JPH0369444B2 - - Google Patents

Description

[Detailed description of the invention] (a) Field of industrial application The present invention relates to an automatic adjustment device for an active filter that can automatically adjust the frequency characteristics of an active filter, and particularly relates to an automatic adjustment device for an active filter that can automatically adjust the frequency characteristics of an active filter. The present invention relates to an automatic adjustment device for an active filter.

(b) Conventional technology Improvements in IC process technology have made it possible to integrate resistors and small-capacity capacitors together with transistors and diodes onto a single pellet. It has become possible to incorporate low-pass filters and high-pass filters, which were constructed from discrete elements, into ICs in the form of active filters. However, when implementing an IC, it is difficult to set the values of resistors and capacitors to desired values due to variations in photoetching accuracy and diffusion conditions, so the cutoff frequency of the filter is determined according to the values of the resistors and capacitors. The drawback was that the sharpness and sharpness changed. Add external pins to IC,
By connecting adjustment circuit elements to the external pins and making adjustments, it is possible to set the various characteristics of the filter as desired, but increasing the number of external pins and external circuit elements is difficult for ICs. Not a desirable thing,
The increase in adjustment steps is also disadvantageous to IC implementation. For that reason,
The applicant of the present invention previously proposed an automatic filter adjustment device and filed an application as Japanese Patent Application No. 107775/1983. According to the above application, a reference signal is applied to an active filter for adjustment, the output signal of the filter is compared with the reference signal, and a control signal corresponding to the difference is applied to the active filter to be adjusted and the active filter for adjustment. By applying the voltage to the variable capacitance diode, the active filter to be adjusted can be automatically adjusted.

(C) Problems to be Solved by the Invention However, since the automatic adjustment of the active filter as in the above application uses only the variable capacitance diode of the filter, it is difficult to adjust when there are large variations in the elements of the filter or temperature changes. I had a problem that I couldn't do it.

(d) Means for Solving the Problems The present invention has been made in view of the above-mentioned points, and includes an active filter to be adjusted, and an active filter for adjustment having characteristics substantially equal to or correlated with the active filter to be adjusted. a filter; and means for applying an input signal to the adjustment active filter;
an amplifier circuit that amplifies the output signal of the adjustment active filter; a comparison circuit that compares the output signal of the amplifier circuit with the input signal and generates a first control signal according to the difference; and the comparison circuit. 1st from
and means for detecting the level of the second control signal and generating a second control signal.

(E) Effect According to the present invention, when the characteristics of the active filter for adjustment are correct, the amount of attenuation by the active filter for adjustment and the amount of amplification by the amplifier circuit become equal, and the levels of both input signals of the comparison circuit match. Therefore, no control signal is generated. Further, if the characteristics of the adjustment filter are out of alignment, the attenuation amount and the amplification amount do not match, so that the first control signal is generated from the comparison circuit. The first control signal is supplied to the adjustment active filter for fine adjustment to adjust the deviation, and is also supplied to means for generating a second control signal. The means compares the first control signal with a reference potential, and if the deviation is large and coarse adjustment is required, a second control signal is supplied to the adjustment active filter to adjust the deviation. Since the characteristics of the active filter to be adjusted and the active filter for adjustment are substantially equal or have a correlation, if the deviation of the active filter for adjustment is adjusted, the deviation of the active filter to be adjusted is also adjusted.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention.
1 is an oscillation circuit that generates a reference signal having a predetermined frequency; 2 is an adjustment active filter to which the reference signal from the oscillation circuit 1 is applied; and 3 includes a variable capacitance diode and a resistor for changing the characteristics of the active filter; is adjustment active filter 2
4 is an amplifier circuit 3 that amplifies the output signal of
and a comparison circuit 5 which compares the levels of the output signals of the oscillation circuit 1 and generates a first control signal for fine adjustment according to the difference; A comparator circuit 6 generates a control signal of "H" when the value is below the lowest value of the control range, and 6 generates a "H" control signal when the control signal is equal to or higher than the highest value of the control range of the variable capacitance diode in the adjustment active filter 2. 7 is a comparison circuit that generates a control signal, and 7 is a so-called pulse generated in response to the rotation of the head of a VTR (video tape recorder).
8 is an input terminal to which an RF switch pulse is applied;
An up-down counter that counts up or down using the RF switch pulse supplied from the up-down counter 8 as a clock, and 9 performs rough adjustment by switching the resistance value in the adjustment active filter according to the output signal from the up-down counter 8. Second
Decoders 10 and 11 that generate control signals are applied with a first control signal from the comparator circuit 4 and a second control signal from the decoder 9, and a first control signal whose characteristics are set equal to those of the active filter 2 for adjustment.
and a second active filter to be adjusted.

