JPH0514105A - Band pass filter - Google Patents

Abstract

PURPOSE:To keep the accuracy of a pass band characteristic constant even when the pass band characteristic attended with a frequency setting change, a change in the operating environment and a secular change is fluctuated. CONSTITUTION:A band pass filter provided with a filter means 11 passing an input signal of a prescribed frequency whose pass band is made adjustable is provided with a monitor signal generating circuit means 13 generating a monitor signal of a prescribed frequency and giving it to an input terminal of the filter means 11, and also provided with a control means 15 adjusting the pass band at a point at which a level of an output signal of the filter means 11 is maximized in response to the monitor signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bandpass filter for passing a signal of a predetermined frequency in an electronic device and giving it to a circuit in the subsequent stage.

[0002]

2. Description of the Related Art In a radio receiver of atable super-heterodyne system, a radio frequency signal to be received (hereinafter referred to as "desired wave") is guided to a subsequent stage while minimizing an amount of attenuation, and an undesired wave (unwanted wave). ) Is sufficiently attenuated, a bandpass filter is arranged in front of the frequency conversion unit that converts the desired wave into a predetermined intermediate frequency. In such a band-pass filter, for example, when a plurality of radio channels arranged in a wide band of about 20 MHz in the 150 MHz band are switched and received, the attenuation characteristic outside the pass band is set steeply to the image frequency. The pass band is variably set in order to suppress the sensitivity of the receiver (image sensitivity) and pass the selected desired wave.

FIG. 4 is a diagram showing a configuration example of a conventional bandpass filter. In the figure, the desired wave given from the antenna is given to the main part (hereinafter, simply referred to as "main part") 40 of the bandpass filter, and its output is connected to the mixer in the subsequent stage.

In the main part 40, a coupling capacitor 41 ₁ , an inductively coupled double-tuned circuit 42 and a coupling capacitor 41 ₂ are connected in series between its input and output terminals. A variable capacitance diode (varicap) 43 ₁ is connected in parallel with a reverse bias to the primary side of the double tuning circuit 42, and a variable capacitance diode 43 ₂ is connected in parallel with a reverse bias to the secondary side of the double tuning circuit 42. It The connection point between the capacitor 41 ₁ and the double-tuned circuit 42 is connected to the connection point between the capacitor 41 ₂ and the double-tuned circuit 42 via the inductors 44 ₁ and 44 ₂ . The connection point of the inductors 44 ₁ and 44 ₂ is grounded via the resistor 45, and the control terminal 4 of the main portion 40 is connected.
8 is connected.

The common contact of the channel changeover switch 46 is connected to a power supply line for supplying a predetermined DC voltage (= + B). The first contact (corresponding to the first desired wave), the second contact (corresponding to the second desired wave) and the third contact (corresponding to the third desired wave) of the channel changeover switch 46. .) Are semi-fixed resistors 47 ₁ and 4 respectively.
It is connected to the control terminal 48 of the main part 40 via 7 ₂ and 47 ₃ .

In the bandpass filter having such a structure,
Compensation voltage (bias voltage) is set in the variable capacitance diodes 43 ₁ and 43 ₂ according to the voltage division ratio between the resistor 45 and any one of the semi-fixed resistors 47 _{1 to} 47 ₃ selected by the channel changeover switch 46. And the double tuning circuit 42
Since the tuning frequency (center frequency of the pass band) is determined, the semi-fixed resistor 47 _{1-47 3} is pre-adjusted to the resistance value which the maximum output is obtained at each desired wave. That is, since the pass band characteristic of the band pass filter is determined by the sharpness of the double tuning circuit 42, even if a plurality of desired waves to be received are arranged over a wide band, they are steep outside each pass band corresponding to the desired wave. Attenuation characteristics can be obtained.

The inductors 44 ₁ and 44 ₂ prevent the desired wave (high frequency component) from affecting the bias voltage of the variable capacitance diodes 43 ₁ and 43 ₂ .

[0008]

[Problems to be Solved by the Invention]
With conventional bandpass filters, change the set frequency
Semi-fixed resistor 47₁~ 47₃The resistance value of
I had to adjust. Also, vibration and other operations
Coping with fluctuations in passband characteristics due to aging of environment and elements
In order to do so, check for fluctuations at regular intervals.
Semi-fixed resistor 47 ₁~ 47₃Need to readjust
It was

The present invention provides a bandpass filter which can maintain the accuracy of the passband characteristic constant even if the passband characteristic changes due to a change in frequency setting, an operating environment and a change over time. To aim.

[0010]

FIG. 1 is a block diagram showing the principle of the present invention. The present invention is a band-pass filter having a filtering means 11 capable of passing an input signal of a predetermined frequency and having an adjustable pass band, wherein a monitor signal of a predetermined frequency is generated and provided to an input end of the filtering means 11. It is characterized in that it is provided with a generation means 13 and a control means 15 for adjusting the pass band at a point where the level of the output signal of the filtering means 11 corresponding to the monitor signal becomes maximum.

