JPS61245748A - Pcm signal transmission system for catv - Google Patents

Abstract

PURPOSE:To improve the frequency accuracy and to eliminate the need for a large sized and expensive oscillator by multiplexing the modulation signal of a fundamental wave for generating local carrier together with a modulated PCM signal, sending the result and recovering the fundamental wave having the same frequency as that at the transmission side at the reception end. CONSTITUTION:The 1st fundamental frequency to obtain each local carrier is sent together with the phase modulation signal of each PCM signal with frequency division multiplex, the result is modulated at a receiving and the 1st fundamental frequency is recovered. Even when a frequency fluctuation is caused in the 1st fundamental frequency generated by an OSC1 at a sending end, the 1st fundamental frequency having the same frequency as that at the sending end is obtained accordingly at the reception end. As a result, the frequency accuracy of an oscillator 13 generating the 1st fundamental frequency is less than a conventional system, e.g., the use of a crystal oscillator without temperature compensation is enough, an equipment is miniaturized and low-cost is attained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a PCM signal transmission system for CATV, and particularly to a PCM signal transmission system for CATV.
The present invention relates to a PCM signal transmission system for CATV that is suitable for transmitting a PCM signal in which voice and data are pulse code modulated through an ATV (cable television) line.

[Conventional technology]

CA'rV [! '°1- is a method of transmitting PCM signals on the 21st line.

The PCM signal is used for subcarrier full multiphase phase modulation (or multilevel amplitude variation WJI4) L, and then this modulation signal is used for local carrier tIi1. tgj7R width modulation and transmitting the required sidebands, the modulated signals of a plurality of PCM signals are frequency division multiplexed and transmitted through a CATV line. Problem] In the above-mentioned Zuo-Song-Gong style, when the television signal is multiplied and transmitted together with the modulation signal of the PCM signal, the local carrier wave for the above-mentioned image width modulation mixes into the band of the television signal. In order to prevent this from causing noise interference, the level of the local carrier wave leaked from the amplitude modulation circuit and transmitted is suppressed to a sufficiently low level. Therefore, on the receiving side,
It is not possible to extract and reproduce the local carrier wave from the received signal.

It is necessary to generate a local carrier wave of the same frequency as the transmitting side and perform amplitude demodulation. Differences in environmental conditions such as temperature between the transmitting side and the receiving side will cause a difference in the frequency of the local carrier wave, but it is necessary to keep this difference in the number of local carrier waves between the transmitting side and the receiving side within the range that allows the system to operate normally. In order to maintain the local carrier wave, the circuit scale of the excavator that generates the local carrier wave increases, resulting in a problem that the device becomes large and expensive. If the pull-in frequency range of the reproduction circuit is (center value) ±250 Hz and the local carrier wave is 125 MHz, the frequency center value on the transmitting side and the receiving side is 125 MHz and the accuracy is ±2.
A local carrier oscillator within X10- is required. To achieve this level of accuracy, a temperature compensated water oscillator (TCXO) must be used on both the transmitting and receiving sides, which is quite large and expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a PCM signal transmission system for CA'l'V which solves the above-mentioned problems and allows the apparatus to be made smaller and cheaper than the conventional apparatus.

[Means for solving problems]

The method of the present invention includes: an oscillating device that generates a first fundamental frequency having a predetermined frequency; a frequency synthesizing means for generating a local carrier wave; a first modulating means for modulating a second local carrier wave with the first fundamental frequency to generate a first modulation signal; Thereafter, a second channel having a two-stage variable circuit 940 amplitude modulates the first local carrier wave to generate a second modulated signal.
modulation means, and the first and second modulation signals t
"i!L convolution and frequency division multiplexing multiplexed signal is CAT
a transmitting device for transmitting to a V line; a demodulating means for M1 for demodulating the first modulated signal included in the multiplexed signal received from the CATV line to reproduce the first fundamental frequency; a frequency synthesizing means for reproducing the first local carrier wave having a frequency that is the sum of the frequency multiplied by the xi fundamental frequency reproduced by the first demodulating means and the frequency of the second fundamental frequency; a two-stage demodulation circuit for demodulating the included second modulated signal with the first local carrier wave reproduced by the frequency synthesizing means and further phase demodulating with the subcarrier wave to reproduce the PCM signal; It is equipped with a second demodulating means and a receiving device having 'f:.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention.

