JP4792908B2 - FM demodulation apparatus and method, and communication apparatus using the same - Google Patents

Description

  The present invention relates to an FM demodulator, a method thereof, and a communication apparatus using the FM demodulator, and more particularly to a receiver that receives FM modulated waves of video signals and audio signals and outputs them as baseband signals. Up) relates to an FM demodulation system suitable for use in an apparatus.

  In the receiving unit of the FPU device for relaying a video signal, an NTSC composite signal (a composite signal of a video signal and a synchronization signal, hereinafter referred to as a video signal for simplification) and an audio signal are FM. The modulated signal is received, FM demodulated, and output.

  FIG. 5 is a functional block diagram of a receiving unit having an FM demodulating unit in such an FPU device. Referring to FIG. 5, the received IF signal is input to the FM demodulating unit 101, subjected to FM demodulation, de-emphasized in the de-emphasis unit 102, and then to a V LPF (video low pass filter) 103 for extracting a video signal. As a result, only the video component is extracted and output via the amplifier 104.

  6 and 7, FIG. 6 shows the frequency spectrum of the input IF signal, and FIG. 7 shows the frequency spectrum of the baseband (BB) band signal obtained as an output. . Referring to FIG. 6, there are video signal components centered on an IF frequency of 130 MHz, and there are three types of audio components, audio # 1, # 2 and O / W (order wire) as shown in the figure. Yes.

  Referring to FIG. 7, the above-described three audio signals include a video signal having a band of 0 to 4.2 MHz and three subcarriers (eg, 6 MHz, 6.5 MHz, and 7 MHz). And FM-modulated signals. Therefore, the V LPF 103 in FIG. 5 is a video low-pass filter provided for extracting only the video signal component shown in FIG.

  The output of the FM demodulator 101 is input to CH BPFs 105 to 107 which are channel bandpass filters for extracting subcarriers including the above-described three types of audio components. Then, FM demodulation sections 108 to 110 perform FM demodulation using subcarriers from local oscillators (LOC) 111 to 113, and input to LPFs 117 to 119 via de-emphasis sections 114 to 116, respectively. These LPFs 117 to 119 extract the above-described three types of audio signals and output them via amplifiers 120 to 122 for level adjustment, respectively.

In addition, there exists patent document 1 as a related technique.
JP-A-6-77737

  In the FM demodulator shown in FIG. 5, since the FM demodulator 101 is an analog signal process, adjustment is necessary to improve accuracy, and the adjustment is complicated. Further, since the IF signal is a high frequency and the frequency band is wide as shown in FIG. 6, the FM demodulator 101 is required to perform high-speed processing in a wide band.

  Furthermore, since the subcarrier frequency of the audio signal shown in FIG. 7 is not fixed and differs depending on the specifications of the user of the FPU device, the frequency characteristics of the CH BPFs 105 to 107 can be adjusted for each user, It is necessary to change the frequency of the local oscillators 111 to 113 for the demodulation units 108 to 110, and these adjustments and changes are extremely complicated. Further, crystal oscillator elements of the local oscillators 111 to 113 are prepared in advance for each user. There is a disadvantage that it is also not necessary in terms of cost.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an FM demodulating apparatus and method and a communication apparatus used therefor, in which high-speed processing is suppressed as much as possible to facilitate circuit design and adjustment, and a crystal oscillator is prepared for each user and adjustment for each user is unnecessary. Is to provide.

An FM demodulator according to the present invention comprises:
An FM demodulator that inputs a carrier wave of a predetermined frequency that is FM-modulated according to a baseband signal including a video signal,
Means for digitizing the carrier wave;
First digital demodulation means for converting the digital output into a baseband using an orthogonal demodulation method using the frequency component of the carrier wave to generate components orthogonal to each other;
Means for down-sampling this orthogonal component ;
First FM demodulation means for performing FM demodulation of the downsampling output ;
Means for deriving the FM demodulated output in analog form;
It is characterized by including.

