JPS6264105A - Frequency modulator - Google Patents

Abstract

PURPOSE:To eliminate the effect of a modulation signal on an output of a phase comparator by inserting a phase correction circuit to a guide line of a reference signal of the phase comparator, adding modulation signal to it and superimposing the same component as a modulation signal included in a comparison signal onto the reference signal. CONSTITUTION:A phase correction circuit 18 superimposed the component of the modulation signal outputted from a VOC 16 on the reference signal and consists of an F-V comparator 19, a voltage controlled amplifier VCA 20 and a phase modulator 21. An output terminal of the converter 19 is connected to a control terminal of the amplifier VCA 20a dn an output terminal of the VCA 20 is connected to a modulation signal input terminal 21a. The modulation signal from a modulation signal input terminal 10a is inputted to the VCO 16, which acts like an FM modulation signal oscillator. The converter 19 generates a DC voltage corresponding to the frequency of a modulation signal, which is used as a control voltage and inputted to the control terminal of the VCA 20. The VCA 20 amplifiers the modulation signal in response to the frequency, inputs it to a phase modulator 21 and the signal from the VCA 20 is used to apply phase modulation to the reference signal inputted from a frequency divider 13.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a frequency (hereinafter referred to as FM) modulator using a PLL (phase-locked loop) circuit.

(Prior Art) Conventionally, a frequency synthesizer controlled by a 1'LL circuit has been used as a transmit carrier generator in a communication device. In this case, FM modulation is generally applied to the voltage controlled oscillator in the PLL circuit, and the PLL circuit
Used as an M modulator.

Let's take a mobile radio communication device such as a car phone as an example of a communication device that uses such a PLL circuit as an FM modulator.
In Fig. 9, the material number ANT is an antenna, which will be explained using Fig. 9.
1 is a shared device for switching transmission and reception.

2 is a first mixer, 3 is an intermediate frequency amplifier, 4 is a second mixer, 5 is a local oscillator, and B is a low frequency output terminal.

7 is a control circuit, 8 is a receiver synthesizer, and these first
A receiving section is formed by a mixer to a receiving section synthesizer 8 and the like. On the other hand, MIC is a microphone, 9 is a microphone amplifier, 1
0 is a transmitter synthesizer, and the output terminal of the microphone amplifier 9 is the modulation signal input terminal l in the transmitter synthesizer IO.
A transmission output terminal 10b of the transmitter synthesizer IO is connected to the duplexer 1, and a control signal line from the control circuit 7 is connected to the channel control signal input terminal 10c. A transmitter is formed from the microphone MIC to the transmitter synthesizer IO. 11
is a display device.

When the power (not shown) is turned on, the control circuit 7 is reset, initial values are set, and the system waits.

It becomes a receiving state. When an incoming call signal from the base station is received by the antenna ANT in this standby state, this incoming call signal is controlled via the duplexer l, the first mixer 2, the intermediate frequency amplifier 3, and the second mixer 4. Input to circuit 7. The control circuit 7 outputs a response signal to this incoming call signal, and this response signal is
A signal specifying an arbitrary communication channel (any one channel out of 800 channels) from the base station is sent from the antenna ANT to the base station via the microphone amplifier 9, the transmitter synthesizer IO, and the duplexer 1. It is input from the ANT and input to the control circuit 7 along the same route as the above-mentioned incoming call signal. The control circuit 7 sends a channel control signal based on this channel designation signal to both synthesizers 8 . The synthesizer 8.10 is outputted to the frequency divider at IO and is switched to the carrier frequency of the channel corresponding to this channel control signal. Thereafter, the audio signal input from the microphone MIC is output from the control circuit 7 at the microphone amplifier 9 as a data transmission output (
This becomes a modulated signal and is input to the transmitter synthesizer 10 from the modulated signal input terminal t (la), and an FM-modulated carrier signal is output from the transmitting output terminal 10b, and this output signal is The signal is transmitted to the base station via the duplexer l and the antenna ANT.In this way, both the transmitter and φreceiver synthesizers 8.10 and 60
Since both synthesizers 8 and 10 must quickly access and lock one channel designated by the base station from among the 0 channels, quick channel switching characteristics are required in a short period of time. Although the above example deals with a case where the number of channels is 800, this type of mobile radio communication device is normally required to have channel switching capability of 1000 channels.

