JP2976455B2 - Oscillation / mixing circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation / mixing circuit used for a second local oscillation circuit and a second mixing circuit of a CATV converter.

2. Description of the Related Art A second local oscillation circuit and a second mixing circuit of a conventional CATV converter are as shown in FIG. 14 to FIG.

 This will be described below with reference to the drawings.

14 is an amplifier, 2 and 4 are matching circuits, 3 is a surface acoustic wave resonator (SAWR), 11 is a capacitor, 12 is an RF signal source, 41 is a second mixing circuit, and 22 is an IF output terminal. . This feature is that the oscillation power is directly extracted from the amplifier output terminal.

FIG. 15 has almost the same configuration as FIG. 14, except that the oscillation power is directly extracted from the input terminal of the SAWR.

FIG. 16 shows that a MOS field effect transistor (F
ET42) is used, 43 to 45 are bias circuits, and 46 is an output coupling capacitance.

Problems to be Solved by the Invention In an oscillation circuit using a SAWR, it is essential to design a high-frequency excitation power (or high-frequency excitation current) to the SAWR in an oscillation operation state to be equal to or less than an allowable value.

For example, if SAWR is used for a long time exceeding the allowable power,
Fatal failures such as a large fluctuation of the oscillation frequency due to the deterioration of the internal electrodes of the SAWR and oscillation stop due to an increase in the insertion loss are caused.

Therefore, when an oscillation circuit using SAWR is put into practical use, it is important how to realize both means for suppressing the high-frequency excitation power below an allowable value and means for measuring the high-frequency excitation power.

In the conventional method as shown in FIGS. 14 and 16, as a means for reducing the high-frequency excitation power to an allowable value or less, for example, the resonance frequency of the SAWR is set in advance to a higher value (for example, 20 KHz) than the oscillation frequency, and At point a in FIG. 9, the closed-loop gain of the oscillation circuit is equivalently reduced, and as a result, the high-frequency excitation power is reduced to an allowable value or less.

In this method, the operating point of the SAWR is equivalent to the point A in the phase characteristic. For example, when the phase characteristic of the amplifier fluctuates due to a change in the ambient temperature, the fluctuation of the oscillation frequency becomes very large, and the SAWR inherently has a stable characteristic. There is a disadvantage that the obtained temperature characteristics cannot be fully utilized.

As a specific means of measuring high-frequency excitation power, a method is used in which a high-frequency high-impedance probe is directly connected to the input or output terminal of the SAWR for measurement. However, there is a drawback that the frequency cannot be reduced by about 50 to 100 KHz, and an error occurs with the actual high-frequency excitation power.

The present invention solves the above problems, and provides a circuit system capable of suppressing the high-frequency excitation power applied to the SAWR to an allowable power or less and correctly measuring the excitation power applied to the SAWR without affecting the oscillation circuit. It is intended to be.

Means for Solving the Problems To solve this problem, the present invention provides an FE of an oscillation circuit.
Insert a resistor between the drain of T and SAWR and / or between the gate of FET and SAWR.
Either the input terminal or the output terminal of the WR is directly connected to the diode mixing circuit via a capacitor, and a resistor is inserted in the DC feedback circuit of the diode mixing circuit,
It constitutes an oscillation / mixing circuit.

Function The present invention allows the closed-loop gain of the oscillation circuit to be freely controlled by inserting resistors on the input and output terminals of the SAWR as in the above-described configuration. Can be easily and reliably realized.

In addition to connecting directly to the diode mixing circuit from the input terminal or output terminal of the SAWR via a capacitor, the power to be measured can be measured by a resistor provided in the DC feedback circuit of the mixing circuit. Since this detection voltage is generated by the detection current obtained by detecting the high-frequency power directly input from the input or output terminal of the SAWR by the diode of the mixer, the detection voltage is correlated with the high-frequency excitation power of the input or output terminal of the SAWR. At the same time, by measuring the detection voltage, the oscillation state of the oscillator is not affected at all.

As described above, according to the present invention, it is possible to easily control the high-frequency excitation power of the SAWR to be equal to or less than the allowable value, and to use the high-frequency excitation power as the detection voltage without affecting the operation of the oscillation circuit at all. Can be measured in a simple way.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an example in which a resistor 5 is inserted between the drain of the FET and SAWR, FIG. 2 shows an example in which a resistor 9 is inserted between the gate of the FET and SAWR, and FIG. FIG. 4 shows that capacitors 6 and 6 are connected so that no DC voltage is applied to SAWR.
In addition to adding 10, resistors 7 and 8 are added for the purpose of DC grounding the input / output terminals of the SAWR. FIGS. 5 and 6 show a configuration in which the output terminal or the input terminal of the SAWR is directly connected to a diode mixing circuit via a capacitor 11, and a resistor 19 is a resistor provided in a DC feedback circuit.
15 is a mixing diode, 12 is an RF signal source, 13 and 14 are a combination circuit of an RF signal source and a diode mixing circuit, 16 is a high-frequency grounding capacitor, and 17, 18, 20, and 21 are intermediate frequency signal output circuits. . Here, the DC feedback circuit of the mixing circuit is 14, 15, 17, 1
Consists of 9,20. In the drawings, the same parts as those in FIGS. 14 to 16 are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 7 shows a specific embodiment of FIG. Where 1a is FE
T represents a bias circuit from 25 to 35. 2a and 2b show an embodiment of the matching circuit 2, and 4a and 4b show an embodiment of the matching circuit 4.
FIG. 8 shows an embodiment including a diode mixing circuit. Figure
Numeral 12 indicates the transmission characteristics of the SAWR (solid lines are phase characteristics, broken lines are selectivity characteristics). FIG. 10 shows an example of a correlation value between the high-frequency excitation power at the input terminal D of the SAWR in FIG. 8 and the detection voltage generated at the point E of the resistor 19 of the diode mixing circuit. FIG. 11 shows the relationship between the oscillation frequency and the detection voltage when the oscillation frequency is adjusted by adjusting 2a and 4a of the matching circuit of FIG.

