JPS6387052A - Data demodulation circuit for fm multiplex broadcast receiver - Google Patents

Abstract

PURPOSE:To obtain an accurate demodulation signal by detecting that both radio data and SDK signals are supplied at a time and leading out a 1st or 2nd multiplier output of a costas loop in response to said detection signal. CONSTITUTION:An SDK detecting circuit 22 detects the output DC component of the 1st multiplier 1 to confirm that both radio data and SDK signals are supplied at a time to the 1st and 2nd multipliers 1 and 2. When only the radio data is supplied, the demodulation data is obtained at the side of the multiplier 1 and then led out via an LPF 5 and a selection switch 21. While the switch 21 is changed over and the demodulation data is obtained at the side of the multiplier 2 when both radio data and SKD signals are supplied at a time.

Description

Detailed Description of the Invention Technical Field The present invention relates to a data demodulation circuit, and more particularly, to a data demodulation circuit for receiving FM broadcast waves including a data signal indicating the type of program content and a radio data signal consisting of a subcarrier whose amplitude is modulated by this data signal. The present invention relates to a data demodulation circuit in a possible FM multiplex broadcast receiver.

BACKGROUND ART When a program of a general broadcasting station is broadcast, information indicating the type of the program content is transmitted as data through multiplex modulation, and the desired program content can be selected on the receiving side based on the demodulated data for radio listening. There is a Radio Data System (RDS) that allows people to enjoy its services.

In this radio data system, the 57KHz third harmonic of the 19KHz stereo pilot signal outside the frequency band of the FM modulation wave is used as a subcarrier, and this 57KHz subcarrier is filtered and biphase (B1
(phase) A data signal indicating coded program content is amplitude-modulated to produce a radio data signal, and this amplitude-modulated subcarrier is frequency-modulated to a main carrier and broadcast.

Also known is a traffic information broadcasting system that provides a service to listeners of car radios and the like by broadcasting traffic information on a time-sharing basis during program broadcasts of general broadcasting stations. In this system, a traffic information station identification signal (S
When broadcasting traffic information, this 57KHz subcarrier is used as a region identification signal (one of 23.75Hz to 53.98Hz) indicating which region the traffic information is for, and also as the current traffic information. is amplitude-modulated by a message identification signal (125 Hz single tone) indicating that it is being broadcast, and this amplitude-modulated subcarrier is frequency-modulated to the main carrier and then broadcast.

In this way, since the 57 KHz subcarrier is used in both the radio data system and the traffic information broadcasting system, in the radio data system, the subcarrier (radio data signal) amplitude-modulated with the data signal is used for traffic information broadcasting. The subcarrier of the radio data system has a phase difference of approximately π/2 with respect to that of the traffic information broadcasting system in order to distinguish it from the message identification signal of the system (subcarrier (SDK signal) whose amplitude is modulated by the DK double signal). That's what I do.

By the way, in an FM multiplex broadcast receiver capable of receiving FM multiplex broadcast waves including radio data signals, a data demodulation circuit that demodulates the radio data signal extracted from the FM detection output is, for example, a Costas loop type PLL (phase Locked or loop) circuits are used. FIG. 3 shows a conventional example of a data demodulation circuit configured with a PLL circuit of the Costas loop type.

In FIG. 3, the radio data signal is transmitted through the first and second multipliers 1 and 2 to the output signal of a VCO (voltage controlled oscillator) 3 and the VCO output to the phase shift circuit 4.
They are separately multiplied by a signal whose phase is delayed by 2, and each multiplication output passes through LPFs (low-pass filters) 5 and 6, respectively, and is multiplied by a third multiplier 7. The error signal, which is the output signal of the third multiplier 7, has its harmonic components cut off by the loop filter 8, and becomes the control voltage of the VCO 3.

The output of the first multiplier 1 that has passed through the LPF 5 is derived as demodulated data.