FIG. 10 is a diagram showing in more detail the transmitter synthesizer 10 in the mobile radio communication device as described above, and shows a conventional example of an FMil modulator using a PLL circuit. In the figure, reference numeral 12 is a reference wave oscillator, 13 is a frequency divider, and the reference wave oscillator 12 and the frequency divider! 3 constitutes a reference wave oscillation means. 14 is phase comparison =, t! j is a low-pass filter, 18 is a voltage controlled oscillator (hereinafter referred to as vCO), 17 is a frequency divider, 10a, job, and 10c are respectively the same modulation signal input terminal, transmission output terminal, and This is an input terminal for channel control signals.

The output from the reference wave oscillator 12 is divided by the frequency divider 13 and the phase of the reference signal outputted from the reference wave oscillation means, and the phase of the comparison signal obtained by dividing the output of the vcoie by the frequency divider 17. are compared by the phase comparator 14, and an error voltage is generated according to the phase difference. Here, the frequency division ratio of the frequency divider 17 is controlled by the control circuit 7. After the error voltage is band-limited by the low-pass filter 5, it is applied as a control voltage to V COI
EI and is controlled so that the frequency of the comparison signal is the same as the frequency of the reference signal. That is, the phase of the comparison signal is locked in synchronization with the phase of the reference signal, and at the same time, a modulation signal is applied from the modulation signal input terminal 10a to V C01B, and the V co to is FM'ii
It operates as a modulated signal oscillator and outputs an FM modulated wave from the transmission output terminal 10b.

To further explain the above operation using a mathematical formula, V C0
If the carrier wave oscillated at 18 is E-Esin (2πft), and the frequency of the modulated signal input from the input terminal lea or CC is f, then the FM modulated wave Efra output from the transmitting output terminal 10b is as follows.

E = Estn (2πf t+ rpus C (Δf/f) sin (2πft))
= (L)1
lΔf: maximum deviation amount.

Furthermore, if the frequency division ratio of the frequency divider 17 is 1/Ml, the comparison signal Ef' outputted via this frequency divider is expressed as (Δf/f/Ml)sin(2πf t))
Error・・・・・・・・・・・・・・・ (2) Therefore,
The comparison signal input to the phase comparator 14 is subjected to FM modulation of Δf/f/Nl.

heavy On the other hand, the reference signal E is input to the phase comparator 14.

Since it is a condition for locking to be the same, the oscillation angular frequency of the reference oscillator 12 is Es1n2πftr.

If the frequency division ratio of the frequency divider 13 is set to 1/N2, then the oscillation angular frequency of the reference oscillator 12 and the frequency division ratio of the frequency divider 13 can be selected so as to satisfy the following equation. Above) is a phase comparator! 4, the comparison signal E' is subjected to an FM change f' of Δf'/f/Ml. The PL and L circuits use this comparison signal E.
・ is brought close to the phase of the reference signal E and the same f■
r. Therefore, the angular frequency ωm of the modulation signal
If (x2πf at) is lower than the natural angular frequency (the limit angular frequency at which the loose PLL responds), which affects the response speed of the PLL circuit, the PLL circuit may respond to FM9jli and the phase comparator! From 4 onwards, an error voltage is generated corresponding to the difference between the reference signal E and the FM modulation of Δf/f/N1, and the resulting control voltage controls V O01B and affects the modulation characteristics. .

This will be further explained with reference to FIGS. 11 and 12. Figure 11 shows the relationship n between the ratio ω /ω of the modulation angular frequency ω and the natural angular frequency layer ω and the frequency phase error.
l n-person, that is, PL
It shows the frequency phase error characteristics of the L circuit. θ on the vertical axis in the figure is the phase of the reference signal, and θ is the phase of the comparison signal. Also, ω when the damping coefficient ζ is taken as a parameter.