FIG. 12 shows the temperature characteristic of the oscillation frequency, and FIG. 13 shows the temperature characteristic of the detection voltage.

Next, the characteristics of the SAWR are shown in FIG. 12. In order to draw out the characteristics of the SAWR as a resonator, for example, the phase characteristic is ± 10%.
It is necessary to make good use of the phase characteristics in the range of 45 degrees in the steep frequency region.

On the other hand, since the insertion loss of the SAWR increases as the frequency departs from the resonance point, it is necessary to increase the closed-loop gain of the oscillation circuit so that the SAWR can be adjusted in a wide frequency range.

On the other hand, the high frequency excitation power of SAWR has an acceptable limit, which must be observed.

The design taking the above into consideration will be described with reference to FIG. 8 as an example. The high-frequency excitation power which becomes maximum near the resonance frequency of the SAWR is determined by, for example, the resistor 5 shown in FIG. By adjusting the matching circuit 2a or 4a, the variation of the SAWR resonance frequency can be absorbed and adjusted to the desired oscillation frequency.
The high frequency excitation power at point D can be easily and accurately measured with the detection voltage at point E.

The resistance value 5 or 9 for the purpose of keeping the high-frequency excitation power below the allowable value is the closed loop of the oscillation circuit due to the selectivity characteristics of the SAWR when the resonance frequency is much different from the desired oscillation frequency (for example, 100 KHz). Since the gain is reduced, it is possible to use the resistors 5, 9 in different ways, such as changing them to smaller values.

Furthermore, if the resistors 5 and 9 are used as variable resistors, adjust the 2a or 4b while monitoring the detection voltage to ensure that the high-frequency excitation power is kept below the allowable value, and that the variation in the SAWR resonance frequency and insertion loss is sufficiently reduced. The absorbed oscillation mixing circuit can be realized.

As described above, according to the present invention, the high-frequency excitation power of the SAWR can be reliably controlled with a simple configuration in which a resistor is inserted between the FET and the SAWR, and a stable oscillation circuit using the SAWR is realized. In addition to the problem that it has been difficult to measure the high-frequency excitation power simply and accurately in the past, it is very difficult to use a diode system in the mixing circuit and to insert a resistor in the DC feedback circuit in FIG. By simple means,
This can be realized only by monitoring the excitation power of the SAWR as a measurement of a DC voltage called a detection voltage, and the industrial effect is extremely high.

[Brief description of the drawings]

FIGS. 1, 2, 3, and 4 are diagrams showing the basic configuration of an oscillation / mixing circuit according to the present invention, and FIGS. 5 and 6 show the configuration of a diode mixing circuit section of the circuit. FIG. 7 is a circuit diagram showing an embodiment of an oscillation circuit of the circuit, FIG. 8 is a circuit diagram showing an embodiment of the oscillation / mixing circuit, and FIG. 9 is a transmission characteristic of SAWR of the circuit. FIG. 10 is a characteristic diagram showing the relationship between the high-frequency excitation power and the detection voltage, FIG. 11 is a characteristic diagram showing the relationship between the adjustment range of the oscillation frequency and the detection voltage, and FIG.
FIG. 13 and FIG. 13 are characteristic diagrams showing the temperature characteristics of the oscillation frequency and the detection voltage, and FIG. 14, FIG. 15, and FIG. 16 are configuration diagrams showing a conventional example. 1 ... amplifier, 2,4 ... matching circuit, 3 ... SAWR (surface acoustic wave resonator).

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03B 5/30-5/42 H03D 7/02

Claims (1)

(57) [Claims] An oscillator circuit comprising a surface acoustic wave resonator (SAWR) and a field effect transistor (FET), and a drain of the FET.
A resistor is inserted between SAWR and / or between the gate of FET and SAWR, and either the input terminal or the output terminal of SAWR is connected directly to the diode mixing circuit via the capacitor, An oscillation / mixing circuit, wherein a resistor is provided in the DC feedback circuit of the diode mixing circuit.