JP2538661Y2 - Phase shift circuit of quadracha detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a phase shift circuit for obtaining a phase shift signal of an FM intermediate frequency signal in a quadature detector for performing FM detection.

[Conventional technology]

The quadrature detector inputs the FM intermediate frequency signal output from the FM intermediate frequency amplifier circuit and a signal obtained by shifting the phase of the FM intermediate frequency signal through a phase shift circuit to a multiplier, and outputs a phase difference between these two signals. The FM demodulated signal is obtained from

By the way, the television broadcasting system is NT
Since they are different like the SC system, the PAL system, and the SFCAM system, the frequency of the audio intermediate frequency signal is also different. For this reason, television receivers and video tape recorders that can switch between a plurality of systems with a changeover switch have been put to practical use, but since a plurality of quadrature detectors corresponding to each system are built in, a circuit is required. There is a disadvantage that the configuration is complicated and the number of parts is increased.

As a solution to such a drawback, by switching a plurality of ceramic discriminators used in the phase shift circuit with a switching circuit, parts other than the ceramic discriminator are shared, and a desired FM intermediate frequency signal is obtained. A quadrature detector for demodulation has been proposed (JP-A-60-27209).

[Problems to be solved by the invention]

However, in the case of the above-described detection circuit, although only one FM demodulation integrated circuit including a limiter amplifier and a multiplier is required, a switching circuit including a switch, a switching diode, an external power supply, and the like is used to configure a phase shift circuit. Because of the necessity, there is a problem that the phase shift circuit becomes complicated and the number of parts increases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a quadrature detector capable of eliminating a switching circuit from a phase shift circuit and obtaining a phase shift signal of a plurality of FM intermediate frequency signals with a simple circuit.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, an FM intermediate frequency signal output from an FM intermediate frequency amplifier circuit and a signal obtained by shifting the phase of the FM intermediate frequency signal through a phase shift circuit are input to a multiplier. In a quadrature detector that obtains an FM demodulated signal from a signal phase difference, the phase shift circuit is configured by connecting a plurality of phase shift circuit units in parallel, and each phase shift circuit unit has an input terminal. , A ceramic discriminator having a single three-terminal resonator tuned to a certain FM intermediate frequency and having an output terminal and a ground terminal, and a first ceramic discriminator connected in series with the input terminal of the ceramic discriminator. A matching resistor, a phase shift capacitor connected in series with the output terminal of the ceramic discriminator, and a connection with the output terminal of the ceramic discriminator. Second connected to the ground
And the FM intermediate frequencies tuned by the ceramic discriminators of each phase shift circuit unit are different from each other.

[Action]

That is, in the conventional case, in order to detect a plurality of frequencies, the phase shift circuit is provided with a switching circuit including a switch, a switching diode, an external power supply, and the like. FM to phase shift phase shift circuit unit consisting of capacitance and matching resistor
Since only a plurality of stages are provided in parallel according to the number of intermediate frequencies, the phase shift circuit is greatly simplified and the number of components is reduced. Therefore, a small and low-cost phase shift circuit can be realized.

〔Example〕

Figure 1 shows an example of a quad Ray tea detector capable detecting an example 5.5MH _z, 3 kinds of FM intermediate frequency signal 6.0MH _z and 6.5MH _z.

In the figure, reference numeral 1 denotes an FM demodulation integrated circuit, on the input side of which is a limiter amplifier 2 at the last stage of an FM intermediate frequency amplifier circuit.
The FM intermediate frequency signal output from the amplifier 2 and a signal obtained by shifting the phase of the FM intermediate frequency signal through a phase shift circuit 3 are input to a multiplier 4. The multiplier 4 detects the phase difference between these two signals, passes the output through a low-pass filter 5 to remove a ripple component, and further amplifies the low-frequency amplifier 6 to obtain a desired FM demodulated signal.

The phase shift circuit 3 has three types of phase shift circuit units 3a, 3b, 3c connected in parallel with each other. The phase shift circuit unit 3a
A ceramic discriminator 10 5.5MH _z, this ceramic discriminator 10 and the phase shift capacitor C ₁ connected in series, a matching resistor R ₁ connected to the ceramic discriminator 10 in series, the ceramic discriminator a discriminator 10 connected in parallel are provided with a matching resistance R _2. Similarly, phase shift circuit unit 3b includes a ceramic discriminator 11 of 6.0MH _z, this ceramic discriminator 11 and the phase shift capacitor C ₂ connected in series, are connected to ceramic discriminator 11 series and a matching resistor R _3, comprises a matching resistor R ₄ connected in parallel with the ceramic discriminator 11, the phase shift circuit units. 3c, ceramic discriminator of 6.5MH _z discriminator 12
When a ceramic discriminator 12 and the phase shifting capacitor connected in series C ₃ and the ceramic discriminator 12 and the matching resistor R ₅ connected in series, a matching resistor connected in parallel with the ceramic discriminator 12 R ₆
Is provided.

