KR970000250Y1 - Frequency modulator using phase fixed loop - Google Patents

Abstract

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Description

Frequency Modulation Device Using Phase Locked Loop

1 is a block diagram showing a conventional FSK or FM modulator performed inside a PLL loop.

2 is a modulation response characteristic curve of the FSK or FM modulator shown in FIG.

3 is a block diagram showing a conventional FSK or FM modulator performed outside the PLL loop.

4 is a modulation response characteristic curve of the FSK or FM modulator shown in FIG.

5 is a block diagram according to an embodiment of a frequency modulation device using a phase locked loop according to the present invention.

6 is a modulation response characteristic curve of the frequency modulator shown in FIG.

* Explanation of symbols for main parts of the drawings

31: temperature compensation crystal oscillator 32: phase detector

33: loop filter 34, 35: voltage controlled oscillator

36: voltage controlled crystal oscillator 37: mixer

38: low pass filter

The present invention relates to a frequency modulation device using a phase locked loop, and more particularly, to a frequency modulator in which a phase locked loop (hereinafter, referred to as a PLL) is mixed with internal and external modulation characteristics.

As shown in FIG. 1, in a conventional heterodyne PLL, a frequency modulation or frequency shift keying is performed by a signal output from the voltage controlled oscillator 5 inside the PLL loop. In a conventional frequency modulator that performs modulation (FSK), the PLL loop bandwidth is affected as shown in FIG. That is, the modulation response characteristic of the high pass filter having the PLL loop bandwidth as the cut-off frequency is obtained. (See Phase Lock Techniques, F. M. Gardner)). In this case, the PLL loop bandwidth must be lowered for better modulation response. Therefore, if the loop bandwidth is lowered, the PLL response time, which is required for the loop to reach a steady state, becomes long due to the characteristics of the PLL loop.

On the other hand, as shown in FIG. 3, the crystal oscillator (6 in FIG. 1) is replaced with a voltage controlled crystal oscillator 25 and a signal output from the voltage controlled crystal oscillator 25 outside of the PLL loop. By performing FM or FSK modulation, as shown in FIG. 4, the PLL loop bandwidth is affected as in the PLL loop internal modulation in FIG. In other words, the modulation response characteristics of a low pass filter having a PLL loop bandwidth as a cutoff frequency are obtained. (See Phase Lock Techiques, F. M. Gardner)) In this case, the PLL loop bandwidth must be increased to improve the modulation response. Therefore, when the loop bandwidth is increased, as in the case where the loop bandwidth is lowered, the PLL response time for the loop to reach a steady state is long due to the characteristics of the PLL loop.

Therefore, according to the frequency modulation device having the modulation response characteristic as shown in FIG. 2 or FIG. 4, in the case of FM modulation for modulating analog voice, a signal with high distortion is output, and FSK modulation for modulating digital data. In this case, there is a lot of jitter and the eye opening becomes narrow, causing a problem in the data.

Therefore, an object of the present invention is to combine the internal modulation characteristics of the high pass filter type using the PLL loop bandwidth as the cutoff frequency and the external modulation characteristics of the low pass filter type using the PLL loop bandwidth as the cutoff frequency. The present invention provides a frequency modulation device for obtaining a constant modulation response characteristic in all bands regardless of the loop bandwidth of the PLL.

Frequency modulation device using a phase locked loop according to the present invention to achieve the above object is a temperature compensation crystal oscillator for making a reference frequency of the phase locked loop; A phase detector for comparing a phase of a reference frequency signal output from the temperature compensation crystal oscillator with a phase of a comparison frequency signal and converting the phase difference into a voltage; A loop filter for filtering and rectifying the voltage output from the phase detector; An adder for modulating a voltage output from the loop filter according to a modulation input signal; A voltage controlled oscillator for varying the frequency according to the voltage modulated by the adder and supplying the frequency modulated output; A voltage controlled crystal oscillator for generating a local oscillation frequency of said phase locked loop and for performing frequency modulation in accordance with said modulation input signal; A mixer for mixing the frequency modulated signal output from the voltage controlled oscillator and the frequency modulated signal output from the voltage controlled crystal oscillator; And a low pass filter (38) for low pass filtering the signal output from the mixer to supply the comparison frequency signal of the phase detector, wherein the internal frequency modulation of the phase locked loop and the voltage controlled crystal oscillator in the voltage controlled oscillator The phase locked loop external frequency modulation in is characterized in that it is performed simultaneously.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

5 is a block diagram according to an embodiment of a frequency modulation device using a phase locked loop according to the present invention.

In the block diagram shown in FIG. 5, the phase of the reference frequency signal output from the temperature compensation crystal oscillator 31 and the temperature compensation crystal oscillator 31 for generating the reference frequency of the PLL and the phase of the comparison frequency signal are shown. The phase detector 32 for converting the phase difference into a voltage, the loop filter 33 for filtering and rectifying the voltage output from the phase detector 32, and the voltage output from the loop filter 33 are compared. An adder 34 that adds to the modulation input signal Vf, a voltage controlled oscillator 35 that performs internal frequency modulation to vary the frequency in accordance with the voltage modulated by the adder 34, and supplies it to the frequency modulation output; A voltage controlled crystal oscillator 36 for generating a local oscillation frequency and performing external frequency modulation by inputting a modulation input signal Vf, and a frequency controlled crystal oscillator 36 outputted from the voltage controlled oscillator 35. ) It made up to the output mixer 37 for mixing the frequency signal output from the mixer 37 to a low-pass filter 38 for supplying a comparison signal of the phase frequency detector 32, low-pass filters.

