JPS63228813A - Timing extracting filter - Google Patents

Abstract

PURPOSE:To basically cope with many requests just with a single type of filter by forming this filter with a piezoelectric oscillator and a voltage control type variable capacity diode. CONSTITUTION:A T-shaped filter is formed with two piezoelectric oscillators X and X' and a variable capacity diode 1 serving as a coupling capacitor. The variable capacity diodes 2 and 3 are connected to the oscillators X and X' respectively. When an ambient temperature T raises, the voltage Va applied to both ends of the diode 1 is increased so that the capacity Cd is set smaller than the capacity Cd0 obtained at a normal temperature. As a result, the control voltages Vb and Vc applied between both terminals of diodes 2 and 3 respectively are decreased and the capacities Cs and Cs' of diodes 2 and 3 are increased to eliminate the frequency variance of both oscillators X and X'. In such a constitution, a filter is obtained with increased band width and a small phase change caused at f0.

Description

[Detailed Description of the Invention] [Summary] A voltage-controlled variable capacitance element is incorporated into a timing extraction filter used in a digital transmission device, and the frequency and phase can be adjusted by controlling the capacitance value of the variable capacitance element using voltage. The present invention discloses a timing extraction filter that can be adjusted to obtain an arbitrary bandwidth that can correspond to the ambient environment such as temperature.

[Industrial Field of Application] The present invention relates to a filter, and particularly to a timing extraction filter.

A timing extraction filter is a filter that extracts timing information (this becomes sampling information for pulse reproduction) from an incoming pulse train using a tank circuit that uses the bit frequency as a tuning frequency, for example in a regenerator of a digital transmission device. It is.

The transmission path has pulse noise and other transmission disturbances, and there is also overlap due to waveform distortion, which deteriorates the quality. During playback, the effects on amplitude must be removed, but the timing must also be correct, so if there is a deviation in timing, the sample values that should be transmitted at regular intervals in each sampling period will be This results in irregular intervals, which causes playback errors.

Therefore, the timing extraction filter must have the function of reproducing the phase of the transmitted pulse at correct time intervals and extracting the pulse repetition frequency component from the equalized waveform sequence.

Timing extraction filters are used in bipolar/unipolar conversion circuits of digital repeaters and multiplex conversion equipment.
It is an important element that plays a role in the pulse regeneration function.

[Prior Art] Fig. 5 shows such a conventional timing extraction filter, in which X and X' are piezoelectric vibrators, and 10 is a coupling capacitor (capacitance Cd), forming a T-type filter. .

Figure 6 shows the attenuation characteristics generally required for a timing extraction filter, with the horizontal axis representing frequency and the vertical axis representing attenuation. The center frequency is the pulse repetition frequency fo of the sending pulse. The dashed line shows the characteristics when a capacitor with a small Cd value is used when the ambient temperature fluctuation range is large, and the dashed-dotted line shows the characteristics when a capacitor with a large Cd value is used when the fluctuation range is small. are shown respectively.

As an actual timing extraction filter, a plurality of filters having different bandwidths as described above are combined in accordance with the temperature fluctuation width of the surrounding environment.

[Problems to be Solved by the Invention] As described above, in conventional timing extraction filters, the characteristics required of the filter differ for each type of digital transmission device, and in particular, there are many requirements for different bandwidths (3 dB bandwidth). , it was necessary to prepare various filters for each type. Therefore, the necessity of using a plurality of filters has been a factor in hindering reductions in filter costs.

Therefore, it is conceivable to use a conventional timing extraction filter to make the capacitance Cd of the coupling capacitor 10 variable in order to correspond to the range of ambient temperature fluctuations.

If the coupling capacitor 10 is made to have a variable capacitance, the frequency and phase cannot be adjusted to temperature fluctuations. This will be explained using the phase-frequency characteristic diagram shown in FIG. 7.

Now, when the temperature T is room temperature (25℃) and the nominal center frequency of the digital transmission device is fo (phase θ0), the phase -
The frequency characteristic is as shown in characteristic (a) in FIG. 7, and the capacitance Cd of the coupling capacitor 10 is assumed to be CdO.

Here, if the temperature T rises to T'(T'>> 25°C), the frequency at phase θ0 changes to C' as shown in characteristic (b).In other words, the phase at frequency f0 changes to becomes θ10 Next, in order to correct this frequency or phase change with the capacitance Cd of the coupling capacitor 10, it is necessary to reduce the value of the capacitance Cd from Cd to Cdo'. , as shown in characteristic (c), the phase slope is inversely proportional to the filter bandwidth, so the phase slope becomes small, and the phase at that time is equal to the frequency f
, changes to θ2. However, at the same time the frequency r
e'', which further deviates from ro. This has been described for the case where the temperature T rises, but even when the temperature T falls, the frequency and phase deviate for the same reason.

As described above, simply making the capacitance Cd variable with respect to temperature fluctuations is insufficient to correct center frequency deviations and phase changes.

Therefore, an object of the present invention is to solve the above problems.
Basically, the aim is to realize a timing extraction filter that can meet a large number of requirements with one type of filter.

[Means for Solving the Problems] FIG. 1 is a diagram showing a timing extraction filter according to the present invention for achieving the above object, which includes two piezoelectric vibrators x and x' and voltage control A coupling capacitor 1 of variable capacitance elements of the shape basically constitutes a T-type filter, and voltage-controlled variable capacitance elements 2 and 3 are connected in series with piezoelectric vibrators x and x' forming T-shaped arms, respectively. insert. Furthermore, a variable resistor for impedance matching is connected in series to the input side of the filter and in parallel to the output side.

