JPS6133700Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a frequency discrimination device, and particularly relates to an improvement of a frequency discrimination device using a piezoelectric resonator.

Ceramic resonators are used in frequency discrimination circuits for FM intermediate frequency signals and TV audio intermediate frequency signals to eliminate adjustment. Especially in the high frequency range, energy trapping type ceramic resonators are often used. By the way, when a ceramic resonator is used in a frequency discrimination circuit, it has the advantage of being small in size, requires no adjustment, and has high selectivity, but has the disadvantage that the frequency discrimination band is fixed. For example, F.M.
There is no problem if the broadcasting frequency band is divided into wide frequency intervals, but if it is divided into narrow frequency intervals, undesirable situations such as mutual interference with adjacent channels may occur. Therefore, even a frequency discrimination circuit using such a ceramic resonator would be extremely effective in the above-mentioned cases if its bandwidth could be easily changed.

Therefore, the main purpose of this invention is to provide a frequency discriminator whose bandwidth or selectivity characteristics can be easily changed in a non-adjustable device.

In summary, this idea uses a multimode ceramic resonator with two terminals and a common ground terminal, and a series circuit of a capacitor and a switch is inserted between one of the terminals and the ground terminal, and this switch is This is a frequency discriminator that changes the bandwidth by switching.

The above-mentioned objects and features of the present invention will become clearer from the following detailed description with reference to the drawings.

FIG. 1 is an electrical circuit diagram showing an embodiment of this invention. In the configuration, the output of the intermediate frequency signal source 1 is provided to a frequency discrimination circuit 2. A load 3 is connected to the output side of the discrimination circuit 2. The frequency discrimination circuit 2 includes a ceramic resonator CER and a capacitor _C0 connected in parallel to the output of the signal source 1.
Including a series circuit with. Further, to the series circuit of the ceramic resonator CER and the capacitor _C0 , a series circuit of diodes D1 and D2 and a series circuit of resistors R1 and R2 connected in opposite directions are respectively connected in parallel. The midpoints of the three series circuits are commonly connected.

Electrode or terminal T of ceramic resonator CER
1, T2, and T3 in detail, the resonator
The terminal T1 of CER is connected to the signal source 1, and the ground electrode or terminal T3 is connected to the capacitor _C0 . Further, a series circuit including a capacitor C _Z and a switch SW is inserted between the other terminal T2 of the ceramic resonator CER and the terminal T3. When the switch SW is in the open state, the operation mode of the frequency discrimination circuit 2 shown in FIG. 1 is the same as that of a well-known circuit, so the details thereof will be omitted.

FIG. 2a shows a multimode ceramic resonator CER included in the frequency discrimination circuit 2 shown in FIG. 1, and FIG. 2b shows its electrical equivalent circuit. Below, with reference to this equivalent circuit, we will explain the characteristic parts of this invention, namely the multimode ceramic resonator CER and its related parts.
The characteristics of its operation will be explained in turn.

First, when the switch SW is the o-side contact, the connection of the ceramic resonator CER is as shown in FIG. 3a. In this case, the impedance |Z| vs. frequency characteristic of the resonator CER is as shown by the curve I _p in FIG. 3b. This third
In figure b, _r1 is the first resonant frequency and _a1 is the first anti-resonant frequency.

Next, when the switch SW is set to the s-side contact, a capacitor C _Z is connected to the ceramic resonator CER, and the connection is as shown in FIG. 4a. In this case, the impedance |Z| vs. frequency characteristic of the resonator CER is the curve I _s in FIG. 4b.
It will be shown as follows. In this Figure 4b, _r2
is the second resonant frequency, _a2 is the anti-resonant frequency, _r3 is the third resonant frequency, and _a3 is the third anti-resonant frequency. The characteristic feature is that the third resonant frequency _r3 is generated by inserting the capacitor C _Z , and the slope of the impedance change between the second resonant frequency _r2 and the second anti-resonant frequency _a2 becomes steep. It is.

