JPH01183907A - Filter circuit - Google Patents

Abstract

PURPOSE:To attain an automatic adjustment by controlling the interruption frequency of the filter of a shifting circuit with the loop of an oscillator, a shifting circuit and a phase comparing circuit. CONSTITUTION:A filter circuit connects the output of an oscillator 1 through a filter 59 to the inverting input of an amplifier 56, connects one edge of resistances 44 and 45 into the non-inverting input of the amplifier 56, connects the input of the filter 59 and other edge of the resistance 44 and the input is executed. The output signal of the oscillator 1 is dislocated to 90 deg. progress (or delay) phase by a shifting circuit 2, the phase comparison is executed for the output signal of the oscillator 1 and the output signal (output signal of 90 deg. progress (or delay) phase of the output signal of the oscillator 1) of the shifting circuit 2 by a phase comparing circuit 3, the output signal of the shifting circuit 2 always becomes the 90 deg. progress (or delay) phase of the output signal of the oscillator and like that, the interruption frequency of the filter 59 is controlled. In the same way, the output signal of the shifting circuit 2 controls the interruption frequency of filters 4 and 5.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to eliminating the need to adjust the cut-off frequency of a filter, and in particular to eliminating the need to adjust the cut-off frequency of a filter by automatically adjusting and controlling the cut-off frequencies of a plurality of filters built into an integrated circuit. This invention relates to a filter circuit that has been adjusted.

[Conventional technology]

A conventionally used filter circuit will be explained with reference to FIG.

A conventional filter circuit 60 incorporating two filters outputs signals inputted from input terminals 6 and 8 to respective output terminals 7 and 9 via respective filters 4 and 5. The output of the voltage control circuit 10 is connected to the control input terminal of each of the filters 4 and 50, and the control input terminal of the voltage control circuit 100 is connected to a reference potential via a variable resistor 11.

Filters 4 and 5 having this configuration change the cutoff frequency by varying the voltage (or current). A voltage (or current) controlled filter that controls the voltage control circuit 1 by varying the variable resistor 11.
By changing the voltage at the output of the voltage control circuit 10, the voltage at the control input terminals of the filters 4 and 5 connected to the output of the voltage control circuit 10 is changed, and the cutoff frequency of each filter 4 and 5 is adjusted.

FIG. 3 shows a specific example of a conventionally used filter circuit 6°. In the filter circuit 60 shown in FIG. 2, which has two built-in filters, the input terminal 6 is connected to the base of the NPN) transistor 120, the collector is connected to the base and collector of the PNP transistor 14, and the base of the PNP transistor 15, The collector of the transistor 15 is connected to the collector of the NPN transistor 13, the base of the NPN transistor 16, and one end of the capacitor 57, and the emitter of the NPN transistor 16 is connected to the base of the NPN transistor 13, one end of the resistor 25, and the output terminal 7. Connect the emitter of the NPN transistor 12.13 and the collector of the NPN transistor 17, connect the emitter of the NPN transistor 17 to the low potential end via the resistor 24, and connect the emitter of the PNP transistor 14.15 to the NPN transistor 17. 16 is connected to the high potential end, and the other end of the capacitor 57, the other end of the resistor 25, and the low potential end are connected to the filter 4, the filter 5 has the same configuration as the filter 4, and the resistor 2 is connected to the high potential end.
N from the connection point of the room pressure control circuit 10 which is connected to the low potential end via the variable resistor 11 and the resistor 28 and the variable resistor 11.
PN) is connected to the base of transistor 17゜23.

Next, adjustment of the cutoff frequency of the filter 4 will be explained.

The cutoff frequency fL of the filter 4 is 2kTr. Capacitor 57: Cst, resistance 24.28; R24,
1R21, variable resistor 11: Ru, potential between high potential end and low potential end; VCClNPN) transistor Ql? Pace emitter voltage; VBE (Ql?), mutual conductance; g□, electron charge: g=6. o 2X 10
−”(c), Portzmann constant: k= 1.38 X
10-23 [W-S/''k], absolute temperature; expressed as T. By changing the variable resistor 11, gm changes, and as a result, the cutoff frequency fL of the filter 4 changes.

