JPS61281613A - Automatic adjusting device for active filter - Google Patents

Abstract

PURPOSE:To adjust automatically the characteristic of an active filter by using an adjusting active filter having a characteristic nearly the same as an active filter to be adjusted or the adjusting active filter having a correlated characteristic and forming them into IC. CONSTITUTION:If the frequency characteristic of the adjusting active filter 2 is deviated due to the variance of components or the like, the level of a DC signal obtained at the output terminal of the 1st level detection circuit is smaller than the level of the DC signal obtained at the output terminal of the 2nd level detection circuit 8 and a control signal in response to the level different is obtained at the output terminal of the comparator circuit 12 and applied to the adjusting active filter 2 and the 1st, 2nd and 3rd active filters 13, 14, 15 to be adjusted so as to adjust the characteristics.

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 in particular, it 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 bypass filters, which were composed of discrete elements such as capacitors and coils, into ICs in the form of active filters.

However, when implementing an IC, it is difficult to set the resistor and capacitor values to desired values due to variations in photoetching accuracy and diffusion conditions, and it is difficult to set the resistor and capacitor values to desired values. The drawback was that the cutoff frequency and sharpness changed. If you add an external pin to the IC and connect an adjustment circuit element to the external pin to make adjustments, you can set the filter's initial characteristics as desired. An increase in the number of elements is not favorable for IC implementation, and an increase in adjustment steps is also disadvantageous for IC implementation. Therefore, the applicant of the present invention:
He first proposed an automatic filter adjustment device and filed a patent application in 1986-3.
The application was filed as No. 844.

According to the above application, when the active filter to be adjusted is not used, a reference signal is applied to the filter, the output signal of the filter is compared with the reference signal, and the filter is automatically adjusted according to the difference. It is made like this.

(c) Problems that the invention seeks to solveHowever,
Automatic adjustment of the active filter as in the above application requires that there will be times when the filter is not used.
It cannot be applied to active filters that are constantly used.

B) Means for Solving the Problems The present invention has been made in view of the above 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 means for applying an input signal to the active filter for adjustment; an amplifier circuit for amplifying the output signal of the active filter for adjustment by a predetermined time; and a means for comparing the input signal and the output signal of the amplifier circuit; The present invention is characterized in that it includes a comparison circuit that generates a control signal according to the difference, and means for supplying the control signal to the active filter to be adjusted and the active filter for adjustment.

(E) Effect According to the present invention, when the percentage of the active filter for adjustment is 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 the two human input signals of the comparison circuit become equal. Since they match, no control signal is generated. Also, if the characteristics of the adjustment filter are off,
Since the amount of attenuation and the amount of amplification do not match, a control signal is generated to change the characteristics of the adjustment filter to adjust the difference. Since the active filter to be adjusted and the active filter for adjustment are substantially equal in percentage 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, in which 11) is an oscillation circuit that generates a reference signal having a predetermined frequency;
2) is an active filter for adjustment to which the reference signal from the oscillation circuit (1) is applied; (3) is an amplifier circuit that amplifies the output signal of the active filter for adjustment (2); (4)
A first level detection circuit includes a clamp circuit (5), a detection circuit (6), and a low-pass filter (7), and generates a first DC signal according to the output signal REP/l/ of the amplifier circuit (3). , (6) is a second level detection circuit consisting of a clamp circuit (9), a detection circuit a0, and a low-pass filter αυ, and generates a second DC signal according to the level of the reference signal; α2 is a second level detection circuit that generates a second DC signal according to the level of the reference signal; Compare the levels of the two DC signals,
a comparison circuit that generates a control signal according to the difference (13,
α and (151 are first, second and third adjusted active filters to which the control signal is applied via the low-pass filter ae. In the embodiment shown in FIG. 1, the adjustment active filter Characteristics of (2) and the first and second
The characteristics of the third transistors α3, Q4, and α9 are set to be substantially equal.

Now, assuming that 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, the frequency characteristics of the adjustment active filter (2) are shown by the solid line A in Figure 2. When the value is correct, the adjustment active filter (2) adjusts the 2MHz signal to 1.
Since it is attenuated by 2 dB, the signal at the output of the amplifier circuit (3) becomes equal to the level of the reference signal. Therefore, the level of the DC signal obtained at the output terminal of the second level detection circuit (4) and the level of the DC signal obtained at the output terminal of the second level detection circuit (6) become equal, and the output signal of the comparison circuit 0 becomes equal. becomes zero. In that case, the active filter for adjustment (2) and the first, second, and third adjusted active filters a3, α4, and α9 are set to have the same circuit configuration and frequency characteristics, and are integrated into an IC on a single pellet. Therefore, the frequency characteristics of the first, second and third adjusted active filters C131, α and a9 are also as shown by solid lines in FIG.