FIG. 12 shows the response characteristic to /ω, that is, the frequency response characteristic of the PLL circuit.

Note that the characteristics shown in FIG. 12 have a damping coefficient ζ of 0.70.
This is from when I was 7 years old.

From these characteristic diagrams, it can be seen that the conventional PL
The L circuit has a modulation angular frequency −ω higher than the natural angular frequency ωn,
It can be said that it does not follow the change in the modulation angular frequency ω, but it does follow the change in the low modulation angular frequency ω. Therefore, using a conventional PLL circuit, f
- The FM modulator modulates the natural angular frequency ω with the angular frequency ω,
It is necessary to design the value of l to be small so as not to affect the modulation signal.
3KHz) as well as lower frequency signals such as the data frequency (0.02 to 10KHz) as described in the explanation of FIG. 10 above, the natural angular frequency ω
However, the channel switching time t is forced to be set even smaller, and the channel switching time t becomes −ω! It can be expressed as In.

(Problems to be Solved by the Invention) In an FM modulator using a conventional PLL circuit, the natural angular frequency ω, which is the response limit frequency, must be set to a small value so as not to affect the modulation signal frequency. As a result, there were various problems with characteristics such as first order.

(b) In low frequency modulation, the deviation signal (R
Wave number shift) control becomes insufficient.

(b) Pull-in time becomes longer, resulting in longer channel switching time.

(c) The capture range becomes narrower and the frequency that can be locked becomes narrower.

(d) The transient response speed becomes slow.

(e) The S/N ratio deteriorates.

As mentioned above, there is a problem in that characteristics essential for a PLL circuit cannot be obtained.

The purpose of this invention was to solve the above-mentioned problems in the conventional FM modulator using the PLL circuit, and (a) provide sufficient deviation control characteristics even for variable signals over a wide band. is obtained. (b) Pull-in time can be shortened and channel switching time can be made faster.

(c) The capture range can be widened and the lockable frequency range can be widened. (d) Transient response characteristics can be made faster. (e) An object of the present invention is to provide an FM modulator that can improve the S/N ratio.

(Means for Solving the Problem) In order to achieve the above object, the frequency modulator according to the present invention has components of the reference signal output from the reference oscillation means and the oscillation signal output from the voltage controlled oscillator. A comparison signal is introduced into a phase comparator, the phase of the reference signal and the phase of the comparison signal are compared by the phase comparator, and the oscillation frequency is controlled based on the phase difference detected by the phase comparator. In the frequency modulator that obtains a frequency modulated wave by adding a modulation signal to the voltage controlled oscillator, a phase correction circuit is interposed in the introduction line of the reference signal, and the modulation signal is added to the phase correction circuit to perform the comparison. superimposing the same component as the modulation signal component included in the signal on the reference signal;
The output of the phase comparator is configured not to be affected by the modulation signal.

(Function) By interposing a phase correction circuit in the introduction line of the reference signal to the phase comparator and adding a modulation signal to this phase correction circuit, the same component as that of the modulation signal included in the comparison signal is superimposed on the reference signal. Therefore, the output of the phase comparator is not affected by the modulation signal, and the PLL circuit operates without being affected by the modulation signal. Therefore, the natural angular frequency ω of the PLL circuit can be set to a sufficiently large value regardless of the modulation angular frequency ω.

(Description of Embodiments) Embodiments of the present invention will be described below based on FIG. 1. In FIG. 1, the same or equivalent components as those in FIGS. 9 and 10 are designated by the same reference numerals and redundant explanations will be omitted.

First, the configuration will be explained. In this embodiment, the 0 phase correction circuit 18 has a phase correction circuit 18 interposed in the introduction line of the reference signal applied to the phase comparator 14.