The device k on the transmitting end side generates an oscillation (
b) A path (O20) 1, a modulator 4 for modulating a second local carrier wave with this first fundamental frequency, and a bandpass filter (BP).
F) Modulation path with 5, PCM signal No. 4 (1) (
6 or (2)) Phase modulation circuit 2-
1 (or 2-2) and modulator 4-1 (or 4-2)
) and bandpass filter (BPP) 5-1 (or 5-2)
A modulation path with a modulation path, a frequency r obtained by multiplying the first fundamental frequency (or frequency multiplication of 7n, 7'C, J fundamental frequency) generated by 0801 and adding the frequency of the second fundamental frequency to the east. A phase-locked loop (PLI) 3-1 (or d3-2) that generates each first local carrier wave with a phase-locked loop (PLI) 3-1 (or d3-2) is used to superimpose the output signals C, DI, and RI of each modulation path to obtain the wave number. CA'r V transmission line 1 as division multiplexed signal
It is equipped with a coupling circuit 6 for sending data to 2.

PCM signal (1) or (
2) (Other than this, illustrations are omitted to avoid duplication of explanation), first tL'% audio signal (or data signal)
It is a signal that is pulse code modulated (with time and division side striping as necessary). For example, the PCM signal (1) undergoes polyphase differential phase modulation on the −J carrier wave in the phase modulation circuit 2-1, undergoes roll-off shaping with a constant vF9T through a Tammetal roll-off filter, and is converted into a phase modulation signal by the modulator 4-1. The zero transformer 4-1 sent to P1, L3-1 amplitude modulates the first local carrier wave sent from Pl, . B)
'F5-1 blocks unnecessary Tsukuda waveband components included in the amplitude modulation signal of 151, passes the 151myo sideband components, and sends this to the coupling circuit 6 as the t-signal D8. , P
The CM signal (2) also undergoes a two-pronged modulation process of phase modulation and amplitude modulation, resulting in 4! The signal, which is a sideband component, is sent to the fully coupled circuit 6. B P iI' 5-1 and 5-2
Then, in order to prevent each local carrier wave from being mixed into the television channel band, the modulators 4-1j? and 4-
On the other hand, sufficiently attenuate the leakage of the local carrier wave from 2.

0801 is the first fundamental frequency (first fundamental frequency IBL)
The 0 modulator 4, which sends the signal to the PLLs 3-1 and 3-2, etc., and also sends it to the first fundamental frequency full addition 4, is a width modulator, and sends a carrier wave of a predetermined frequency from the 08CI to the first It is amplitude modulated using the fundamental network wave and sent to BPF5. BP1'5 suppresses out-of-band components other than the double-side band components contained in this amplitude modulated signal, and sends this as signal C to the coupling circuit 6. The coupling circuit 6 generates a multiplexed signal t-CAT in which the signals C, D, and (etc.) are superimposed.
V transmission path 12 transmission path 〇 The device on the receiving end side includes a distribution circuit 7 that distributes the multiplexed signal sent through the CATV transmission path 12 to each demodulation path. A demodulation path for the signal C, comprising a bandpass filter (BPF) 8 and a demodulator 9 (and a multiplier 10), a bandpass filter (BPF) 8
-1 (or 8-2) and demodulator 9-1 (or 9-2)
2) and the phase numeral circuit 1l-1 (or 1l-2) and t
A PLL 3- generates a 6th local carrier wave having a frequency obtained by multiplying the total frequency of the output signal of the demodulation path of the signal R (or Dt) and the demodulation path of the signal C and adding the second fundamental frequency in full. 1 (or 3-2).