The FM demodulation method according to the present invention includes:
An FM demodulation method in which a carrier wave having a predetermined frequency that is FM-modulated according to a baseband signal including a video signal is input,
Digitizing the carrier;
A first quadrature demodulation step for converting the digital output into a baseband band by a quadrature demodulation method using the frequency component of the carrier wave to generate components orthogonal to each other;
Down-sampling this orthogonal component ;
A first FM demodulation step for FM demodulation of the downsampled output ;
Deriving the FM demodulated output in analog form;
It is characterized by including.

  A communication apparatus according to the present invention uses the above-described FM demodulator.

  According to the present invention, since the quadrature demodulation method is adopted and the digital signal processing is performed, there is an effect that low-speed processing is possible, and even if the subcarrier frequency differs for each user, There is an effect that it is possible to easily cope with the change by changing only the above.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. Referring to FIG. 1, the IF signal of the FM modulated wave having the frequency spectrum shown in FIG. 6 is input to the FM demodulator 1, FM demodulated, and down-converted to a baseband band as shown in FIG. The As will be described later, the FM demodulator 1 performs digital processing.

  The FM demodulated output is supplied to the de-emphasis unit 2 and subjected to de-emphasis processing, and input to a V LPF (video low-pass filter) 3 for selectively passing a video signal. The video output by the V LPF 3 is converted into an analog signal by a DAC (digital analog converter) 4 and then output as a video signal via the LPF 5 and the amplifier 6.

  The signals having the frequency spectrum shown in FIG. 7 that have been converted to the baseband by the FM demodulator 1 are input to channel bandpass filters (CH BPF) 7 to 9 for audio signal extraction, respectively, and audios # 1 and # 2 , O / W three types of subcarrier signals are extracted. The outputs of these CH BPFs 7 to 9 are respectively input to the thinning units 10 to 12 and subjected to thinning (down sampling) processing.

  This thinning process is performed for the following reason. That is, at the time of digitization in the FM demodulator 1, digital conversion is performed at a high sampling frequency because the video component is included, but downsampling is performed because the audio component may be at a lower sampling frequency. The thinning process is performed.

  Then, the FM demodulating units 13 to 15 perform digital FM demodulation, respectively, and input to the DAC 22 via the thinning units 16 to 18 and the de-emphasis units 19 to 21. In the DAC 22, three types of audio signals of audio # 1, # 2, and O / W are obtained through analogized level adjusting amplifiers 23 to 25.

  FIG. 2 is a functional block diagram showing an example of the FM demodulator 1 of FIG. 1, and has a general digital FM demodulation function. Referring to FIG. 2, the IF input is digitized by the ADC 30 and input to the delay unit 51 and the phase conversion unit 52. The delay unit 51 adjusts the delay of the output of the ADC 30 and corrects the processing delay by the phase conversion unit 52.

  The phase conversion unit 52 generates a signal component orthogonal to the output signal component of the delay unit 51. If the signal component of the delay unit 51 is a sin (sine) component, the phase conversion unit 52 generates a cos (cosine) component. Is. The phase calculation unit 53 detects the phase of an FM-modulated signal, and is expressed in polar coordinates from mutually orthogonal components (sin and cos) expressed in an xy coordinate system that is an orthogonal coordinate. The r component and the θ component are converted to detect the θ component, that is, the phase.

Therefore, the phase calculation unit 53 has a function of calculating the θ component by converting from the orthogonal coordinate system to the polar coordinate system,
θ = tan ⁻¹ y / x
It has a function to calculate the following formula. Therefore, when components (x, y) orthogonal to each other are input, a circuit that immediately outputs θ using a conversion table obtained by calculating the above equation in advance can be provided.

