JPH06303038A - Fm detection circuit - Google Patents

Abstract

PURPOSE:To provide an FM detection circuit requiring no adjustment whose variable oscillating frequency range is wide by forming a phase shifter having a broad frequency characteristic not deteriorating a frequency characteristic of a piezoelectric resonator. CONSTITUTION:The detection circuit relates to the quadrature system FM detection circuit detecting an FM signal by multiplying the FM signal with a signal resulting from changing a phase of the FM signal by a phase shifter 10. The phase shifter 10 includes 1st and 2nd resistors 12, 13 of bridge connection, a piezoelectric resonator 11 and a capacitor 14, the FM signal is applied between the terminals of the 1st resistor 12 and the piezoelectric resonator 11 connected in series and the 2nd resistor 13 and the capacitor 14 connected in series, an intermediate connecting point between the 1st resistor 12 and the piezoelectric resonator 11 and the 2nd resistor 13 and the capacitor 14 is connected respectively to a differential amplifier 15, from which a signal obtained by changing the phase of the FM signal is extracted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM detector circuit for detecting a change in frequency of an FM wave as a change in voltage, and more particularly to a quadrature type FM detector circuit.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a conventional quadrature FM detection circuit, 1 is a phase shifter, 2 is a piezoelectric resonator, 3
Is a resistor, 4 is a capacitor, 5 is a limiter, 6 is a multiplier, 7 is a low-pass type wave reactor (hereinafter abbreviated as LPF),
Reference numeral 8 is an input terminal, and 9 is an output terminal. The phase shifter 1 has a phase shift characteristic as shown in FIG. 2 by shifting the phase by 90 degrees by the capacitor 4 and buffering the phase of the piezoelectric resonator 2 by the resistor 3. First, F input from the input terminal 8
The amplitude of the M wave is limited by the limiter 5, one of its outputs is directly input to the multiplier 6, and the other is input to the multiplier 6 via the phase shifter 1. The phase shifter 1 causes a phase delay of 0 to 180 degrees depending on the frequency of the input signal as shown in FIG. The multiplier 6 multiplies the signal with no phase lag and the signal with phase lag to obtain the LPF.
By passing through 7, voltage-frequency characteristics (hereinafter, abbreviated as VF characteristics) as shown in FIG. 3 can be obtained.

[0003]

As described above, the conventional phase shifter 1 is composed of the piezoelectric resonator 2, the resistor 3 and the capacitor 4. However, in this case, due to the reactance component of the capacitor 4, as shown in FIG.
There is a problem in that the characteristic of No. 2 deteriorates from A to B, and the VF characteristic of the FM detection circuit becomes narrow. Therefore, an object of the present invention is to provide an FM detection circuit which has a wide variable frequency range and a wide phase shift characteristic without degrading the frequency characteristic of the piezoelectric resonator and has a wide F-V characteristic.

[0004]

In order to achieve the above object, the present invention provides an FM detection circuit for performing FM detection by multiplying an FM signal by a signal in which the phase of the FM signal is changed by a phase shifter. In the above-mentioned phase shifter, the phase shifter includes bridge-connected first and second resistors, a piezoelectric resonator and a capacitor, and a series connection of the first resistor and the piezoelectric resonator, and the second resistor and the capacitor. An FM signal is supplied between both ends of each, and the intermediate connection points of the first resistor and the piezoelectric resonator, and the second resistor and the capacitor are connected to the differential amplifier, and the phase is changed from the differential amplifier. It is configured to take out a signal.

[0005]

The phase shifter includes a bridge circuit including a piezoelectric resonator, two resistors and one capacitor, a first resistor and a piezoelectric resonator of the bridge circuit, and a second resistor and a capacitor. It is configured with a differential amplifier that differentially extracts the output from the connection point. Therefore, the output of the phase shifter is the second
Is the difference between the signal divided by the resistor and the capacitor and the signal divided by the first resistor and the piezoelectric resonator. Particularly, since the piezoelectric resonator side is composed of a series circuit of the piezoelectric resonator and the first resistor, the original bandwidth ΔF of the resonator is not narrowed. Therefore, it is possible to obtain a wide phase shift characteristic using the wide frequency characteristic of the piezoelectric resonator as it is.

[0006]

FIG. 5 shows an example of an FM detection circuit according to the present invention. 10 is a phase shifter, 11 is a piezoelectric resonator, 12 and 13 are resistors, 14 is a capacitor, 15 is a differential amplifier, and 16 is a limiter. , 17 is a multiplier, 18 is a low-pass reactor (hereinafter abbreviated as LPF), 19 is an input terminal, and 20 is an output terminal. The configuration excluding the phase shifter 10 is the same as the conventional one.

In the phase shifter 10, the piezoelectric resonator 11
, The resistors 12, 13 and the capacitor 14 are bridge-connected, and the piezoelectric resonator 11 and the resistor 12, which are connected in series,
The resistor 13 and the capacitor 14 are connected in parallel with each other between the input terminal 10a and the ground terminal 10b. The output of the limiter 16 is input to the input terminal 10a. The connection point between the piezoelectric resonator 11 and the resistor 12 and the connection point between the resistor 13 and the capacitor 14 are connected to the positive input and the negative input of the differential amplifier 15, respectively. Limiter 16
And the output of the differential amplifier 15 are input to the multiplier 17, and the output of the multiplier 17 is input to the LPF 18. The resistance value of the resistor 12 and 13, the impedance Z ₀ at frequency (f _c) which corresponds to the middle of the series resonant frequency (f _r) and the parallel resonance frequency (f _a) of the piezoelectric resonator 11 as shown in FIG. 6 And the capacitance value of the capacitor 14 is the same value as the parallel capacitance of the piezoelectric resonator 11.

