JPS63227111A - Narrow band-pass filter - Google Patents

Abstract

PURPOSE:To obstruct a level variation and a phase deviation in a filter output signal by providing a band-pass filter constituted of a switched capacitor circuit in accordance with a prescribed input signal, and a clock signal generating means for driving having a frequency of an integer multiple of a frequency of its output signal. CONSTITUTION:A narrow band-pass filter is constituted of a band-pass filter 1 constituted of a switched capacitor circuit, a phase difference detecting circuit 2, a low-pass filter 3, a voltage controlled oscillator 4, and a frequency divider 5. By such a constitution, one phase locking system is formed by the circuit 2, the filter 3, the oscillator 4 and the frequency divider 5, and in a stationary state, a frequency of a clock signal for driving sent to the filter 1 from the oscillator 4 is set to N times of a frequency of an output signal of the filter 1. On the other hand, the center frequency of the filter 1 is designed to 1/N of the frequency of the clock signal, therefore, a frequency of an object tone signal in a signal inputted to the filter 1 through a terminal 101 always coincides with the center frequency of the filter 1, and a normal output is generated to a terminal 102.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a narrow band filter, and particularly to a narrow band filter that can handle multiple tone signals in blur, Y-to-bel, and car telephones.

[Conventional technology]

In recent years, there has been an increasing demand for communication systems such as pagers and car phones that use multiple tone signals as an information transmission means, detect the presence or absence of the tone signals on the receiving side, and perform various controls. There is. Conventionally, in such communication systems, a very narrow bandpass filter is generally used on the receiving side to extract the desired tone signal from noise and a large number of adjacent tone signals. be.

[Problem that the invention seeks to solve]

When using the conventional narrowband filter described above, the passband characteristics are extremely narrow, so fluctuations in the frequency of the input tone signal or deviations in the center frequency of the narrowband filter itself cannot be ignored. Since the frequency of the tone signal and the center frequency of the narrowband filter do not match, the level, phase, etc. of the output signal of the narrowband filter vary significantly. For this reason, there is a drawback that the detection level of the output tone signal fluctuates each time the communication partner changes, and if phase information is attached to the tone signal, the above-mentioned phase fluctuation in the tone signal output Therefore, there is a drawback that an erroneous signal may be detected on the receiving side, resulting in a malfunction.

[Means for solving problems]

The narrowband filter of the present invention includes a bandpass filter configured by a switched capacitor circuit in response to a predetermined input signal, and a driving clock signal that generates a driving clock signal having a frequency that is an integral multiple of the frequency of the output signal of the bandpass filter. and clock signal generation means for driving the bandpass filter.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing the main parts of a first embodiment of the present invention. As shown in FIG. 1, this embodiment includes a bandpass filter 1 constituted by a switched capacitor circuit, a phase difference detection circuit 2, a reduction filter 3, a voltage controlled oscillator 4, a frequency divider 5, It is equipped with

In FIG. 1, a phase difference detection circuit 2, a reduction filter 3,
The voltage controlled oscillator 4 and the frequency divider 5 form a phase synchronization system using the output signal of the bandpass filter 1 as a reference signal.

An input signal including a plurality of tone signals inputted through a terminal 101 is outputted via a bandpass filter 1 and inputted into a phase difference detection circuit 2 as a reference signal for the phase synchronization system. A signal with a frequency of 1/N (N is a positive integer) of the frequency of the driving clock signal output from the voltage controlled oscillator 4 via the frequency divider 5 is also input to the phase difference detection circuit 2. , the phase is compared with the output signal of the bandpass filter 1 described above, and a phase error signal corresponding to the phase difference is generated and sent to the reduction filter 3. The phase error signal smoothed by the low-pass filter 3 is input to the voltage controlled oscillator 4 as a phase control signal to control the frequency of the driving clock signal generated by the voltage controlled oscillator 4. The clock signal is sent for driving to a bandpass filter 1 constituted by a switched capacitor circuit, and the clock frequency is divided by N by a frequency divider 5 and input to a phase difference detection circuit 2.

