JPS60100812A - Tracking type band pass filter - Google Patents

Abstract

PURPOSE:To prevent a hang-up phenomenon by using a frequency error detecting circuit which delivers a signal corresponding to the frequency error between an input signal and a reference signal and a voltage control oscillator which is controlled by the output of said error detecting circuit so that the frequency error becomes minimum, and produces the reference signal. CONSTITUTION:The outputs of LPF16 and 18 are supplied to the input of double balanced modulators 12 and 13 and orthogonal to each other since a pi/2 phase difference is given to the output signal of a voltage control oscillator 21. The output of the LPF18 has a 90 deg. phase advance via a differentiator 22 and therefore both inputs have same phases or adverse phases at the input of a multiplier 23. Then a signal proportional to the difference frequency between the input signal and the output signal of the oscillator 21 is produced at the output of the multiplier 23. The output of the multiplier 23 is applied to the oscillator 21 as the control voltage via a loop filter 24 having a proper transmission function F(S). Thus the feedback control so that the minimum difference is obtained between an input frequency and the output signal frequency of the oscillator 21.

Description

[Detailed Description of the Invention] Technical Field of the Invention Pertaining to a p-wave device that tracks so that the center frequency of the passband always matches the input frequency, in particular, such a p-wave device is used for low-frequency F-waves. This invention relates to a tracking type band p-wave device realized using a device.

Prior Art and Problems The most common example of a conventional tracking p-wave device is a phase-locked loop (PLL) as shown in FIG.

The phase locked circuit performs voltage control on an error signal obtained by comparing the phases of the output signal of the voltage controlled oscillator 1 and the input signal with the phase comparator 2 through a loop filter 3 having an appropriate transfer function F(s). By feeding back as a control voltage to the oscillator 10, an output that is phase-synchronized with the input signal is obtained from the voltage controlled oscillator 1.P1 is a tracking type band F wave generator that generates an output that has an extremely narrow band and tracks the input frequency. ing.

However, if the input signal arrives intermittently in a phase-locked circuit line, it takes a long time to establish synchronization, and if there is noise in the input signal, the time required to establish synchronization becomes abnormally long. There is a problem that a hang-up phenomenon occurs.

Tracking type band P-wave generators are often used for reference carrier regeneration in the receiving side demodulator of PSK-TDMA communication system, but the above-mentioned hang-up phenomenon causes tracking type band P-wave generators to be used in PSK-TDMA communication systems. This is a fatal drawback when used in communication systems.

OBJECTS OF THE INVENTION The present invention attempts to solve the problems of the prior art, and its purpose is to provide a tracking type band offshore transducer that does not cause the hang-up phenomenon.

Embodiments of the Invention The tracking type band p wave generator of the present invention has a known low-pass filter waveform band p waveform.
It is a development of wave equipment. First, a description will be given of the low-frequency off-shore waveform band transducer shown in FIG.

In FIG. 2, the input signal is split into two by an in-phase hybrid 11, and double balanced modulators 12 and 13, respectively.
is applied to the first AC input terminal of. On the other hand, the reference oscillator 14 generates a reference signal in the input signal frequency band, and the reference signal is divided into two by the orthogonal hybrid 15 with a phase difference of π/2, and each of the two divided signals is double balanced. It is applied to the second AC input terminals of modulators 12 and 13. The signal at the DC output terminal of the double-balanced modulator 12 is band-limited through the low-pass p-wave filter 16 and then applied to the first AC input terminal of the double-balanced modulator 17 . Further, the output of the double-balanced modulator 13 is band-limited through a low-pass filter 18 and then applied to a first DC input terminal of a double-balanced modulator 19 . The same reference signal as at the second AC input terminal of the double-balanced modulators 12, 13 is applied to the AC input terminals of the double-balanced modulators 17 and 19, respectively. of the AC output terminals of devices 17 and 19 (
i-1': Obtain the output signal by combining through all in-phase hybrid nods.

With this configuration, between the input and output signal terminals, the low-frequency r wave generator 1 is connected between the reference oscillator 140 and the reference signal frequency.
Characteristics as a bandpass F-wave device having upper and lower bands 11'Vl equal to the cutoff frequencies of 6 and 18 can be obtained.

However, the low-pass P waveform bandpass filter shown in FIG. 2 has a constant center frequency and cannot operate as a tracking wave filter. The present invention replaces the reference oscillator with a variable-frequency voltage-controlled oscillator in the low-frequency Te waveform band p-wave generator shown in FIG. By controlling the oscillation frequency of the oscillator, a tracking type band-wave device is realized.

FIG. 3 shows the configuration of an embodiment of a tracking type band r-wave device of the present invention, in which the same parts as in FIG. 2 are designated by the same numbers, and 21 is a voltage control Oscillator, 2
2 is a differentiator, vane is a multiplier, and s is a loop filter.

In FIG. 3, between the input terminal of the in-phase hybrid 11 and the output terminal of the in-phase hybrid, the cut-off frequencies of the low-pass filters 16 and 18 are connected with the output signal frequency of the voltage controlled oscillator 21 as the center. Similar to the case shown in FIG. 2, this device exhibits characteristics as a low-pass filter waveform band P-wave device having upper and lower pass bands determined by the above.

On the other hand, in FIG. 3, the output of the low frequency T waver 16 is applied to one input of the multiplier n, and the output of the low frequency F waver 18 is applied to the other input via the differentiator 22.