  The phase information detected by the phase calculation unit 53 is input to the phase difference detection unit 60 at the next stage, and a phase difference (Δθ) that is a difference from the phase information before one sampling is detected. That is, in the phase difference detection unit 60, the delay element 54 and the subtractor 55 detect the difference between the phase information of the data before one sampling and the phase information of the current sampling data. This phase difference information, that is, frequency information is derived as an FM demodulated output in the baseband shown in FIG.

  In the circuit configuration of FIG. 2, since the FM signal is directly demodulated without down-converting the IF signal band, all processes need to be performed at high speed, which is not practical. Therefore, the circuit shown in FIG. 3 is used as another example of the FM demodulator 1 shown in FIG.

  Referring to FIG. 3, the IF signal is digitized by the ADC 30 and input to the quadrature demodulation unit 31. The quadrature demodulating unit 31 multiplies by 130 MHz that is an IF frequency from an NCO (Numerical Controlled Oscillator) 34, thereby down-converting to the baseband band of FIG. This IF setting of the NCO 34 is performed by a digital control signal.

  More specifically, the IF signal digitized by the ADC 30 is branched into two and input to the multipliers 32 and 33, and multiplied by mutually orthogonal IF frequency components (sin component and cos component) output from the NCO 34. And down-converted to a baseband signal.

  The orthogonal baseband signals are respectively input to the thinning units 35 and 36 for downsampling, and then are derived to an FM demodulating unit including a phase calculation unit 37 and a phase difference detection unit 60 in the next stage.

  The phase calculation unit 37 and the phase difference detection unit 60 are the same as the phase calculation unit 53 and the phase difference detection unit 60 described with reference to FIG.

  In this way, the IF input is digitized, and the quadrature demodulation unit 31 down-converts it to the baseband band to generate the sin component and the cos component, which are quadrature components, so that the phase calculation can be performed in the baseband band. The processing speed can be reduced. Moreover, since the NCO 34 by digital control can be used for setting the local frequency of the FM demodulator 1, the control signal can also be digital, and adjustment and setting are extremely easy.

  FIG. 4 is a diagram showing still another example of the FM demodulator 1 in FIG. 1. The IF signal is directly input to the quadrature demodulator 40 without being digitized by the ADC, and the analog signal is used as a base signal. Down-converted to band bandwidth. The quadrature demodulator 40 includes multipliers 41 and 42, a local oscillator 43 that generates an IF frequency of 130 MHz, and a phase shifter 44 that shifts the IF frequency by 90 degrees.

  The mutually orthogonal components (sin and cos) obtained by the multipliers 41 and 42 are digitized by the ADCs 45 and 46, respectively, and input to the phase calculation unit 47 of the next stage. As described with reference to FIG. Calculated. This phase information is input to the phase difference detector 60 at the next stage. This phase difference detection unit 60 is the same as the phase difference detection unit 60 of FIG.

  In this example, since the quadrature demodulator 40 is an analog process, the quadrature accuracy and level accuracy by the IF frequency phase shifter 44 are required and adjustment is required. The unit 47, the phase difference detection unit 60, and the like have an advantage that high-speed processing is not required because of the baseband band.

  Note that the circuit configuration obtained by removing the ADC 30 from the FM demodulation unit shown in FIG. 3 is used for the FM demodulation units 13 to 15 of the audio signal shown in FIG. In this case, the input to the quadrature demodulator 31 is the subcarriers of the three audio signals in FIG. 7, and the NCO 34 is set by digital control signals b to d for setting the frequency of each subcarrier. It becomes.

  Further, since the CH BPFs 7 to 9 as the channel filters of FIG. 1 can be digital filters, it is possible to easily cope with the specifications for each user only by changing the coefficients of the digital filters.

  The FM demodulating device of the above embodiment is suitable for use in the receiving unit of the FPU device, but it is needless to say that the FM demodulating device can be used in the receiving unit of a general FM radio communication device without being limited thereto.