Now, if the oscillation frequency of the reference signal generated from the oscillation circuit 1 is 2 MHz, and the amplification factor of the amplifier circuit 3 is 12 dB, then when the frequency characteristic of the adjustment active filter 2 is the correct value as shown by the solid line A in Figure 2, Since the 2 MHz signal is attenuated by 12 dB by the adjustment active filter 2, the signal at the output terminal of the amplifier circuit 3 becomes equal to the level of the reference signal. At this time, the output signal generated from the comparison circuit 4 is supplied to the variable capacitance diode in the adjustment active filter 2 to determine a predetermined filter characteristic, and is also supplied to the comparison circuits 5 and 6 to be compared with a reference voltage. Since the voltage of the output signal is within the control range of the variable capacitance diode in the adjustment active filter 2, the comparator circuit 5 outputs an "L" signal to terminal A, and the comparator circuit 6 outputs an "L" signal to terminal B. Generate a signal. Therefore, even if the up-down counter 8 is supplied with the RF switch pulse from the terminal 7, it does not count and does not change the state of the counter and generates a constant reference signal, and the decoder 9 is connected to the resistor in the active filter 2 for adjustment. For example, change the value to “1/
2R'' is supplied to the adjustment active filter 2 and the first and second adjusted active filters 10 and 11. The active filter 2 for adjustment and the first and second active filters 10 and 11 to be adjusted have the same circuit configuration and frequency characteristics, and are integrated into an IC on a single pellet. The frequency characteristics of the adjustment active filters 10 and 11 are also as shown by the solid line A in FIG.

Next, if the frequency characteristics of the adjustment active filter 2 deviate as shown by the dashed-dotted line B in Figure 2 due to element variations, temperature changes, etc., the 2MHz reference signal from the oscillation circuit 1 will be attenuated by 36 dB in the adjustment active filter 2. and in the amplifier circuit 3
Since the signal is amplified by 12 dB, an output signal that is attenuated by 24 dB with respect to the reference signal is generated at the output terminal of the amplifier circuit 3. Therefore, the level of the AC signal obtained at the output end of the amplifier circuit 3 is lower than the level of the AC signal obtained at the output end of the oscillation circuit 1, and the level of the AC signal obtained at the output end of the comparison circuit 4 is lower than that of the AC signal obtained at the output end of the oscillation circuit 1. A control signal is generated. When the voltage of the control signal is lower than the lowest value (V _L ) of the control voltage of the variable capacitance diode in the adjustment active filter 2, the comparison circuit 5
A signal of "H" is generated at terminal A. Therefore, the up-down counter 8 receives the RF signal generated approximately 6H before the vertical synchronization signal in the video signal supplied from the terminal 7.
Count down the switch pulse and decoder 9
generates a signal that lowers the resistance value in the adjustment active filter 2 from the above-mentioned initial value "1/2R", for example, an output signal that lowers the resistance value to "1/3R". Therefore, the output signal is applied to the adjustment active filter 2 and the first and second adjusted active filters 10 and 11, and the resistance values of each are adjusted. It is adjusted to the dashed line C. Therefore, the voltage of the control signal of the comparison circuit 4 is within the control voltage range of the variable capacitance diode in the adjustment active filter 2, and the control signal from the comparison circuit 4 is applied to the adjustment active filter 2, the first and Since the voltage is applied to the second adjusted active filters 10 and 11,
Each of the variable capacitance diodes is adjusted, and their characteristics are adjusted from the one-dot chain line C to the solid line A in FIG. Note that the rising and falling edges of the RF switch pulse supplied from terminal 7 are located in parts of the video signal that are not displayed on the screen.
It is possible to prevent disturbances in the filter characteristics from appearing on the screen when adjusting the resistance value. Similarly, when the voltage of the control signal from the comparator circuit 4 is higher than the maximum value (V _H ) of the control voltage of the variable capacitance diode in the active filter 2 for adjustment, the comparator circuit 6 outputs an "H" signal. Generated at terminal B. Therefore, the up-down counter 8 up-counts the RF switch pulse, and the decoder 8 sends a signal that increases the resistance value in the adjustment active filter 2 from the initial value "1/2R", for example, changes the resistance value to "R". Generates an output signal that Therefore, the output signal is applied to the adjustment active filter 2 and the first and second adjusted active filters 10 and 11,
Each resistance value is adjusted.

