JPH0433403A - Broad band voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To attain miniaturization by matching the combined impedance between impedance of an impedance circuit and input capacitance of an active element with the output impedance of an oscillator section. CONSTITUTION:After an active element (FET) 19 is selected, the resistance of resistors 14, 17 and the inductance of inductors 15, 16, 18 are selected so that the combined impedance of a bridged T type low pass filter circuit comprising a gate-source capacitance 29 being an input capacitance of the FET 19, the resistors 14, 17 and the inductors 15, 16, 18 and a gate resistor 61 is in matching with the output impedance of an oscillator section 25 within a required oscillating frequency range. Thus, the matching circuit section 26 and the broad band amplifier section are integrated and miniaturization is attained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a voltage controlled oscillator (VCO) used in measuring instruments, radar, satellite broadcasting receivers, etc. , the oscillation output is constant,
This invention relates to a wideband voltage controlled oscillator suitable for miniaturization.

[Prior Art] Conventionally, this type of wideband voltage controlled oscillator is composed of an oscillator section, a matching circuit section, and a wideband amplifier section.The matching circuit section has an amplification function, and is designed independently of the amplifier section. It had been.

That is, as a design procedure, first, an oscillator section having a required oscillation frequency band is designed, and an active element having a sufficient gain in this band is selected.

Next, the input stage of the wideband amplifier section was designed so that the above active element had an input impedance value (50Ω), which was a standardized interface.

When designing this conventional wideband voltage controlled oscillator, only the wideband amplifier section had the amplification function over a wideband.

In addition, since the output impedance of the oscillator section shows a negative resistance of 0Ω or less, the matching circuit section has a low impedance that matches the output impedance of the oscillator section so as to satisfy the oscillation conditions over a wide band. circuit has been adopted. Furthermore, the matching circuit section was composed only of passive elements.

As such a wideband voltage controlled oscillator, for example, the 10th
There is something like the one shown in the figure.

The wideband voltage controlled oscillator shown in FIG. 10 is composed of a single oscillator section 25, a matching circuit section consisting of a quarter wavelength converter 50, and a wideband amplifier section 55.

The wideband amplifier section 55 is a 90' hybrid 51.52
and two FETs 53.

The input stage 90° hybrid 51 has an amplifier section 55 with an input impedance of 50Ω, and an output stage 90° hybrid 51.
The 0'' hybrid 52 is for matching with the load 24 having an impedance of 50Ω.

[Problems to be Solved by the Invention] As described above, in the conventional wideband voltage controlled oscillator, the impedance of the matching circuit section is designed such that the input impedance of the subsequent wideband amplifier section is 50Ω.

The broadband amplifier section required a 90° hybrid 51 to set the input impedance to 50Ω. Furthermore, as shown in FIG. 10, two active elements (FETs) 53 are installed at the rear stage of the 90' hybrid 51.
This was necessary due to the characteristics of hybrids.

For this reason, the wideband amplifier section of a conventional wideband voltage controlled oscillator requires at least two active elements (F
ET) 53, and others are required.

Since there are restrictions on the size of the matching circuit 50, there is a limit to miniaturization of the matching circuit 50.
There was a problem in that it was difficult to convert the device into a microwave IC.

An object of the present invention is to provide a wideband voltage controlled oscillator suitable for miniaturization by integrating a matching circuit section and a wideband amplifier section and measuring impedance matching.

[Means for Solving the Problem] To achieve the above object, the present application provides the following invention.

That is, the present invention provides a broadband voltage controlled oscillator, comprising an oscillator section and a matching circuit section, and the matching circuit section includes an impedance circuit consisting of a plurality of passive elements following the oscillator section, and an impedance circuit connected to the impedance circuit. and one or more subsequent active elements, the combined impedance of the impedance of the impedance circuit and the input capacitance of the active element matching the output impedance of the oscillator section.

Further, the active element of the above-mentioned matching circuit section can also be constituted by one transistor.

Furthermore, the impedance circuit includes three inductors connected in a T-shape, and a bridging resistor bridging the inductors.
It is also possible to include a terminating resistor.

