JPH01311624A - Frequency modulation transmitter - Google Patents

Abstract

PURPOSE:To uniformize frequency modulation(FM modulation) sensitivity for the change of the oscillation frequency of a voltage controlled oscillator(VCO) by changing the level of modulated input corresponding to the change of a control signal which controls the oscillation frequency of the VCO in a PLL loop. CONSTITUTION:The modulated input from a microphone 6 is supplied to an electronic attenuator 9 via an audio amplifier 7 and a low-pass filter(LPF)8, and its output becomes the modulated input of the VCO1. The control voltage of the VCO outputted from the LPF5 of a frequency synthesizer having the PLL loop consisting of the VCO1, a programmable divider 4, a reference frequency signal oscillator 3, a phase comparator 2, and the LPF5 is converted to a DC voltage by a DC voltage conversion amplifier 10, and the damping quantity of the electronic attenuator 9 is controlled corresponding to the DC voltage. In such a way, it is possible to nearly uniformize the FM modulation sensitivity for the change of the oscillation frequency of the VCO.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency modulation (hereinafter abbreviated as FM) transmitter having a frequency synthesizer.

[Summary of the Invention] In a frequency modulation transmitter configured to perform frequency modulation by applying a modulation input to a frequency synthesizer having a PLL loop, a voltage controlled oscillator (
A low-pass filter (L) that controls the oscillation frequency of the VCO)
By changing the level of the modulation input in response to changes in the output control signal of the PF, the FM modulation sensitivity is made uniform with respect to changes in the oscillation frequency of the vCO.

[Prior Art] FIG. 5 shows an example of the oscillation frequency characteristic of a vCO, which is an oscillator of a frequency synthesizer of a conventional FM transmitter of this type, and FIG. 6 shows an example of the modulation sensitivity characteristic.

Particularly problematic is the modulation sensitivity characteristic shown in Figure 6. The ideal value is as shown by the dotted line, but in reality, due to the non-linearity of the vCO voltage variable capacitor and other circuit elements, the curve shape as shown in the solid line Become. In order to correct this curved modulation sensitivity characteristic, conventionally, a configuration as shown in FIG. 7 or 8, for example, has been adopted. In FIG. 7, 1 is VCo, 2
is a phase comparator, 3 is a reference frequency signal oscillator, and 5 is an LPF.
, 11 are frequency dividers, and these circuits constitute a frequency synthesizer consisting of a PLL loop.

6 is microphone, 7 is audio amplifier, 8 is LPF
, 12 is a channel controller, 13 is a level converter, 14
is a switch controller, 15, 16 and 17 are switches,
R,, R2, and R1 are variable resistors, and the audio output from the microphone 6 is outputted as a modulation input to VC:01 via the audio amplifier 7, LPF 8, variable resistors R~R1, and switches 15~17. the frequency modulated signal is output from the VCOL.

In the above-mentioned FM transmitter, the variable resistors R1 to R1 are set such that their respective resistance values provide a modulation input level corresponding to the oscillation frequency band channel of vCO, and the channel controller 12 controls the frequency division of the frequency divider 11. Activate any of the switches 15 to 17 according to the ratio to adjust the variable resistors R4 to
I am trying to correct the modulation sensitivity characteristics by selecting R3 and changing the modulation input level of the VCOL.

Further, in the FM transmitter shown in FIG. 8, the gain of the amplifier 19 is changed according to the oscillation frequency band channel of the vCO set in advance by the central processing unit 18.
We are trying to correct the modulation sensitivity by making the modulation input level variable. Note that in FIG. 8, 2 is a phase comparator.

[Problems to be Solved by the Invention] However, as described above, the relationship between the VCO oscillation frequency and its modulation sensitivity in the conventional FM receiver has a characteristic as shown in FIG. Since the modulation sensitivity is discontinuous by dividing it into 3 or 4,
The degree of modulation changes abruptly before and after switching the modulation input level, which is undesirable.

[Object of the Invention] An object of the present invention is to provide a frequency synthesizer type FM transmitter with a uniform FM modulation degree in order to improve the above-mentioned drawbacks.

[Means for Solving the Problems] In order to achieve the above object, a frequency modulation transmitter according to the present invention includes a vCO, a frequency dividing means for frequency dividing an output signal of the vCO, and an output signal of the frequency dividing means. A frequency synthesizer including a phase comparator for comparison with a reference frequency, and an LPF for converting the output of the phase comparator into a control signal for the vCO in a PLL loop, and a frequency division ratio of the frequency dividing means is variably set. A frequency modulation transmitter configured to perform frequency modulation by applying a modulation input to the frequency synthesizer,
The present invention further includes means for changing the modulation input level in response to changes in the VCO control signal output from the LPF.

[Operation] When the vCO control signal output from the LPF in the PLL loop of the frequency synthesizer changes.