The output of the phase shifter 10 is a signal divided by the resistor 13 and the capacitor 14 (having a phase of about 45 in the vicinity of f _c).
Since the difference between the signal obtained by rotating the signal 12) and the signal divided by the resistor 12 and the piezoelectric resonator 11 (the signal obtained by rotating the phase by 0 ± 90 degrees around the center of f _c ) is f _c as shown in FIG. Centered on 9
A phase shift characteristic changed by 0 ± about 90 degrees (or −90 ± about 90 degrees) is obtained.

As described above, in the present invention, since the circuit on the piezoelectric resonator side is composed of the series circuit of the piezoelectric resonator 11 and the resistor 12, the original bandwidth ΔF of the resonator is not deteriorated. As a result, it is possible to obtain a wide phase shift characteristic using the wide frequency characteristic of the resonator 11 as it is. Hereinafter, the reason will be described using mathematical expressions.

First, when the gain G of the phase shifter 10 is expressed by an equation,
It is as follows.

[Equation 1] In the equation, Z is the impedance of the piezoelectric resonator 11, R is the resistance value of the resistors 12 and 13, and C is the capacitor 1.
4 is the capacitance value.

Since the center frequency f _c of the phase shift characteristic is the frequency at which the phase becomes 90 degrees or −90 degrees, the conditional expression at that time is as follows. ω _c · C · Z = 1 ... In this case, the gain G is as follows.

[Equation 2] Here, if R = Z, the maximum value of the gain G is 1.

At this time, the impedance Z of the piezoelectric resonator 11 is expressed by the following equation.

[Equation 3] Substituting the expression into the expression gives:

[Equation 4] Here, when the capacitance value of the capacitor 14 is set to be the same as the parallel capacitance of the piezoelectric resonator 11 (C = C ₁ + C ₀ ), the equation is as follows.

[Equation 5]

The equation and ω _c = 2πf _c , ω _a = 2πf _a ,
From the relationship of ω _r = 2πf _r , f _c is obtained as follows.

[Equation 6]

As is clear from the equation, f _c is the resistance 1
It can be seen that it is not affected by Nos. 2, 13 and capacitor 14. Further, since f _c is substantially the center point of f _a and f _r of the piezoelectric resonator 11, the characteristics of the resonator 11 can be effectively used. In addition, the temperature characteristic of the capacitor 14 is determined by the piezoelectric resonator 1
By setting the same as the parallel capacitance of 1, the temperature characteristic of f _c is dominated by the temperature characteristics of f _a and f _r of the piezoelectric resonator 11,
If a resonator having excellent temperature characteristics is used, the temperature characteristics of frequency can be stabilized. Further, the gain G of the phase shifter 10 has a single-peak characteristic in which it is maximized at f _c as shown in FIG. 7, so that an erroneous oscillation is unlikely to occur at other frequencies.

FIG. 8 shows another embodiment of the present invention in which the piezoelectric resonator 11 and the capacitor 14 are put in one package 21, and the capacitor 14 is made of the same material as the piezoelectric resonator 11. Specifically, the resonator and the capacitor may be formed on a common piezoelectric ceramic substrate. With this configuration, it is possible to minimize the initial variation in f _{c and} the variation in temperature characteristics. In addition, the same effect as that of the first embodiment is obtained.

[0016]

As is apparent from the above description, according to the present invention, the phase shifter is a bridge circuit of a piezoelectric resonator, two resistors and one capacitor, and a piezoelectric resonator of this bridge circuit. And a resistor, and a differential amplifier that differentially extracts the output from the connection point of the capacitor and the resistor, so that an FM detection circuit with a wide variable oscillation frequency range can be obtained without degrading the frequency characteristics of the piezoelectric resonator. You can Further, by setting the capacitance value of the capacitor to the same value as the parallel capacitance of the piezoelectric resonator, the oscillation frequency is determined by the characteristics of the piezoelectric resonator, and it is possible to obtain a highly stable and highly accurate unadjusted FM detection circuit. it can.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a conventional FM detection circuit.

FIG. 2 is a phase shift characteristic diagram of a conventional phase shifter.

FIG. 3 is a voltage-frequency characteristic of a conventional FM detection circuit.

FIG. 4 is a frequency-impedance characteristic diagram of a piezoelectric resonator.

FIG. 5 is a circuit diagram of an FM detection circuit according to the present invention.

FIG. 6 is a diagram showing a relationship between an intermediate frequency and impedance.

FIG. 7 is a frequency-gain and phase characteristic diagram of the FM detection circuit of the present invention.

FIG. 8 is a circuit diagram of another embodiment of the FM detection circuit according to the present invention.

[Explanation of symbols]

 10 Phase Shifter 11 Piezoelectric Resonator 12, 13 Resistance 14 Capacitor 15 Differential Amplifier 16 Limiter 17 Multiplier 18 Low Pass Type Reactor

Claims (1)

[Claims] 1. An FM detection circuit for performing FM detection by multiplying an FM signal and a signal obtained by changing the phase of an FM signal by a phase shifter, wherein the phase shifter comprises bridge-connected first and first signals. A first resistor including a second resistor, a piezoelectric resonator, and a capacitor and connected in series;
The FM signal is supplied between both ends of the resistor and the piezoelectric resonator, and the second resistor and the capacitor, and the intermediate connection points of the first resistor and the piezoelectric resonator, and the second resistor and the capacitor are connected to each other. An FM detection circuit connected to a dynamic amplifier and configured to take out a signal whose phase has been changed from a differential amplifier.