JPS5910087B2 - Frequency synthesizer FM receiver - Google Patents

Description

[Detailed description of the invention] The present invention relates to a frequency synthesizer FM receiver.

A conventional frequency synthesizer FM receiver is constructed as shown in FIG.

That is, a high frequency amplification circuit 1 having a paractor-tuned circuit,
The receiver main body is composed of a mixing circuit 2, an intermediate frequency amplification circuit 3, an FM detection circuit 4, a stereo demodulation circuit 5, and a local oscillator 6 having the function of a voltage controlled oscillator.
The oscillation frequency of the crystal oscillator 9 is divided sequentially by the frequency divider 7 and the variable frequency divider 8, while the oscillation frequency of the crystal oscillator 9 as a reference oscillator is divided by the frequency divider 10. A phase comparator 11 compares the phase with the output of the frequency divider 10, and the output of the phase comparator 11 is passed through a pass filter 12 and an amplifier 13.
The oscillation frequency of the local oscillator 6 is controlled by the DC component in the output of the phase comparator 11, and the varactor tuning circuit of the high frequency amplifier circuit 1 is controlled by the DC component, and the variable frequency divider By setting a frequency division ratio of 8 using a frequency division ratio setter 14, the receiving frequency can be set.

Note that 15 is an antenna.

On the other hand, unlike Japan, where the FM broadcast channel plan is in 100kHz increments, it is similar to that seen in some parts of Europe.
There are cases where irregular frequencies such as 5kHz are used, or where frequencies are allocated at unequal intervals, such as in the Republic of South Africa.

Therefore, a frequency synthesizer FM receiver for use in areas where the above frequency allocation is carried out is 25
It is desirable that the configuration is such that the receiving frequency can be set at intervals of 12.5 kHz or 12.5 kHz.

However, a frequency synthesizer F that can set the reception frequency in increments of 25 kHz or 12.5 kHz
When using the M receiver for automatic tuning, there is a drawback that it is difficult to match the frequency of the broadcasting station precisely because the band is narrow, and the conventional reception frequency is set to every 100 kHz. However, when scanning at the same speed as a conventional frequency synthesizer FM receiver, the scanning speed decreases.

The present invention has been made in view of the above, and it is an object of the present invention to provide a frequency synthesizer FM receiver that eliminates the above-mentioned drawbacks.

The present invention will be explained below with reference to Examples.

FIG. 2 is a block diagram of a first embodiment of the invention.

In FIG. 2, the frequency synthesizer F shown in FIG.
The same components as in the M receiver are given the same reference numerals.

This embodiment uses the conventional frequency synthesizer F shown in FIG.
In the M receiver, the crystal oscillator 9 serving as a reference oscillator is replaced with a crystal oscillator 16 having a function as a voltage controlled oscillator, and a smoothing circuit consisting of a resistor 18 and a capacitor 19 is connected to the output end of the FM detection circuit 4. , the output of the smoothing circuit and the intermediate frequency signal from the intermediate frequency amplifier circuit 3 are input, and the electric field strength of the received signal is above a certain level,
And the output of the FM detection circuit 4 based on the received signal is the so-called S
A reception detection circuit 17 is provided to detect tuning within a predetermined range of the curve, and the output of the reception detection circuit 17 is used to switch the selector switch 20, so that the output from the FM detection circuit 4 is controlled as if it were an automatic frequency control circuit. The DC output that has passed through the smoothing circuit is amplified by an amplifier 21 and then applied to the crystal oscillator 16 to change the oscillation frequency of the crystal oscillator 16.

Therefore, in the frequency synthesizer FM receiver of this embodiment configured as described above, when there is no broadcast radio wave near the tuning frequency corresponding to the frequency division ratio of the variable frequency divider 8 set by the frequency division ratio setting device 14, Or, even if it exists, it is weak and not at a level sufficient to activate the reception detection circuit 17, the changeover switch 20 is switched to the position shown in FIG.
The operation of the frequency synthesizer FM receiver is quite similar to the operation of a conventional frequency synthesizer FM receiver.