The BPF 8 is a bandpass filter for passing the signal Ct included in the multiplexed signal and suppressing other unnecessary components. Demodulator 9ri envelope detector, signal C
The first fundamental frequency of the local carrier wave is detected by envelope level detection. The multiplier 10 is a frequency multiplier, and the US
It has a multiplication factor equal to the multiplication ratio of the frequency of the signal sent from ei to the PLLs 3-1 and 3-2 with respect to the first fundamental frequency. Therefore, if the first fundamental frequency is directly transmitted from 08C1 to PLLs 3-1 and 3-2 without being multiplied by the transmitter, this multiplier IO is also unnecessary. This signal C
The output signals of the demodulation path are sent to PLLs 3-1 and 3-2, converted into first local carrier waves, and sent to demodulators 9-1 and 9-2, respectively. On the other hand, the analogy is a signal.
In the demodulation path, the signal D1 included in the multiplexed signal passes through BPF8-1, and then @! PLL with adjuster 9-1
The PCM signal (1) is demodulated by the first local carrier wave sent from 3-1, and further demodulated by the phase demodulation circuit 11-1 to reproduce the PCM signal (1). Similarly, the signal 1 passes through its demodulation path and undergoes a 92-stage demodulation process to reproduce the PCM signal (2).

FIGS. 2(a) and 2(b) are diagrams showing an example of the configuration of the 08CI in this embodiment, respectively. Oscillator 1
3 generates a first fundamental frequency of a predetermined frequency. Same figure (
a) The first fundamental frequency generated by the oscillator 13 is transmitted to the modulator 4
PLL3-1 (and 3-2) as is.
etc.).

In the same figure (b), the first fundamental frequency is sent to the modulator 4, and each PL
LIC [This shows a case where a sub-fundamental frequency obtained by frequency-multiplying the first fundamental frequency by a multiplier 10 is sent.

FIG. 3 shows PLL 3-1 (or 3-3) in this embodiment.
2 etc.) is a block diagram showing an example of the configuration.

The phase detector (PD) 31 detects the first fundamental frequency (Rurui side fundamental frequency) sent from t) SCI and the frequency divider 36.
Detects the phase difference with the signal sent from the
The detection signal, which has passed through the PF32 and whose frequency components have been suppressed, is sent to the voltage controlled oscillator (vCO) 33. The oVCO 33 responds to the detection signal by decreasing the absolute value of the voltage. Change the oscillation network wave number. VC
The output signal of O33 is sent to the modulator 4-1 as a local carrier wave, and is also sent to the mixer 35.
4 is a signal sent from the VCO 33 and an oscillator 34
receives the second fundamental frequency sent out by the frequency divider 36, and generates a mixed signal having a frequency equal to the difference between the two frequencies.
send to The frequency divider 36 divides the frequency of the mixed signal and sends it to the PD 31. The PLL 3-1 operates to converge to a synchronous state, that is, a state in which the voltage of the detection signal is equal to zero. 08
The first fundamental frequency (
Alternatively, the frequency of the sub-fundamental frequency is f1, the frequency of the second fundamental frequency is f2, and the division ratio of the frequency divider 36 is N.
Then, the frequency fL of the output signal of the PLL 3-1 in the synchronized state, that is, the local carrier wave, is expressed as (1) fL=N-ft+f*.

FIG. 4 shows signals C, D, and 2 in this embodiment.

