JPH0516685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a variable frequency oscillation device that has high stability and can be used in standard signal generators and the like that can facilitate FM modulation.

Prior Art FIG. 3 shows a conventional variable frequency oscillator. The configuration of this conventional example will be explained below with reference to FIG. 3. In FIG. 3, 1 is a variable frequency oscillator, and this variable frequency oscillator 1 oscillates at the resonance frequency of the variable capacitance diode 1a and the coil 1b, and the capacitance of the variable capacitance diode 1a changes as the DC bias voltage changes. Change the oscillation frequency and output from the output terminal A1c. Further, the output terminal B1d is connected to the input terminal 2a of the variable frequency divider 2. The variable frequency divider 2 divides the signal at the input terminal 2a according to the frequency set by the frequency setting circuit 3, outputs a comparison signal from the output terminal 2c, and is connected to the input terminal 6a of the phase comparator 6. ing. The frequency setting circuit 3 sends out a digital control signal according to a set frequency, and is connected to the setting terminal 2b of the variable frequency divider 2. A high-precision crystal oscillator 4 is connected to an input terminal 5a of a fixed frequency divider 5. The fixed frequency divider 5 divides the signal of the high-precision crystal oscillator 4 to a predetermined frequency division ratio, and outputs a reference signal from the output terminal 5b to the input terminal 6b of the phase comparator 6. A phase comparator 6 compares the phases of the reference signal from the fixed frequency divider 5 and the comparison signal from the variable oscillator 2, and outputs no signal if the phases match, and outputs an error signal if the phases differ. 7
is an integrator A consisting of an operational amplifier A1, resistors R1 and R2, and a capacitor C1, which smoothes the pulsed error signal. 8 further smooths the insufficient smoothing by the integrator A7, so that the control signal applied to the variable capacitance diode 1a of the variable frequency oscillator 1 becomes a signal sufficiently close to the DC voltage.

9 is an FM mode setting device which, when operated when an FM modulated signal is required, controls the switch 11 and uses the audio frequency from the FM modulation signal section 10 to drive the variable capacitance diode 1a. The FM modulated wave is obtained from the output terminal 1c by superimposing it on the current DC voltage.

Next, the operation of the above conventional example will be explained. Third
In the figure, when the desired frequency is set in the frequency setting circuit 3, the frequency setting circuit 3 sends the reference signal to the setting terminal 2b of the variable frequency divider 2 by dividing the frequency of the signal from the high-precision crystal oscillator 4 using the fixed frequency divider 5. A comparison signal is output from the variable frequency divider 2 by sending a digital control signal that sets a frequency division ratio such that the frequency of the signal and a comparison signal obtained by dividing the desired frequency signal match. . The phase comparator 6 compares the phases of the reference signal and the comparison signal, and if the phases are different, outputs a pulse-like error signal to the integrator A7.

The above error signal is sufficiently smoothed by the integrator A7 and the low-pass filter 8, becomes a DC voltage component signal, and is applied to the variable capacitance diode 1a of the variable frequency oscillator 1, thereby changing the capacitance and controlling the oscillation frequency. do. By repeating this, a signal converged to the desired frequency is output from the output terminal 1c.

Problems to be solved by the invention However, variable frequency oscillators are generally
It has both a mode that applies FM modulation and a mode that does not apply FM modulation (for example, AM modulation or no modulation), and like the conventional example above, only phase synchronization control is required.
When trying to control a variable frequency oscillator circuit, in order to increase the stability of the phase-locked loop, the gain and time constant of integrator A7 must be increased, so the response speed to converge to the desired frequency is slow. A drawback.

Due to the phase-locked loop, even if the frequencies match, the error signal continues to be output until the phases match, so in S/N measurement, FM modulation (equivalent to S) is turned off and noise (equivalent to N) is measured. ,
Since the FM noise caused by the error signal is added to the noise, the noise level also decreases as the error signal amount decreases, so the disadvantage is that it takes a long time until the noise level becomes stable and S/N measurement can be performed.

That's what it means. There were two major drawbacks mentioned above.

The present invention eliminates the drawbacks of the conventional example, and in a mode without FM modulation, has high frequency stability, which is an advantage of phase synchronization control, and converges on the desired frequency with a faster response speed than the conventional example. However, when used in a mode that applies FM modulation, due to frequency control, which is an advantage of period comparison control.
The objective is to achieve faster stability of the FM noise level (compared to phase synchronization control).

Means for Solving the Problem In order to achieve the above object, the present invention uses period synchronization control to pull in the vicinity of the convergence frequency when in a mode in which FM modulation is not applied, and then switches to phase synchronization control. The configuration is such that when the mode is in which FM modulation is applied, the control is switched to period synchronous control.

Effects Due to the above configuration, the present invention has frequency stability equivalent to that of a standard high-precision crystal oscillator circuit in modes other than FM modulation, converges at a faster response speed than conventional ones, and in FM modulation mode, It has almost the same stability as a high-precision crystal oscillator circuit, and has the effect of being able to measure the S/N of FM modulation faster than phase synchronization control.

Embodiment The configuration of an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of a variable frequency oscillator according to an embodiment of the present invention, and FIG. 2 is a signal waveform diagram of the same embodiment. In FIG. 1, blocks having the same functions as those of the conventional example are given the same numbers. The error amount detection circuit 12 low-pass filters the error signal using a resistor R5 and a capacitor C3.
The threshold level of the C-MOS gate U1 is used to send a control signal to the switch control circuit 13 and the reset signal controller 15 when the pulse width exceeds a predetermined pulse width.