Next, broadcast radio waves exist at or near the tuning frequency corresponding to the frequency division ratio of the variable frequency divider 8 set by the frequency division ratio setter 14, and have an electric field strength of a certain level or higher, and the FM
When the detection circuit 4 detects that the output of the FM detection circuit 4 corresponding to the broadcast radio wave is tuned within a certain range, the reception detection circuit 17 switches the changeover switch 20 to the smoothing circuit side.

Therefore, the DC component in the output of the FM detection circuit 4 that has passed through the smoothing circuit changes the oscillation frequency of the crystal oscillator 16.

Therefore, the output of the phase comparator 11 changes the tuning frequency of the varactor tuning circuit in the high frequency amplifier circuit 1 to a frequency that matches the frequency of the broadcast radio wave that operated the reception detection circuit 17, and also changes the oscillation frequency of the local oscillator 6. By multiplying the oscillation frequency of the changed crystal oscillator 16 by the frequency division ratio of the variable divider 8, it acts in a direction to make the DC component in the output of the FM detection circuit 4 zero, that is, to achieve positive tuning.

For example, the tuning frequency is set to 1 by setting the frequency division ratio setter 14.
It is assumed that the frequency is varied in 0 0 kHz steps, and now 8 0 kHz. When set to O MHz, the oscillation frequency of the local oscillator 6 is lower by the intermediate frequency 10, 7 MHz 6 9
．． 3 MHz.

Therefore, 80. There is no broadcast radio wave at 0 MHz, but 80 MHz. Assume that a broadcast radio wave of 0 2 5 MHz exists.

8 0. Broadcast radio waves of 0.25 MHz are within the band of the intermediate frequency amplification circuit 3, and 80. 0 2 5
If the electric field period level of the MHz broadcast radio wave is above a certain level, the reception detection circuit 17 is activated, the selector switch 20 is switched, the oscillation frequency of the crystal oscillator 16 is changed, and the tuning frequency is set to 80. 0 2 5 MHz, and the oscillation frequency of the local oscillator 6 is 6 9. 3 2 5
MHz, and acts to achieve positive tuning.

Therefore, the reception frequency set by the variable frequency divider 8 of the frequency synthesizer FM receiver is 80. Even though the frequency is O O MHz, it is possible to receive broadcasts of 8 0.0 2 5 MHz with positive tuning.

Next, a second embodiment of the present invention will be described.

FIG. 3 is a block diagram of a second embodiment of the present invention,
A distortion detection loop is used in place of the so-called automatic frequency control circuit in the first embodiment of the present invention.

Further, in FIG. 3, the same components as those of the frequency synthesizer FM receiver according to the first embodiment of the present invention shown in FIG. 2 are given the same reference numerals.

In this embodiment, the frequency synthesizer FM receiver of the first embodiment of the present invention is provided with an oscillator 23 that oscillates an output at a predetermined oscillation angular frequency P that does not affect the received signal of the FM receiver. The oscillation output of
is applied to the local oscillator 6 through the frequency synthesizer F.
The intermediate frequency signal of the M receiver is configured to be frequency modulated by the oscillation frequency of the oscillator 23, and the oscillator 23
a delay circuit 26 for delaying the output of the FM detection circuit 4; a doubling circuit 27 for doubling the output of the delay circuit 26; A high-pass filter 29 for extracting the demodulated output and a doubling circuit 2 for the output of the high-pass filter 29
Synchronize with the output of 7? It is equipped with a distortion detection circuit 22 consisting of a synchronous detection circuit 28 which generates a wave, and when the selector switch 20 is switched to the distortion detection circuit 22 side by the output of the reception detection circuit 17, the output of the distortion detection circuit 22 is amplified by the amplifier 25. Crystal oscillator 16
is applied to change the oscillation frequency of the crystal oscillator 16.

In the frequency synthesizer FM receiver configured as described above, the output of the local oscillator 6 is frequency-tuned by the oscillation angular frequency p of the oscillator 23, and the angular frequency p is included in the intermediate frequency signal.
A modulated signal with a constant level is generated.

First, the operation of the distortion detection circuit 22 will be explained.