It is a block diagram of an embodiment of the invention. It is a figure which shows an example of the FM demodulation part of FIG. It is a figure which shows the other example of the FM demodulation part of FIG. It is a figure which shows the further another example of the FM demodulation part of FIG. It is a block diagram for demonstrating a prior art example. It is a figure which shows the frequency spectrum of IF signal. It is a figure which shows the frequency spectrum of a baseband signal.

Explanation of symbols

1,13-15 FM demodulator
2,19-21 Deemphasis section
3 V LPF (video low pass filter)
4,22 DAC (digital analog converter)
5 LPF
6, 23-25 amplifier
7-9 CH BPF (channel bandpass filter)
10-12, 16-18,
35, 36 Thinning part
30, 45, 46 ADC (analog-digital converter)
31, 40 Quadrature demodulation unit 32, 33, 41, 42 Multiplier
34 NCO
37, 47, 53 Phase calculator
38, 48, 54 delay element
39, 49, 55 Subtractor
51 Delay part
52 Phase converter
60 Phase difference detector

Claims (10)

An FM demodulator that inputs a carrier wave of a predetermined frequency that is FM-modulated according to a baseband signal including a video signal,
Means for digitizing the carrier wave;
First digital demodulation means for converting the digital output into a baseband using an orthogonal demodulation method using the frequency component of the carrier wave to generate components orthogonal to each other;
Means for down-sampling this orthogonal component ;
First FM demodulation means for performing FM demodulation of the downsampling output ;
Means for deriving the FM demodulated output in analog form;
An FM demodulator comprising: The baseband signal includes a subcarrier component that is FM-modulated by an audio signal, and the carrier wave is FM-modulated according to the baseband signal.
Means for extracting the subcarrier component from the output of the first FM demodulation means;
Second orthogonal demodulation means for generating components orthogonal to each other by orthogonal demodulation using the frequency component of the subcarrier, and the extracted output;
Second FM demodulation means for performing FM demodulation of the audio signal based on the orthogonal component;
Means for deriving the FM demodulated output in analog form;
The FM demodulator according to claim 1, further comprising: Each of the first and second FM demodulation means includes:
Means for calculating phase information based on the orthogonal components;
Means for detecting the difference between this phase information and the phase information before one sampling and deriving it as an FM demodulated output;
The FM demodulator according to claim 2, further comprising: 3. The FM demodulator according to claim 2, wherein the frequency component of the subcarrier in the second orthogonal demodulator is generated by an NCO (Numerically Controlled Oscillator) . An FM demodulation method in which a carrier wave having a predetermined frequency that is FM-modulated according to a baseband signal including a video signal is input,
Digitizing the carrier;
A first quadrature demodulation step for converting the digital output into a baseband band by a quadrature demodulation method using the frequency component of the carrier wave to generate components orthogonal to each other;
Down-sampling this orthogonal component;
A first FM demodulation step for FM demodulation of the downsampled output;
Deriving the FM demodulated output in analog form;
An FM demodulation method comprising: The baseband signal includes a subcarrier component that is FM-modulated by an audio signal, and the carrier wave is FM-modulated according to the baseband signal.
Extracting the subcarrier component from the output of the first FM demodulator;
A second quadrature demodulation step for generating components that are orthogonal to each other by the quadrature demodulation method using the frequency component of the subcarrier from the extracted output;
A second FM demodulation step for FM demodulation of the audio signal based on the orthogonal component;
Deriving the FM demodulated output in analog form;
The FM demodulation method according to claim 5, further comprising : Each of the first and second FM demodulation steps includes:
Calculating phase information based on the orthogonal components;
Detecting a difference between this phase information and the phase information before one sampling and deriving it as an FM demodulated output;
The FM demodulation method according to claim 6, further comprising : 7. The FM demodulation method according to claim 6, wherein the frequency component of the subcarrier in the second orthogonal demodulation step is generated by an NCO (Numerically Controlled Oscillator) . A communication apparatus comprising the FM demodulator according to claim 1. The communication apparatus according to claim 9, wherein the communication apparatus is an FPU (Field Pick Up) apparatus.

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