It superimposes the modulation signal component included in the frequency modulated wave output from the VOC 18 on the reference signal, and includes an F-■ converter 19, a voltage control amplifier (hereinafter referred to as VCA) 20,
and a phase modulator 21. The modulation signal input terminal 10a is connected to the F-V converter 19 and the VC
The output terminal of the F-V converter 19 is connected to the control terminal of the vCA 20 in each totomo connected to the A2G,
The output terminal of the frequency divider 13 is connected to the reference signal input terminal 21b of the 0-phase modulator 21, in which the output terminal of the VCA 20 is connected to the modulation signal input terminal 21a of the phase modulator 21. The output terminal 21c is connected to the reference signal input terminal of the phase comparator 14. Note that the details of the internal circuit configuration of the phase modulator 21 will be described later.

Next, the effect will be explained.

A modulation signal from the modulation signal input terminal 10a is input to VColB to operate the VC01B as an FM modulation signal oscillator, and the modulation signal is input to the phase correction circuit 18.
It also inputs to the F-V converter 18 and V CA 20 at. The F-V converter 18 generates a DC voltage corresponding to the frequency of the modulation signal, and inputs this DC voltage as a control voltage to the control terminal of the VCA 20. VCA20
amplifies the modulated signal according to its frequency, the amplified output signal of the VCA 20 is input to the phase modulator 21, and the signal from this VCA 20 is used to phase modulate the reference signal input from the frequency divider 13 side. do.

The above phase modulation effect, etc. will be explained in more detail below.

For convenience of explanation, the change m from the modulation signal input terminal 10a
Consider a case where the signal is input only to the phase correction circuit 18 side and not to vCOIB.

Modulated signal E (t) −Ecos (2πfllt)
Then, the F-V converter 9 sends a DC voltage corresponding to that frequency to the VCA 2G as a control voltage.
If the amplification degree of VCA20(7) is A, then VCA2(7)
The modulated signal E (t) output from 1 is E (t) = A@Ecas (2πf t)...
・(4)■ is obtained. On the other hand, from the input terminal 21b to the phase modulator 2I
The reference signal E to be input to is shown in equation (3), and the phase modulator 21 modulates the phase (hereinafter referred to as PM) of the reference signal of equation (3) with the modulation signal of equation (4). The PM modulation signal E output from the modulator 21 is pm E =Esin((2πft/N2)+pm
r Δθcos (2πf town)) Δθ: Phase shift ・・・・・・・・・・・・(5)
becomes.

Next, consider the case where the modulated signal is input only to the v co to side and is not input to the 1-phase correction circuit 18.

At this time, the frequency divided signal E2. which is output from the transmission output terminal 10b of v co to. ' is exactly the same as shown in equations (1) and (2) of the prior art. If the signal E' of the above equation (2) is rewritten here.

f 鳳E' = Esi n ((2, wf t/N
t) +f shoes
C(Δf/f/Nl)s,X
n (2πflt) )■ ・・・・・・・・・・・・・・・ (2).

The relationship between equations (5) and (2) above is further illustrated in Figure 2 (
This will be explained using A) and CB). Signal C in the same figure (B) shows the change in angular frequency in the modulation signal component of the FM modulated wave, and represents the modulation signal component in the W4 signal E' of equation (2) above. , and the signal shown in FIG.
This is obtained by converting the ya component (change in modulation signal component) into a change in phase. It is known that the FM modulated wave is equivalently subjected to PM modulation, and this will be described later using FIGS. 3 and 4. On the other hand, the signal a in FIG.
) formula, that is, the correction PM generated by the phase correction circuit 18
m represents the modulated signal E. Therefore, the phase change (signal b) of the modulated signal component in the frequency-divided signal E' input to the phase comparator 14 and the PM modulated signal E (
The signal a) has the same phase as p■, and if 80 = Δf#/Nl, then in the phase modulator 21, the reference signal E is converted to the PM modulation signal E by r
p■ The phase-modulated signal contains the same component as the modulation signal component in the frequency-divided signal EfII', so the output of the phase comparator 14 is not affected by the modulation signal component.'Then, the FM modulated wave is equivalent The fact that the signal is subjected to PM modulation and the corresponding daily functions of the phase correction circuit will be further explained with reference to FIGS. 3 and 4. FIG. 3 shows the F modulation index (Δf/f/Fil) with respect to the frequency f of the modulation signal, where F/Ml) is expressed as a phase shift.
The same graph shows the frequency division ratio N1-3Q of the frequency divider 17 as a numerical example.
OG and the frequency deviation amount Δf is ±8 KH2.
-, in the case of FM modulation, the frequency deviation amount Δf is the same for the frequency f of the modulation signal.

