JPH01251840A - Frequency shift keying type modulator - Google Patents

Abstract

PURPOSE:To avoid deterioration of the anti-waveform distortion characteristics and the anti-adjacent frequency disturbance characteristics by forming a waveform shaping part to properly cut the high frequency component and also produce a shaped waveform suited to a voltage control oscillator. CONSTITUTION:The control voltage value set for control of a voltage control oscillator 52 is temporarily stored in a memory part 43 and then taken out. Then the parameters are properly selected among a digital filter 47, a D/A converter 49 and an analog filter 50 and the shaping output is applied to the oscillator 52 so that said shaping output is suited to the oscillator 52 and at the same time the noises are cut. The output of the oscillator 52 is partly fed back and the frequency of the feedback signal received from the oscillator 52 is detected by a counter 56 based on a prescribed reference frequency. This detecting signal is compared with the control voltage stored in the part 43 to the oscillator 52. Thus the control voltage value stored in the part 43 is sequentailly corrected. As a result, an optimum modulation signal is obtained without deteriorating the anti-waveform distortion characteristics and the anti- adjacent frequency disturbance frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency shift keying modulator suitable for high-speed data communications.

[Conventional technology]

Conventionally, this type of frequency shift keying (FSK) modulator often uses a phase-locked loop (PLL) circuit. Historically, this PLL circuit has 193
It was introduced in 2002 as an electronic servo system for stabilizing the local oscillation frequency in super-hetero gain receivers.

FIG. 3 shows the basic configuration of the PLL circuit.

In the figure, a voltage controlled oscillator (VCO) 11 is of a free-running type, and its oscillation frequency is usually determined by an external collector. The frequency 50 of the output signal 12 of this VCO is fed back to the scale detector 13, where it is compared with the input frequency f of the input signal 14.

The output 15 of this phase detector 13 is called an error voltage, and is the difference between the frequency (rt to), the human input signal 14 and VCol.
It is given as an average value DC voltage proportional to the phase difference Δ0 with the output signal 12 of 1. The low pass filter 16 operates to remove high frequency noise from the error voltage 15 and return the error voltage 15 to VColl to form a loop. In this way, when the phase rotation state occurs, VCol
The output frequency f0 of l becomes equal to the human power frequency f,.

Figure 4 shows a conventional FSK using such a PLL circuit.
This is a representation of a modulator.

The input signal 21 is input to a variable frequency divider circuit 22 .

The variable frequency divider circuit 22 changes the frequency division ratio 1/N according to the marks and spaces included in the human input signal 21 and sends the frequency division output 23 to the phase comparator 24 . The phase comparator 24 is further supplied with a divided output 29 of a frequency dividing circuit 28 that divides the reference output 27 of the reference frequency oscillation circuit 25 . And the phase of these divided outputs 23.29 -
An error output 31 corresponding to the phase difference is sent to a voltage controlled oscillator 33 via a low-pass filter 32. This voltage controlled oscillator 33 generates an output voltage 34 of the low-pass filter 32.
An oscillation output 35 having a frequency corresponding to the frequency is given, and the negative part is fed back to the variable frequency divider circuit 22. Below, as in the case of Figure 3,
When the phase rotor state is entered, the number of cycles 21112 of the human input signal 21 and the oscillation output 35 match.

[Problem to be solved by the invention]

As explained above, in the conventional FSK modulator,
A low-pass filter is provided between the phase comparator and the voltage-controlled oscillator to remove noise that causes unnecessary radiation and to narrow the occupied bandwidth.

For this reason, the conventional FSX modulator has a problem of poor transient characteristics, making it unsuitable for high-speed digital communications.

SUMMARY OF THE INVENTION An object of the present invention is to provide an FSX modulator whose waveform distortion characteristics and adjacent frequency interference characteristics do not deteriorate even when used in high-speed digital communications.

[Means to solve the problem]

The FSX modulator of the present invention includes a voltage controlled oscillator that generates mark and space frequencies according to mark and space frequencies of digital modulation data, a storage circuit that stores control voltage values that control this voltage controlled oscillator, and a storage circuit that stores control voltage values that control this voltage controlled oscillator. a waveform shaping section that shapes the voltage value stored in the circuit into a waveform suitable for the voltage controlled oscillator and sends it to the voltage controlled oscillator, and the voltage controlled by a predetermined reference frequency and the output of the waveform shaping section. Counter means for detecting the output frequency of the controlled oscillator and outputting detected data, the detected data output from this counter means, and the above-mentioned storage circuit! The storage circuit includes a comparison circuit that compares the voltage value stored in the memory circuit and corrects the voltage value stored in the storage circuit according to the deviation thereof.

Therefore, when using the FSK modulator according to the present invention, before the input data is applied to the voltage controlled oscillator, instead of using a simple low-pass filter as in the past, high frequency components that cause unnecessary radiation are appropriately blocked. In addition, a waveform shaping section that outputs a shaped waveform suitable for the voltage controlled oscillator is provided, so the FSX
Even when the modulator is used for high-speed digital data communication, it is possible to prevent the waveform distortion characteristics and adjacent frequency interference characteristics from deteriorating.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 1 is a block diagram showing the configuration of this embodiment.