[0011]

According to the present invention, the monitor signal generating means 13 gives the monitor signal to the filtering means 11, and the control means 15 passes the signal to the point where the level of the output signal obtained from the filtering means 11 in accordance with the monitor signal becomes maximum. Adjust the band.

That is, since the pass band of the band pass filter is automatically adjusted to the point where the maximum sensitivity is obtained for the input signal to be passed, the characteristic fluctuations due to the operating environment, the aging of the element, and the like are absorbed to produce. In some cases, the adjustment work at the time of shipping is unnecessary, and the readjustment work associated with the frequency change during operation is also unnecessary.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a diagram showing an embodiment of the present invention.

In the figure, components having the same configurations and functions as those shown in FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted here. Antenna 21 is
It is connected to one contact of the main part 40 and the high frequency switch 22. The output of the main part 40 is connected to the first intermediate frequency amplifier via the mixer 23. Main part 40 and mixer 2
The connection point with 3 is connected to a microprocessor (CPU) 27 via an amplifier 24, a detector 25, and an analog-digital converter (A / D) 26. The microprocessor 27 is a digital-analog converter (D / A).
It is connected to the control terminal of the main part 40 via 28. Further, the microprocessor 27 is connected to the frequency synthesizer section 29, and its output is connected to the common contact of the high frequency switch 22. The microprocessor 27 is connected to the control terminal of the high-frequency switch 22, and the other contact is connected to the local oscillation frequency injection terminal of the mixer 23. The channel changeover switch 46 is connected to the microprocessor 27.

Regarding the correspondence between this embodiment and the block diagram shown in FIG. 1, the main part 40 of the pass band filter is shown.
Corresponds to the filtering means 11, the frequency synthesizer 29 and the high frequency switch 22 correspond to the monitor signal generating means 13, and the amplifier 24, the detector 25, the analog-digital converter 26, the microprocessor 27 and the digital-
The analog converter 28 corresponds to the control means 15.

FIG. 3 is a flow chart showing the operation of this embodiment. The operation of this embodiment will be described below with reference to FIGS. The microprocessor 27 causes the frequency synthesizer unit 29 to generate the frequency of the desired wave designated by the channel changeover switch 46 at the time of initial setting when the power is turned on (FIG. 3 (1)), and controls the high frequency switch 22 to control the frequency synthesizer. The output of the section 29 is connected to the main section 40 (FIG. 3 (2)). In addition, the microprocessor 27
Through the digital-analog converter 28.
The minimum compensation voltage (= A ₁ ) within the variable range is set to 0 (FIG. 3 (3)), and the level (= D ₁ ) of the signal output from the main portion 40 is set in accordance with the compensation voltage by the amplifier 24. , Through the detector 25 and the analog-digital converter 26,
It is memorized (Fig. 3 (4)).

The microprocessor 27 is the first such
When the period setting is completed, the digital-analog converter 28
A value one step higher than the preset value for the compensation voltage via
(= A ₂) (Fig. 3 (5)), and the main
The level of the signal output from the main part 40 (= D₂) The amplifier
24, detector 25 and analog-digital converter 2
Captured via 6 and stored (FIG. 3 (6)). In addition,
In this way, the i-processor 27 can increase the compensation voltage by one step.
The signal output from the main part 40 by setting the difference between
Level (= D₁, D₂), D₁> D₂Inequality of
If true, signal level D₁Compensation voltage A corresponding to
₁Through the analog-digital converter 26
It is set to 0 (Fig. 3 (7)).

That is, the microprocessor 27 takes advantage of the fact that the main portion 40 is constructed by using a double tuning circuit, and its pass band characteristic is set to a steep single peak characteristic in order to suppress the image frequency. The compensation voltage corresponding to the peak point of the unimodal characteristic is obtained and set while shifting the compensation voltage step by step.

However, if the above inequality does not hold, the microprocessor 27 further increases the value by one step (= A _{k + 1} (k) via the digital-analog converter 28.
= 2 to (n-1)) (FIG. 3 (5)), and the level (= D _{k + 1} (k = 2) of the signal output from the main part 40 according to the compensation voltage. ~ (N-1))) (Fig. 3
(6)). Here, n represents the maximum value of the number indicating the variable step of the compensation voltage. The microprocessor 27 again compares the above-mentioned signal level D _{k + 1} with the corresponding signal level D _k before updating the compensation voltage, and when the inequality of D _k > D _{k + 1} holds, the compensation voltage A _k becomes the main value. Fixedly set to part 40 (Fig. 3 (7))
However, if the inequality does not hold, the compensation voltage is set to a value one step higher and the same processing is repeated (FIGS. 3 (5) to (6)).