As mentioned above, the phase difference detection circuit 2, the low-pass filter 3, the voltage-controlled oscillator 4, and the frequency divider 5 form a phase synchronization system. The frequency of the driving clock signal sent to the bandpass filter 1 is equal to N times the frequency of the output signal of the bandpass filter 1.

On the other hand, since the center frequency of the bandpass filter 1 is designed to be equal to 1/N of the frequency ' of the driving clock signal, the center frequency of the bandpass filter 1 is The frequency of the tone signal and the center frequency of the bandpass filter 1 are always maintained in the same state,
A desired predetermined tone signal is output from the terminal 102 at a normal level and a normal phase.

Next, a second embodiment of the present invention will be described.

FIG. 2 is a block diagram showing the main parts of the second embodiment,
A bandpass filter 6 composed of a stretched capacitor circuit, a phase difference detection circuit 7, a switch 8, and a frequency divider 9
and 10.

In FIG. 2, a signal inputted to the bandpass filter 6 via the terminal 103 is outputted via the bandpass filter 6 and inputted to the phase difference detection circuit 7. On the other hand, from terminals 105 and 106, reference signals having reference frequencies of fil and f12 are input to the switch 8, which is controlled by a switching control signal input from the phase difference detection circuit 7 to select either one of the reference signals. A reference signal is selected and sent to frequency divider 9. In the frequency divider 9, the frequency of the reference signal sent from the switch 8 is divided by Ml (Ml is a positive integer) and outputted, and is input to the bandpass filter 6 and also to the frequency divider 10. is input. In the frequency divider 10, the frequency of the reference signal divided by M is further divided by M2 and input to the phase difference detection circuit 7.

In this case, the frequency fi! of the reference signal! and f1□ are set so that the following equation holds true for the frequency fo of the input signal from the terminal 103 to the bandpass filter 6.

f, 1= f o X M I X M 2+Δff
12=f OX M 1X M 2-Δf In the above equation, Δ is a predetermined minute frequency deviation value. Therefore,
In the phase difference detection circuit 7, the reference frequency is set to fl, corresponding to the frequency difference between the output signal input from the bandpass filter 6 and the frequency-divided reference signal input from the frequency divider 10.
A switching control signal for selecting one of the two reference signals 5, l and f1□, which is more suitable for the frequency of the input signal, is generated and sent to the switch 8. In the switch 8, in response to the input of the two reference signals inputted from the terminals 105 and 106, one of the reference signals that matches the above-mentioned input signal is selected and sent to the frequency divider 9. The operation of is already explained.

Therefore, in the second embodiment, the frequencies of the clock signal input to drive the bandpass filter 6 via the frequency divider 9 are f, XM2+Δf/M1 and f,XM2
-Δf/M, the bandpass filter 6 is automatically adjusted to match M2 times the frequency fo of the input signal to the bandpass filter 6. A predetermined tone signal is output at a normal level and a normal phase.

〔Effect of the invention〕

As explained above, the present invention can prevent level fluctuations and phase deviations in the filter output signal by automatically adjusting the center frequency in the bandpass characteristic so as to always correspond to the frequency of the input signal. There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of a first embodiment of the invention, and FIG. 2 is a block diagram showing the main parts of a second embodiment of the invention. 1.6... Bandpass filter, 2,7... Phase difference detection circuit, 3... Low pass filter, 4... Voltage controlled oscillator,
5.9.10... Frequency divider, 8... Switcher. Agent Patent Attorney Oto Uchihara Figure 2

Claims (1)

[Claims] A bandpass filter configured by a switched capacitor circuit in response to a predetermined input signal, and a clock that drives the bandpass filter by generating a driving clock signal having a frequency that is an integral multiple of the frequency of the output signal of the bandpass filter. A narrowband filter comprising: signal generating means.