JPS6175479A - Driving method of switched capacitor filter - Google Patents

Abstract

PURPOSE:To vary respective characteristic constants of a switched capacitor filter independently by varying only a clock frequency. CONSTITUTION:A gain coefficient H as one of characteristic constants of a band-pass filter BPF is expressed by an equation. When B, B', and B'' are selected with selection S1, S2, and S3, clocks CK31, CK32, and CK33 appear at clock input terminals phi1, phi2, and phi3. When the frequency of the clock CK33 is fS, a frequency-gain characteristic is V1. On the other hand, when C'' is selected with the selection switch S3 with the output of the 3rd counter 403, clocks CK31', CK32', and CK33' appear at the clock input terminals phi1, phi2, and phi3. Consequently, a gain characteristic V2 is obtained and only a coefficient H has a half characteristic. Namely, the clock frequency fS3 is a half as high as a basic clock frequency fS, so it is substituted in the equation to vary only the coefficient H.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a switch capacitor filter.
In particular, the present invention relates to a method for driving a switched capacitor filter suitable for arbitrarily and independently changing characteristic constants only by clock frequency.

[Background of the invention]

First, the equivalent resistance due to the switch capacitor will be briefly explained.

Parts 1E(a) to 1E(d) are intended to explain in principle how equivalent resistance can be obtained by a switched capacitor. In Figure 1, terminal ■.

Figure 1 (
When the analog switch (hereinafter referred to as switch) 8Wz such as MO8T is turned on as shown in a), the capacitor C has a charge Q! expressed as Q2=Cv2. is being charged. In this state, when the switch SW2 is turned on as shown in Fig. 1(b), the charge on the capacitor C becomes Ql=Cvl (F), and the charge ΔQ, which is the difference between Qt and Qz, flows into the terminal ■. It turns out. That is, the charge ΔQ is as follows.

ΔQ-(h-Qz=C(Vt-Vx)"・
(1) Here, if the switch SWz is turned on again as shown in FIG. 1(C), the charge on the capacitor C becomes Qz=CVz, and the charge is the same as the charge ΔQ shown in equation a). It is clear that the current flows from the capacitor C to the terminal ■.

Therefore, if the above operation is repeated with a period T,
Charge 4Q moves through capacitor C with period T), and as a result, current i expressed by equation 0) flows from terminal 2 to terminal 2 on an average basis.

1=jQ/T=C(Vl-Vz)/T ・-・・+
(2) On the other hand, when the voltages at both ends of the resistor R are vl and V, respectively, as shown in FIG. 2(d), the current i3 flowing through the resistor R is as follows.

in = (Vl-V2)/R-・”・”-(3)
If i=i, then the following equation (4) is obtained from equations (2) and (3).

几=T/C=1/(fC)・・・・・・・・・
(4) However, f is the switching frequency.

In this way, the equivalent resistance of a switched capacitor is determined by the ratio between the capacitance value (C) of capacitor C and the switching period T, and by changing the period T, the equivalent resistance can be determined without changing the capacitance value of capacitor C. It can be changed to

The switched capacitor circuit described above is a basic circuit, but in reality, circuits such as those shown in FIGS. 1(e) and 1(f), which are less susceptible to the effects of parasitic capacitance, are used. In FIG. 1 (f), φ indicates an inverted version of the clock.

The switch capacitor circuit was created by using the above switch capacitor circuit as the resistance element of the filter circuit.
It's a filter. Depending on the application of the switched capacitor filter, it may be necessary to arbitrarily change the filter characteristic constants.

- Conventionally, as a method of varying the characteristic constant of a switched capacitor filter, for example,
As shown in Japanese Patent No. 6, a filter is known in which the switching period of each switching element is set to vary the filter characteristics. However, this method has the disadvantage that all the switch groups must be individually controlled in order to change the characteristic constants independently.

[Purpose of the invention]

The purpose of the present invention is to provide a switch capacitor that allows each characteristic constant of a filter to be changed independently only by changing the clock frequency.
Niraru provides a method for driving the filter.

[Summary of the invention]

In order to achieve the above object, the present invention aims to improve the center frequency J'O, which is a characteristic constant of a switched capacitor filter.
+The switch group is roughly divided into three, and these are controlled independently so that the selectivity Q and gain coefficient H can be arbitrarily and independently changed only by the clock frequency.

That is, the present invention provides a switched capacitor filter in which a plurality of switched capacitor circuits each including an analog switch and a capacitor driven by a clock signal of a predetermined frequency are used as resistance elements of the filter circuit. is divided into a plurality of groups, and the clock frequency element included in the characteristic expression of the filter characteristic constant to be changed is changed for each group.One characteristic constant of the filter is individually changed, The present invention is also characterized in that other characteristic constants including the same element as the clock frequency element to be changed are changed accordingly.

[Embodiments of the invention]

Next, embodiments of a method for driving a switched capacitor filter according to the present invention will be described with reference to the drawings.

1.First embodiment- A first embodiment of the present invention is shown in FIGS. 1 to 5.