[Operation] As mentioned above, the composite impedance of the input capacitance of the active element and the impedance of the impedance circuit is set to 1.
By directly matching the output impedance of the oscillator section, it is possible to eliminate impedance matching means such as a 90' hybrid that was present at the input stage of the conventional broadband amplifier section.

Furthermore, since a 90° hybrid is not used, an amplification function can be obtained in the necessary frequency band with only one active element.

[Example 1] Hereinafter, an example of the present invention will be described based on FIGS. 1 to 9.

A first embodiment will be described based on FIGS. 1 to 3.

FIG. 1 is a circuit diagram of a prototype broadband voltage controlled oscillator. The broadband voltage controlled oscillator includes an oscillator section 25
．． It consists of a matching circuit section 26, and a 50Ω load resistor 24 is connected thereto.

The oscillator section 25 includes a FET 6 for one oscillation, varactors (variable capacitance diodes) 2 and 7 for frequency variation added to the gate and source of the FET 6, and the varactors 2 and 7.
It also includes a gate inductor 4 that determines the oscillation frequency, and compensation inductors 1 and 10 that are added in parallel to the varactors 2 and 7 to correct the frequency and widen the band. The compensation inductors 1 and 10 are composed of the varactors 2 and 7 and the FE
The T6 bias coil also works.

The control voltage to the varactors 2 and 7 is supplied to the reverse applied voltage input terminal 5.
Added from.

Also included in the oscillator section 25 are capacitors 3, 8, 11 and 13 for cutting direct current, 12 a source resistor for self-biasing the FET, and 9 a bias coil for the FET.

The matching circuit section 26 includes the bridging resistor 14. An impedance circuit consisting of a terminating resistor 17 and three inductors 15, 16, and 18 connected in a T-shape, and an active element FET 1.
Contains 9.

It is also included in the matching circuit section 26. 22 is a bias coil for the FET, 20 and 23 are capacitors for cutting direct current, and 21 is a source resistor for self-biasing the FET.

A method for selecting passive elements and FETs constituting an impedance circuit will be explained with reference to FIG.

Figure 2 shows the impedance circuit and FET shown in Figure 1.
A bridge T-type impedance circuit is shown which is an equivalent circuit of a circuit consisting of an input capacitance 29 of . Reference numeral 61 denotes an input resistance (gate resistance) of the input section of the FET, but since this resistance value is small, it can be ignored.

This equivalent circuit is also called a bridged T-type low-pass filter circuit because of the circuit shape and the band characteristic of passing a low frequency band.

FET 19 is selected to have a cutoff characteristic that provides sufficient gain within the required oscillation frequency band of the broadband voltage controlled oscillator. Namely.

A FET 19 is selected that has a gate width and a gate length that match the required value of the cutoff frequency.

After the FET 19 is selected, the gate-source capacitance 29, which is the input capacitance of the FET 19, is
and resistor 14.17 and inductor 15.16,1
8 and the gate resistor 61, the resistor 14, 17 and the inductor 15, 16, .
Set 18 element values.

These element values can be arbitrarily set as follows according to various requirements such as the required frequency band, oscillation output, and isolation characteristics between the load side and the oscillator side.

If you want to widen the band, use resistor 14. ．． Make 17 smaller,
In addition, the inductors 15 and 16 may also be made smaller to lower the input impedance Zm.

In addition, in order to increase the output, the gain of the matching circuit may be increased by increasing the resistor 14.17.

In order to improve the isolation characteristics, resistor 14.
17 should be made smaller.

Figure 3 shows the prototype circuit shown in Figure 1, with varactors 2,
This is an example in which the oscillation frequency and output power were actually measured when the voltage applied to 7 was changed.

The GaAsFET used has a size of 0.3 μm (gate length) x 300 p m (gate @
) GaAs NESFET (Toshiba JS8818A
-AS), and the varactor (manufactured by M/A-COM, USA) has a capacitance change ratio (C2/C20) of 10, and C2=1.
pF (HA-46470) was used. The type of varactor is a GaAs super-step junction varactor (h
hyperabrupt varactor).

