JPH01318410A - Frequency modulator - Google Patents

Abstract

PURPOSE:To prevent the generation of undesired radiation during the working of a frequency converter by preparing a synchronism detector to detect the phase step-out of a phase synchronizing circuit and outputting a serial data signal to a variable divider via a serial data signal generated only when the step-out is detected. CONSTITUTION:A synchronism detector 8 is set between a phase comparator 4 and a serial data signal generator 7. In this case, the detector 8 consists of an AM wave detector which is generally used. In case the error signal of a phase comparator 4 fluctuates due to the step-out, the negative voltage is taken out after the rectification carried out by a wave detecting circuit 13 consisting of the capacitors C1 and C2, a diode D1 and the resistances R1 and R2. Then the signal is outputted to the generator 7 via a buffer amplifier 12 only in a step-out state. Meanwhile the serial data signal is surely produced and then stopped after the step-out state. Thus it is possible to exclude the disturbance signal mixed into the input signal and to prevent the undesired radiation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency modulator, and more particularly to a synthesizer type frequency modulator that variably controls frequency.

(Prior Art) Conventionally, synthesizer-type frequency modulators have been widely used in wireless communication equipment because the oscillation frequency can be easily varied. Instead of changing the reference frequency in the phase-locked circuit, it is common to change the frequency division ratio of the frequency divider in the phase-locked circuit using external serial data.

FIG. 3 is a block circuit diagram of an example of a conventional frequency synthesizer type frequency modulator. In the figure, 1 is a modulation input terminal, 2 is a voltage controlled oscillator (VCO), 3 is a variable frequency divider, 4 is a phase comparator, 5 is a reference signal generator, 6 is a reduction filter, and 7 is a serial data signal. It is a generator.

In this configuration, the frequency division ratio in the variable frequency divider 3 is determined by the frequency division ratio data signal, that is, the serial data signal sent from the serial data signal generator 7. Then, the phase comparator 4 detects the phase difference between the frequency signal obtained by dividing the output frequency of the voltage controlled oscillator 2 into 17H by the variable frequency divider 3 and the reference frequency signal output from the reference signal oscillator 5. The phase error voltage thus obtained is applied to the voltage controlled oscillator 2 through a reduction filter 6 provided for loop stabilization to control its oscillation frequency. As a result, in a state in which the phases are synchronized, the voltage controlled oscillator 2 outputs a signal that is N times the reference signal frequency and has the same stability as the reference frequency.

[Problem to be solved by the invention]

In the conventional frequency modulator described above, once the serial data signal is sent from the serial data signal generator 7 to the variable frequency divider 3 and the frequency division ratio is determined, there is no need to change the oscillation frequency. As far as possible, the same serial data continues to be repeatedly applied to the variable frequency divider 3 during its operation. However, since this type of serial data signal is composed of a rectangular wave logic signal, the signal also contains many high frequency components, and the noise enters the modulation loop as an interference signal, causing the modulation signal to be distorted. There is a problem in that the voltage controlled oscillator 2 is modulated and unnecessary radiation is generated.

An object of the present invention is to provide a frequency modulator that prevents generation of unnecessary radiation.

[Means to solve the problem]

The frequency modulator of the present invention detects phase synchronization in the phase synchronization circuit, and outputs serial data from a serial data signal generator only when this phase synchronization is detected. The configuration includes a synchronous detector that outputs a signal to a variable frequency divider.

[Effect]

In the above configuration, the serial data signal is output from the serial data signal generator to the variable frequency divider only when phase synchronization is lost, so the output of the serial data signal is stopped during synchronization, and the serial data signal is Unnecessary radiation during operation caused by radiation can be suppressed.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block circuit diagram of an embodiment of the present invention, and the same parts as in FIG. 3 are given the same reference numerals. That is, in the figure, 1 is the modulation input terminal, 2 is the voltage controlled oscillator (V
CO), 3 is a variable frequency divider, 4 is a phase comparator, 5 is a reference signal generator, 6 is a reduction filter, and 7 is a serial data signal generator, which constitute a phase locked loop (PLL). It constitutes a frequency synthesizer.

