and 23 are choke coils.

The intermediate frequency signal is applied to the hybrid circuit 14 via the capacitor 8, distributed with a phase difference of 180°, and then connected to the FET II, 1 via the capacitors 19 and 20, respectively.
It is added to gate G of 2. In addition, the local oscillation signal is sent to the rough trace hybrid circuit 13 via the capacitor 21.
The local oscillation signal applied to the terminal (2) and distributed to the terminals (2) and (2) is applied to the drain D of FET II and 12, respectively. Note that matching stubs are formed on the terminals (1) and (2).

At the gate G of FETl1.12, there is a choke coil 2.
A gate bias voltage Vg is applied via 2.23,
Source S is grounded. A local oscillation signal is applied to the drain D of this FET 11.12, an intermediate frequency signal is applied to the gate G, and a frequency-converted signal is output from the drain D and applied to the terminals (2) and (2). This frequency-converted output signal is synthesized at terminal ■ and sent to output terminal 1.
Output from 7.

Similar to the conventional example using a diode, the local oscillation signal has a phase difference of 180° to terminal ■, so the leakage local oscillation signal can be suppressed, and the propagation from terminal The propagation from ■ to terminal ■ has a phase difference of 180°, but the hybrid circuit 14 converts the intermediate frequency signal to 1
By distributing the signals with a phase difference of 80°, the signals are combined at the terminal (2) in the same phase.

This example shows the case where the drain bias voltage of FET II, 12 is set to Ov, and there is no need to form a bias current path to the rough trace type hybrid circuit 13, so there is no deterioration of ultra-high frequency characteristics. There are advantages. Further, the gate bias voltage Vg is set at a relatively low frequency f0. Since it is added to the gate G to which the intermediate frequency signal of is applied, the configuration of the choke coils 22 and 23 is also relatively simple.

FIG. 6 is a frequency conversion characteristic curve diagram, in which the intermediate frequency signal f
IF is 900MHz, local oscillation signal frequency fL is 13
．． 38037 GHz, and when obtaining the frequencies ft and +BF of the frequency conversion output signal, the local oscillation signal power is 5.2 dBm, 7.6 dBm, 9.8 dBm, and 1, respectively.
Intermediate frequency signal power (dB
It shows the converted output power [dBm] with respect to m). Note that the dotted line when the local oscillation signal power is 9.8 dBm indicates the characteristic when spurious adjustment is performed. Also, the leakage of the local oscillation signal to the terminal ■ of the rat race type hybrid circuit 13 is as follows for the output of 14.28037 GHz.
It was -10dB or less.

〔Effect of the invention〕

As explained above, in the present invention, the source S of the FET is grounded, an intermediate frequency signal is applied to the gate G, a local oscillation signal is applied to the drain D, and a frequency-converted output signal is output from the drain D. On the gate G side, a circuit that matches only low-frequency intermediate frequency signals is provided, which simplifies the configuration of the matching circuit. Since the local oscillation signal with a frequency higher than the frequency of the intermediate frequency signal and the frequency-converted output signal have similar frequency bands, the matching circuit common to them can also have a relatively simple configuration.

Furthermore, even if the drain bias voltage is set to 0, frequency conversion is possible, so the structure is simpler than that of the conventional example shown in FIG. Note that it is also possible to improve the conversion gain by adding a configuration for applying a drain bias voltage. Moreover, the price of microwave FETs is rapidly decreasing due to the expansion of applications and increase in production volume, so it is possible to reduce costs as a microwave frequency converter.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a drain current characteristic curve diagram, Fig. 3 is an explanatory diagram of local oscillation signal application operation, Fig. 4 is an explanatory diagram of drain waveform, and Fig. 5 is a diagram of the present invention. Figure 6 is a frequency conversion characteristic curve diagram, Figure 7 is a conventional frequency converter using FETs, and Figure 8 is a conventional frequency converter using diodes. It is a vessel. 1.11. ], 2 is FET, S is source, G is gate,
D is the drain, 2.3 is a matching circuit, 4 is a circuit generator, 13 is a rough trace type hybrid circuit, 14 is 18
0° hybrid circuit, 15 is an input terminal for an intermediate frequency signal, 16 is an input terminal for a local oscillation signal, 17 is a frequency conversion output terminal, 18 to 21 are capacitors, and 22 and 23 are choke coils.

Claims (1)

[Scope of Claims] A microwave field effect transistor (1), a circuit for inputting a relatively low frequency signal whose frequency is to be converted into the gate (G) of the microwave field effect transistor (1), and the micro wave field effect transistor (1). Drain of wave field effect transistor (1) (
A circuit for adding a local oscillation signal to D) and deriving a frequency-converted signal;
) and a circuit for grounding the frequency converter.