Note that C2 indicates the capacitance of the varactor when the voltage applied to the varactors 2 and 7 is 2V, and C20 indicates the capacitance of the varactor when the applied voltage is 2V.
The capacitance of the above varactor when V is shown.

The resistance value of the bridging resistor 14 is 15Ω, the resistance value of the terminating resistor 17 is also 15Ω, the inductance of the inductor 15.16 is 0.2nH, and the inductance of the inductor 18 is 0.
．． It is 1 nH.

A flat output power was obtained with respect to a one-octave oscillation frequency change, and this broadband voltage-controlled oscillator exhibits excellent characteristics.

The second embodiment will be explained based on FIGS. 4 to 7.

In this embodiment, some of the components of the oscillator section of the first embodiment are changed.

The second embodiment of the broadband voltage controlled oscillator shown in FIG. 4 is composed of an oscillator section 41 and a matching circuit section 26,
A 0Ω load resistor 24 is connected.

The matching circuit section 26 includes a bridging resistor 14, a terminating resistor 17, inductors 15, 16, 18, and an FET 19 whose source is grounded.

The oscillator section 41 is a GaAs super-stepped junction varactor (
42
It uses one piece. The varactor 42 has a characteristic of having a large capacitance change ratio. A capacitor 11 attached to the source of the FET 6 whose source is grounded to the varactor 42
This constitutes an oscillator with a capacitive feedback single-varactor configuration. According to this configuration, two varactors are used.
Although the oscillation frequency band is a little narrower than when using only one, it has the advantage that the oscillation frequency fluctuation with respect to temperature changes is small.

Figure 5 shows the resistance 1 of the impedance circuit shown in Figure 4.
4.17, an equivalent circuit of a circuit consisting of inductors 15, 16, 18, a gate-source capacitance 29 of an active element (FET 19), and a gate resistance is shown. This circuit is also called a bridged T-type low-pass filter circuit.

FIGS. 6 and 7 show examples in which the broadband voltage controlled oscillator shown in FIG. 4 was prototyped and the oscillation frequency and output power were measured when the voltage applied to the varactor 42 was varied from Ov to 20V.

Figure 6 shows the measured values of the X-band broadband voltage controlled oscillator.
FIG. 7 shows measured values of a Ku band broadband voltage controlled oscillator.

The GaAsFETs used are the oscillator section 41 and the matching circuit section 2.
6 Both 0.3 p m (gate length)
A GaAs MESFET (Toshiba JS8818A-AS) with a gate width of C2=1 pF (HA-4647
0) was used in Figure 7.

Note that C2 indicates the varactor capacitance when the voltage applied to the varactor 42 is 2V, and C20 indicates the capacitance of the varactor when the applied voltage is 20V.

The resistance value of the bridging resistor 14 is 20Ω, the resistance value of the terminating resistor 17 is also 20Ω, the inductance of the inductor 15.16 is 0.2nH, and the inductance of the inductor 18 is 0.
, in)l.

From Figure 6, the X-band broadband voltage controlled oscillator has an applied voltage of 0.
~20V, oscillation frequency 7.9~13, 1G
Hz and output power of 12.5±1.2 dBm.

Moreover, from FIG. 7, the Ku band broadband voltage controlled oscillator has an oscillation frequency of 12.8 to 1 for applied voltages of 0 to 20 V.
It can be seen that it has a performance of 8.2GHz and an output power of 12.5±1°3 dBm.

All broadband voltage controlled oscillators exhibit excellent characteristics.

A third embodiment is shown in FIG.

In this embodiment, a bridging T-type impedance circuit according to the present invention is applied to the matching circuit section 26 of a fixed frequency oscillator, and the matching circuit section 26 is the matching circuit section 26 of the broadband voltage controlled oscillator shown in FIG. It has a similar configuration.

The oscillator section shown in FIG. 8 is a dielectric oscillation circuit 84 using a dielectric, and includes a FET 6.5° microstrip line 80 for one oscillation, a 50 ohm terminating resistor 81, an open stub 82, a dielectric resonator 83, and a compensation It has an inductor 85.

In addition, 11.13 is a capacitor for DC cut,
12 is the source resistance for FET self-bias, 9 is the FE
This is a bias coil for T.