Let the output S of the high frequency amplifier circuit 1 be S1=cosω1t,
Output s/ of local oscillator 6 when there is no output of oscillator 23
2 is S'2=cosω2t, and when the output S1 of the high-frequency amplifier circuit 1 and the output 4 of the local oscillator are applied to the mixing circuit 2, the output g3 of the mixing circuit 2 has (ω1-ω2) and (ω
1-ω2) outputs of both frequency components appear.

Now, if we take only the (ω1-ω2) component, S'3=cos
(ω−ω2)t=cosω.

It becomes ot. Here ω.

0-ω1-ω2. Therefore, the output S4- of the oscillator 23
When the output of the local oscillator 6 is frequency modulated by cospt, it becomes a mixed circuit 2 FM wave.

After this FM wave passes through the bandpass filter of the intermediate frequency amplification circuit 3, the output FM wave generally has distortion in its phase.

The output obtained by demodulating this distorted FM wave by the FM detection circuit 4 has a distortion component of K1αp2Δω2cos2pt - K2β2pΔω2s in 2p t - (1) with respect to the fundamental wave Δωcospt, if we focus only on the second harmonic. known to occur.

Here, p; the angular frequency of the oscillator 23, that is, the modulation angular frequency α3; the third derivative β2 of the amplitude characteristic of the bandpass filter of the intermediate frequency amplifier circuit 3; the second derivative of the phase characteristic of the bandpass filter of the intermediate frequency amplifier circuit 3; Order differential coefficient Δω: angular frequency deviation K1K2; constant.

Therefore, the output S5 of the output of the FM detection circuit 4 which has passed through the high-pass filter 29 is S5 - Δωc o s p t k1α3p2Δω2c
os2pt-k2β2pΔω2s in 2 p t
...-(2).

Distortion D caused by the amplitude characteristics of the bandpass filter
A case where α - k1 α3 p2 Δω2 cos2pt and distortion Dβ - k2 β2 p Δω2 sin 2 pt caused by the phase characteristics are Dα >> Dβ will be described.

In this case, the output g, is (The output S'5 is the output when focusing only on the distortion due to the amplitude characteristics of the band filter in the output S5 that has passed through the high-pass filter 29.

Similarly, the output when focusing only on the distortion caused by the phase characteristic is written as 85.

)s/. =Δωcospt+k1α3p2Δω2.

os2pt・・・・・・(3) becomes.

This output g5 becomes one input of the synchronous detection circuit 28.

The other input of the synchronous detection circuit 28 is a signal S/6 obtained by doubling the output S4 of the oscillator 23 by a doubling circuit 27.
Shizuichi cos 2pt.

Therefore, the output of the synchronous detection circuit 28 becomes S/7.

On the other hand, the third-order differential coefficient of the amplitude characteristic of the bandpass filter of the intermediate frequency amplification circuit 3 is normally expressed as ω, which is the center angular frequency of the bandpass filter.

The horizontal axis shows the center angular frequency ω.

If we take the detuning angular frequency from , it changes as shown in FIG.

Therefore, the central angular frequency ω.

In the vicinity, the third-order differential coefficient α3 of the amplitude characteristic of the bandpass filter is α3−kO(ω−ω.

) can be approximated by

k here. is a constant. Therefore, the output S'7 of the synchronous detection circuit 28 becomes, and the output S'7 of the synchronous detection circuit 28 becomes zero when the operating angular frequency ω is ω=ω0, positive when ω0>ω, and negative when ω0<ω. The central angular frequency ω is determined by the angular frequency ω.

It is a direct current voltage that changes from positive to negative around .

Therefore, the output S/7 of the synchronous detection circuit 28 is amplified by the amplifier 25 to change the oscillation frequency of the crystal oscillator 16, and this changed oscillation frequency of the crystal oscillator 16 changes the oscillation frequency of the local oscillator 6, The angular frequency ω of S.

0 is always the center angular frequency ω of the intermediate frequency bandpass filter
.

The frequency synthesizer FM receiver operates in a state where the distortion Dα due to the amplitude oscillation of the bandpass filter of the intermediate frequency amplification circuit 3 is minimized.

In the above explanation, the delay circuit 26 was ignored, but since the output g3 of the mixing circuit 2 passes through the band pass filter of the intermediate frequency amplification circuit 3, the output 4 of the high pass filter 29 is passed through the doubling circuit. It reaches the synchronous detector 28 with a delay from the output S6 of 27.

