JPS593888B2 - FM receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM receiver that can always receive signals with minimum distortion.

It is known that the sources of distortion in FM receivers are intermediate frequency bandpass filters and demodulators.
The intermediate frequency band pass filter and demodulator are provided in the M receiver to suppress the occurrence of distortion in the intermediate frequency band pass filter and demodulator.

However, these conventional methods are still insufficient and cannot always receive signals with minimum distortion. Therefore, the present applicant has developed an FM receiver (hereinafter referred to in this specification to be distinguished from a conventional FM receiver) that detects the distortion itself, controls the distortion so that it is always at a minimum, and can always receive data with minimal distortion. This FM receiver is referred to as an FM receiver with distortion detection loop.

) was filed. This FM receiver with distortion detection loop
In the receiver, means for frequency modulating the intermediate frequency signal of the FM receiver at a predetermined modulation frequency, means for demodulating the frequency modulated intermediate frequency signal at the modulation frequency, and demodulating output from the demodulating means are The present invention is characterized by comprising means for performing synchronous detection at a frequency twice the modulation frequency, and means for controlling the oscillation frequency of the local oscillator of the FM receiver using the detection output after the synchronous detection.

An embodiment of this FM receiver with a distortion detection loop includes an antenna 1, a high frequency amplifier 2, a mixer 3, a first
and a second input terminal, the output of which is modulated by the output frequency of the modulation frequency oscillator 11 applied to the first input terminal, and by the DC voltage applied to the second input terminal, that is, the output voltage of the amplifier 16. FM with a local oscillator 4 whose output frequency changes, an intermediate frequency bandpass filter 5, an intermediate frequency amplifier 6, a demodulator 7, a low frequency amplifier 8 and a speaker 9
Configure the receiver.

On the other hand, the output of the modulation frequency oscillator 11 is input to the delay circuit 12, and the output of the delay circuit 12 is input to the double multiplier 13.
The output of the multiplier 13 is used as one input of a multiplier 14 which together with a low-pass filter 15 constitutes a synchronous detector, and the other input of the multiplier 14 is the output of the demodulator 7 passed through a high-pass filter 10. The output of 14 is multiplier 14
The output of the low-pass filter 15 is input to the amplifier 16, and the output of the amplifier 16 is applied to the second input terminal of the local oscillator 4 as described above. In this case, the output angular frequency p of the modulation frequency oscillator 11 is selected to be an angular frequency that does not affect the FM received signal.

In the FM receiver with a distortion detection loop configured as described above, the output of the local oscillator 4 is frequency-modulated by the output angular frequency p of the modulation frequency oscillator 11, and the intermediate frequency signal in the received signal has a constant level of angular frequency p. A modulated signal is generated.

Now let the output of the high frequency amplifier 2 be S1=COSω,t,
Local oscillator 4 when there is no output of modulation frequency oscillator 11
When the output of the high-frequency amplifier 2, S, and the output S2' of the local oscillator 4 are applied to the mixer 3, the output S3' of the mixer 3 becomes (ω1-ω2) and ( Outputs of both frequency components of ω1+ω2) appear, but if we take only the (ω1-ω2) component now, S37=COSω00
It becomes t.

Here ω. o2(ω1-ω2). Therefore, at the output S4cOspt of the modulation frequency oscillator 11, the local oscillator 4
When the output of the mixer 3 is frequency modulated, the output S3 of the mixer 3 becomes an FM wave of Δω S3=COS(ω00t−−Sinpt).

When this FM wave passes through the intermediate frequency band pass filter 5, it is distorted by the amplitude characteristics and phase characteristics of the intermediate frequency band pass filter 5.