Filters 4 and 5 with different cutoff frequencies can be obtained by changing the capacitors 57 and 58 and the resistors 24 and 26.

[Problem that the invention seeks to solve]

In the conventional filter circuit described above, it is necessary to focus on the cutoff frequency of one of a plurality of filters and adjust the variable resistor 11 so that the desired frequency is achieved, and automatic adjustment is not performed. There were drawbacks.

[Means for solving problems]

The filter circuit of the present invention has a plurality of electric FE (or current) controlled filters (hereinafter abbreviated as filters) that vary the voltage (or current) and change the cut-off frequency of the filter,
The signal input terminal of a phase shift circuit that changes the phase of the input signal by varying the voltage (or current) of the output of the oscillator and the phase comparator circuit 3
The signal output terminal of the phase shift circuit is connected to the second input of the phase comparison circuit 3, and the output of the phase comparison circuit is connected to the control input terminals of the plurality of filters. It has that.

〔Example〕

Next, the present invention will be explained using FIG.

The filter circuit of the present invention converts the output of the oscillator 1 into the filter 5.
9 to the inverting input of amplifier 56 and resistor 44 .
45 is connected to the non-inverting input of the amplifier 56, the filter 590 input and the other end of the resistor 44 are connected as an input, and the other end of the resistor 45 is connected to the input/output of the amplifier 56 as an output. 2, the input of the phase shift circuit 20 is connected to the first input of the phase comparison circuit 3, the output of the phase shift circuit 2 is connected to the second input of the phase comparison circuit 3, and the output of the phase comparison circuit 3 is connected. The configuration is such that the control input terminal of the phase shift circuit 20 is connected to the control input terminal of the filter 4.5, and the output signal of the oscillator l is connected to the phase shift circuit 20.
The output signal of the oscillator l and the output signal of the phase shift circuit 2 are shifted in phase by 90 degrees in the phase comparator circuit 3 and the output signal of the phase shift circuit 2 (
The output signal of the oscillator 1 is phase-compared with the output signal that is 90 degrees ahead (or behind) of the output signal of the oscillator, so that the output signal of the phase shift circuit 2 is always in the phase that is 90 degrees ahead (or behind) of the output signal of the oscillator. The cutoff frequency of the filter 59 is controlled.Similarly, the output signal of the phase shift circuit 2 controls the cutoff frequency of the filters 4 and 5.

Next, control of the cutoff frequency of the filter 4.5 will be explained using the specific embodiment shown in FIG.

The output of the oscillator 1 is transferred to the NPN transistor 31 of the phase shifting circuit 2.
The base of the NPN transistor is connected to the non-inverting input of the amplifier 56 and the base of the NPN) transistor 40 of the phase comparator circuit 3 via the resistor 44, and the collector of the NPN transistor is connected to the base and collector of the PNP) transistor 29 and the base of the PNP) transistor 30. The collector of the PNP transistor 30 is connected to the collector of the NPN transistor 32, the base of the NPN transistor 33, and one end of the capacitor 52, and the emitter of the NPN transistor 33 is connected to the base of the NPN transistor 32 and the inverting input of the amplifier 560. It is connected to one end of the resistor 43 and connected from the output of the amplifier 56 to the non-inverting input of the amplifier 56 via the resistor 45.
1. Connect the emitter of 32 and the collector of NPN) transistor 34, connect the emitter of NPN) transistor 34 to the low potential end via resistor 42, and
The emitters of NPN) transistors 35 and 36 are connected to the collectors of NPN) transistors 35 and 36, and the collectors of NPN) transistors 35 and 37 are connected to one end of a resistor 46.
38 and one end of the resistor 47 and the base of the transistor 39 and one end of the capacitor 53 are connected.
N) Connect the emitters of transistors 37 and 38 and the collector of NPN) transistor 41, insert a resistor 41 between the emitter of NPN) transistor 4o and the emitter of NPN) transistor 41, and connect the emitters of NPN) transistor 40 and 41 to each other. Insert a resistor 48.50 between the potential terminals, NPN)
Connect the bases of transistors 35 and 38 and the output of amplifier 56 (NPN) transistors 36 and 37 and bias power supply 54
A bias power supply 55 is connected to the base of the NPN) transistor 41, and the collector of the PNP transistor 39 is connected to the low potential end via the resistor 51. 34° Connect to the base of 17.23, connect the emitter of PNP) transistor 29.30, the collector of NPN) transistor 33, and the other end of resistor 46.47 to the high potential end, and connect the resistor 43 to the low potential end. In the filter circuit formed by connecting the phase shift circuit 2, the phase comparison circuit 3, and the filters 4 and 5 as in the conventional example (Fig. 3), the phase characteristic β of the phase shift circuit is
(ω) is given by β(,)=2jan-' ω/ω, where is NPN) The mutual contactance g of the differential amplifier consisting of transistors 31 and 32. and capacitor 53 (C
At the cutoff frequency ω, determined from a, Ca = g m
/ C53.

