JPH0550883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a local oscillation circuit in high frequency heterodyne signal processing.

Conventional technology In recent years, local oscillator circuits have been used in satellite broadcasting receivers and
With the development of CATV converters, local oscillation circuits that oscillate in the 1 to 2 GHz band have come into widespread use.

Figure 2 shows a conventional local oscillation circuit, in which 1 is an oscillation transistor, 2 is a bias resistor, 3 is a bypass capacitor, 4 is a choke coil, 5 is an emitter resistor, 6 and 7 are coupling capacitors, 8 is a bias resistor, 9 is a variable capacitance diode, 10 is a resonator, 11 is a bias resistor, 12 is a bypass capacitor, 13 is a small capacitor,
14 is a switch diode, 15 is a coupling capacitance, 2
A is a tuning voltage terminal, 2B+ power supply terminal, 2C is an oscillation output terminal, and 2D is a switch terminal.

In such a local oscillation circuit, when power is applied to the collector of the transistor 1 from the + power supply terminal 2B and the collector is grounded by the bypass capacitor 3, the impedance seen from the base side of the transistor 1 becomes a negative characteristic. If a resonant line is connected here, this circuit compensates the phase with the resonant line and oscillates at a frequency of 2nπ (n=±0, 1, 2, . . . ). Since the emitter of the oscillation transistor 3 is connected in series with an emitter resistor 5 for current limiting and a chiyoke coil 4 for taking out the output and grounded, the oscillation output is transmitted via the coupling capacitor 6. It can be taken out from the oscillation output terminal 2C. On the other hand, in the resonant line, a variable capacitance diode 9, a resonator 10, and a switch diode 14 are connected in series via a coupling capacitor 15 via a coupling capacitor 7, and the other end is grounded. A tuning voltage is applied to the cathode of the variable capacitance diode 9 from the tuning voltage terminal 2A via the bias resistor 8. Further, a direct current potential that can turn on and off the switch diode 14 is applied from the switch terminal 2D via the bias resistor 11 to the anode of the switch diode 14 as necessary.

FIG. 3 is a characteristic diagram of the tuning voltage oscillation frequency, where curve A is the characteristic when the switch diode 14 is on, and curve B is the characteristic when the switch diode 14 is on.
This is the curve when it is turned off. When the switch diode 14 is turned off, the reverse bias capacitance becomes less than 1PF. Since this capacitance is connected in series to the resonant path, the resonant capacitance is controlled to be small, and the change in the oscillation frequency with respect to the change in the tuning voltage shifts to the side where the oscillation frequency is higher than the curve A.

Furthermore, the transistor used as the oscillation transistor 1 has a maximum upper limit frequency of several GHz or more,
The reverse bias capacitance of the collector base of such transistors is often around 1PF, and experiments have shown that in a resonant system, this capacitance behaves as if it were connected in series. Therefore, in a general-purpose configuration using such an oscillation transistor 1 and a switch diode 14, curves A and B do not overlap when a tuning voltage of 1 to 30 volts is used. Even if there were, the range would be extremely narrow and the situation would be impractical. In order to avoid this, a small capacity 13 of about 1 to 2 PF is inserted as shown in Figure 2.
The characteristic of curve C in the figure can be obtained. [Refer to Japanese Unexamined Patent Publication No. 59-149405] Problems to be Solved by the Invention In such a conventional configuration, the small capacitance 13 added when the switch diode 14 is in the on state reduces the impedance of the resonance system, especially the phase characteristics. The problem is that the tuning voltage that satisfies the oscillation conditions becomes discontinuous and oscillates at a frequency other than the desired frequency, or in the worst case, oscillation stops.

An object of the present invention is to provide a local oscillation circuit that can obtain the characteristics shown by curves A and C in FIG. 3 and can also stabilize the characteristics.

Means for Solving the Problems In the local oscillation circuit of the present invention, the collector of the oscillation transistor is grounded in an alternating current manner, and a variable capacitance diode, a resonator or a resonant line, and a switch diode section are connected between the base and the ground. are connected in series in an alternating current manner, applying a tuning potential to the variable capacitance diode to extract a target oscillation frequency output, and switching the oscillation frequency with respect to the tuning potential by conduction/non-conduction of the switch diode section,
The switch diode section is configured such that a plurality of switch diodes are connected in parallel or series-parallel so that the conduction resistance value is smaller than the conduction resistance value of one switch diode when conducting, and larger than the reverse bias capacity of one switch diode when non-conducting. It is characterized by

Effects According to this configuration, the switch diode section has a plurality of switch diodes connected in parallel or series-parallel, which increases the reverse bias capacity of the switch diode and at the same time reduces the conduction resistance when the switch diode is in the on state. can be reduced and the operation becomes extremely stable.