The modulation index Δf/f changes as shown in Figure 3, and when the frequency f of the frequency fJRm changes, if the frequency deviation Δf remains the same, the phase deviation Δθ changes as It changes as shown in the figure. 3 and 4 show the same characteristics as FM modulation and PM modulation. And weird lol
Even if the frequency f of the R@ signal is changed, the input level of the variable signal may remain constant in the case of FM modulation, but if you want to obtain the same phase modulation characteristics as FM modulation,
For modulation, the input level of No. 1 (■) must be changed depending on the frequency f of No. A@.

Therefore, a phase correction circuit 1 for superimposing the same component as the modulation signal component +s in the frequency divided signal E' on the reference signal.
On the other hand, the F-V converter 9 and the VCA 20 are operated at 9, and the F-V converter 1g generates a DC voltage at a level corresponding to the number f of the number f, and this DC voltage is controlled by the voltage i. The signal is input to the control terminal of the VCA 20 as a signal. The VCA 20 amplifies the modulation signal according to this control voltage, and outputs the modulation signal input terminal 21 of the phase modulator.
I am having input to a.

Next, a configuration example of the phase modulator 21 in the phase correction circuit 18 and its modulation function will be explained using FIGS. 5 to 8. Figure 5 is a configuration example, Figure 6 is the frequency characteristic, Figure 7 is the 6
The phase change characteristic corresponding to the figure, and FIG. 8 shows the C/V characteristic of the varicap diode. First, the configuration of the phase modulator 18 will be described with reference to FIG. 5. 21a, 21
b, and 21c, as shown in FIG.
A modulation signal input terminal, a reference signal input terminal, and a phase-corrected reference signal output terminal, respectively, and 21d is a power supply terminal. Also, resistor 22 and varicap diode 2fj
A circuit that generates a phase shift Δθ is configured. The resistor 23 is an input resistor, the resistors 24 and 25 are bias resistors, and the capacitor 27 is a DC blocking capacitor.

If the resistance value of the resistor 22 is R, the quantity value of the varicap diode 2B is 0.5, and the cut-off frequency is f, then f1 has a value of 1/2πRCj, as shown in Figure 6!
- It is designed to be the f1 point. Therefore, by varying the junction capacitance C1 of this varicap diode 26, f
By varying the cutoff frequency f1 from -Δf to +Δf1, as shown in FIG.
A phase change in the range ˜+Δθ is obtained.

°Next, in order to move the cutoff frequency f1, it is only necessary to vary the junction capacitance C1 of the barrier cap diode 27. To explain this using the C/V characteristics shown in Figure WI) 8, the C/V characteristics are proportionally It is only necessary to set the bias voltage within a range in which it changes.Therefore, as the level of the modulation signal input from the modulation signal input terminal 21a changes from +ΔV to -ΔV, the junction capacitance C6 changes within the range from +ΔC to -ΔC, and as a result, the modulation It is possible to generate a phase shift Δθ of an amount corresponding to the level of the modulation signal input from the signal input terminal 21a.

Since the phase modulator 21 functions in this way, by selecting the amplification degree of the VCA 20 controlled by the output of the F-■ converter 8, the level of the modulation signal input from the modulation signal input terminal 21a is set to the required level, Frequency deviation Δf/f/N1 and PMllill in FM modulation as described above
The phase shift layers Δθ can be made the same.

