JPH04150513A - Filter circuit - Google Patents

Abstract

PURPOSE:To simplify configuration, and to reduce the number of parts so that cost can be reduced and a filter circuit can be made advantageous for being made into an IC by providing a first separation circuit and a second separation circuit which are specified respectively. CONSTITUTION:This circuit is provided with the first separation circuit 21 which separates the component of the prescribed frequency band of an input signal and the second separation circuit 31 which inputs the output of the first separation circuit 21 and separates further the component of the prescribed frequency band in it. Accordingly, since the output of the high frequency band, for instance, of the first separation circuit 21 is frequency-divided by the second separation circuit 31, by making both separation circuits operate as what is called a band pass filter, the signal of the prescribed frequency band can be separated. Thus, since the signals of a large number of the frequency bands can be separated by a small number of the filter circuits, the configuration can be simplified, and the number of parts can be reduced, and the filter circuit can be made advantageous for being made into the low-cost IC.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a filter circuit that separates components in a predetermined frequency band from an input signal.

[Conventional technology]

In audio devices, graphic equalizers are used to adjust the level of each predetermined frequency band so as to obtain overall desired frequency characteristics.

FIG. 7 is a block diagram showing the configuration of an example of a conventional graphic equalizer.

In this example, one low-pass filter 1, three band-pass filters 2 to 4, and one bypass filter 5 are connected in parallel, and each filter has a capacitor la that determines its frequency characteristics. , lb to 5a, 5
It has b. The input signal is input in parallel to each filter 1 to 5, the low pass filter 1 separates the component in the lowest frequency band, and the bypass filter 5 separates the component in the highest frequency band. The bandpass filters 2 to 4 separate signals in a lower frequency band, an intermediate frequency band, or a higher frequency band within these intermediate frequency bands.

The outputs of each of the filters 1 to 5 are input to multipliers 6 to 10, respectively, and the desired coefficients are multiplied by □ to 5. The outputs of the multipliers 6 to 10 are input to an adder 11, where they are added to 1. It is supplied to the speaker via an amplifier (not shown), etc.
A sound is emitted.

[Problem to be solved by the invention]

In this way, conventional graphic equalizers are provided with a number of filters corresponding to the number of frequency bands to be separated. As a result, the structure becomes complicated, the number of parts increases, and the cost becomes high. Also,
This was particularly disadvantageous for IC implementation.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a filter circuit that can simplify the configuration, reduce the number of parts, reduce costs, and is advantageous for IC implementation.

[Means to solve the problem]

The filter circuit of the present invention includes a first separation circuit that separates high frequency band components of an input signal, and a filter circuit that receives input of high frequency band components output from the first separation circuit, and receives the input of the high frequency band components output from the first separation circuit. It is characterized by comprising a second separation circuit that separates band components.

[Operation] In the filter circuit of the present invention, the high frequency band output of the first separation circuit is further frequency-divided by the second separation circuit. Therefore, both separation circuits can function as a so-called band-pass filter to separate signals in a predetermined frequency band.

〔Example〕

Next, an embodiment of the filter circuit of the present invention will be described.

FIG. 2 is a block diagram showing the configuration of an embodiment of a gyrator filter circuit used in the filter circuit of the present invention.

The emitters of the NPN transistors 52 and 53 are differentially connected via resistors 54 and 55, and the connection point between the resistors 54 and 55 is grounded via a constant current source 61. The collector of the NPN transistor 52 is connected to a predetermined reference voltage Vce.
The collectors of the N transistors 53 are each connected to a reference voltage V cc /2 via a capacitor 64 . The emitters of NPN transistors 56 and 57 are also connected to resistor 5.
A connection point between the resistors 58 and 59 is connected to the ground through a constant current source 62. The collector of the NPN transistor 56 is connected to the reference voltage Vcc,
The collector of the NPN transistor 57 is connected to the NP? It is connected to the base of V transistor 52. Also connected to the base of the NPN transistor 52 is a signal source 51 that outputs a signal as a voltage change.

The NPN transistor 60 has its base connected to the collector of the NPN transistor 57, its collector connected to the reference voltage ■■, its emitter connected to the bases of the NPN transistors 53 and 57, and a constant current [63] and grounded.

Next, its operation will be explained.