The output of the oscillator l is sent to the phase comparator circuit 3 via the phase shift circuit 2, and a signal with a 90° phase delay is sent to the NPN) transistor 35.36.
The signal from the oscillator 1 is input to the other input (the base of the NPN transistor 40), and the phases of these two signals are compared and the difference is smoothed by the capacitor 53. G of each filter is input to the base of the NPN) transistors 34, 17, and 23 through the phase shift circuit 2 and the filter 4°5. The phase shift circuit 2
The output of the oscillator 1 is 90° in phase with the output signal of the oscillator 1. At that time, g, the other filter 4.50g. is also determined in the same way as equation (1), and the cutoff frequency of each filter 4, 5 is f u41r f L (51 is f L+a = g
m/2πC5,.

fL(5+:gIIl/2πaSS).

For each filter 4 and 50g, not only can the cutoff frequency of each filter 4 and 5 be changed by setting a ratio between the resistors 42 and 24.26, but also the cutoff frequency of each filter 4 and 5 can be changed by setting a ratio between the capacitors 57 and 58.52. You can change the frequency and get the desired filter characteristics.

〔Effect of the invention〕

As explained above, the present invention controls the cut-off frequencies of the filter 59 of the phase shift circuit 2 and the filters 4 and 5 using the loop of the oscillator 1, the phase shift circuit 2, and the phase comparison circuit 3. The cutoff frequency was previously matched by adjusting the variable resistor 11, but now it is possible to do this automatically.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a conventional block diagram, FIG. 3 is a specific conventional embodiment, and FIG. 4 is a specific implementation circuit diagram of FIG. 1... Oscillator, 2... Phase shift circuit, 3.
...Phase comparator circuit, 4,5.59...Filter, 6,8...Filter input, 7.9.
... Filter output, 10 ... Voltage control circuit, 11 ... Variable resistor, 57.58°52.
53... Capacitor, 12, 13, 16゜17
．． 18, 19, 22, 23, 31, 32, 33° 34.
35, 36, 37, 38, 40.41...NP
N) Transistor, 14, 15, 20, 21, 29, 30
゜39...PNP transistor, 54.55
...Bias power supply, 24.25.26.27.
28.42.43°44, 45.46.47.48.4
9.50.51...Resistor, 56...Amplifier, 60...Conventional filter circuit. Agent Patent Attorney Oto Uchihara〉 3 1st Old

Claims (1)

[Claims] It has a control type filter that changes the cut-off frequency of the filter,
The output of the oscillator is connected to the signal input terminal of the phase shift circuit and the first input of the phase comparison circuit, and the signal output terminal of the phase shift circuit is connected to the second input of the phase comparison circuit. A filter circuit characterized in that an output of the circuit is connected to control input terminals of the plurality of control type filters and a control input terminal of the phase shift circuit.