The phase shift circuit 3 will be described in more detail. The ceramic discriminators 10, 11, and 12 are three-terminal resonators, and are provided between the limiter amplifier 2 and the multiplier 4 in parallel. Input electrodes are each resistor R ₁ of the ceramic discriminator 10, 11, 12, R _3, through R ₅ are connected to the limiter amplifier 2, phase capacitance C ₁ of the output electrode is 90 degree phase shift, C ₂ , Multiplier 4 via C ₃
It is connected to the. Further, between the input terminal of the output electrode and the phase-shift capacitor C ₁ -C ₃ of each ceramic discriminator 10, 11, 12, resistors R _2, R _4, one end of which is grounded, the other end of R ₆ Is connected.

The ground electrodes of the ceramic discriminators 10, 11, 12 are all grounded.

In the quadracha detector with the above configuration, FM
When FM intermediate frequency signal 5.5MH _z from the limiter amplifier 2 of the demodulation integrated circuit 1 is inputted to the phase shift circuit 3, the signal 3
Of pieces of ceramic discriminator, only through the ceramic discriminator 10 5.5MH _z, phase capacitance C ₁
Are input to the multiplier 4. Therefore, FM of 5.5MH _z from the output terminal of the FM demodulation integrated circuit 1
Only a demodulated signal of the intermediate frequency signal can be obtained.

Similarly, from the limiter amplifier 2 of the FM demodulation integrated circuit 1
When FM intermediate frequency signal 6.0MH _z or 6.5MH _z is input to the phase shift circuit 3, the signal passes through only the ceramic click discriminator 11 or 12 of 6.0MH _z or 6.5MH _z, phase volume
After being phase-shifted at C ₂ or C ₃ , it is input to the multiplier 4. Therefore, from the output end of the integrated circuit 1 for FM demodulation, 6.
Only it is possible to obtain a demodulated signal of the FM intermediate frequency signal 0MH _z or 6.5MH _z.

Figure 2 is shows the amplitude and phase characteristics of the phase shift circuit 3, 5.5MH _z, 6.0MH _z and as is clear from FIG.
For both 6.5MH _z, the nominal center frequency and a phase of 90 degrees is approximately equal, and since a good linearity of the phase characteristic around the center frequency, it can be seen that to obtain a good phase characteristic.

For example, when detecting two types of FM intermediate frequency signals, the present invention is compared with a conventional phase shift circuit (see Japanese Patent Application Laid-Open No. 60-27209). In both cases, two ceramic discriminators and two capacitors are used. Similarly, two switches are required. However, in the present invention, the number of matching resistors is four less than that of the conventional example, and four switches, four switching diodes, and an external power supply are not required. Therefore, in the present invention, the number of components of the phase shift circuit is significantly smaller than that of the conventional example, and the size and cost are reduced.

Although the above embodiment has described the phase shift circuit for detecting three types of FM intermediate frequency signals, the present invention can be similarly applied to a phase shift circuit for performing two types or four or more types of detection. .

Further, although a three-terminal resonator is used as the ceramic discriminator, a resonator in which a series resonator and a parallel resonator are connected to a ladder can be used. However, in the case of the ladder type, the differential gain bandwidth tends to be wide,
H _z, 6.0MH _z, in the case of performing a plurality of detection in a relatively narrow range as 6.5MH _z is to become susceptible to mutual interference,
It is desirable to use a three-terminal resonator.

[Effect of the invention]

As is clear from the above description, the phase shift circuit of the present invention is:
Since a plurality of phase shift circuit units consisting of a ceramic discriminator, a phase shift capacitor, and a matching resistor are connected in parallel, it is possible to demodulate multiple FM intermediate frequency signals and eliminate the need for a switching circuit. As a result, the circuit is significantly simplified and the number of components is reduced as compared with the related art. Therefore, a small and low-cost phase shift circuit can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a quadrature detector using the phase shift circuit according to the present invention, and FIG. 2 is an amplitude / phase characteristic diagram of the phase shift circuit. 1 ... FM demodulation integrated circuit, 2 ... Limiter amplifier, 3 ...
… Phase shift circuit, 3a, 3b, 3c… Phase shift circuit unit, 4… Multiplier, 5… Low pass filter, 6… Low frequency amplifier, 10,11,12… Ceramic discriminator,
C _{1 to} C ₃ …… Phase shift capacitance, R _{1 to} R ₆ …… Matching resistance.

Claims (1)

(57) [Scope of request for utility model registration] 1. An FM intermediate frequency signal output from an FM intermediate frequency amplifier circuit and a signal obtained by shifting the phase of the FM intermediate frequency signal through a phase shift circuit are input to a multiplier. In a quadrature detector configured to obtain a demodulated signal, the phase shift circuit is configured by connecting a plurality of phase shift circuit units in parallel, and each phase shift circuit unit has an input terminal, an output terminal, and a ground terminal. A ceramic discriminator comprising a single three-terminal resonator tuned to a certain FM intermediate frequency; a first matching resistor connected in series with an input terminal of the ceramic discriminator; A phase shift capacitor connected in series with the output terminal of the discriminator, and connected between the output terminal of this ceramic discriminator and the ground. The second
Wherein the FM intermediate frequencies tuned by the ceramic discriminators of each phase shift circuit unit are different from each other.