Embodiment Hereinafter, an embodiment of the present invention will be described based on FIG. FIG. 1 shows a local oscillation circuit of the present invention,
Components having the same functions as those of the conventional example shown in FIG. 2 are given the same reference numerals. Figure 1 differs from Figure 2 in the following points.

In other words, the small capacitor 13 is removed in FIG. 1, and a switch diode section 17 is provided in which switch diodes 14 and 16 are connected in parallel to the series circuit of the variable capacitance diode 9 and the resonator 10. 18 represents the stray capacitance due to mounting. As a result, the reverse bias capacitance of the switch diode is doubled compared to the case shown in Figure 2, the resistance component when conducting is halved, the Q of the resonant circuit is increased, and operation becomes stable, and the effect of stray capacitance is will also decrease. As a result, two curves A and C in FIG. 3 can be obtained. In the figure, point D, E
The points indicate the minimum and maximum points of the tuning potential, F point, G
The dots indicate the required range of oscillation frequency. H
The point is the maximum oscillation frequency of curve A, the point is the minimum oscillation frequency of curve B, and the range (-H) is the range that cannot be covered by curves A and B. However, according to the present invention, the switch diode 14,
Since the curve when 16 is off is like C, its minimum oscillation frequency is the frequency at point J, which is smaller than the maximum oscillation frequency H of curve A (when the switch diode is on), so the necessary range F to G are all obtainable.

By arranging the two switch diodes 14 and 16 in parallel in this manner, the stability of the circuit is increased and the variable range of the oscillation frequency can be switched by the switch means to continuously maintain the necessary range.

In addition, in the above embodiment, the switch diode section 1
7 uses two switch diodes, 14 and 16, but the number may be increased if the required reverse bias capacitance is small. Further, when the required reverse bias capacitance is not an integral multiple of one reverse bias capacitance, the desired reverse bias capacitance can be obtained by combining switch diodes in series and parallel.

Furthermore, when mounting the switch diodes in the switch diode section 17, by mounting them back to back with mounting boards in between, it is possible to switch the same point on the resonant line with a plurality of switch diodes.

Effects of the Invention As described above, the local oscillation circuit of the present invention includes a variable capacitance diode at the base of the oscillation transistor,
A resonator or a line and a circuit in which multiple switch diodes are connected in parallel or some of them in series are connected in series in an AC manner, and when conductive, the induced resistance value is smaller than that of a single switch diode, and the circuit is non-conductive. Since the reverse bias capacity is sometimes larger than the reverse bias capacity of one switch diode, it is possible to operate stably over a wider frequency range.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the local oscillation circuit of the present invention, FIG. 2 is a block diagram of a conventional local oscillation circuit, and FIG. 3 is a diagram showing the relationship between tuning voltage and oscillation frequency. DESCRIPTION OF SYMBOLS 1... Oscillation transistor, 3... Bypass capacitor, 9... Variable capacitance diode, 10... Resonator, 14, 16... Switch diode, 17...
...Switch diode section, 2A...Tuning voltage terminal, 2B...+ power supply terminal, 2C...Oscillation output terminal, 2D...Switch terminal.

Claims (1)

[Claims] 1. The collector of the oscillation transistor is grounded in an alternating current manner, and a variable capacitance diode, a resonator or a resonant line, and a switch diode part are connected in series in an alternating current manner between the base and the ground, A tuning potential is applied to the variable capacitance diode to extract a target oscillation frequency output, and the oscillation frequency is switched with respect to the tuning potential by conduction/non-conduction of the switch diode section, and the switch diode section is configured to include a plurality of switch diodes. A local oscillator circuit in which the conduction resistance value is smaller than the conduction resistance value of one switch diode when conducting, and larger than the reverse bias capacity of one switch diode when non-conducting, by connecting them in parallel or in series and parallel. 2. The local oscillation circuit according to claim 1, wherein each diode of the switch diode section is separately mounted on both sides of a mounting board constituting a resonant line.