JPS58133005A - Fm demodulator - Google Patents

Abstract

PURPOSE:To have an extremely high degree of channel selection, by using a band pass filter having a sharp pass characteristics. CONSTITUTION:Both center frequency of a desired wave and frequency of a local osillator 30 are set at omega1, and therefore the center frequencies of band pass filters 51 and 52 are also set at omega1. At the same time, the ideal characteristics are set for these filters. Here the outputs of the filters 51 and 52 are set as R1T=A1sin(omega1+st) and R2t=A2cos (omega1t+st) respectively. The outputs of differentiating circuit 61 and 62 are shown by equations 1 and 2. Therefore the output of a multiplier circuit 71 is shown by an equation 3, and the output of a multiplier circuit 72 is shown by an equation 4. Therefore the output of a subtractor circuit 73 is shown by an equation 5. Then a transmitting signal (vt) can be demodulated by deleting which is a constant. In such a way, the degree of channel selection can be extremely increased by using such filters having sharp pass characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION Misfiring relates to FM demodulation IIk, and 41 relates to modification of the FM demodulator using a quadrature detector. As an FM demodulator,
Up until now, methods using quadrature detectors have been used, for example, References Showa Gei Nen Tatami Kōkai Hikaku No. 1m3 ``Shu IIIL Number Discriminator Circuit'' or British Patent Jl No. 11110m ``-dmlat
@rf@r FM Signals J (Notice 1r
rs capital ■ month) is known to 5. When such an FM demodulator is applied to frequency-divided channels whose center frequencies are spaced a certain distance apart, the channel selectivity is that when receiving a certain desired channel, how much influence from other channels is received. However, it was insufficient to be able to avoid it.

The object of the present invention is to eliminate this drawback and provide an FM demodulator with sufficient channel selectivity.

According to the present invention, there is provided a local oscillator having local oscillation outputs of $111 and iris 2 whose phases differ by 900, and first and second local oscillators whose inputs are the received FM modulated wave and the first and second local oscillation outputs, respectively. #2 frequency converter, first and second band pass filters that receive the outputs of the first and #11E2 frequency converters as inputs, and a part of the output of the scissors first band pass filter. a first differentiating circuit that inputs the output of the band-pass filter of the JI11 and the output of the second differentiating circuit. and a second multiplier whose inputs are the output of the second bandpass filter and the output of the first differentiation circuit, and the output of the first multiplier is This objective can be achieved by inputting the output of the second multiplier to a subtraction circuit and using the resulting output as a demodulated output.

A detailed explanation will be given below using drawings and formulas.

FIG. 1 is a profile diagram showing an embodiment of the present invention. The FM signal input to the input trend lO is generally expressed as follows.

Rtt+ = A cos (duck t+a(t))...
・・・・・・・・・・・・(1) Kogo de Muha! @, m
, is the center frequency! There is and there is. In this work, β is the brutality index #l (4 is the hen-koshi entry signal.

The output of the local oscillation grace is 1(t) = la II & (Shizu 0...)
...song... old... body), the output of JIII's frequency converter 4 is -1 (t) = mu 5 in ((he - 鴫 -) tl5 (t)) 10 Ax 51j ((-, +#)
t + s(g))”...(4).111
The output of the frequency conversion 5122 of 2 is Rjt) = B*
"((So * -"e) t + a(t)) + ml pot [(-60-) Seishi a(t Lee...(2).&
Although the second term on the right side of (t) and &(t) is a high-order component, it is easy to remove it because its frequency is significantly different from the fundamental component of the 111th term.

In the frequency division channel, when S* channels are used simultaneously, it takes ms to separate only the desired channel compared to the above case. When there are multiple receiving hexagons, K is calculated from formula (4) (51).
, the spectrum of the output of the frequency converter is 5 as shown in m2tjA.

In order to select only a desired channel from these 5KII channels, a conventional quadrature detection frequency discriminator uses a low-pass filter. However, it is generally difficult to make the pass characteristics of a low-pass filter steep, and it has been impossible to extremely reduce interference between adjacent channels and channels. As is well known, a band-pass J1 filter using a ceramic resonator or a crystal resonator exhibits an extremely steep pass characteristic, thereby reducing interference between adjacent channels and thereby increasing channel selectivity.

Now, for the sake of simplicity, it is assumed that the frequency difference between the center frequency of the desired wave and the local oscillator is a ring, and therefore the center frequency of the bandpass filter is a part of this value. Also, let's assume that the characteristics of the filter are arbitrary. Bandpass filter 51
, 52 are as follows.

Rs(t)”＄” [t+5(t))・・・・・・・・・
・・・・・・・・・・・・ 俤）&(tl = AsCXl
5 (Q g + alt) ) −・−・−−−−
・−・・−−−−(7) The output of mold fighting 1161, 62 is m'&) = blood (s + / f (t)) ai (*** +
#(t))-1)&(1)=+, ^l[-1,000 β 豐(woon)sin(mt+s(處)]...misery). Therefore, the output of the multiplication path 71 is c,<t>
=-Pigeon [Town+β* (t)) m”(St+1(1)
)−・・・・・・The output of the multiplier circuit n is: 9g)=j4AJtsu+βw(t))Sulfurωt+5(t))
・・・・・・・・・・・・・・・It becomes the axis.

Therefore, the subtraction circuit nI)aS force is D(t)=(,
(t) −(1, (t)=A14(&=+β9 (t)
'l ------・ill. Since - is a constant, if this is removed, the transmitted signal V (#) can be demodulated.

That’s all! As explained above, in the present invention, since a band pass filter with a steep pass characteristic can be used, the channel selectivity can be extremely improved.

[Brief explanation of drawings]

Fig. 1 is a profile diagram showing an embodiment of the present invention, and Fig. 2 is a schematic diagram of the frequency converter output spectrum when receiving a frequency division channel. 21 and 22 are frequency converters;
(9) is a local oscillator, lead is a 90° phase shifter, 5152 is an imperial pass filter, 61.62 is a differential circuit, and 71. 72 is a multiplication path, 73 is a subtraction path, and 74 is a demodulation output terminal. ! Figure 1 Taotzu

Claims (1)

[Claims] tithm oscillation aS having ml and second local oscillation outputs whose phases are different by zero, and first and second frequencies whose inputs are the received FM modulated wave and the first and 1/s2 ss oscillation outputs, respectively. iris 1 and 11, each having a number, a transducer, and the respective outputs of the first and kite 2 skin agility transducers as inputs;
112 band-pass filter, a differential path of Ml which receives a part of the output of the first band-pass filter as input, and a jll which takes part of the output of the second band-pass filter as input.
an irises 10 which receives as inputs the differentiating circuit of E2, the output of the band pass filter III), and the output of the second differentiating path;
a multiplier; and a second multiplier that receives as input the output of the @2 bandpass filter and the output of the first differentiation circuit, and multiplies the output of the Isl multiplier by the $112. The FMg modulator is designed to input the output of the modulator to the subtractor 1111 to obtain a demodulated output.