Here, the radio data signal is a double-sideband carrier suppressed signal, and if the data component is the A1 carrier wave and ω, then the signal level V is expressed as V-Acosωt, and the phase of the output of VCO3 is shifted by φ. and the first multiplier 1
If the output of is vl and the output of the second multiplier 2 is Vl, then
2) eosφ+(A/2)CO8 (2(L) to 1φ)
・・・・・・(1) Vl −Acosωt X5in(ω° is 1φ)−(A
/2) sinφ+(A/2) sin(2ωt+φ)...
...(2) becomes. The second term in each of the above equations (1) and (2) is removed by the LPF 5.6, and the first term is multiplied by the third multiplier 7. If the output of the third multiplier 7 is v3, then V 3- (A/2) cosφ×(A/2) sinφ-
(A218) sin2φ (3). By passing this through a loop filter 8, a control voltage for the VCO 3 is generated. Also,(
If the phase difference φ becomes zero in the first term of equation 1), the output of the LPF 5 becomes A/2, and this output can be derived as demodulated data.

In the conventional data demodulation circuit configured in this way, when the SDK signal of the traffic information broadcasting system is received simultaneously with the radio data signal, there is a phase difference of π/2 between the subcarriers of both signals, and the SDK signal has an amplitude of Since it is a modulated wave and has a subcarrier, it has the disadvantage that it synchronizes with the Costas loop or SDK signal, making it impossible to demodulate the data.

SUMMARY OF THE INVENTION The present invention has been made to eliminate the drawbacks of the conventional ones as described above, and provides an FM that can accurately demodulate data even when an SDK signal of a traffic information broadcasting system is received simultaneously with a radio data signal. An object of the present invention is to provide a data demodulation circuit in a multiplex broadcast receiver.

The data demodulation circuit in the FM multiplex broadcast receiver according to the present invention has means for detecting that a radio data signal and an SDK signal are input simultaneously and generating a detection signal, and when this detection signal is not generated, the Costas loop The output of the first multiplier is derived as demodulated data, and the output of the second multiplier is derived as demodulated data only when the detection signal is generated.

Example Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram schematically showing the basic configuration of an FM multiplex broadcast receiver. In the figure, the front end 11 selects a desired station from the FM multiplex broadcast wave received by the antenna 10, converts it to an intermediate frequency (10.7 MHz), and then supplies it to the FM detector 13 via the IF amplifier 12. be done. The detection output of the FM detector 13 is supplied to an MPX (multiplex) demodulation circuit 14, and in the case of stereo broadcasting, is separated into L (left) and R (right) channel audio signals.

Furthermore, when the detection output of the FM detector 13 passes through the filter 15, a 57 KHz subcarrier, that is, a radio data signal, amplitude modulated by the biphase coded data signal is extracted and demodulated by the PLL circuit 16. . This demodulated output is supplied to a digital (D) PLL circuit 17 and a decoder 18. In the DPLL circuit 17,
A clock for data demodulation is generated based on the demodulated output of the PLL circuit 16. The generated clock is supplied to the gate circuit 19. The lock detection circuit 20 is a DPL
It detects that the L circuit 17 is locked and generates a lock detection signal, which is supplied to the gate circuit 191 to control the circuit 19 to be in an open (oven) state. In the decoder 18, the biphase coded data signal which is the demodulated output of the PLL circuit 16 is decoded in synchronization with the clock generated by the DPLL circuit 17, and is output as data indicating the type of program content of the radio broadcast. .

FIG. 2 shows a PL that constitutes a data demodulation circuit according to the present invention.
3 is a block diagram showing one embodiment of the L circuit 16, in which parts equivalent to those in FIG. 3 are designated by the same reference numerals. In the figure, the basic configuration of the Costas loop type PLL circuit is the same as that in FIG. 21 and a selection switch 21 which detects the DC component of the output of the first multiplier 1 that has passed through the LPF 5, for example, and generates a detection signal.
An SDK detection circuit 22 that performs switching control is provided. The selection switch 21 normally selects the output of the first multiplier 1, and selects the output of the second multiplier 2 only when a detection signal is generated from the SDK detection circuit 22. The selected output of this selection switch 21 is derived as demodulated data. The SDK detection circuit 22 detects that the radio data signal and the SDK signal are simultaneously input to the first and second multipliers 1 and 2 by detecting the DC component of the output of the first multiplier 1. .