Now, the magnitude relationship between the resonance frequency and the anti-resonance frequency is _r1 < _r2 < _a2 < _a1 . Figure 5a
The impedance of Figure 3b and Figure 4b |Z
|The necessary parts of the frequency characteristics are shown overlapping. Furthermore, the intersection point of both characteristic curves, that is, frequency ₀ , can be set to ₀ = _r1 + _a1 /2 = _r2 + _a2 /2 by optimally selecting the value of the capacitor C _Z . Also, the impedance of the ceramic resonator CER at frequency ₀ is
By selecting the capacitance value of the capacitor C ₀ so that Z ₀ = 1/ω _{0 C 0} (however, ω ₀ = 2π ₀ ), the respective demodulation characteristics as shown in Figure 5b can be obtained. is obtained. In this Figure 5b, the curve
₀ is the demodulation characteristic when the switch SW shown in FIG. 2 is at the o-side contact, and curve _s is the demodulation characteristic when the switch SW is at the s-side contact. This fifth
As is clear from Figure a, the curve I _s when the switch SW is set to the s-side contact is steeper than the curve I _p when the switch SW is set to the o-side contact. Therefore, as can be seen from Figure 5b, the switch SW
The curve _s when the switch SW is connected to the s side is the contact point on the s side.
It has a narrower band and higher output than the curve _p when it is used as a side contact. Therefore, switch SW
By switching the O/S side contact, the selectivity characteristic or bandwidth can be changed.

Although the switch SW described above is shown as a manually operable contact switch, it may also be configured as a non-contact switch such as a semiconductor switching element.

As described above, according to this invention, a multi-mode piezoelectric resonator is used in a conventional frequency discrimination circuit, one terminal is used in a frequency discrimination mode using a normal two-terminal piezoelectric resonator, and the other terminal is used in a frequency discrimination mode using a normal two-terminal piezoelectric resonator. A capacitor with an appropriately selected capacitance value is connected to the switch, and a changeover switch is connected in series, so that broadband characteristics and narrowband/high sensitivity characteristics can be easily shared by simply switching this changeover switch. Note that a type of resonator having two divided electrodes in which the ground side terminal is not a common terminal may be used. In this case, the earth side electrode divided into two parts is connected and used.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram of a frequency discriminator showing an embodiment of this invention. FIG. 2a shows a multi-mode ceramic resonator of the circuit of FIG. 1, and FIG. 2b is an electrical equivalent circuit diagram thereof. FIG. 3a is a diagram showing the connection mode of the multimode ceramic resonator, and FIG. 3b is a diagram showing the connection mode of the multimode ceramic resonator shown in FIG.
3 shows the frequency vs. impedance characteristics. FIG. 4a is a diagram showing the connection mode between a ceramic resonator and a capacitor, and FIG.
This figure shows the frequency versus impedance characteristic between terminals T1 and T3 of the circuit shown in Figure a. FIG. 5a is a frequency vs. impedance characteristic in which the main parts of FIGS. 3b and 4b are overlapped. FIG. 5b shows its demodulation characteristics. In the figures, the same reference numerals indicate the same or equivalent parts, CER is a multimode ceramic resonator, T1 is the first terminal of the multimode ceramic resonator CER, T2 is the second terminal, T3 is the ground terminal, C _Z and C _O are capacitors, D1 and D2 are diodes, R1 and R2 are resistors, and SW is a switch.

Claims (1)

[Claims for Utility Model Registration] A frequency discriminator circuit including a series circuit of a multimode piezoelectric resonator and a first capacitor, and receiving an intermediate frequency signal at both ends of the series circuit, comprising: a first capacitor of the multimode piezoelectric resonator; a terminal receives the intermediate frequency signal, and a second terminal and a third terminal of the multimode piezoelectric resonator receive the intermediate frequency signal;
A series circuit of a second capacitor and switching means is inserted between the terminals of the multimode piezoelectric resonator, and the third terminal of the multimode piezoelectric resonator is connected to the first capacitor. .