Now, in response to the signal voltage applied from the signal source 51 to the base of the NPN transistor S2, current flows through the resistors 54 and 55 in the direction shown by the arrow in the figure.The current flows through the resistors 58 and 59 in the direction shown by the arrow in the figure. Let the current flowing through the capacitor 64 (capacitance CL) be 12, the voltage at the connection point between the capacitor 64 (capacitance CL) and the collector of the NPN transistor 53 be x, and the voltage at the connection point of the NPN transistor 60 be
Letting y be the potential output from the emitter of , the following equation holds true.

That is, if the base voltage of the NPN transistor 52 due to the signal 'g51 is 1, the base voltage of the NPN transistor 53 is y.

Ignoring the voltage between the pace emitters of NPNh transistors 52 and 53, 1-y=i□r, so 11=(1y)/f", ・ ・ ・ ・ ・ (
1). Here, r is the combined resistance of resistors 54 and 55.

Assuming that the base current of the NPN transistor 56 is sufficiently smaller than the current ii, most of the current i flows through the capacitor 64, so x=i□/(jωC)... (2) Become.

Also, the base voltage of the NPN transistor 56 is x, NP
Since the base voltage of the N transistor 57 is y, ignoring the base-emitter voltage of both transistors, x-y= l, r2 Therefore, L= (x-y)/r', ・ ・ ・ ・ ・ (
3). Here, r2 is the combined resistance of resistors 58 and 59.

Assuming that the base current of the NPN transistor 60 is sufficiently smaller than the current 12, most of the current i flows through the capacitor 65 (capacitance CX), so the following equation holds true.

y=1+iz/ (jωCl) ... (4
) Substituting equation (1) into equation (2), Si= j (11C
,r.

Then, the following formula is obtained.

:c=xx/(JωCt)=(13')/(JωCxl
'z)=(1y)/Si... (5) Also, by substituting equation (3) into equation (4), S * = Jω
C, rt, the following equation is obtained.

y=l+i*/(j (1)Cx)=1+(x-y)/
(j (11C2r,)=1+(x-y)/S,...
... (6) By solving the above equations (5) and (6), the following equation is obtained.

y= (1+8182)/ (1+S□+SyoS,)・
・ ・ ・ ・ (7) x= 1/ (1+S□+5xSz)” ” ”
” ” (8) Also, in equations (1) and (3), (7)′
By substituting the equation and equation (8), the following equation is obtained.

1x=(1/ r' L) (Sx) / (1+
S□10 St S2)... (9) i! =(1/r2)(-SISri/(1+s□+S,S
, )... (10) When Sl and S are set to O in the above equation (7), y=1. Also, by transforming equation (7), y=(1/S, S, +1)/(1/S□S, +1/S2
+1)... (11) Therefore, if Sl, S, are set to ω in equation (11), y
=l. Furthermore, since the equation (7) holds y==Q at the frequency that makes the numerator 0, the equation (7) has the characteristics of a trap circuit that traps the frequency that makes the numerator 0.

This trap frequency ft is 1+S, S, = 1-ω"c, C2rLr, = Q, so from equation (12), f t = 1/ (2x (C1C2r, ra) '
)... (13) becomes.

Also, equation (8) shows the frequency characteristics of the low-pass filter since x=1 when S, , S, is set to o, and X=O when set to ■.

Furthermore, in equation (9), if s,,s, is set to 0, then i
□=0. Also, if we transform equation (9).

iyo-(1/ryo)/(1/S□+1+S,)・
・ ... (14) Therefore, if S,,S, is set to ω, then i-work=0.

Equation (9) can also be transformed as shown below.

i□=(1/rt)(1-(1+S)/(1+s
□÷S□82))... (15) Therefore, when the frequency satisfies 1 + S z s z = O, equation (15) becomes i□ = 1/ri, so (
Equation 15) (Equation (9)) shows the characteristics of a bandpass filter. Since its center frequency is a frequency that satisfies 1+5iS2=O, it is the same as the trap frequency in Equation (7).

Next, in equation (10), if S, S, and l are O, then 12=Q. Also, by transforming equation (10), 1z=(1/rz)(1)/(1/5iS-+1/S-
+1)... (16) In Equation (16), S, if S2 is set to ω, then
i,=-17r, that is, equation (10) shows the characteristics of the bypass filter.

As described above, in this case, the resistor 54.・55,58.5
9. Capacitors 64, 65, NPN transistor 52,
53, 56, 57, 60, constant current sources 61, 62, 63, and other circuit elements constitute one separation circuit, but if the voltage y is output, this circuit becomes a trap circuit, and the voltage If the output is a low-pass filter,
If the current i□ is used as an output, it becomes a bandpass filter, and if the current main 2 is used as an output, it becomes a bypass filter.