The output of the low-pass filter 16 and the output of the low-pass filter 18 are connected to one input of the double-balanced modulator [, 13] in the previous stage, and the output signals of the voltage controlled oscillator 21 are mutually π/ 2
Since they are added with a phase difference of , they are orthogonal to each other. Since the output of the low-pass filter 18 passes through the differentiator 22 and advances in phase by 90 degrees, the output of the multiplier 23 is in phase or out of phase with the input signal and the voltage controlled oscillator 21. generates an output proportional to the difference frequency between the output signal and the output signal. The operation of such a frequency error detection means is described in Japanese Patent Application No. 57-172164 filed by the same applicant.
It is explained in detail in the issue.

The output line of the multiplier* passes through a loop filter having an appropriate transfer function F(s), and is applied as a control voltage to the voltage controlled oscillator 21, thereby increasing the difference between the input signal frequency and the output signal frequency of the voltage controlled oscillator 21. Feedback control is performed to minimize the error.

As described above, according to the circuit of the embodiment shown in FIG. 3, the tracking type band P-wave device has a center frequency that tracks the input signal frequency and has a pass band with a constant frequency width above and below the center frequency. The following characteristics can be obtained.

FIG. 4 shows the configuration of another embodiment of the tracking type band p-wave device of the present invention. The figure shows an example in which the Kinoto FJA is applied to a reference carrier recovery circuit for QPSK demodulation. The same parts as in Fig. 3 are indicated by the same numbers, and the lines are multipliers,
26 is a frequency divider, 27 is a first-order low-frequency p-wave filter, and 27 is a first-order high-frequency p-wave filter.

In FIG. 4, the output of a double-balanced modulator is applied to one input of the multiplier 23 via a first-order low-frequency F-wave generator;
The output of the double-balanced modulator 13 is applied to the other input via a first-order high frequency amplifier.

As a result, the multiplier 23 generates an output proportional to the difference frequency between the input signal and the output signal of the voltage controlled oscillator 21. Note that such frequency error detection means is already well known. The output signal of the multiplier n is applied as a control voltage to the voltage controlled oscillator 21 through a loop filter, so that the output signal frequency of the voltage controlled oscillator 21 changes to follow the input signal frequency. As a result, as in the case shown in FIG. It exhibits the characteristics of a tracking type band p-wave device, which has above and below.

On the other hand, the input QPSK wave is multiplied by four by a quadruple multiplier section to obtain a signal with no phase fluctuation as the fourth harmonic. This signal is applied to the input terminal of the in-phase hybrid 11,
The signal is taken out from the output terminal of the in-phase hybrid 20, thereby limiting the band and improving the signal-to-noise ratio.

The output signal of the in-phase hybrid 20 is divided by four by a frequency divider 26 to reproduce a reference carrier consisting of the original input signal frequency at its output.

The nine-tracking type band F-wave device shown in FIG. 4 has a low frequency P-wave device of 27. By using the frequency error detection means consisting of the high-frequency p-wave unit and the multiplier 23, etc., it is advantageous in that the tracking frequency range can be determined independently of the bandwidth in the band p-wave characteristic, and the frequency Since a differentiator is not used as the error detection means, the circuit configuration is easy and the frequency discrimination characteristics can be easily changed.

According to the tracking type band V-wave device of the present invention as described in detail,
In a low-waveform band transducer with a reference signal at the center frequency and a pass band with a constant frequency width above and below the center frequency,
A frequency error detection means that generates an output signal according to the error between the input signal and the reference signal, and a voltage controlled oscillator whose oscillation frequency is controlled by the output voltage of the frequency error detection means and generates the reference signal are provided. It is possible to realize a tracking type band p-wave device with the input signal as the center frequency and having a pass band with a constant frequency width above and below the center frequency. In addition, since the tracking type bandpass filter of the present invention does not perform phase synchronization, no hang-up phenomenon occurs, and since tracking is performed quickly by frequency control, the center frequency can always be made to match the input frequency. Therefore, it is possible to realize excellent single-wavelength device characteristics.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the configuration of a phase synchronized circuit, Fig. 2 is a diagram showing an example of the configuration of a low-frequency p waveform band Oki transducer, and Figs.
Each figure is a diagram showing the configuration of an embodiment of a tracking type band F-wave device of the present invention. 1... Voltage controlled oscillator, 2... Phase comparator, 3...
・Loop filter, 11... In-phase no\Ibrid, 1
2.13...Double balanced modulator, 14...Reference oscillator, 15...Quadrature hybrid, 16, 18...
Low-pass P-wave device, 17.19...Double balanced modulator, Adder...In-phase/'s hybrid, 21...Voltage controlled oscillator, 22...Differentiator, Field...Multiplier , 24... Loop filter, Redundant... 4 multiplier, 26... 4 frequency divider, 27...-Next low-pass waveform generator, 28...-Next high-pass F Wave equipment. Patent applicant Fujitsu Limited

Claims (1)

[Claims] A frequency error that generates an output signal according to the frequency difference between an input signal and the reference signal in a low-pass p-waveform band p-wave generator that has a reference signal as a center frequency and has a pass band with a constant frequency width above and below the center frequency. 1. A tracking type bandpass filter comprising: a detection means; and a voltage controlled oscillator that generates the reference signal by being controlled so that the frequency difference is minimized by the output voltage of the frequency error detection means.