FIG. 2 is a spectrum diagram showing the frequency arrangement of FIG. Signal C has a spectrum with double sidebands separated by the frequency of the carrier wave input to the modulator 4 and two fundamental frequencies above and below the carrier wave, and thus occupies a bandwidth of twice the fundamental frequency. do. The signals RI and RI each have the desired sideband spectrum after amplitude modulation and therefore occupy the same bandwidth as the phase modulated and roll-off shaped signal. , the first fundamental frequency for obtaining each local carrier wave is frequency division multiplexed and transmitted together with the phase modulation signal of each PCM signal, and demodulated at the receiving end to reproduce the first fundamental frequency. Therefore, even if a frequency fluctuation occurs in the first fundamental frequency where 08CI is generated on the transmitting end side, it is possible to immediately respond to this and obtain the first fundamental frequency at the same frequency as that on the transmitting end side on the receiving end side. O that can be done, that is,
The first term N''f* on the right side of equation (1) is the same on the transmitting end and receiving end.As a result, the frequency accuracy of the oscillator 13 that generates the first fundamental frequency is lower than before. For example, a crystal oscillator without temperature compensation can be used, making it smaller and cheaper than before.As is clear from the above explanation, the frequency of the local carrier wave at the transmitting end and receiving end is The difference in numbers is PL, L3-1 (or 3-3) in F4 translation, respectively.
(2, etc.) depends only on the difference in the frequency f of the second fundamental frequency. The frequency f is the frequency division ratio N in equation (1)
By increasing , the oscillator 340 frequency that generates the second fundamental frequency can be set low, and the frequency of the oscillator 340 that generates the second fundamental frequency can also be lowered by N degrees.
For example, it is sufficient to use all the crystal oscillators that do not compensate for temperature and summer, and a small and low-cost oscillator can be used.In this way, the formula (1
) By generating the local carrier wave using a PLL that performs all frequency conversion, the means for generating the local carrier wave can be made smaller and lower in price than in the past. Furthermore, the frequency (fL) of the local carrier wave is limited to an integer multiple of the frequency of the first fundamental frequency, but may be selected to any desired value.

Although this embodiment shows a case where the amplitude modulation signal of the first fundamental frequency is additionally multiplexed, the modulation method of the fundamental frequency need not be limited to amplitude modulation (AM), and frequency modulation (FM)
) or frequency shift keying (FSK), it is obvious that the first fundamental frequency can be additionally multiplexed, and the same effects as in the present embodiment can be obtained.

As is clear from the above description, the present invention involves multiplexing and transmitting a fundamental wave modulation signal for local carrier generation together with a modulation signal of a PCM signal, so that a fundamental wave having the same frequency as that on the transmitting end side can be transmitted on the receiving end side. By regenerating , the frequency nIL is high, so there is no need to use a large and expensive oscillator, and it is possible to realize a PCM signal transmission system for CATV that can make the device smaller and cheaper than before.

[Brief explanation of the drawing]

Fig. 1, Fig. 2 (a) and (b), and Fig. 3 are diagrams showing the embodiment of the present invention, respectively, and Fig. 4 is the spectrum showing the frequency distribution of the embodiment of the present invention. It is a diagram. 1...Oscillation concave path (O20), 2-1.2-2.
...Phase modulation circuit, 3-1.3-2...
Phase-locked loop (PLL), 4, 4-1, 4-2
...Modulator, 5,5-1.5-2.8.8-1
．． 8-2... Bandpass filter (BPF), 6...
...Coupling circuit, 7...Distribution circuit, 9゜9-
1.9-2... Demodulator, 10... Multiplier, 11-1.11-2... Phase demodulation circuit. Man 1 figure

Claims (1)

[Scope of Claims] Oscillating means for generating a first fundamental frequency having a predetermined frequency; and a first fundamental frequency having a frequency that is the sum of a frequency multiplied by the first fundamental frequency and a frequency of the second fundamental frequency. a frequency synthesizing means for generating a local carrier wave; a first modulating means for modulating a second local carrier wave with the first fundamental frequency to generate a first modulation signal; and a subcarrier phase modulated with a PCM signal. and second modulation means having a two-stage modulation circuit that amplitude-modulates the first local carrier wave to generate a second modulation signal, and superimposes the first and second modulation signals to generate a second modulation signal. a transmitter that transmits a multiplexed signal that has been divided and multiplexed to a CATV line; and a transmitter that demodulates the first modulated signal included in the multiplexed signal received from the CATV line to reproduce the first fundamental frequency. and reproducing the first local carrier wave having a frequency that is the sum of the frequency multiplied by the first fundamental frequency and the frequency of the second fundamental frequency reproduced by the first demodulating means. frequency synthesizing means for demodulating the second modulated signal included in the multiplexed signal using the first local carrier wave reproduced by the frequency synthesizing means, and further phase demodulating using the subcarrier wave to generate the PCM signal. 1. A PCM signal transmission system for CATV, comprising: a receiving device having a second demodulating means having a two-stage demodulating circuit for reproducing the PCM signal.