Further, as a result of such iterative processing, when the compensation voltage corresponding to the peak point of the unimodal characteristic cannot be obtained even when the compensation voltage is set to the maximum value (= A _n ), the microprocessor is used. Reference numeral 27 sets the compensation voltage (= A _n ) at which the output signal level of the bandpass filter becomes maximum within the variable range of the compensation voltage in the main portion 40 via the digital-analog converter 28 (FIG. 3 (8)). ).

When the compensation voltage is fixedly set by the processing described above, the microprocessor 27 controls the frequency synthesizer section 29 to generate the first local oscillation frequency corresponding to the desired wave (FIG. 3 (9)) and high frequency. The switch 23 is controlled to connect the mixer 23 to the frequency synthesizer unit 29 (FIG. 3 (10)). The mixer 23 generates a frequency component of the sum difference between the above-mentioned first local oscillation frequency and the desired wave given via the main part 40, and either one of them is selectively amplified by the first intermediate frequency amplifier. ..

Further, the microprocessor 27 sequentially monitors the radio channel designated by the channel changeover switch 46 in such a normal reception state, and when the radio channel is switched, the above-mentioned processing for a new desired wave is performed. Then, the pass band of the main part 40 is automatically adjusted (FIGS. 3 (1) to (12)).

When the processing shown in FIGS. 3 (1) to 3 (8) is being performed, the frequency synthesizer section 29 generates a desired wave frequency different from the first local oscillation frequency. Although normal operation is not performed, such processing can be completed within a few tens of milliseconds after initial setting or channel switching, so there is almost no problem in the operation of the receiver.

As described above, according to the present embodiment, the pass band of the band pass filter is automatically adjusted to the point corresponding to the maximum sensitivity in response to the request for switching the wireless channel. There is no need for adjustment and readjustment associated with a change in the frequency of the radio channel, and readjustment for the characteristics of the elements constituting the bandpass filter, such as secular change, vibration, and other operating environment.

Although the present embodiment is an application example of the present invention in a receiver of the double superheterodyne system, the present invention is not limited to such a receiver, and is required to filter a signal of a predetermined frequency. Any electronic device can be applied.

Further, in the present embodiment, the frequency of the desired wave is given to the main part 40 by using the frequency synthesizer part 29 for generating the local oscillation frequency in the normal receiving state, but the present invention has such a structure. For example, a variable frequency oscillator capable of intermittently controlling the output signal may be provided separately from the frequency synthesizer unit 29, and a multiplexer may be used instead of the high frequency switch 22.

Further, in this embodiment, the compensation voltage for obtaining the maximum sensitivity to the desired wave is set by the control of the software executed by the microprocessor 27, but the present invention is not limited to such a configuration. For example, similar processing may be performed using dedicated hardware.

The bandpass filter is required to have an algorithm for convergence to the compensation voltage corresponding to the variable range of the compensation voltage (passband) variably controlled by the microprocessor 27, the unit variable width and the maximum output level of the main part 40. It is possible to adopt one that is adapted to the required pass band characteristic, the accuracy required for automatic adjustment, the adjustment required time, and the like.

[0029]

As described above, according to the present invention, since the pass band of the band pass filter is automatically adjusted to the point where the output signal level becomes maximum with respect to the input signal to be filtered, the operating environment and the secular change can be avoided. The accompanying characteristic fluctuations are absorbed, and readjustment due to frequency changes during operation becomes unnecessary.

That is, in the electronic device to which the present invention is applied, the inspection and adjustment of the characteristics of the band pass filter during production, shipping and operation are saved, so that the number of adjustment steps is reduced and the maintenance is simplified compared to the conventional example. In addition, the performance can be improved, and the quality of the device and the cost can be reduced as a whole.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of this embodiment.

FIG. 4 is a diagram showing a configuration example of a conventional bandpass filter.

[Explanation of symbols]

11 Filtering Means 13 Monitor Signal Generating Means 15 Control Means 21 Antennas 22 High Frequency Switches 23 Mixers 24 Amplifiers 25 Detectors 26 Analog-Digital Converters (A / D) 27 Microprocessors (CPU) 28 Digital-Analog Converters (D / D) A) 29 frequency synthesizer section 40 main section of pass band filter 41 ₁ , 41 ₂ capacitor 42 double tuning circuit 43 ₁ , 43 ₂ variable capacitance diode 44 ₁ , 44 ₂ inductor 45 resistor 46 channel changeover switch 47 ₁ , 47 ₂ , 47 ₃ Semi-fixed resistor 48 Control terminal

Claims (1)

Claim: What is claimed is: 1. A band pass filter, comprising: a filtering means (11) capable of passing an input signal of a predetermined frequency and adjusting a pass band, wherein the monitor signal of the predetermined frequency is generated. Monitor signal generating means (13) applied to the input end of the filtering means (11)
And a control means (15) for adjusting the pass band at a point where the level of the output signal of the filtering means (11) corresponding to the monitor signal becomes maximum.