[Function] In the timing extraction filter shown in FIG. 1, by changing the capacitance Cd of the coupling capacitor 1 by voltage control,
The variable capacitance element 2.3 inserted into the filter arm is used to select the filter bandwidth according to the magnitude of the ambient temperature fluctuation range and to correct the frequency and phase shift caused by changing the capacitance Cd. Capacity is changed by voltage control.

Furthermore, since the input/output impedance changes by changing the capacitance Cd of the coupling capacitor 1, the variable resistor 4.5
is adjusted to achieve impedance matching.

[Embodiment] The timing extraction filter of the present invention will be described below with reference to the embodiment shown in FIG.

In FIG. 2, two piezoelectric vibrators, such as a ceramic vibrator, a LiTaO31* element, a composite vibrator made of a constant elastic metal and a piezoelectric ceramic, etc., are used.
x' and a variable capacitor (varactor) as a coupling capacitor
A T-type filter is formed from the diode 1, and a variable capacitance diode and a diode 2 are connected in series to the two oscillators x and x', respectively.
．． Connect 3. When the capacitance Cd of the variable capacitance diode l is changed, the input/output impedance of the filter also changes, so in order to adjust it with an external additional resistor (fixed resistor), a variable resistor is connected in series to the input side AA' of the filter. A variable resistor 5 is connected in parallel to the output side BB'.

Terminals aa'', bb', and cc' are provided at both ends of the variable capacitance diode 1.2.3, respectively, and control voltages Va, Vb, and Vc are applied to each terminal, respectively. Since the capacitance C of a variable capacitance diode is almost inversely proportional to the voltage as shown in Figure 3, the capacitance can be changed by selecting an appropriate voltage.The equivalent circuit of this voltage-controlled timing extraction filter is shown in Figure 4. Shown below.

Next, in the operation of the above embodiment, a case where the ambient temperature fluctuation is large will first be described. As shown in Figure 7,
Assuming that the ambient temperature T rises significantly from the normal temperature of 25°C,
The center frequency ro of the filter changes to rc'. At this time, the voltage Va applied to both ends of the variable capacitance diode 1 is increased to make the capacitance Cd smaller than the capacitance Cdo at room temperature, and to widen the bandwidth (1/QL). However, although the bandwidth becomes wider, the center frequency is shifted from [0 to fc'' and the phase at fo is shifted from θ. to θ2. Therefore, the voltage applied between each terminal of the variable capacitance diode 2. By decreasing the control voltages vb and Vc and increasing the capacitances Cs and Cs' of the variable capacitance diodes 2.3 so as to cancel the frequency fluctuations of the oscillators X and X', the result shown in Fig. 7(d) is obtained. , the center frequency returns to the fo side, and fc'
and the phase at [0 is θ.

The value becomes closer to θ3. That is, at room temperature of 25°C, the center frequency is f. , the phase becomes θ0, and when the temperature rises, the frequency change remains the same but the bandwidth widens (the slope of the characteristic curve in Figure 7 decreases), so a filter with a small phase change in fo becomes realizable.

Although the case where the ambient temperature T has increased has been described, even when the ambient temperature T has decreased, the same operation as above may be performed since the capacitance Cd is made smaller.

Furthermore, when the fluctuation in the ambient temperature is small, it is necessary to narrow the bandwidth, and in this case, conversely, the voltage V& is decreased so that the capacitance Cd of the variable capacitance diode 1 increases. The center frequency at this time is f.

If the voltages Vb and Vc are increased so that the capacitances Cs and Cs' of the variable capacitance diodes 2.3 become smaller and the phase shift accordingly becomes smaller, the frequency f. The phase can be brought close to θ0.

[Effects of the Invention] As described above, according to the timing extraction filter of the present invention, since the filter is configured from a piezoelectric vibrator and a voltage-controlled variable capacitance diode, one type of timing extraction filter can be used for various filters. This can contribute to reducing the cost of filters.

In addition, even after it is installed in a transmission device, even if it becomes necessary to change the filter bandwidth due to changes in the environment around the device, desired filter characteristics can be easily achieved by changing the control voltage from the outside. It has the great advantage of being able to

[Brief explanation of the drawing]

FIG. 1 is a conceptual configuration diagram of a timing extraction filter according to the present invention, FIG. 2 is a diagram showing an embodiment of the timing extraction filter of the present invention, and FIG. 3 is a diagram showing voltage-capacitance characteristics of a variable capacitance diode. FIG. 4 is an equivalent circuit diagram of the timing extraction filter of the present invention shown in FIG. 2, FIG. 5 is a diagram showing a conventional timing extraction filter, and FIG. 6 is a filter characteristic diagram of the timing extraction filter with respect to temperature fluctuation width. FIG. 7 is a graph showing the frequency-phase characteristics of the timing extraction filter. 1 to 3, X and X' are piezoelectric vibrators, 1.2.3 is a variable capacitance diode, and 4.5 is a variable resistor. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] (1) In a timing extraction filter having a T-shaped configuration of two piezoelectric vibrators (X, X') and a coupling capacitor (1), the coupling capacitor (1) is a voltage-controlled variable capacitor, and the piezoelectric vibration Voltage-controlled variable capacitance elements (2, 3) are connected in series with the filters (X, X'), and impedance matching elements (4, 5) are added to the input and output sides of the filter. A timing extraction filter featuring: (2) The coupling capacitor (1) and the variable capacitance element (2)
The timing extraction filter according to claim 1, wherein a voltage-controlled variable capacitance diode is used in , 3). (3) A variable resistor is used as the impedance matching element (4, 5), and is added in series to the input side of the filter and in parallel to the output side of the filter. Timing extraction filter.