The oscillation frequency is determined by the 50Ω microstrip line 80, the dielectric resonator 83, and the open stub 82.

A fixed frequency oscillator using a dielectric resonator has a stable oscillation frequency, low noise, and a flat and compact oscillator section (the size of the dielectric resonator is 6III x diameter
It has the advantage that it can be made with a height of 2.4 mm (when oscillating at around 10 GFIz).

Therefore, the dielectric resonator and the matching circuit section according to the present invention,
That is, by combining an impedance circuit consisting of an inductor and a resistor with the matching circuit section consisting of one FET, a small fixed frequency oscillator having excellent pulling characteristics and output characteristics can be realized.

A fourth embodiment is shown in FIG.

In this embodiment, the FET 19 of the matching circuit section 26 shown in FIG. 1 is replaced with a bipolar transistor 31 with a common emitter.
It has the same configuration as .

Current bipolar transistors are suitable for use in lower frequency bands (approximately 8 GHz or less) than FETs.
By using the bipolar transistor 31, there is an advantage that the noise level in the low frequency band can be reduced.

[Effects of the Invention] Since the present invention is configured as described above, it produces effects as described below.

According to the present invention, by integrating the matching circuit section and the wideband amplifier section and measuring the impedance matching with one oscillator section, the matching circuit section and the wideband amplifier section are integrated, and a wideband voltage controlled oscillator suitable for miniaturization is created. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a broadband voltage controlled oscillator according to a first embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of a circuit consisting of the impedance circuit shown in FIG. Figure 3 is a graph showing the actual measured values of the oscillation frequency and output power when changing the voltage applied to the varactor, obtained by prototyping the circuit of the first embodiment, and Figure 4 is a graph of the second embodiment of the present invention. A circuit diagram showing a broadband voltage controlled oscillator according to FIG. 5, the impedance circuit and FET shown in FIG.
Equivalent circuit diagram of a circuit consisting of input capacitance, No. 6
7 and 7 are graphs showing actual measured values of oscillation frequency and output power when changing the voltage applied to the varactor, which were obtained by prototyping the circuit of the second embodiment in the X band and Ku band, respectively, FIG. 8 is a circuit diagram showing the configuration of a third embodiment in which the present invention is applied to a matching circuit section of a fixed frequency oscillator, and FIG. 9 is a circuit diagram showing the configuration of a fourth embodiment in which a bipolar transistor is used as an active element in the matching circuit section. FIG. 10 is a circuit diagram showing a conventional wideband voltage controlled oscillator. 1.10... Compensation inductor, 2,7... Varactor, 5... Reverse applied voltage input terminal, 6.19... FET, 14.17... Resistor, 15° 16.18...・Inductor, 24...Load resistance, 2
5... Oscillator section, 26... Matching circuit section, 31...
Bipolar transistor, 42...Hyperstep junction varactor. 80...50Ω microstrip line, 82...
Open stub, 83...dielectric resonator.

Claims (1)

[Claims] 1. A broadband voltage controlled oscillator comprising an oscillator section and a matching circuit section, wherein the matching circuit section includes an impedance circuit comprising a plurality of passive elements following the oscillator section, and the impedance circuit. and one or more active elements following the impedance circuit, wherein a composite impedance of the impedance of the impedance circuit and the input capacitance of the active element matches the output impedance of the oscillator section. . 2. The broadband voltage controlled oscillator according to claim 1, wherein the passive elements of the matching circuit section are an inductor and a resistor. 3. The wideband voltage controlled oscillator according to claim 1 or 2, wherein the active element of the matching circuit section comprises one transistor. 4. A band voltage controlled oscillator comprising an oscillator section and a matching circuit section, wherein the matching circuit section includes an impedance circuit following the oscillator section and one or more active elements following the impedance circuit. The circuit consists of three inductors connected in a T-shape, a bridging resistor bridging the inductors, and a terminating resistor, and the combined impedance of the impedance of the impedance circuit and the input capacitance of the active element is A wideband voltage controlled oscillator characterized by matching the output impedance of the oscillator section.