In such a configuration, when only the radio data signal is input, demodulated data is obtained on the first multiplier 1 side as explained in FIG. It will be derived via

On the other hand, considering the case where the SDK signal is input simultaneously with the radio data signal, when the radio data signal and the SDK signal are combined, the input signal level Vin becomes V in −A slnωt + (1+ B ) co
sωt-A + l+B cos(ωt+θ) ・
++ (4), and the Costas loop will be synchronized with eO8ωt. Here, 1 indicates the traffic information bureau identification signal (SK multiplied signal component) which is a carrier wave, and B indicates the area identification signal (BK multiplied signal component or BK multiplied signal and message identification signal (DK multiplied signal component), respectively. ), the radio data signal is represented by sinωt because the SDK signal is 19 regardless of the presence or absence of the radio data signal.
This is because it is synchronized with three times the KHz stereo pilot signal, so that if the two signals coexist, the radio data signal will be phase shifted by π/2. Here, if we calculate V,, V2 and cut the harmonic components, we get ¥+ -VinX cosωt-*(1+B)/2
- (5) V2-VlnX sinωt -4-A/
2 − (6), and the demodulated data is output not from the first multiplier 1 side but from the second multiplier 2 side.

Furthermore, when the radio data signal and the SDK signal are input at the same time, the first multiplier 1 outputs a DC component (1/2), as is clear from equation (5).

The SDK detection circuit 22 detects this DC component (1/2), generates a detection signal, and switches the selection switch 21 to the second multiplier 2 side.

Thereby, even if a radio data signal and an SDK signal are input at the same time, demodulated data can be reliably derived. At this time, the SK multiplied signal SDK detection circuit 2
2, the B K/D K signal can be taken out from the first multiplier 1 side.

Further, even when only the SDK signal is input, the SK multiplied signal and the BK/DK signal can be accurately detected in synchronization with the SDK signal.

In the above embodiment, a signal phase-shifted by π/2 with respect to the output of the VCOB was obtained using the phase shift circuit 4. By doing so, it is also possible to obtain a signal having a phase difference of π/2.

In addition, the SDK detection circuit 22 detects the DC component based on the SK double signal (traffic information bureau identification signal) of the SDK signal, but it also detects the BK double signal (area identification signal) which is always transmitted at the same time as the SK double signal. The DC component may be detected by detecting the DC component, and the same effect as in the above embodiment can be obtained.

As described in detail of the invention, according to the data demodulation circuit according to the present invention, the output of the first multiplier of the Costas loop is usually derived as demodulated data, and the radio data signal and the SDK signal are input simultaneously. In some cases, this is detected and the output of the second multiplier is derived as demodulated data, so even if the SDK signal is received at the same time as the radio data signal, the data indicating the content of the radio program can be accurately demodulated. can do.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an outline of the basic configuration of an FM multiplex broadcast receiver, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a block diagram showing a conventional example. Explanation of symbols of main parts 1, 2. 7... Multiplier 3... Voltage controlled oscillator (V CO) 8...
...Loop filter 13...FM detector 17...Digital PLL circuit 21...
・Selection switch

Claims (2)

[Claims] (1) A data demodulation circuit in an FM multiplex broadcast receiver capable of receiving FM broadcast waves including a data signal indicating the type of program content and a radio data signal consisting of a first subcarrier amplitude-modulated by the data signal. and a voltage controlled oscillator that generates a reference signal having the same frequency as the first subcarrier, and multiplying the radio data signal by the reference signal and a signal having a phase difference of approximately π/2 from the reference signal, respectively. a first and second multiplier; a third multiplier that multiplies the outputs of the first and second multipliers; and a third multiplier that removes harmonic components of the output of the third multiplier to generate the voltage. A loop filter serves as a control voltage for a controlled oscillator, and a second subcarrier having a phase difference of approximately π/2 from the first subcarrier and amplitude modulated by a predetermined signal is simultaneously transmitted to the radio data signal. a detection means that detects input to the first and second multipliers and generates a detection signal, and each output of the first and second multipliers is set as two inputs, and when the detection signal is generated; 1. A data demodulation circuit in an FM multiplex broadcast receiver, comprising: selection means for selecting the output of the second multiplier only when the selection means selects the output of the second multiplier, and derives the output of the selection means as demodulated data. (2) Data demodulation in the FM multiplex broadcast receiver according to claim 1, wherein the detection means detects a DC component of the output of the first multiplier to generate a detection signal. circuit.