Next, if the frequency characteristics of the active filter for adjustment (2) deviate as shown by the dashed-dotted line B in Figure 2 due to variations in the elements, the 2 MHz reference signal from the oscillation circuit (1) 24 in (2)
Since the dB wave is attenuated and amplified by 12 dB in the amplifier circuit (3), an output signal whose wave is attenuated by 13 dB with respect to the reference signal is generated at the output terminal of the amplifier circuit (3). Therefore, the level of the DC signal obtained at the output terminal of the second level detection circuit (4) is lower than the level of the DC signal obtained at the output terminal of the second level detection circuit (6), and the comparison circuit α A control signal corresponding to the level difference is generated at the output end of the output terminal.

Then, the control signal is applied to the adjustment active filter (2).
) and the first, second and third adjusted active filters a3
, α leakage, and C9, their characteristics become the second
The state is adjusted from the one-dot chain 9B to the state shown by the solid line A in the figure.

Adjustment active filter (2), first, second and third
Active filters as shown in FIG. 3 are used as the adjusted active filters a9, α and C151. The active filter includes first and second transistors (I7) and an α barrel, a first . The second and third resistors (1
gI, (2■ and Cυ, and the first and second capacitors (
2 and (c), and the first and second variable capacitance diodes (
(C) and (C), and its high cutoff frequency ω0 is (C1) Co1t Ct > Cot, Rs > o
). Then, the first and second variable capacitance diodes (
Since the capacitances 2 and (c) are set according to the level of the control signal applied to the control terminal (a), the high cutoff frequency ω of the active filter is determined according to the control signal. is decided. For example, when the level of the control signal is a predetermined value X, the active filter in FIG. 3 has a frequency characteristic along the solid line in FIG. The values of the fourth and second variable capacitance diodes (I) and (C) become small, and the high cutoff frequency ω
. moves to a high frequency range, and the frequency characteristic shifts to the double-dot chain wAC side in FIG.

Further, when the level of the control signal is higher than the predetermined value X, the values of the first and second variable capacitance diodes (C) and (C) become large, and the high cutoff frequency ω. moves to a lower frequency range, and the frequency characteristics shift toward the dashed-dotted line B in FIG. Therefore,
By applying an appropriate control signal to the control terminal (A), the frequency characteristics of the active filter can be changed freely.

Adjustment active filter (2) and first, second and third
The active filters to be adjusted 0, αa, and αQ do not necessarily need to have the same configuration and the same characteristics as in the embodiment, but it is sufficient that they have a predetermined correlation. In that case, in order to maintain the predetermined correlation, a predetermined conversion circuit is installed between the output terminal of the low-pass filter block and the first, second, and third adjusted active filters (131, α-X, and C9). need to be inserted.

(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 into an IC together with the active filter to be adjusted, and Since a control signal generated in response to a characteristic shift of the active filter for adjustment 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 IC bins and external parts. Further, according to the present invention, there is no need to perform special modifications to the active filter to be adjusted, so that various IC-based active filters can be automatically adjusted.

[Brief explanation of the drawing]

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 characteristic diagram showing a specific circuit example of an active filter. Explanation of main figure numbers (1)...Oscillation circuit, (2)...Adjustment active filter, (3)...Amplification circuit, α...Comparison circuit, α3) α41 (15), ...Adjusted active filter. Applicant Sanyo Electric Co., Ltd. and 1 other representative Patent attorney Shizuo Sano Figure 2 r@zuft (Hz)

Claims (1)

[Claims] (1) an active filter to be adjusted; an active filter for adjustment having characteristics substantially equal to or correlated with the active filter to be adjusted; means for applying an input signal to the active filter for adjustment; an amplifier circuit that amplifies an output signal; a comparison circuit that compares the input signal with the output signal of the amplifier circuit and generates a control signal according to the difference; and a comparison circuit that generates a control signal according to the difference; and means for supplying the active filter to the active filter.