As shown in FIG. 1, the switched capacitor equivalent resistance SC1 is composed of a switch S W t =8 Ws and a capacitor Crt. The same applies to the other switched capacitor equivalent resistances 802, SCm, and SC4. Cs, Cx are integrating capacitors 100 and 20
0 is an operational amplifier. A switched capacitor filter is equivalent to replacing the resistance element of an active 7-ilter with a switched capacitor equivalent resistance.

Switches 8Wt and 8W2 are ONL when clock input terminal φl is @1#, switches 8W1 and SWa
is turned on when the clock input terminal φl is 11". The switches SWa and 8W7 are turned on when the clock input terminal φ2 is 11".
When the clock input terminal φ2 is @1, ONL, the switch 8Ws, and the SW circuit are turned on. Furthermore, switch 8W...

5W12m 8W1g and swl are ONL when the clock input terminal φ3 is 11", and the switch 5W1s.

5Ws4. SW1? and 5Wta are turned ON when the clock input terminal φ3 is @1''. In other words, the switched capacitor equivalent resistors SC1 and SC2 operate by applying independent clocks to the clock input terminals φ1 and φ1 and φ2 and φ1. SCs and SC4 operate by applying the same clock to clock input terminals φ3 and φ1.

In the circuit shown in FIG. 1, the output of the operational amplifier 100 is the output of a second-order bandpass filter, and the output of the operational amplifier 200 is the output of the second-order low-pass filter.

First, the bandpass filter will be explained.

The following equation shows the transfer function of the bandpass filter.

However, ω0 : Angular frequency Q : Selectivity H : Gain coefficient In the circuit of FIG. φ3
and φ3 are divided into three groups and given. Than this,
The characteristic constant of the bandpass filter can be expressed by the following equation.

Here, in the circuit of FIG. 1, 1.1 is the clock frequency applied to the clock input terminals φl and φ1, L2 is the clock frequency applied to the clock input terminals φ2 and φ2, f
, 3 are clock frequencies given to the clock input terminals φ3 and φ3. Further, the clock input terminal φ1 provides an inverted clock to φ1, φ2 to φ2, and φ3 to φ3.

First, the case of changing the center frequency fo will be explained. Focusing on the above equation (6), the center frequency f0 is expressed as a function of the capacitors Cr3 s Cr4 m c and C2, and also as a function of the clock frequency fax. That is, in order to arbitrarily change the center frequency fo, the capacitor Crs s which is a parameter of equation (6)
It can be understood that in addition to changing the values of Cr4 sc and C2, it can be changed by arbitrarily changing the clock frequency fsa. The clock frequency f mentioned above
Since ms is also a parameter of the selectivity Q according to equation ('1), the selectivity Q is also changed at the same time. Therefore, in order to change only the center frequency fo without changing the selectivity Q, 1.2 must also be changed to match the fax. Furthermore, f,! If you change , you will also change the gain coefficient H according to equation (8), so you will also have to change f and curtain according to Ls. Considering the above, FIG. 2(a) shows a clock wiring diagram for changing only the center frequency fo.

In FIG. 2(a), the clock input terminal φ turtle.

For φ2 and φ3, the basic clock frequency f shown in FIG.
The clock CK s of φ1. φ2 and φ3 K,
A clock CK4 is provided by inverting the clock CKs.

The frequency-gain characteristic at this time is shown by Vt in FIG. 4(a). In vl in FIG. 4(a), the center frequency fo is 10
An example of 0Hz is shown. On the other hand, the clock CKs whose frequency is if.

CK a as φl, φ2 . φ3 and φ1. φ2゜φ
3, as shown in v2 in Fig. 4(a), only the center frequency fo is 5 which is 1 times vl in Fig. 4(a).
It becomes 0Hz. It is easy to understand that if this is substituted for the clock frequency, fo becomes 1 times. Furthermore, a clock CKs with a frequency of 2f.

CKz to φ1. φ2. φ3 and φ1. φ2. When given to φ3, the fourth factor (as shown in v3 in the fathom), the center frequency fo becomes 200H2, which is twice V in FIG. 4(a).

It is also clear that fo can be doubled by substituting φ3 and the clock frequency of φ3 into equation (6). Confirming the above, the clock input terminal φ1. φ2 and φ3
and φ1. By giving clocks with the same period to φ2 and φ3 and varying the frequency of this clock,
It will be understood that only the center frequency fo can be arbitrarily varied.

Table 1 shows the relationship between the clock input terminals explained above, the clock, and the correspondence of their effects.

Next, an example of changing only the selectivity Q will be explained.

Focusing on (7) 2 above, the selectivity Q can be expressed as a function of the clock frequency Lx and fms.

That is, in order to arbitrarily change the selectivity Q, f ml
This can be achieved by arbitrarily changing the fax number and fax number. However, changing f,3 also changes the center frequency f, so in order to change only the selectivity Q, it is better to change the fax. However, f,2
(as described above) is also related to the gain coefficient H, so f,1 must also be changed in accordance with f12. FIG. 2(b) shows a clock wiring diagram for changing only Q.