A delay time equal to this delay time is given to the delay circuit 26 to delay the output of the oscillator 23, and the synchronous detection circuit 2B
The phases of the outputs s'5 and 86 are made to match at the input terminal of the .

In this way, the result described above is obtained.

Next, a case will be explained in which there is a relationship where the distortion Dα of the amplitude characteristic is less than the distortion Dβ of the phase characteristic.

In this case, the output S5 of the high-pass filter 29 is S5=Δ
ωcospt−k2β2pΔω2sin2pt,
This output becomes one input of the synchronous detection circuit 28.

Further, the delay time of the delay circuit 26 is doubled as that of the oscillator 23.

The output of the 62 multiplier circuit 26 is 86.

Therefore, the output S7 of the synchronous detection circuit 28 is becomes.

On the other hand, the second-order differential coefficient β2 of the phase characteristic of the bandpass filter of the intermediate frequency amplification circuit 3 is normally set to the center angular frequency of the bandpass filter by ω.

When closed, the deviation frequency from the central angular frequency width is plotted on the horizontal axis and changes as shown in FIG.

Therefore, the second derivative coefficient β2 of the phase characteristic of the bandpass filter near the central angular frequency width is β2=KO(o)−ω
.

) can be approximated by

Therefore, the output S7 of the synchronous detection circuit 28 is becomes.

Here i. is a constant. As is clear from the above, the output S7 of the synchronous detection circuit 28 has a center angular frequency ω due to the operating angular frequency ω, similar to the output S7 described above, although its polarity is different.

It is a direct current voltage that changes from positive to negative around .

Therefore, the output S7 of the synchronous detection circuit 28 is amplified by the amplifier 25 to change the oscillation frequency of the crystal oscillator 16, and this changed oscillation frequency of the crystal oscillator 16 changes the oscillation frequency of the local oscillator 6, Angular frequency ω.

0 is always the center angular frequency ω of the intermediate frequency bandpass filter
.

The frequency synthesizer FM receiver operates in a state where the distortion Dβ due to the phase characteristics of the bandpass filter of the intermediate frequency amplification circuit 3 is minimized.

Note that in the above explanation, the delay circuit 26 causes the doubler circuit 2
7, but as mentioned above, the output signal S5 of the high-pass filter 29 lags behind the output S6 of the doubler circuit 27, so in addition to A, the delay time of the delay circuit 26 is set to increase the radian order. If a phase difference is established, the above-mentioned result can be obtained as is.

Above, we have explained the case where the distortion Dα due to the amplitude characteristic of the bandpass filter of the intermediate frequency amplification circuit 3 and the distortion Dβ due to the phase characteristic have the relationship Dα>>Dβ and Dα<<Dβ. Once determined, it is determined by the filter whether Dα>>Dβ or Dα<<Dβ.

Therefore, the distortion D determined by the target bandpass filter
The delay time of the delay circuit 26 may be set based on the relationship between α and Dβ.

Here, the frequency synthesizer FM of the second embodiment of the present invention
Returning to the receiver, when there is no broadcast radio wave near the tuning frequency corresponding to the frequency division ratio of the variable frequency divider 8 set by the frequency division ratio setter 14, or even if there is, the reception detection circuit 17 When the level is not high enough to activate the frequency synthesizer FM receiver, the selector switch 20 is switched to the position shown in FIG. The operation is exactly the same as that of .

Next, broadcast radio waves exist at or near the tuning frequency corresponding to the frequency division ratio of the variable frequency divider 8 set by the frequency division ratio setter 14, and have an electric field strength of a certain level or higher, and the FM
When the detection circuit 4 detects that the output of the FM detection circuit 4 corresponding to the broadcast radio wave is tuned within a certain range, the reception detection circuit 17 switches the changeover switch 20 to the distortion detection circuit 2.
Switch to side 2.

Therefore, as described above, the oscillation frequency of the crystal oscillator 16 is changed by the output of the synchronous detection circuit 28, that is, the output of the distortion detection circuit 22.

