JPS6068703A - Fm demodulating method and circuit by digital delay and self correlation - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Backlash of the Invention Telephone signals are applied to power lines at frequencies higher than the power frequency, both inside buildings and over long distance power lines. Complex circuitry is required to demodulate high frequency signals and convert them to digital form.

The pending Yoneyama Special Application No. 422.9112 describes an autocorrelation type receiver that does not require individual parts so that the three receivers can be configured completely digitally. There is C. When realizing the autocorrelation part of this receiver, if the autocorrelation shift register has a predetermined fixed delay with respect to the carrier frequency of the FM signal, the baseband signal is forced to change to the carrier frequency. It was found that there is a direct linear relationship with . Furthermore, it has been found that changes in the amplitude of a signal can be extracted in response to changes in frequency or phase. The fact that the amplitude changes as a function of frequency satisfies the conditions for an FM discriminator, which is a detector for FM signals. When the received FM signal is processed by a digital autocorrelation circuit, the output voltage of the discriminator is
The magnitude follows the change in frequency. In telecommunications applications, when digital systems are involved, the output of the FM discriminator of the present invention is similar to digital signals. ie, "on" or "A-off", with the duty cycle depending on the amplitude of the audio signal voltage applied to the C carrier by the transmitter. By using the discriminator of the present invention, the FM telephone receiving machine can be made simpler and simpler, since the phase-locked loop (1) LL) type decoder used in the Tongtong 1J telephone circuit is not required.

It is therefore an object of the present invention to develop an improved FM system using the autocorrelation/j equation as an FM detector without the need for phase-shifting circuits or other energy storage equations such as phase-locked loop f+ts decoders. The purpose is to provide telephone circuits.

SUMMARY OF THE INVENTION 1 The present invention provides a self-411U9... for Ftvl signals that includes a comparator, a shift register, and a flip-flop circuit.
Provides type 1 receiver. Shift 1...Resistor 141 multiplies the FM signal by a certain starting and delay time to create a two-component signal. Wave a component twice the carrier wave and use the paceband component to calculate the amplitude and frequency? Make 1 hollyhock 1 division with skin number. By selecting a constant delay with respect to the carrier frequency of the FM signal, the resultant signal is approximately equal to the digital representation of the FM signal.

[General Description of the Invention 1 The mathematical derivation of the white self-correlation proximate IMI number for baseband A-G A request f(t), 112 transmission frequency WC, and FM signal is as follows. That's right.

FM signal 1sin(wc-+-f(t))t(1) If this signal is delayed by a certain time τ, FM signal 1si
nl, (wc+f(t))(t-τ)) (2) Formula (1)
When multiplied by

x(t)=sin(wc}-giant L))t-sin[(w
w=wc'+
When r(t) is defined, equation (3) becomes as follows.

x(t)=sinwresi++w(t-r) Using the theorem of trigonometric functions, equation (3) becomes as follows.

x(t)=1. /2[cos(wt-w(t-r))-
cos(wL+w(t-r))]=1/2coswr-
The second term of 1/2 COS (2wt-wr) equation (4) is a high frequency component, and the low frequency component of this can be removed by a wave generator. The first term in equation (4) is a direct current value that does not change over time. However, the W term changes over time, and changes above and below the level when the DC level is modulated 0 (f(t)=O). This value is based on the carrier frequency (WC) and a constant delay (
It is determined by the relationship between

wc=π/2 (or equivalent value) By choosing , the first term of equation (4) becomes as follows.

X(t)=silo(φ=f(t)τ》−C is si++x for small perturbations around φ radians
=x Therefore, for a small change in the input month - Ji A Jingo, using equation (6), equation (5) becomes as follows.

<3) x(t) (low frequency) f(t)'<7) Equation (
7》 is expressed as the first term (
1/2coswτ) A-geo modulation (4) f(t) is shown to be linearly reproduced.

As with the active FM discriminator, the width variation of the carrier signal appears in the audio range, so τ, the human input signal should be passed through the limiter. Not only does this reduce the effect of carrier amplitude changes, but the human signal is "squared" and the autocorrelation effect has more of a duty cycle than the sinusoidal effect and is therefore more linear. The first term is a cosine function of the product of the carrier frequency (fc) and a constant delay τ.

As in the case of FM transmission, the carrier frequency changes over time, so the DC level also changes. Cosine is a non-linear relation (
5) Although it is a number, for small changes around ±π/2 [
Okay, there's a straight line area. Proper constant delay time and medium (6)
By choosing the combination V with the heart frequency, this self-4u relation effect can be reduced to FM block? It can be used as a separate device.

The second term (1/2cos(2wt-wτ)) is a binary frequency component that is of no interest to FM detection, and therefore can be easily removed by a low-frequency waveform filter.
A circuit to test the idea of this correlation using extension time was drawn up as described below.

[Description of a Preferred Embodiment] FIG. 1 shows an autocorrelation circuit 10 used in the autocorrelation type receiver described in the above-mentioned US Pat. For more information on this receiver, please refer to this US patent application. In the present invention, the receiver circuit will be described as including a bandpass waveform generator 11 that senses an incoming FM signal having a carrier frequency fc. The signal is then processed by limiter 12.
Contains a limiter to eliminate carrier wave amplitude changes. The delay circuit 13 will be explained in detail later with reference to FIG. 2, but 1.
25 divided by the carrier frequency. As previously mentioned, this constant delay is an important feature of the invention since no phase shifting circuitry is required. li
} In the calculator 22, the current signal (2
0), then the low-pass wave ′j! 416, and then output to the telephone circuit.