The active filter 2 for adjustment, the first and second active filters 10 and 11 to be adjusted are as follows:
A circuit as shown in FIG. 3 is used. The active filter includes first and second transistors 12
and 13, and first and second variable resistance sections 14 and 1
5, a third resistor 16, a decoder 17, and first and second variable capacitance diodes 18 and 19. Note that the first variable resistance section 14 includes resistors 20 to 22.
and switch circuits 23 to 25, and the second variable resistance section 15 consists of resistors 26 to 28 and switch circuits 29 to 31. The high cutoff frequency ω ₀ of the active filter in Figure 3 is [However, R ₁ and R ₂ are the resistance values of the first and second variable resistance sections 14 and 15, and C ₁ and C ₂ are the capacitances of the first and second variable capacitance diodes 18 and 19.] Since the resistance values of the first and second variable resistance sections 14 and 15 are set according to the control signal generated by the decoder 17, the high cutoff frequency ω ₀ of the active filter is determined according to the control signal. . For example, the values of the resistors 20 to 22 of the first variable resistance section 14 are all set equally to R, the values of the second variable resistance section 15 and each resistance are set to R, and the values of the first variable resistance section 14 and the second variable resistance section 15 are set to the same value. The configuration should be such that the resistance values can be switched in conjunction with each other. That is, when a signal (H, L, H) is generated from the decoder 17,
Switch circuits 23 and 25 of the first variable resistance section 14
and switch circuits 29 and 3 of the second variable resistance section 15
1 is turned on, the first and second variable resistance sections 14 and 1
The resistance value of 5 becomes "1/2R". At this time, the frequency characteristics of the active filter in Fig. 3 are expressed as
Let the solid line in the figure be A. Also, from the decoder 17 (H,
When the signals H, H) are generated, the switch circuits of the first and second variable resistance sections 14 and 15 are all turned on, and the resistance values of the first and second variable resistance sections 14 and 15 respectively become "1/3R". "become. Therefore, the frequency characteristics shift to a higher frequency range as shown by the dashed line D in FIG. Similarly, when a signal (H, L, L) is generated from the decoder 17, the frequency characteristics shift to a lower frequency range as indicated by the dashed line B in FIG. Furthermore, the active filter having the frequency characteristic determined by the setting of the resistance value can be further modified by changing the values of the variable capacitance diodes 18 and 19 using a control signal supplied from the control terminal C, to obtain a characteristic near the frequency characteristic. can be obtained. Note that the output signal of the decoder 17 corresponds to the output signal of the up-down counter 8 in FIG. That is, for example, when the output signal of the up-down counter 8 is the initial value (10), the output signal of the decoder 17 becomes (H, L, H), and when it is (11), it becomes (H, H, H), and (01). ) when (H, L,
L).

The active filter 2 for adjustment and the first and second active filters 10 and 11 to be adjusted in FIG. It is sufficient. In that case, it is necessary to insert a predetermined conversion circuit between the output terminal of the decoder 9 and the first and second adjusted active filters 10 and 11 so as to maintain the predetermined correlation.

(g) Effects of the Invention As described above, according to the present invention, an active filter for adjustment having substantially the same characteristics or characteristics correlated with the active filter to be adjusted is integrated with the active filter to be adjusted, and the adjustment Since a control signal generated in accordance with a deviation in the characteristics of the active filter is applied to the active filter to be adjusted, the characteristics of the active filter can be automatically adjusted. Therefore, it is possible to reduce the adjustment process and the number of external pins and external parts of the IC. In addition, since the filter characteristics are adjusted using two components, a resistor and a variable capacitance diode, adjustment is possible even when there are large variations in elements or temperature changes, and even when the control range of the variable capacitance diode is narrow, desired frequency characteristics can be achieved. It is possible to provide an active filter having the following characteristics. Furthermore, as in the embodiment, since the time point for adjusting the resistance is determined by the RF switch pulse, it is possible to prevent disturbances in the filter characteristics due to the adjustment of the resistance from adversely affecting the screen.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram for explaining the present invention, and FIG. 3 is a circuit diagram showing a specific circuit example of an active filter. Explanation of main figure numbers, 1...Oscillation circuit, 2...Adjustment active filter, 4, 5, 6...Comparison circuit, 8...Up/down counter, 9...Decoder, 10, 11...Adjusted active filter.

Claims (1)

[Claims] 1. An active filter to be adjusted that includes a variable capacitance diode and a variable resistor, an active filter for adjustment that has characteristics substantially equal to or correlated with the active filter to be adjusted and that includes a variable capacitance diode and a variable resistor, and an active filter for adjustment that includes a variable capacitance diode and a variable resistor. means for applying an input signal to the filter;
an amplifier circuit that amplifies the output signal of the adjustment active filter; a comparison circuit that compares the output signal of the amplifier circuit with the input signal and generates a first control signal according to the difference; and the comparison circuit. 1st from
means for detecting the level of a control signal of the comparator circuit and generating a second control signal, and supplying the first control signal from the comparison circuit to the variable capacitance diode of the active filter to be adjusted and the active filter for adjustment. An automatic adjustment device for an active filter, characterized in that it performs fine adjustment and also performs coarse adjustment by supplying the second control signal to a variable resistor of an active filter to be adjusted and an active filter for adjustment.