Therefore, the output of the phase comparator 11 changes the tuning frequency of the varactor tuning circuit of the high frequency amplifier circuit 1 to a frequency that matches the frequency of the broadcast radio wave that operated the reception detection circuit 17, and also changes the oscillation frequency of the local oscillator 6. The oscillation frequency of the crystal oscillator 16 is multiplied by the frequency division ratio of the variable frequency divider 8,
By changing the intermediate frequency signal in a direction that minimizes distortion, it is possible to receive broadcasts with minimum distortion by activating the reception detection circuit 17.

For example, as in the case of the first embodiment, the tuning frequency is set to 100 kHz by setting the dividing ratio setter 14.
For example, 80.
When set to 0 MHz, 80. 0MH
There is no broadcast radio wave for z, but 8 0.0 2 5M
Assuming that Hz broadcast radio waves exist, 80.02
The 5 MHz broadcast radio wave is within the band of the intermediate frequency amplifier circuit 3, and if the field strength level of the 80.025 MHz broadcast radio wave is above a certain level, the reception detection circuit 17 is activated and the tuned frequency is 8 0.0 2 5 MHz. , local oscillator 6
The oscillation frequency becomes the intermediate frequency with the minimum distortion, and even though the reception frequency set by the division ratio of the variable frequency divider 8 of the frequency synthesizer FM receiver is 80.00MHz, the oscillation frequency is 80.00MHz. .02 5MHz broadcast can be received with minimum distortion.

As explained above, according to the present invention, for example, 25kHz
Broadcasting on an odd number of frequencies such as 100
It can be received by a frequency synthesizer FM receiver configured to allow reception frequencies to be set at intervals of kHz or 50kHz, and the configuration for this is also simple.

Furthermore, the scanning time during automatic tuning does not become long.

Furthermore, in the case of automatic tuning or preset tuning, there is an advantage that the scanning circuit and preset circuit of the currently used frequency synthesizer FM receiver that sets the reception frequency at 100 kHz intervals can be used as is.

Further, there is an advantage that the frequency synthesizer can be used as a component of a distortion-free receiving circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional frequency synthesizer FM receiver. FIG. 2 is a block diagram of the first embodiment of the present invention. FIG. 3 is a block diagram of a second embodiment of the invention. FIG. 4 is a block diagram of a distortion detection circuit according to a second embodiment of the present invention. FIG. 5 and FIG. 6 are diagrams for explaining the operation of the second embodiment of the present invention. 1... High frequency amplification circuit, 2... Mixing circuit, 3... Intermediate frequency amplification circuit, 4...
FM detection circuit, 5... Stereo demodulation circuit, 6.
... Local oscillator, 7 and 10 ... Frequency divider, 8 ... Variable frequency divider, 9 and 16 ...
...Reference oscillator, 11... Phase comparator, 12.
...Low pass filter, 13, 21 and 25.
...Amplifier, 14...Divide ratio setter, 1
7... Reception detection circuit, 20... Changeover switch, 22... Distortion detection circuit, 26...
・Delay circuit, 27...2 multiplier circuit, 28...
... Synchronous detection circuit, 29 ... High pass filter.

Claims (1)

[Claims] 1 Equipped with a phase comparator that compares the phase of the frequency obtained by dividing the oscillation frequency of the local oscillator of the superheterodyne receiver by a variable frequency divider and the oscillation frequency of the reference oscillator, and uses the DC component in the output of the phase comparator to In a frequency synthesizer FM receiver that controls the oscillation frequency and tuning frequency of the local oscillator and allows the reception frequency to be set by setting the division ratio of the variable frequency divider, the reference oscillator has the function of a voltage-controlled oscillator. In addition, a reception detection circuit is provided which operates upon detecting that the electric field strength of the received radio wave is above a certain level and that the output of the FM detection circuit due to the received radio wave is within a predetermined range, and the reception detection circuit is activated. A frequency synthesizer characterized in that the oscillation frequency of a reference oscillator is changed so as to obtain a tuning frequency and an intermediate frequency adapted to the reception frequency at which the reception detection circuit is activated by a predetermined signal component in the output signal of the FM detection circuit. FM receiver.