The switch control circuit 13 includes a gate circuit and a J.K.
It is composed of a flip-flop and a comparator, and sends a control signal to the switch circuit A14 using signals from the error amount detection circuit 12 and the FM mode/other mode switch 17. The switch circuit A14 is closed when a period-locked loop is in effect, reducing the gain of the integrator B16, and operates in the opposite manner when a phase-locked loop is in effect, each operating in a stable loop state. The reset signal controller 15 continues to send out the reset signal in accordance with the control signal from the FM mode/other mode switch 17 in the FM mode, and as long as the output signal of the error amount detection circuit 12 is output in the other mode. A reset signal is sent out, and when the output signal disappears, the sending out of the reset signal is stopped. The integrator B16 is configured so that the gain of the operational amplifier A1 can be switched. Reference numeral 17 denotes an FM mode/other mode switch which controls the reset signal controller 15, the error amount detection circuit 12, and the switch 11.

Next, the operation of the above embodiment will be explained. 1st
In Figures 1 and 2, when the operator changes the set frequency in a mode other than FM mode, the FM mode/other mode switch 17 specifies the other mode.
a. Similar to the conventional example, the phase comparator 6 outputs an error signal 16a having a pulse width proportional to the frequency error. In the error amount detection circuit 12, the C-MOS gate U1 is turned on by the signal 17a of the FM mode/other mode switch 17, so the resistor R5 and the capacitor C are turned on.
3, the output signal 12b is sent to the switch control circuit 13. The switch control circuit 13 closes the switch circuit A14 and reduces the gain of the operational amplifier A1 16b. The FM mode/other mode switch 17 also sends a control signal 17a to the reset signal controller 15, and while the error amount detection circuit 12 continues to output the output signal 12b, the reset signal controller 15 sends out the reset signal 15a. Work like you do. The variable frequency divider 3 and fixed frequency divider 5 are reset by this reset signal 15a.
Operate in a synchronized state. In this state, the phase comparator 6 operates as a period comparator 16a. As a result, the frequency error range corresponding to the pulse width set by the error amount detection circuit 12 is reached earlier than in phase synchronization. When the pulse width becomes equal to or less than the pulse width set by the error amount detection circuit 12, the switch control circuit 13 operates in the opposite direction, and the reset signal controller 15 also stops sending out the reset signal 15a, entering a phase-locked loop state, and the high-precision crystal The frequency converges to the set frequency with stability equivalent to that of the oscillator 4. As a result, compared to convergence using only a phase-locked loop, there is an advantage that it converges faster while maintaining the same stability.

Next, when the operator changes the set frequency in FM mode, the 17 FM mode/other mode switch will switch to FM mode.
A control signal specifying the mode is sent out, and the reset signal controller 15 continues sending out the reset signal, and at the same time controls the switch control circuit 13 to close the switch circuit A14 and close the integrator C.
This reduces the gain of the periodic control loop and stabilizes the periodic control loop. It also controls the switch 11 and operates so that the audio signal of the FM modulation signal section 10 is superimposed on the DC voltage that drives the variable capacitance diode 1a. By sending the reset signal, the variable frequency divider 3 and fixed frequency divider 5 are synchronized,
6 operates as a period comparator and controls the frequency.

Effects of the Invention As is clear from the above embodiments, the present invention provides FM
When in the mode where no modulation is applied, the frequency is pulled in to the vicinity of the convergence frequency using periodic synchronous control, and from there it switches to phase synchronous control, and when the mode applies FM modulation, it switches to periodic synchronous control. In the non-modulated mode, it has the same frequency stability as the standard high-precision crystal oscillator circuit, and in the FM modulation mode, it has the same stability as the standard high-precision crystal oscillator circuit, and the FM This has the effect of making it possible to measure the S/N of modulation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a variable frequency oscillator according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram of the same embodiment, and FIG. 3 is a block diagram of a conventional variable frequency oscillator. 1... Frequency variable oscillator, 3... Frequency setting circuit, 2... Variable frequency divider, 4... High precision crystal oscillator, 5... Fixed frequency divider, 6... Phase comparator, 7...
...Integrator A, 8...Low pass filter, 9...FM mode setter, 10...FM modulation signal section, 11...
Switch, 12...Error amount detection circuit, 13...Switch control circuit, 14...Switch circuit A, 15...
...Reset signal controller, 16...Integrator B, 17
...FM mode/other mode switch.

Claims (1)

[Claims] 1. A variable frequency oscillator whose oscillation frequency changes according to a control voltage, a variable frequency divider whose frequency division ratio changes according to a set desired oscillation frequency, and which divides the signal of the variable frequency oscillator; A phase comparator that compares the signal of the variable frequency divider and a reference signal of the crystal oscillator circuit and sends out a phase difference signal, and a control signal that switches a switch circuit to change the time constant and send the control to the variable frequency oscillator. An integrator that sends out voltage and when set to FM mode
An FM mode/other mode switch that sends out an FM mode signal and the phase difference signal of the phase comparator are integrated, and when the phase difference is greater than a predetermined phase difference, the switch circuit of the integrator is activated so that the time constant becomes small. An error amount detection circuit that sends out the above control signal, and a reset signal that continues to be sent to the variable frequency divider when the above FM mode signal is input, and output of the error amount detection circuit signal when in the other modes. A variable frequency oscillator comprising a reset signal controller that sends out a reset signal only during a period of time.