Since the modulation level for vCO can also be changed, V
The modulation sensitivity becomes uniform with respect to changes in the CO oscillation frequency.

[Example] The present invention will be explained in more detail using an example with reference to one drawing, but these are merely illustrative, and various modifications and improvements can be made without going beyond the scope of the present invention. Of course it is possible.

FIG. 1 is a block diagram showing the configuration of an embodiment of a frequency modulation transmitter according to the present invention. In FIG. 1, reference numbers common to FIG. 8 are the same as those in FIG. 9 represents an electronic attenuator, and 10 represents a DC voltage conversion amplifier.

As shown in the figure, the above embodiment includes a frequency synthesizer having a PLL loop consisting of a VCOL, a programmable divider 4, a reference frequency signal oscillator 3, a phase comparator 2 and an LPF 5, a microphone 6, an audio amplifier 7. LP
In the FM transmitter equipped with modulation input generation means consisting of F8, for example, an electronic attenuator 9 is connected between the VCOl and the LPF 8, and the electronic attenuator 9 is connected to the output of the LPF 5 of the PLL loop. 1
It is configured to control with an output of 0.

In the above embodiment, the vCO control voltage output from the LPF 5 is converted to a DC voltage by the DC voltage conversion amplifier 10,
The amount of attenuation of the electronic attenuator 9 is controlled according to this DC voltage. The modulation input from the microphone 6 is given to the electronic attenuator 9 via the audio amplifier 7 and the LPF 8, and its output becomes the modulation input of the VCOl, so the electronic attenuator 9 is applied in response to the VCO control voltage as shown in FIG. By controlling the amount of attenuation of , the modulation input level of vCO can be changed so as to have a characteristic opposite to that of the broken line shown in Fig. 2, and the modulation sensitivity can be changed as shown by the solid line in Fig. 2 with respect to changes in the vCO oscillation frequency. It can be made almost uniform.

An example of the configuration of the electronic attenuator 9 and the DC voltage conversion amplifier 10 is shown in FIG. 4. The electronic attenuator 9 includes, for example, transistors Tr1. It is composed of a Darlington circuit 22 consisting of a Tr, an amplifier 24, etc., and its human power 23 is connected to the LPF 8, its output 25 to VC:01, and the Darlington circuit 22 is connected to the output of the DC voltage conversion amplifier 10. .

When the vCO control voltage output from the LPF 5 in the PLL loop is applied to the input 21 of the DC voltage conversion amplifier 10, the output DC voltage becomes the input to the Darlington circuit 22, and accordingly, the voltage between the collector and emitter of the transistor Tr2 is , that is, the impedance between the input of the amplifier 24 and ground changes.

The input level of amplifier 24 is controlled. Therefore, the amount of attenuation of the electronic attenuator 9 is controlled in response to changes in the vCO control voltage.

Note that the electronic attenuator 9 may be an AGC circuit or the like, and in short, it may be any device that can control the modulation input level of the VCO in accordance with its control signal.

[Effects of the Invention] As described above, according to the present invention, in an FM transmitter equipped with a frequency synthesizer, the FM modulation sensitivity can be made almost constant with respect to changes in the oscillation frequency of the VCO.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of an FM transmitter according to the present invention, FIG. 2 is a correction characteristic diagram according to the present invention, and FIG.
Figure 4 shows the level variable characteristics of the device according to the present invention.
The figure is a circuit diagram of an electronic attenuator and a DC voltage conversion amplifier, FIG. 5 is a vCO oscillation frequency characteristic diagram, and FIG. 6 is a VCO modulation sensitivity characteristic diagram. Fig. 7 is a block diagram of an FM transmitter equipped with a conventional correction circuit, Fig. 8 is a block diagram of an FM transmitter equipped with another conventional correction circuit, and Fig. 9 is a characteristic after conventional correction. It is a figure which shows an example. 1・・・・・・・・・vCQ, 2・・・・・・・・・
Phase comparator, 3... Reference frequency signal oscillator, 4... Programmable divider, 5... LPF, 6...・
...Microphone, 7...Audio amplifier, 8...LPF, 9...
...Electronic attenuator or AGC amplifier, 1
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Claims (1)

[Claims] (a) a voltage controlled oscillator, (b) frequency dividing means for frequency dividing the output signal of the voltage controlled oscillator, (c) a phase comparator for comparing the output of the frequency dividing means with a reference frequency, and (d) a frequency synthesizer including in a loop a low-pass filter that converts the output of the phase comparator into a control signal for the voltage-controlled oscillator, and in which the frequency division ratio of the frequency dividing means is variably set; A frequency modulation transmitter configured to perform frequency modulation by applying a modulation input to a synthesizer, further comprising (e) means for changing the modulation input level in response to a change in the control signal of the output of the low-pass filter. A frequency modulation transmitter comprising: