JPH0326021A - Microwave frequency synthesizer - Google Patents

Abstract

PURPOSE:To expand the control voltage range with simple constitution by employing a 2nd operational amplifier as a control voltage regulator, and adopting a bipolar power supply for the power supply. CONSTITUTION:A control voltage adjusting device 4 adjusting a control voltage variable range of a voltage controlled oscillator(VCO) 5 is provided with a 2nd operator and a bipolar power supply is employed for the 2nd operational amplifier. A loop filter 3 receives an output of a phase comparator 2 and eliminates generated comparison noise according to a phase difference from a reference oscillator 1. Resistors 7, 8 in the control voltage regulator 4 prevents a maximum voltage of an output of the loop filter 3 from being inputted to the operational amplifier and the DC gain of the regulator 4 depends on the division ratio of the resistors 7, 8 and resistors 9-11. Thus, the VCO control voltage range is widened and a stable PLL loop is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of 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.

[Summary of the invention]

In a microwave frequency synthesizer, when an operational amplifier is used as a loop filter, its maximum amplitude is about 70 to 80% of the power supply voltage, and the control voltage range of the VCO becomes narrow. If both positive and negative power supplies are used as the power supply in an attempt to expand the control voltage range 17, a forward voltage may be applied to the varactor during the start-up operation of the circuit, and the PLL loop may not operate.

Therefore, by setting the operational amplifier power supply for the loop filter to the voltage between the positive power supply and GND, using the second operational amplifier as the control voltage range adjuster, and making the power supply the positive and negative power supplies, the control voltage can be increased to 80 to 90. Improved. Also,
This expanded range of control voltage is the range in which the Q of the varactor decreases, so the Q of the resonator incorporating the varactor is
C/N can also be maintained by arranging the varactor at a portion shifted from the maximum magnetic field portion so as to minimize the decrease in C/N.

[Conventional technology]

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

A phase comparator 2 compares the phase of a reference oscillator 1 with the phase of a signal obtained by frequency-dividing a VCO (voltage controlled oscillator) 5 using a programmable counter 6, and feeds the error signal to the VCO 5 through a loop filter 3. By doing this, a predetermined frequency can be obtained, and by changing the division ratio of the programmable counter 6, the frequency can be changed.

That is, by changing the set value of the programmable counter 6, the output frequency can be obtained within the oscillation range of the VCO 5. Here, the loop filter 3 is often an operational amplifier that has a large DC gain and can remove common mode noise from the t source. It is necessary to be able to control the VCO within the range of the output voltage of this operational amplifier, including changes due to temperature and voltage fluctuations. On the other hand, local oscillators for communication equipment need to have a good C/N ratio, so the varactor diode used for CO must have a high Q (
However, varactor diodes with high Q often have a small rate of change in capacitance. Therefore, the control range may be exceeded due to temperature changes, etc., and it is necessary to widen the voltage range of the roof filter.
ov, the output voltage will be narrow to about 1.5v to 8.5v.

Since the capacitance change of the varactor diode is greatest when the reverse voltage is near QV, the frequency variable range becomes narrow.

When an operational amplifier is used in the loop filter 3, if the low voltage terminal of the power supply is connected to a negative voltage at ground potential in order to widen the output voltage range, during a transient response when the power is turned on, negative voltage will be applied to the canode. is applied and the anode of the varactor is set to ground potential, a forward voltage may be applied and control may become uncontrollable.

In this case, the anode side of the varactor should be connected to the negative power supply, but the anode end should be disconnected from the ground using direct current.
And at high frequencies. Setting the circuit to open or short mode increases the size of the circuit and increases the instability of its characteristics.

Furthermore, when the applied voltage to the varactor diode is low, the Q is low and the varactor diode is used, so the applied voltage is increased and the variable frequency range is limited to a narrow range.

[Problem to be solved by the invention]

In the conventional technology, as described above, instability occurred due to the use of negative voltage and the expansion of the control voltage range.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a microwave frequency synthesizer that can overcome these drawbacks and expand the control voltage range with a simple configuration.