In the figure, human input data 41 as modulated data is input to a switch 42 . This switch 42 sends an address signal 45 to a storage circuit 43 based on voltage values corresponding to mark and space frequencies included in input data 41, and extracts a control voltage signal 46 from this storage circuit 43.

This control voltage signal 46 selected by the switch 42 is then sent to a digital filter 47. This digital filter 47, together with the next D/A converter 49 and analog filter 50, cuts off high frequency components appropriately in order to remove noise, and further forms a shaped waveform suitable for the subsequent voltage controlled oscillator 52, as will be described later. Output.

The voltage controlled oscillator 52 receives the shaped output 54 from the waveform shaping section 53 and outputs the output signal 5 as an FSK modulator.
5, a portion of which is sent to counter 56. Upon receiving this, the counter 56 measures the frequency of the output signal 55 of the voltage controlled oscillator 52 based on the reference frequency signal 58 from the reference frequency oscillator 57. This measurement signal 58 is sent to a computing unit 59. The arithmetic unit 59 that receives this measurement signal 58 compares it with the voltage value stored in the storage circuit 43 . And when there is a deviation between the two,
The control voltage signal 46 containing the mark frequency and space frequency, which is stored in the memory circuit 43, is corrected.

Next, the waveform shaping section 53 will be explained in detail with reference to FIG. 2. Human data 41 as modulated data (a in the figure)
is a square wave, and if it is modulated as is, the occupied frequency bandwidth will be widened. If left as is, it will be easy to pick up noise that causes unnecessary radiation, so high frequencies are cut off through the analog filter 50, which is a low-pass filter (see b in the figure). As this analog filter 50, for example, a lag filter made up of a resistor and a capacitor is used. However, as is clear from the figure, the waveform in this case changes exponentially, and although it still contains many high-frequency components (rising and falling parts of the waveform), waveform distortion (square waveform) (collapse) is large. From the point of view of effective use of radio waves, it is desirable that the signal band falls within a predetermined range and that there is no interference between codes. Therefore, as a method for realizing such a waveform that is close to the ideal, it is possible to use a Blackman window used in fast Fourier transform (C in the figure). Therefore, in this embodiment, the circuit parameters of the digital filter 47, D/A converter 49, and analog filter 50 are adjusted to obtain a waveform close to the ideal waveform as described above. In that case, the output waveform of the D/A converter 49 and the output waveform of the analog filter 50, that is, the voltage controlled oscillator 5
The input control voltages for 2 are as shown in dle in the figure, respectively.

〔Effect of the invention〕

In this way, the FSK modulator of the present invention temporarily stores the control voltage value for controlling the voltage-side oscillator in the storage section, takes out the stored control voltage value, and makes the FSK modulator suitable for the voltage-controlled oscillator and eliminates noise. In order to be able to shut off, the parameters of the digital filter, D/A converter, and analog filter are appropriately selected, a shaped output is given to the voltage controlled oscillator, a part of the output of this voltage controlled oscillator is fed back, and the A counter detects the frequency of the feedback signal from the voltage-controlled oscillator using a predetermined reference frequency, and compares this detection signal with the control voltage for the voltage-controlled oscillator stored in the storage circuit to generate the control signal stored in the storage circuit. By sequentially correcting the voltage value, an optimum modulated signal can be provided without deteriorating waveform distortion characteristics and adjacent frequency interference characteristics even in high-speed digital data communication.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the FSK modulator according to the present invention, FIG. 2 is a diagram showing the operation of the waveform shaping section in FIG. 1, and FIG. 3 is a block diagram showing the basic configuration of a PLL circuit. FIG. 4 is a block diagram showing a conventional FSK modulator. 43... Memory circuit, 53... Waveform shaping section, 56... Counter, 59... Arithmetic circuit. Applicant NEC Corporation Agent
Patent Attorney Umeo Yamauchi Higashi 1, 4 illustrations, 2 figs. 3

Claims (1)

[Claims] A voltage controlled oscillator that generates mark and space frequencies according to marks and spaces of digital modulation data, a memory circuit that stores a control voltage value that controls the voltage controlled oscillator, and a memory circuit that stores control voltage values that control the voltage controlled oscillator. a waveform shaping section that shapes the voltage value into a waveform suitable for the voltage controlled oscillator and sends it to the voltage controlled oscillator; and the voltage control that is controlled by the output of the filter means based on a predetermined reference frequency. counter means for detecting the output frequency of the oscillator and outputting detected data; and comparing the detected data output from the counter means with the voltage value stored in the storage circuit, and storing the voltage value in the storage circuit according to the deviation. A frequency shift keying type modulator, comprising: a comparator circuit for correcting a voltage value.