In this way, the correction PM generated by the phase correction circuit 18
The modulated signal is superimposed on the reference signal, and the superimposed part of the PMQ signal is made the same as the modulated signal component in the minute signal E' of equation (2), which is the comparison signal.

As a result, the output of the phase comparator 14 is not affected by the modulation signal component.To give a numerical example, the frequency division ratio of the frequency divider 17 is set to 1/N.
1-1/3000, and when Δf is ±8 KHz, Δθ is ±0.152' and ±0 for the modulation signal frequencies I KHz, 100Hz, and 10Hz, respectively.
1.52°, and ±15.2°.

(Effects of the Invention) As explained above, according to the frequency modulator of the present invention, 1
By interposing a phase correction circuit in the introduction line of the reference signal to the phase comparator and adding the modulation signal to this phase correction circuit, the same component as that of the modulation signal included in the comparison signal is superimposed on the reference signal. The output of the phase comparator is not affected by the modulation signal, and the PLL circuit can operate without being affected by the modulation signal, and the natural angular frequency, which is its response limit frequency, is sufficiently maintained regardless of the modulation signal. Can be set to a large value. Therefore, (a)
Sufficient deviation control is possible even for modulated signals over a wide band. (b) Pull-in time can be shortened, and channel switching time can be shortened. (c) The capture range can be widened and the lockable frequency range can be widened.

(d) Transient response speed can be increased. (e) Very good characteristics such as an improved S/N ratio can be obtained.

[Brief explanation of drawings]

1 to 8 show embodiments of the frequency modulator according to the present invention.'141rl! J is a system diagram, FIG. 2 is a waveform diagram showing modulation signal components superimposed on the reference signal, etc., FIG. 3 is a characteristic diagram showing the FM modulation index with respect to the frequency of the modulation signal, and FIG. 4 corresponds to the above characteristics. Characteristic diagram of phase shift with respect to frequency of modulated signal Figure 5 is a circuit diagram showing the phase correction circuit in Figure WS1 in more detail, Figure 6 is a characteristic diagram showing the frequency characteristics of the phase correction circuit as above, Figure 7 is same as above. A characteristic diagram showing the phase change characteristics corresponding to the frequency characteristics, Figure 8 shows the C/V of the varicap diode in the phase correction circuit.
A characteristic diagram showing the characteristics, FIG. 9 is a system diagram showing a mobile radio communication device to which a conventional frequency modulator is applied, and FIG. 10 is a system diagram showing a conventional frequency modulator applied to the same communication device.
FIG. 1 is a characteristic diagram showing frequency phase error characteristics of a frequency modulator using a PLL circuit, and FIG. 12 is a characteristic diagram showing frequency response characteristics of a frequency modulator using a PLL circuit. 10a=modulation signal input terminal, 10b: transmission output terminal, 1
0c: Channel control signal input terminal. 12: Reference wave oscillator, 13. l? : Frequency divider, 14: Phase comparator, 15: Low pass filter, 18: ? ! !
Pressure controlled oscillator, 18: Phase correction circuit. 19: F-V converter, 20: Voltage control amplifier. 21: Phase modulator, 2B: Varicap diode. Figure 1 Figure 2

Claims (1)

[Claims] A reference signal outputted from the reference oscillation means and a comparison signal which is a component of the oscillation signal outputted from the voltage controlled oscillator are introduced into a phase comparator, and the phase of the reference signal and the phase of the comparison signal are compared. In a frequency modulator that obtains a frequency modulated wave by adding a modulation signal to the voltage controlled oscillator, the oscillation frequency of which is controlled based on the phase difference detected by the phase comparator, an introduction line for the reference signal; By interposing a phase correction circuit in the phase correction circuit and adding the modulation signal to the phase correction circuit, the same component as that of the modulation signal included in the comparison signal is superimposed on the reference signal, and the output of the phase comparator is A frequency modulator characterized in that it is not influenced by the modulation signal.