[Means to solve 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 compared to the prior art shown in FIG.

[Effect]

As a result, the embodiment shown in FIG. 1 allows the control range to be widened. Figure 3 shows an example of a VCO resonant section, in which the varactor diode 12 is not set near P1 or P4, but P2.
By arranging them nearby, a drop in C/N is prevented.

〔Example〕

FIG. 2 shows a concrete implementation circuit example of a loop filter and a voltage control regulator. The loop filter 3 in FIG. 2 receives the phase comparator output and removes generated comparison noise according to the phase difference with the reference oscillator (so-called charge pump). Resistors 7 and 8 in 4 prevent the maximum voltage of the output of 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.

FIG. 3 shows an embodiment of the vCO Iburibe, and the output terminal of the control voltage regulator 4 in FIG. 2 is connected to the varactor control voltage application terminal 14. The anode side of the varactor 12 is connected to the ground potential via the center conductor, and the cathode side is connected to the ground potential by direct current through the insulating plate 13. A varactor control voltage is applied so that point P1 is in short mode in terms of high frequency. A small hole is made in this resonant part, a conductor is inserted, and it is coupled with an external transistor 15 to cause oscillation, and the VCO is controlled. Figure 5 shows the impedance of each part of this resonant part on a Smith chart. It is something that The resistance component is P. or P4
When added to the point, the loss is greatest, and the Q
It is expected that the amount will decrease. Therefore, the varactor voltage is low (C
If the impedance zp3 in the case (v==max) is moved away from the real axis, the drop in Q will be reduced.

There are two advantages to shifting the varactors.

The first is the expansion of the variable range, an example of which is shown in FIG. 6 using a Smith chart. When the normalized impedance changes by 0.3 from the short end of the varactor, Cmax and Cm when the position is not shifted.
The angle difference of irx is 400, whereas the difference in angle of irx is 02.
is 45°, and it can be expected that the frequency variable range will expand.

The second is securing C/N. Since a high frequency current flows near the normalized impedance O, the loss due to the resistance of the varactor becomes large, and Q tends to decrease. When the normalized impedance is around O, the varactor Q is low C m
If it is set to ax, the Q of the resonator will decrease and the C/N will decrease.

The amount e to shift the position of the varactor is 2π as an approximate solution.
ω I=τ=T (C: speed of light) is set to 0.1 to 0.5, and the position of the varactor becomes a coaxial resonator. (However, U: angular velocity at the center frequency) [Effects of the Invention] According to the present invention, the VCO control voltage range is widened and a stable PLL loop can be maintained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention, FIG. 2 is a circuit diagram showing an embodiment of the loop filter and control voltage range adjuster of the present invention, and FIG. 3 is the structure of the VCO resonance section of the present invention. 4 are block diagrams showing the overall conventional configuration, FIG. 5 is a diagram showing the impedance of each part in FIG. 3, and FIG. 6 is a diagram for explaining the expansion of the variable range. 1: Reference oscillation e. 5: VCO, 6: Poop counter, 7~1l: Resistor that determines DC gain, 1
2: Varactor diode, 3: Insulating plate, 14: Varactor control voltage application terminal, 15: } transistor. Figure 4 Figure 6-112-

Claims (1)

[Claims] 1. In a communication device including a voltage controlled oscillator using a varactor diode as a variable frequency element, and a built-in microwave local oscillator that controls the output frequency of the voltage controlled oscillator by a phase locked loop, the phase locked loop is configured. A first operational amplifier is used as a loop filter, and a second operational amplifier is provided which receives the output of the first operational amplifier and adjusts the control voltage variable range of the voltage controlled oscillator, and the first operational amplifier is connected to a positive power supply. , wherein a positive and negative power source is used for the second operational amplifier, and the varactor diode is arranged offset from a position where the magnetic field of the high Q resonance part in the voltage controlled oscillator is maximum. frequency synthesizer.