FIG. 6 is a modulation response characteristic curve of the frequency modulation device shown in FIG. 5, wherein the modulation characteristics of the output frequency signal f _OUT according to the frequency fv of the modulation input signal Vf are shown in FIG. The PLL is configured by mixing the internal modulation characteristics of the high pass filter type using the PLL loop bandwidth as the cutoff frequency and the external modulation characteristics of the low pass filter type using the PLL loop bandwidth as the cutoff frequency as shown in FIG. It can be seen that the modulation bandwidth is constant in all bands regardless of the loop bandwidth, that is, the cutoff frequency.

Then, the operation of the present invention will be described with reference to FIG. 5 and FIG.

Referring to FIG. 5, the temperature compensation crystal oscillator 31 generates and applies a reference frequency fr of the PLL to the phase detector 32.

The phase detector 32 mixes the phase of the reference frequency fr and the output frequency of the voltage controlled crystal oscillator 36, which is a local oscillator of the heterodyne PLL, and the output frequency of the voltage controlled oscillator 35, and then the low pass filter. The phases of the comparison frequencies f _IF made by passing through 38 are compared, and the phase difference is converted into a voltage and applied to the loop filter 33.

The loop filter 33 filters, rectifies and outputs the output voltage of the phase detector 32 to the adder 34.

At this time, when frequency modulation such as FM or FSK modulation is to be performed in the heterodyne PLL, the modulation input signal Vf is applied to the adder 34 and the voltage controlled crystal oscillator 36, respectively.

The adder 34 adds the modulation input signal Vf and the output voltage of the loop filter 33 to modulate the voltage output from the phase detector 32 and applies the voltage to the voltage controlled oscillator 35, and the voltage controlled oscillator 35. ) Outputs an output frequency signal f _OUT that varies in accordance with the output voltage of the adder 34.

The voltage controlled crystal oscillator 36 is a local oscillator of the heterodyne PLL, and performs FM or FSK modulation on the modulator input signal Vf and applies it to the mixer 37. At this time, the frequency modulation in the voltage controlled crystal oscillator 36 and the frequency modulation in the voltage controlled oscillator 35 described above are performed at the same time.

The mixer 37 mixes the frequency modulated signals of the voltage controlled oscillators 34 and 35 and the frequency modulated signals of the voltage controlled crystal oscillator 36 and applies them to the low pass filter LPF 38.

The low pass filter 38 removes an intermodulation product of the output signal of the mixer 37 and applies it to the phase detector 32 as a comparison frequency signal f _IF .

Therefore, by simultaneously performing FM and FSK modulation on the voltage controlled oscillator 35 inside the PLL loop and the voltage controlled crystal oscillator 36 outside the loop, in the entire frequency band of the modulation input signal Vf as shown in FIG. Constant modulation response characteristics can be obtained.

That is, the frequency modulation device shown in FIG. 5 is a mixture of modulation response characteristics (FIG. 2) by PLL internal modulation shown in FIG. 1 and PLL external modulation characteristics (FIG. 4) shown in FIG. As shown in FIG. 6, a constant modulation response characteristic is obtained in all bands regardless of the PLL loop bandwidth.

As described above, in the frequency modulation device using the phase locked loop according to the present invention, the frequency of the modulated input signal is performed by simultaneously performing FM or FSK modulation on the voltage controlled oscillator located inside the PLL loop and the voltage controlled crystal oscillator located outside the PLL loop. There is an advantage in that a constant modulation response characteristic can be obtained in a band.

Therefore, in FM modulation that modulates an analog voice signal, a modulation response characteristic with low distortion can be obtained. In FSK modulation that modulates digital data, a modulation response characteristic with low jitter and a wide open eye can be obtained, thereby reducing data error. .

Claims (3)

(Correction) a temperature compensation crystal oscillator 31 for creating a reference frequency of the phase locked loop; A phase detector 32 for comparing the phase of the reference frequency signal output from the temperature compensation crystal oscillator 31 with the phase of the comparison frequency signal and converting the phase difference into a voltage; A loop filter 33 for filtering and rectifying the voltage output from the phase detector 32; An adder (34) for modulating the voltage output from the loop filter (33) in accordance with a modulation input signal; A voltage controlled oscillator 35 for varying the frequency according to the voltage modulated by the adder 34 and supplying the frequency modulated output; A voltage controlled crystal oscillator (36) for generating a local oscillation frequency of said phase locked loop and for performing frequency modulation in accordance with said modulation input signal; A mixer (37) for mixing the frequency modulated signal output from the voltage controlled oscillator (35) and the frequency modulated signal output from the voltage controlled crystal oscillator (36); And a low pass filter 38 for low pass filtering the signal output from the mixer 37 and supplying it as a comparison frequency signal of the phase detector 32, wherein the phase locked loop in the voltage controlled oscillator 35 is provided. A frequency modulation device using a phase locked loop, characterized in that internal frequency modulation and phase locked loop external frequency modulation in the voltage controlled crystal oscillator (36) are performed simultaneously. (delete) (delete)