JPS5814767B2 - Rejector circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistor circuit that reduces characteristic deterioration due to the presence of sub-resonance in a vibrating element.

Generally, in signal transmission devices, a rejector circuit using a crystal resonator or a mechanical resonator is used so as not to transmit a specific frequency component.

FIG. 1 is a block configuration diagram showing this type of circuit. If the impedance of the circuit forming the series arm is ZA, and the impedance of the circuit forming the parallel arm is ZB, then the conventional ZA,
Both ZBs are secondary circuit networks.

It also satisfies ZA-ZB-R2 (rLR is the characteristic impedance of the circuit).

When using a crystal oscillator XO in a conventional rejector circuit,
The maximum sub-resonant frequency often exists at about 1.1 times the main resonant frequency fo.

Therefore, the loss characteristics of the rejector circuit are as shown in FIG.

That is, the characteristics of the resistor circuit are greatly degraded at the sub-resonant frequency.

Figure 3 shows an equivalent circuit diagram of a crystal resonator, with Lo, co,
Ro is the value for the main resonant frequency fo, fQ=1/2π■
LS, CS, and RS have a relationship of fs=1/2π■ with respect to the subresonant frequency fs.

It is also known that the smaller the value of the equivalent resistance RO, the greater the attenuation at the main resonant frequency fo shown in Figure 2, and the smaller the equivalent inductance Lo, the greater the attenuation in a wider range of the attenuation curve. There is.

It was also found that the larger the equivalent resistance RS at the sub-resonant frequency fS, the more desirable the characteristics for the resistor.
Conventionally, in order to satisfy this desire, a plurality of crystal resonators having subresonant frequencies slightly different from each other were connected in parallel, as shown by the broken lines in FIG.

Therefore, the equivalent resistance Ro at the main resonant frequency fQ is reduced to one value approximately divided by the number of parallel connections.
Although the characteristics of the resistor circuit were improved, selection of the crystal resonator and adjustment after connection became complicated, making the circuit larger and more expensive.

The aim of the present invention is to obtain a resistor circuit that is easy to adjust and has good characteristics using a circuit with a simple configuration.

Embodiments of the present invention shown in the drawings will be described below.

In the circuit diagram shown in FIG. 4, the parts surrounded by one-dot chain lines in the series and parallel arms indicate inductance elements and capacitance elements added to make each arm a fourth-order all-pass circuit network.

Then, the values of the elements are selected so that the resonant frequency of the added element matches the sub-resonant frequency fS in FIG. 2 and that |ZA(fo)l>|ZA(fS)|.

ZA(fo) indicates the impedance of the series arm at the main resonant frequency fO, and ZA(fs) indicates the impedance of the series arm at the sub-resonant frequency fs.

FIG. 5 shows the overall frequency characteristics of the series arm impedance ZA.

As can be seen from Figure 5, the order of ZA is 4th, with 2 zeros and 2 poles.
There are one more each than in the following cases.

Since the slopes of the curves near fo and fs are steep, there is a large difference in the amount of attenuation between the two, which reduces the influence of sub-resonance as a rejector circuit.

In particular, it has been found from calculations that the larger |ZA(fo)|, the greater the attenuation over a wider band can be obtained, so better effects can be obtained by selecting the above-mentioned elements.

In this way, according to the present invention, a circuit with a simple configuration, easy adjustment, and good characteristics can be obtained at low cost.

[Brief explanation of the drawing]

Figure 1 shows a conventional resistor circuit, and Figure 2 shows a conventional resistor circuit.
3 is an equivalent circuit diagram of a crystal resonator, FIG. 4 is a diagram showing an embodiment of the present invention, and FIG. 5 is a diagram showing frequency characteristics of impedance ZA. XO...Crystal oscillator.

Claims (1)

[Claims] 1. In a rejector circuit in which a resonant element is connected to the series arm of the all-pass circuit network and the resonant frequency of the resonant element is used as a stop band, a combination circuit of an inductance element and a capacitance element is further added to the series arm and the parallel arm, and vibration 1. A rejector circuit characterized in that the series arm and the parallel arm excluding the element are each made into a fourth-order all-pass circuit network, and the resonant frequency of the added circuit is set as the sub-resonant frequency of the vibrating element.