JP2543984B2 - Microwave frequency synthesizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a PLL microwave frequency synthesizer used in a television microwave repeater, and is intended to expand the frequency variable range thereof.

[Outline of Invention]

When an operational amplifier is used for the loop filter in the microwave frequency synthesizer, the maximum amplitude becomes about 70 to 80% of the power supply voltage, and the control voltage range of the VCO becomes narrow. When both positive and negative power supplies are used to expand the control voltage range, a forward voltage is applied to the varactor at the time of the circuit rising operation, and the PLL loop may not operate.

Therefore, by using the operational amplifier power supply for the loop filter as the voltage between the positive power supply and the GND, and using the second operational amplifier as the control voltage range adjuster, and the positive and negative power supply as the power supply, the control voltage becomes 80 to 90%. Be improved. Further, since the expanded range of the control voltage is the range in which the Q of the varactor is lowered, the varactor is placed in a portion deviated from the maximum magnetic field portion so as to minimize the Q reduction of the resonator incorporating the varactor. C / N can also be maintained by arranging them.

[Conventional technology]

FIG. 4 shows a block diagram of a basic frequency synthesizer.

By comparing the phase of the reference oscillator 1 and the phase of the signal obtained by dividing the VCO (voltage controlled oscillator) 5 with the programmable counter 6 with the phase comparator 2, and feeding back the error signal to the VCO 5 through the loop filter 3. A predetermined frequency can be obtained, and the frequency can be changed by changing the frequency division ratio of the programmable counter 6. That is, by changing the set value of the programmable counter 6, the output frequency can be obtained within the oscillation range of VCO5. Here, the loop filter 3 is often an operational amplifier having a large DC gain and capable of removing common mode noise from the power supply. It is necessary to be able to control the VCO by including changes due to temperature and voltage fluctuations within the output voltage range of this operational amplifier. On the other hand, the local oscillator for communication equipment needs to have a good C / N, so the varactor diode used for the VCO must have a high Q. However, a varactor diode with a high Q often has a small capacitance change rate.
Therefore, the control range may be exceeded due to temperature changes, etc., and it is necessary to widen the voltage range of the loop filter.
For example, if the power supply of the operational amplifier is + 10V, 0V, the output voltage will be narrow at about 1.5V to 8.5V. The capacitance change of the varactor diode is largest when the reverse voltage is near 0 V, so the frequency variable range becomes narrow.

When an operational amplifier is used for the loop filter 3, if the low voltage terminal of the power supply is connected to a negative voltage instead of the ground potential in order to widen the output voltage range, a negative voltage is applied to the varactor cathode during transient response at power up. Therefore, if the anode of the varactor is set to ground potential, a forward voltage may be applied and control may become impossible.

In this case, the anode side of the varactor may be connected to the negative power source, but if the anode end is separated from the ground in a direct current and the open or short mode is set at a high frequency, the circuit becomes large and the characteristic becomes unstable. Increase.

If the voltage applied to the varactor diode is low, Q
Therefore, the applied voltage was increased and used, and the variable range of frequency was limited to a narrow range.

[Problems to be Solved by the Invention]

In the prior art, instability was caused by using the negative voltage and widening the control voltage range as described above. Therefore, an object of the present invention is to solve these drawbacks and to provide a microwave frequency synthesizer capable of expanding the control voltage range with a simple configuration.

[Means for solving the problem]

FIG. 1 is a block diagram of an embodiment of the present invention, which has a configuration in which a control voltage regulator 4 is added as compared with the prior art of FIG.

[Action]

As a result, the control voltage range can be widened by the embodiment shown in FIG. FIG. 3 shows an embodiment of the VCO resonance section, in which the varactor diode 12 is arranged near P ₂ instead of near P ₁ or P ₄ to prevent a decrease in C / N.

