JPS6336743Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an FM demodulator using a piezoelectric resonator.

Conventionally, FM demodulators that obtain audio signals from the FM intermediate frequency output from an amplitude-limiting amplifier have been used as ratio detectors, differential peak detectors, foostasiele FM demodulators, and pulse-count FM demodulators. A variety of other methods are known.

For example, as shown in FIG. 1, a ratio detection device includes a piezoelectric resonator X ₁ , diodes D ₁ , D ₂ ,
one using capacitors C ₁ , C ₂ and resistors R ₁ , R ₂ , R ₃ , or a winding L ₁ connected to a width-limiting amplifier (not shown), as shown in FIG. The winding L ₁
A transistor T consisting of coils L ₂ and L ₃ coupled to diodes D ₃ , D ₄ and a capacitor C ₃
~C ₆ and resistors R ₃ and R ₄ are generally known.

In addition, as a differential peak detection device, as shown in FIG.
It is generally known that the output of the tuning circuit 12 is inputted to a tuning circuit 12 consisting of a coil L ₄ and capacitors C ₇ and C ₈ , and the output of the tuning circuit 12 is inputted to a differential amplifier 13.

By the way, the ratio detection devices shown in FIGS. 1 and 2 have a large number of parts, and the ratio detection device shown in FIG. ₂ uses coils L ₁ , L ₂ and L ₃ . , L ₂ and L ₃ must be adjusted, which has the disadvantage of increasing the adjustment cost.

In addition, although the differential peak detection device shown in Figure 3 has a relatively small number of parts, it uses coil L ₄ , so it is necessary to adjust the inductance of coil L ₄ , which results in the ratio shown in Figure 2. Like the detection device, it has the disadvantage of high adjustment cost.

The present invention was made to eliminate the above-mentioned drawbacks of conventional FM demodulators, and its purpose is to realize a non-adjustable FM demodulator that uses a two-terminal resonator and has a small number of parts.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

In the present invention, as shown in FIG. 4, a first series circuit 2 consisting of a two-terminal resonator X ₁₁ and a resistor R ₁₁ is connected between the output of the amplitude limiting amplifier 20 and the ground.
A second series circuit 22 consisting of a 1- and 2-terminal resonator X ₁₂ and _{a resistor R 12 is} connected, and _a connection point 23 between the 2-terminal resonator Connection points 24 between the two-terminal resonator X ₁₂ and the resistor R ₁₂ of the series circuit 22 are connected to input terminals 26 and 27 of a differential amplifier 25, respectively.

The FM demodulator is configured as described above, the output voltage of the amplitude limiting amplifier 20 is set to V ₁ , and the first series circuit 21
The output voltage at the connection point 23 between the two-terminal resonator X ₁₁ and the resistor R ₁₁ is e ₁ , and the two-terminal resonator of the second series circuit 22
Connection point _{24 between two-terminal resonator X 12 and} resistor R ₁₂
If the output voltage of is e ₂ , the output voltages e ₁ and e ₂ are expressed by the following equations.

e ₁ = X ₁₁ / _{R 11} + _{X 11 V 1 ... (} 1) _{e 2 = R 12 / R 12} + X is the minimum,
Since the reactance X reaches its maximum at the anti-resonant frequency Fa, the output voltages e ₁ and e ₂ vary with frequency as shown by curves l ₁ and l ₂ in FIG. 5.

The output _e3 of the differential amplifier 25 which amplifies the difference between the output voltages _e1 and _e2 is expressed as follows: _X11 = _X12 =X, _R11 = _R12 =
If R, then from the first and second equations, _e1 - _e2 = X-R/X + _Rv1 . At = Fr, X≒0 and _e1 - _e2 ≒ _-V1 .
= Fa, X → ∞, e ₁ − e ₂ ≒ + V ₁ , and X = R
When _e1 - _e2 =0, the differential amplifier 25
From this, the FM demodulation characteristic (so-called S curve) shown by curve _l3 in FIG. 5 can be obtained.

As can be seen from the above, two terminal resonators X ₁₁ and X ₁₂
The reactance characteristics of R ₁₁ and R ₁₂ are equal, and the resonant frequency Fr and anti-resonant frequency Fa of these two two-terminal resonators X _{11 and}
When the resistance value R of is made to match the reactance X ₀ of the resonators X ₁₁ and X ₁₂ at frequency = (Fr + Fa) / 2 (when R = X ₀ ), the FM demodulation characteristics are , the sensitivity, distortion rate, etc. will be the best.

As is clear from the detailed description above, the present invention provides a circuit network consisting of two two-terminal resonators and two resistors between the amplitude limiting amplifier and the differential amplifier. Since the FM demodulation signal is obtained from the differential amplifier by connecting to the Since there is no need to use it, it is easy to integrate it into an integrated circuit, and it has the advantage of reducing the number of parts.

[Brief explanation of the drawing]

1 to 3 are circuit diagrams of a conventional FM demodulator, FIG. 4 is a circuit diagram of an FM demodulator according to the present invention, and FIG. 5 is an explanatory diagram of the operation of the FM demodulator shown in FIG. FIG. 6 is an explanatory diagram of reactance characteristics of a two-terminal resonator. 20... Amplitude limiting amplifier, 21... First series circuit (R ₁₁ ... Resistor, X ₁₁ ... 2-terminal resonator), 22
...Second series circuit ( _R12 ...Resistor, _X12 ...2-terminal resonator), 23, 24...Connection point, 25...Differential amplifier, 26, 27...Input terminal.

Claims (1)

[Scope of utility model registration request] A first series circuit consisting of a two-terminal resonator and a resistor, which is formed by connecting a two-terminal resonator to the ground side between the output of the amplitude limiting amplifier and the ground, and a second series circuit, which is formed by connecting the resistor to the ground side. A second series circuit consisting of a terminal resonator and a resistor is connected to each other, and a connection point between the two-terminal resonator and the resistor in the first series circuit and a connection point between the two-terminal resonator and the resistor in the second series circuit. An FM demodulator characterized in that each of the FM demodulators is connected to the input terminal of a differential amplifier.