The output of demodulating this distorted FM wave by the demodulator 7 is:
If we focus only on the second harmonic, for the fundamental wave ΔωCOspt, K1α3P2Δω2c0s2pt−K2β2PΔω2s
A distortion component of in2pt is generated.

where p; modulation angular frequency α3; third-order differential coefficient of the amplitude characteristics of the intermediate frequency band-pass filter 5 β2: second-order differential coefficient of the phase characteristics of the intermediate-frequency band-pass filter 5 Δω: angular frequency deviation K1 to K2 ; is a constant.

Therefore, the output S6 of the demodulator 7 is S6=ΔωCOSpt+K1α3P2Δω2c0s2p
t-K2β2PΔω2sin2pt, and if we now pay attention to the distortion of the amplitude characteristic (distortion of the amplitude characteristic Dα=K
1α3P2Δω2c0s2pt>distortion of phase characteristic Dβ2K2β2PΔω2sin2pt.

) The output of the demodulator 7 becomes S6', and S6'=ΔωCOS
pt+K1α3P2Δω2c0s2pt. This S
6' is input as one input of the multiplier 14, and the output frequency of the modulation frequency oscillator 11, which is input to the other side of the multiplier 14, is doubled and the phase of the signal S6' is combined by the delay circuit 12. '-COs2pt in the multiplier 14. As a result, the DC component K1α3P2Δω2 of the output S8' of the multiplier 14 is outputted as the output S9' of the low-pass filter 15. On the other hand, the third-order differential coefficient α3 of the amplitude characteristic of the intermediate frequency bandpass filter 5 usually sets the central angular frequency of the intermediate frequency bandpass filter 5 to ω.

When the operating angular frequency is ω, the linear function of the detuning frequency α3=−KO(ω−ω) near the center angular frequency.
) can be approximated by KO is a constant. Therefore, the output S9' of the low-pass filter 15 is S9'=-1KO
Kl(ω-ωo)P2Δω2, when the operating angular frequency ω is ω-ωo, S,7=0, and when ω>ωo, S9'<0
, ω く ω. When S,′〉0, the operating angular frequency ω
Therefore, the central angular frequency ω. It is a direct current voltage that changes from positive to negative around . Therefore, the output S of the low-pass filter 15
9' is amplified by the amplifier 16, inputted to the second input terminal of the local oscillator 4, and outputted from the low-pass filter 15.
, ', the angular frequency ω00 of the output S of the mixer 3 is always the center angular frequency ω of the intermediate frequency bandpass filter 5.

It acts to bring it closer to . Therefore, FM with distortion detection loop
The receiver always operates to minimize the distortion Dα of the amplitude characteristic of the intermediate frequency bandpass filter 5. The above also applies to the distortion Dβ of the phase characteristic of the intermediate frequency band pass filter 5, and by simply changing the delay time of the delay circuit 12, the FM receiver with a distortion detection loop can always maintain the phase characteristic of the intermediate frequency band pass filter 5. It can be operated to minimize the distortion Dβ.

A detailed explanation thereof will be omitted. In this specification, local oscillator 4, modulation frequency oscillator 11. Delay circuit 12
, a doubler 13, a multiplier 14, a low-pass filter 15, and an amplifier 16 are referred to as a distortion detection loop.
An FM receiver not equipped with this distortion detection loop is referred to as a normal receiver.

As mentioned above, an FM receiver with a distortion detection loop can always perform reception with minimum distortion, but even if the oscillation frequency of the local oscillator 4 is mechanically changed by operating the variable capacitor of the local oscillator 4, Since the distortion detection loop operates and the oscillation frequency of the local oscillator 4 is electrically controlled so as to be in a state of minimum distortion, the tuning knob has a disadvantage of poor operability.

In view of the above, the present invention is intended to improve the operability of the tuning knob of an FM receiver with a distortion detection loop. The present invention will be explained below using examples.

FIG. 2 is a block diagram of one embodiment of the present invention.