The digital detection circuit 17 of the autocorrelation type receiver 10 is the second one.
A cross detection device such as comparator 18 is shown in the figure. This comparator changes the band-limited incoming FM signal [C from a sinusoidal waveform A to a rectangular waveform B by limiting the power squared.

The signal is sampled by the D-type flip-flop 19, and the delay time is determined by the clock (CK) of the n-stage shift register 9 that constitutes the delay circuit 13 of FIG.
The clock C applied to the clock line 15 connecting the clock (GK) of the loop 19 to the human input is multiplied by one. Flipfu [Itsubu 19σ) QOFJ child is shift l ~
- Connected to the D terminal of register 9, shift 1 - - Q terminal of register 9 is connected to one input of exclusive NOR game 1.22. The other power of exclusive Noah Gut 22 is connected via line 20 to line 23. Line 23 interconnects the QQ'A terminal of flipflop 19 and the D terminal of shift register 9. The NOR gate 22 is constructed as a digital 11}D device, the output of which is passed through a suitable low-pass IP waveform, such as waveform generator 16 of FIG. As mentioned above, remove high frequency components.

The clock signal applied to the check line 15 consists of the carrier frequency ([.), the number of stages of the shift register 14 (11), and a constant delay time (τ
). , I#2 transmission frequency is 200Kl-1
When using a 12-stage CMOS shift register 14, a sample frequency of 1.92 MllZ was selected. A two-pole 34001-12 low-frequency wave filter 16 is used to separate the A-geo signal, and the A-geo quality of the resulting signal is commonly used in power line circuits and stereo radio circuits. A comparison was made with the type of phase-locked loop decoding circuit used.

The audio A quality of this audio A signal was equal to or better than that obtained from a bedside power line decoder.

By increasing the frequency of the input signal ([C]) and measuring the audio output signal expressed in volts, we evaluated the effectiveness of the detection circuit 17 with respect to the autocorrelation response. Graph C in FIG. It shows a near-linear response in volts as a direct function of the human power frequency in volts.

The first term of DC {l11 on both sides of the carrier frequency
The linearity of is best seen in the graph of FIG. 4, which shows the output signal as a function of frequency on either side of the carrier. The IC is set at the carrier frequency (c=155Kl-1l)
Constant 6] Delay Moe 1+'. l (yo, 11 (i.25Kt
-1z and 193. Centered on Gate Kl-IZ, 155
Note that there are two linear regions on either side of Kl-IZ.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an FM receiver using the FM detector of the present invention, Fig. 2 is a schematic diagram of the FM detector used in the receiver of Fig. 1, and Fig. 3 is a schematic diagram of the FM detector used in the receiver of Fig. 2. Figure 4 shows the relationship between autocorrelation response and frequency.
12 to 215Kl-IZ(7) is a graph showing the relationship between the autocorrelation output and the frequency. Explanation of main symbols 9: n-stage shift register, 18: comparator, 19: flip-flop, 22: IJ} Alternative Noah Goo 1~-21-

Claims (1)

[Claims] 1) A crossing detection means for squaring the incoming FMm transmission frequency signal to limit the number of squares, and sampling the carrier signal and multiplying the signal by a predetermined extension signal. sampling delay means;
an FM discriminator circuit which removes selected frequency components from the multiplied signal; 2) 'l'JrF A 1:M discrimination circuit in the FM discrimination circuit according to claim 1), wherein the zero crossing detection means is formed by a die A-de limiter. 3) In the FM discriminator circuit described in Patent W [Claim 1] (゛, the FM discriminator circuit in which the sampling prolongation means is formed on the side of an autocorrelation circuit C. 4) In the patent claim [1jlll] 5) In the FM discrimination circuit described in claim 3, the autocorrelation 6. In the }-M discrimination circuit according to claim 5), the autocorrelation circuit also includes at least one flip-flop. Circuit. 7》In the FM discrimination circuit described in claim 6), the at least one flip knob and the shift registers are interconnected by a common link line. FM discrimination circuit. 8) An FM discrimination circuit in which the near extension time is a mathematical function of the carrier frequency. 9) In the FM discrimination circuit according to claim 1, the FM carrier wave number is 109 to 215Kl-IZ.
FM discrimination circuit. 10》T M described in Special Feature 8' [iIilf Requirement Range 9>
In the discriminator circuit, the delay time is n/1.25 times the reciprocal of the carrier frequency. 11) Square and limit the FM carrier frequency signal,
An FM detection method comprising the steps of creating an autocorrelation with respect to a certain delay time of the signal and extracting a specific high frequency component from the temporally delayed signal. 12》In the FM detection method described in claim 11), the autocorrelation generates an “M signal,” in which ×(t) is delayed.
where WC is the carrier frequency and τ is the delay time, the formula x(t)
1 sin(wc+f(t))t-sin[wc0r(t
))(t-r)]. 13) The FM detection method according to claim 11), wherein the autocorrelation is such that the signal is sampled at 11 times the carrier frequency. 14) In the FM detection method described in Particular i' [Claim 13], the time delay is equal to
An FM detection method obtained by connecting a common clock line between shift registers of stages. 15) In the FM detection method described in claim 13), the FM detection yj method includes a step of multiplying the delayed signal. 16) The FM detection method according to claim 15, which includes the step of modulating the multiplied signal through a modulation reduction device.