In this configuration, the serial data signal generator 7 is configured so that its operation can be controlled from the outside, that is, the sending/stopping of the serial data signal can be controlled, and the output of the phase comparator 4 and A synchronization detector 8 is inserted between the serial data signal generator 7 and the serial data signal generator 7.

When the phase synchronization circuit is out of synchronization due to turning on the power or changing the division ratio, the synchronization detector 8 detects this out of synchronization state and starts the serial data signal generator 7 to generate a serial data signal. That is, the frequency division ratio data signal is outputted, and the frequency division ratio data signal is continuously inputted to the variable frequency divider 3. On the other hand, when the phase synchronization circuit reaches a synchronized state, the synchronization detector 8 stops operating and controls the serial data signal generator 7 to stop sending out the frequency division ratio data signal.

Note that even when the transmission of this frequency division ratio data signal is stopped, the time variable frequency divider 3 internally latches the frequency division ratio data immediately before the output signal of the serial data signal generator 7 stops being transmitted. , even if the frequency division ratio data signal is not supplied thereafter, there is no problem and the synchronized state can be maintained.

FIG. 2 is a circuit diagram showing a specific configuration of FIG. 1. The synchronization detector 8 is composed of a commonly used AM detector, and when the error signal of the phase comparator 4 fluctuates due to loss of synchronization, the capacitor CI+C2, the diode D+, and the resistor R
.

The serial data signal generator 7 includes a clock oscillator 10 that is the basis of a serial data signal, a clock controller 11 that controls the oscillator, and a serial data generator 9. The serial data generator 9 outputs a serial data signal a and a strobe signal for timing identification to be sent after the last bit of serial data is sent based on the output of the clock oscillator 10. Also,
The clock oscillator 10 outputs a clock signal C for taking in serial data.

The variable frequency divider 3 sequentially takes in the serial data a at the timing of the clock signal C, and performs an operation of fixing the frequency division ratio using the strobe signal. Therefore, when the phase synchronized circuit enters a synchronized state and the control signal from the synchronization detector 8 stops and the operation of the serial data signal generation circuit 7 stops, the variable frequency divider 3 assumes that the division ratio is fixed. Therefore, even if the serial data signal is interrupted midway, no operational problems will occur.

As a result of the above effects, the serial data signal that causes unnecessary radiation is sent only when the power is turned on or when the frequency division ratio is changed, etc., and when synchronization occurs, creating a condition where it is stopped during normal operation. , generation of interference signals due to serial data signals is suppressed.

[Effects of the Invention] As explained above, the present invention detects phase synchronization loss in a phase synchronization circuit, and only when this phase synchronization loss is detected, transmits the serial data signal from the serial data signal generator to the variable frequency divider. Since it is equipped with a synchronization detector for output, it is possible to reliably generate a serial data signal while the phase is out of synchronization, and to stop the serial data signal after entering the synchronization state, preventing it from being mixed into the input signal. This has the effect of eliminating unwanted interference signals and preventing unnecessary radiation.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an embodiment of the frequency modulator of the present invention, FIG. 2 is a specific circuit diagram of FIG. 1, and FIG. 3 is a block circuit diagram of a conventional frequency modulator. 1... Modulation input terminal, 2... Voltage controlled oscillator, 3...
...Variable frequency divider, 4...Phase comparator, 5...Reference signal oscillator, 6...Low pass filter, 7...Serial data signal generator, 8...Synchronization detector , 9... serial data generator, 10... clock oscillator, 11...
Clock controller, 12... Buffer amplifier, 13... Detection circuit, a... Serial data signal, b... Strobe signal, C... Clock signal.

Claims (1)

[Claims] 1. A voltage controlled oscillator, a variable frequency divider that divides the output signal of this voltage controlled oscillator, a phase comparator that compares the output signal of this variable frequency divider with a reference frequency, and a In a frequency modulator having a serial data signal generator for setting a frequency ratio, the serial data signal generator is connected to the phase comparator to detect phase synchronization, and only when this phase synchronization is detected, the serial data signal generator A frequency modulator comprising a synchronous detector that outputs a serial data signal.