In FIG. 2, the same components as in the FM receiver with distortion detection loop shown in FIG. 1 are given the same reference numerals. As shown in FIG. 2, this embodiment uses an FM with a distortion detection loop shown in FIG.
The receiver further includes a modulation frequency oscillator 11 and a local oscillator 4.
A switch element 17 is connected between the amplifier 16 and the first input terminal of the local oscillator 4, a switch element 18 is connected between the amplifier 16 and the second input terminal of the local oscillator 4, and a touch switch 20 is connected to the tuning knob 19.
are provided respectively, and when the tuning knob 19 is used to select a channel, that is, when a part of the human body, such as a finger, touches the tuning knob 19, the switch elements 17 and 18 are opened by the output of the touch switch 20. When selecting a broadcast station, that is, when a part of the human body touches the tuning knob 19, the touch switch 20 outputs an output and switches the switch elements 17 and 18 into an open state.

Therefore, the distortion detection loop is disconnected. Therefore, the output frequency of the local oscillator 4 can be changed by operating the tuning knob 19 in the same way as in a normal FM receiver, and the operability of the tuning knob 19 can be improved.

Further, when the operation of the tuning knob 19 is completed, that is, when the human body is not in contact with the tuning knob 19, for example, when the finger is removed from the tuning knob, the switch elements 17 and 18 are closed and the distortion detection loop is activated again. do. Note that although the strain detection loop is separated by the switch elements 17 and 18 in the above example, either one of the switch elements 17 or 18 may be omitted.

Next, other embodiments of the present invention will be described. FIG. 3 is a block diagram of another embodiment of the invention. This example is the first
The FM receiver with a distortion detection loop shown in the figure further includes a bandpass filter 21 whose input is the output of the intermediate frequency amplifier 6.
, a demodulator 22 which receives the output of the bandpass filter 21 as an input, a NAND gate 23 which inputs the output of the demodulator 22 into one input terminal, and a touch switch 20 connected to the tuning knob 19. is input to the other input terminal of the NAND gate 23.

In addition, the output terminal of the modulation frequency oscillator 11 and the local oscillator 4
Switching elements 17 and 18 each driven by the output of the NAND gate 23 are connected between the first input terminal of the amplifier 16 and the second input terminal of the local oscillator 4, respectively. do. Let us now assume that the bandwidth of the bandpass filter 24 is Fb, and its center frequency is the center frequency F of the intermediate frequency bandpass filter.

shall be. Therefore, when the intermediate frequency of the FM receiver with distortion detection loop is within the bandwidth Fb of the bandpass filter 21, the demodulator 22 outputs an output, and one input terminal of the NAND gate 23 receives a high potential output "1". Furthermore, when the signal is outside the bandwidth Fb, a low potential output of 60° is input to one input terminal of the NAND gate 23.

On the other hand, when the tuning knob 19 is touched by a human body, the touch switch 20 outputs a low potential output "O", and when not touched, the touch switch 20 outputs a high potential output 6 pins. Therefore, the output of the NAND gate 23 generates an output according to the truth table shown in Table 1.

Note that when the output of the NAND gate 23 is at a high potential "1", the switch elements 17 and 18 are turned off, and when the output of the NAND gate 23 is at a low potential "1", the switch elements 17 and 18 are turned on.

That is, when a person touches the tuning knob 19, the switch elements 17 and 18 are turned off and the distortion detection loop is disconnected.

Further, the distortion detection loop operates only when the tuning knob 19 is not touched by a person and the operating frequency of the intermediate frequency stage of the FM receiver with the distortion detection loop is within the bandwidth Fb of the bandpass filter 21. Therefore, when a broadcasting station is selected, that is, when a person touches the tuning knob, the distortion detection loop is disconnected and operates like a normal FM receiver, and the tuning knob 19
The operability of the tuning knob 19 is similar to that of a normal FM receiver, and the operability of the tuning knob 19 is improved.