FIG. 1 shows an embodiment in which a graphic equalizer is constructed using the separation circuit shown in FIG.

In FIG. 1, separation circuits 21 and 31 are configured as shown in FIG. 2. Capacitors 22 and 23 corresponding to capacitors 64 and 65 in FIG. 2 are externally mounted. In the separation circuit 21, the output voltage X (low-pass filter output), the output current ii (band-pass filter output), and the output current 12 (bypass filter output) are used, and the low-pass filter output is input to the multiplier 24, Bandpass filter output is multiplier 2
5, and each coefficient is multiplied by k. The bypass filter output of the separation circuit 21 is supplied to the separation circuit 31 at the subsequent stage. Also in this separation circuit 31, a capacitor 32 corresponding to the capacitors 64 and 65 in FIG.
．． 33 has an external configuration.

Also in the separation circuit 31, a low-pass filter output (output voltage x), a band-pass filter output (output current i),
and the bypass filter output (output current 12) are utilized, respectively. Of course, the cutoff frequency and center frequency of the separation circuit 31 are set to a higher band than the cutoff frequency and center frequency of the separation circuit 21. Result 1
The bypass filter output of the separation circuit 21 is separated into a low-pass filter output, a band-pass filter output, and a bypass filter output of the separation circuit 31, resulting in two band-pass filter outputs and one bypass filter output.

The low-pass filter (band-pass filter) output, the band-pass filter output, and the bypass filter output of the separation circuit 31 are input to multipliers 34, 35, and 36, respectively, and the coefficients are as follows: k4. multiplied by k.

The outputs of the multipliers 24, 25, 34, 35, and 36 are input to an adder 41 and added. The output of the adder 41 is outputted to a speaker or the like via an amplifier (not shown) and emitted as sound.

Therefore, by adjusting the coefficient or 5 appropriately,
Desired frequency characteristics can be achieved.

The gyrator filter circuit of FIG. 1 is connected so that the frequency characteristic of the trap characteristic is realized as the output voltage y with respect to the signal voltage of the signal source S1. When the gyrator filter circuit is used as a bandpass filter, lowpass filter, or bypass filter, it is connected as shown in FIG. 3, FIG. 4, or FIG. 5, respectively.

In the case of FIG. 3, the signal source 51 is connected to one end of the capacitor 64, and one end of the capacitor C2 is connected to the reference voltage V cc /
Connected to 2. The other configurations are the same as in FIG. 2. In this case, the output voltage at each point'/+
X and the output current i(vi'x) are linear.

y=S1/(1+S-work+S-work S2) ・ ・ ・ ・ ・ (17) : c =< S L + S t s * ) /
< l + S x + s x s z )・・
・ ・ ・ (18) i-work=-S-work/ (1+s+SIS,) ・ ・ ・
・ ・ (19) i2=S・S2/ (1+s□+S・S2)・・
・ ・ ・ (20) That is, the output voltage y (same as the output current i) has a bandpass filter characteristic, and the output current i□ has a bypass filter characteristic. Therefore, the circuit shown in FIG. 3 can also be used as the separation circuit 21, 31 in FIG.

In contrast, in FIG. 4, one end of the capacitor 65 is connected to the reference voltage V cc /2.

The other configurations are the same as those in FIG. 2. In this case, the following equation holds.

y=1/ (1+81+S工S,) ・ (21) X” (1+82)/ (1+Sz+5zSz)・
・ ・ ・ ・ (22) x, = (1/rt) (St+5xS2]/(i+s, +
s, sz)・ ・ ・ ・ ・ (23) i*=(1/rz)(Sz)/(1+s,+81S,)
・ ・ ・ ・ ・ (24) In addition to the output voltage y having low-pass filter characteristics, the output current 12 has band-pass filter characteristics.

In the case of FIG. 5, the signal source 51 is connected to one end of the capacitor 65, and the base of the NPN transistor 52 is grounded. The other configurations are the same as in FIG. 2.

In this case, the following equation holds.

y=S□S2/ (1+81+S□S,)...
(25) z=-8,/(1+51+S,52)i,=(-1
/rt) (SiSz)/(1+S, +S, Sz)・・
・ ・ ・ (27) iz=(-1/ rz)(Sz+St 82)/(1+
S1+S1 S2) (28) The output voltage y and the output current i have bypass filter characteristics, and the output voltage X has bandpass filter characteristics.