〔Example〕

FIG. 2 shows an example of a concrete implementation circuit of the loop filter and the voltage control regulator. The loop filter 3 of FIG. 2 receives the output of the phase comparator, and according to the phase difference with the reference oscillator,
The generated comparison noise is removed (so-called charge pump). Resistors 7 and 8 in 4 prevent the maximum voltage of the output of the loop filter 3 from being input to the operational amplifier. The DC gain of the control voltage regulator 4 is determined by the division ratio of the resistors 7 and 8 and the resistors 9-11.

As mentioned above, for example, the power supply of the operational amplifier is +
If it is 10V, 0V, the output voltage of loop filter 3 is about + 1.5V
Since it is in the range of + 8.5V, the output voltage of the voltage control regulator does not become a negative voltage at this voltage.

FIG. 3 shows an embodiment of the VCO resonating unit, and the output terminal of the control voltage regulator 4 of FIG. 2 is connected to the varactor control voltage applying terminal 14. The anode side of the varactor 12 is connected to the ground potential via the center conductor, and the cathode side of the varactor 12 is inspected by the insulating plate 13 from the ground potential for direct current so that the varactor control voltage is applied. The point ₁ is set to the short mode. A VCO is constructed by making a small hole in this resonance part and inserting a conductor so as to couple with the external transistor 15 for oscillation.

FIG. 5 shows the impedance of each part of the resonance part on a Smith chart. When the resistance component is added to the points P ₁ or P _4, the loss is the largest and the Q of the resonator decreases. Below, the capacitance value of the varactor diode is Cv, the maximum value of Cv is Cmax, and the minimum value of Cv is Cmin.
It will be described as. Therefore, the varactor voltage is low (C _v = ma
If the impedance Z _p3 in the case of x) is separated from the real axis, Q will decrease less.

There are two advantages to shifting the varactors. The first is the expansion of the variable range, and an example is shown in FIG. 6 using a Smith chart. Varactor normalization impedance change Is 0.1 to 0.5 and the varactor position is a place where the normalized impedance deviates by 0.3 from the short end of the coaxial resonator, the angular difference O ₁ between Cmax and Cmin when the position is not displaced is 40.
When it is shifted, the O ₂ becomes 45 °, and it can be expected that the variable range of the frequency will widen.

The second is to secure C / N. Since a high-frequency current flows in the vicinity of the normalized impedance 0, the loss due to the resistance of the varactor becomes large and the Q tends to decrease. When the normalized impedance is around 0, and the varactor Q is low at Cmax, the Q of the resonator is lowered and the C / N is lowered.

The amount l for shifting the position of the varactor is an approximate solution Becomes (However, ω: angular velocity at the center frequency) [Effect of the Invention] According to the present invention, the VCO control voltage range is widened and stable P
LL loop can be maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention, FIG. 2 is a circuit diagram showing one embodiment of the loop filter and control voltage range adjuster of the present invention, and FIG. 3 is the structure of the VCO resonance part of the present invention. FIGS. 4 and 5 are block diagrams showing the entire structure of the prior art, FIG. 5 is a diagram showing the impedance of each part of FIG. 3, and FIG. 6 is a diagram for explaining the expansion of the variable range. 1: Reference oscillator, 5: VCO, 6: Programmable counter, 7 to 11:
Resistor that determines DC gain, 12: Varactor diode, 13: Insulation plate, 14: Varactor control voltage application terminal, 15: Transistor.

Claims (1)

(57) [Claims] 1. A communication device comprising a voltage controlled oscillator using a varactor diode as a frequency variable element, and including a microwave local oscillator for controlling an output frequency of the voltage controlled oscillator by a phase locked loop. A first operational amplifier is used as a loop filter that configures the first operational amplifier, and a second operational amplifier that adjusts the control voltage variable range of the voltage controlled oscillator by receiving the output of the first operational amplifier is provided. Is a positive power supply, a positive / negative power supply is used for the second operational amplifier, and
The varactor diode is connected to the high Q in the voltage controlled oscillator.
A microwave frequency synthesizer, characterized in that it is arranged so as to be displaced from the position where the magnetic field of the resonance part is maximum.