Also, while the tuning knob 19 is being operated, the tuning knob 19
If the intermediate frequency is within the bandwidth Fb of the bandpass filter 21 when the contact with the human body is removed, the distortion detection loop operates in this state and changes the output frequency of the local oscillator 4 to minimize distortion. is automatically controlled to minimize distortion.

Further, the change in the distortion caused by the intermediate frequency band pass filter 5 with respect to the detuning frequency is determined by the intermediate frequency band pass filter 5.
Depending on the situation, if the horizontal axis represents the frequency and the vertical axis represents the distortion level, the center frequency F is obtained as shown in Fig. 4. Only Dena Fl
, f2, etc. may have multiple stable points. Therefore, as shown in FIG. 4, a bandpass filter 2 with a bandwidth Fb is
1, the distortion detection loop acts only within this bandwidth Fb, so the distortion detection loop does not act at other stable points such as Fl and f2 in FIG. Next, a modified example of this example will be described.

First, instead of the bandpass filter 21 and demodulator 22,
A Schmitts circuit is provided to amplify the DC output of the demodulator 7 with an S-shaped characteristic output using an absolute value amplifier, and to detect a constant level of the output of the absolute value amplifier, and inputs the output of the Schmitts circuit to one input terminal of the NAND gate 26. By doing so, the same functions and effects as those of the other embodiments described above can be obtained.

Further, even if a noise amplifier that detects noise appearing in the output of the demodulator 7 is used, the same operation and effect as in the other embodiments can be obtained. As described above, according to the present invention, the operability of the tuning knob of an FM receiver with a distortion detection loop is improved.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an FM receiver that the applicant previously applied for. FIG. 2 is a block diagram of one embodiment of the present invention. FIG. 3 is a block diagram of another embodiment of the present invention. FIG. 4 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 3. 2...High frequency amplifier, 3...Mixer, 4...Local oscillator, 5...Intermediate frequency band pass filter, 6... Intermediate frequency amplifiers, 7 and 22...
... Demodulator, 10 ... High pass filter, 1
1...Modulation frequency oscillator, 12...Delay circuit, 13...2 multiplier, 14...
Multiplier, 15...Low pass filter, 16...
...Amplifier, 17 and 18...Switch element, 19...Tuning knob, 20...
Touch switch, 21...Band pass filter, 23...Nand gate.

Claims (1)

[Scope of Claims] 1. means for frequency modulating an intermediate frequency signal at a predetermined modulation frequency, means for demodulating the frequency modulated intermediate frequency signal at the modulation frequency, and demodulating output from the demodulating means for modulating the frequency of the intermediate frequency signal. In an FM receiver equipped with means for synchronously detecting at a frequency twice the frequency and means for controlling the oscillation frequency of a local oscillator using the detection output after the synchronous detection, the tuning knob is being operated or not being operated. a detection circuit that detects this, and at least a first switch element that is driven by the output of the detection circuit and turns on and off the detected output, or a second switch element that turns on and off the signal of the modulation frequency. 1. An FM receiver comprising: one switch element, and during operation of the tuning knob, the switch element is turned off to stop controlling the oscillation frequency of the local oscillator by the detection output. 2 means for frequency modulating an intermediate frequency signal at a predetermined modulation frequency; means for demodulating the intermediate frequency signal frequency modulated at the modulation frequency; and demodulating output from the demodulating means at a frequency twice the modulation frequency. In the FM receiver, the FM receiver is equipped with means for synchronously detecting the oscillator, and means for controlling the oscillation frequency of the local oscillator using the detection output after the synchronous detection, the first step detecting whether the tuning knob is being operated or not being operated.
a detection circuit, at least one of a first switch element that turns on and off the detection output or a second switch element that turns on and off the signal of the modulation frequency; a second detection circuit that detects that the tuning knob is present in the band; and a gate circuit that receives the outputs of the first detection circuit and the second detection circuit as input; and only when the intermediate frequency signal exists within the predetermined band, the switch element is turned on to control the oscillation frequency of the local oscillator using the detection output.