The numerators of equations (24) (Fig. 4) and (26) (Fig. 5) are different from the cases (S, ) in equations (9) (Fig. 2) and (19) (Fig. 3). , S2. Therefore, although it is possible to achieve bandpass filter characteristics,
The level of the center frequency is lower than in the cases of FIGS. 2 and 3. Therefore, when the bandpass filter outputs of the gyrator filter circuits of FIGS. 4 and 5 are used in the separation circuits 21 and 31 of FIG. 1, it is necessary to add a circuit for compensating the output level.

Next, with reference to FIG. 6, a specific example of a configuration for transmitting the output of the bypass filter in the preceding stage to the low-pass filter in the succeeding stage will be described.

In FIG. 6, elements 52a to 63a and 71a,
72a represents the preceding stage separation circuit 21, and elements 52b to 63b, 71b, and 72b represent the subsequent stage separation circuit 31,
They are composed of each. Elements 52a to 63a and 5
2b to 63b are the elements 52 in FIGS. 2 to 5.
They correspond to 71a, 72a, 72a, and 63, respectively.
71b.

72b is a resistor.

Between these two isolation circuits are resistors 81 to 84, diodes 85, NPN)-transistors 86°87.89
, PNP transistor 88. Constant current source 90.91.92
A readout circuit 100 consisting of the following is inserted.

A low-pass filter output is taken out from the collector of the NPN transistor 53a of the separation circuit 21, and is supplied to the base of the NPN transistor 86 via the resistor 81.

Further, a trap filter output is taken out from the emitter of the NPN transistor 60a of the separation circuit 21, and is supplied to the base of the NPN transistor 87 via the resistor 82. If we assume that the low-pass filter output from the collector of the NPN transistor 53a is the same and the values of the resistors 81 and 83 are equal, then a value obtained by dividing the low-pass filter output by the resistors 81 and 83 is applied to the base of the NPN transistor 86. Therefore, the base voltage of the NPN transistor 86 becomes L/2. In addition, NPN transistors 86 and 87
Since the emitter of is differentially connected to the constant current source 90,
The base voltage of the NPN transistor 87 follows the base voltage of the NPN transistor 86 and becomes L/2.

On the other hand, the trap filter output can be considered to be a combination of the low-pass filter output and the bypass filter output H, so it can be expressed as L+H. now,
Assuming that the voltage at the emitter of the NPN transistor 89 connected to one end of the resistor 84 is A, and the values of the resistors 82 and 84 connected to the base of the NPN transistor 87 are equal, the difference between the trap filter output and the voltage A is resistance 82
Since the value divided by and 84 becomes the base voltage of the NPN transistor 87, the following equation holds true.

(L+H-A)/2=L/2 From the above formula, A=H. That is, the bypass filter output H of the separation circuit 21 can be taken from the emitter of the NPN transistor 89.

This bypass filter output is the NP of the next stage separation circuit 31.
It is supplied to the base of N transistor 52b. Therefore,
When the low-pass filter output of the separation circuit 31 is taken out from the collector of the NPN transistor 53b of the separation circuit 31, a frequency band from the cutoff frequency of the bypass filter of the separation circuit 21 to the cutoff frequency of the low-pass filter of the separation circuit 31 is separated. A bandpass filter output will be obtained.

〔Effect of the invention〕

As described above, according to the filter circuit of the present invention, the high frequency band output of the first separation circuit is further divided into frequency bands by the second separation circuit, so that the two separation circuits are used to filter the bandpass filter. can be realized. Therefore, signals in a large number of frequency bands can be separated with a small number of filter circuits. As a result, the configuration is simplified, the number of parts is small, and it is advantageous for low-cost IC implementation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of a graphic equalizer to which the filter circuit of the present invention is applied, and FIGS. A circuit diagram showing the configuration of an embodiment, FIG. 6 is a circuit diagram showing the configuration of another embodiment of the filter circuit of the present invention,
FIG. 7 is a block diagram showing the configuration of an example of a conventional graphic equalizer. 1...Low pass filters 2 to 4...Band pass filter 5...Bypass filters 6 to 10...Multiplier 11...Adder 21.31...Separation circuit 51...Signal source number Figure Figure Figure 4 Figure B Figure 7 Procedural Amendment (Master) June 18, 1991

Claims (1)

[Claims] A first separation circuit that separates high frequency band components of an input signal; A filter circuit comprising: a second separation circuit that separates band components.