In FIG. 2(b), clock input terminal φ1. Clock CKg is applied to φ2 and φ3, and φ1. The frequency-gain characteristic when the clock CK+t- is applied to φ2 and φ3 is shown in vl in FIG. 4(b). This is v in Figure 4(a).
It is exactly the same as l. On the other hand, clock CKs is applied to clock input terminals φ1 and φ2.

By applying a clock CKs to φ1 and φ2, and further applying a clock CK1% to φ3 and a clock CKz to φ3, it is possible to obtain a characteristic in which only the selectivity Q is doubled, as shown in ■2' in Fig. 4(b). . Furthermore, leaving φ3 and φ3 as they are, clocks CK1, φ1 and φ2 are applied to φ1 and φ2.
When clock CK 2 is applied to 2 and 2, the result is shown in Fig. 4(b).
As shown in V3', only the selectivity Q can obtain a characteristic of 1 times. From the above, it can be understood that by making the clock terminals φl, φ2, and φ1 and φ2 bare, the clock can be arbitrarily varied, and only the selectivity Q can be arbitrarily varied. Table 2 shows the relationship between each clock input terminal and the clock described above and the correspondence of their effects.

Table 2 Next, an example in which only the gain coefficient H is changed will be explained. Focusing on (8) 2 above, the gain coefficient H is a function of the clock frequencies Lt and Lx. That is, the gain coefficient H can be arbitrarily changed by arbitrarily changing Lx and f,2. Furthermore (8
) By arbitrarily changing only Lt, the gain coefficient H can be changed independently. The wiring diagram of the clock at this time is shown in FIG. 2(e).

Since the clock frequency Lt relates only to the gain coefficient H of the characteristic equation of the bandpass filter, the gain coefficient H can be arbitrarily and independently varied by arbitrarily varying fm1. 1st
Clock input terminal φ1 of the circuit shown in the figure. φ2. φ3 and φ1
．． φ2. The frequency-gain characteristics when clocks CKs and CK4 are applied to φ3 are shown in vl in FIG. 4(C). This is exactly the same as vl in FIG.
When CK3 and CK4 of frequency f, which are basic clocks, are given to , respectively, and clocks CKs and CKa of frequency Σf1 are given to φ1 and φ1, v2" in FIG. 4(C) is given.
As shown in , the gain coefficient H becomes 7 times.

Furthermore, a clock CK1 with a frequency of 2f is applied to φ1 and φl.
and CKz, the gain coefficient H doubles as shown in Fig. 4(c) cD V 3''.
It can be understood that by arbitrarily varying the clock frequency of and φl, only the gain coefficient H can be arbitrarily varied. Table 3 shows the relationship between each clock input terminal and the clock described above and the correspondence of their effects.

Although the bandpass filter in the circuit shown in FIG. 1 has been described above in Table 3, the lowpass filter will now be described.

The transfer function of the low-pass filter is shown in the following equation.

ω0: Angular frequency ゛Q: Selectivity H: Cutoff frequency tlf, which is a characteristic constant of the gain coefficient low-pass filter,
is expressed in exactly the same way as Equation (6) for a bandpass filter, so Equation (6) is used by replacing fo with f. Moreover, the selectivity Q is exactly the same as the equation (7). However, in the case of a low-pass filter, the gain coefficient H can be expressed by the following equation.

First, an example will be described in which only the cutoff wave number f is changed.

Focusing on equation (6), just like the bandpass filter, by arbitrarily changing the clock frequency fax)
, shear fault wave number f. can be changed arbitrarily.

FIG. 5(a) shows frequency-gain characteristics when the cutoff layer wave number f is arbitrarily changed. That is, in the circuit of FIG. 1, for the characteristic v4 when the clock CKs is applied to the clock input terminals φl, φ2 and φ3, and the clock CK4 is applied to the clock input terminals φtmφ2 and φ3, φ1. The characteristics in which the clock CKs is applied to φ2 and φ3, and the clock CKa is applied to φ1° and φ2 and φ3 are Vs, and the cutoff layer wave number f becomes 1 times. Furthermore, a clock CKt with a frequency of 2f is applied to φl, φ2, and φ3, and a clock C1 is applied to φl, φ2, and φ3.
The characteristics of each inverted clock CK2 are v
6, indicating that the cutoff wave number f is doubled. The above relationships are summarized in Table 4.

Table 4 Next, an example in which only the selectivity Q is changed will be described. Focusing on equation (7), just like the bandpass filter, only the selectivity Q can be changed arbitrarily by leaving the clock input terminals φ1 and φ2 and φ1 and φ2 bare in the circuit shown in FIG. 1 and varying the clock arbitrarily. It can be changed to Figure 5 (b
) shows the frequency-gain characteristics with the selectivity Q arbitrarily changed.

That is, with respect to the characteristic shown by v4 in FIG. 5(b), the characteristic when the clock CKs is applied to the clock input terminals φ1 and φ2, and the clock CKa is applied to φl and φ2 is V5'.
Selectivity Q is doubled. Furthermore, it can be seen that the characteristic when clock CK* is applied to 1φl and φ3, and clock CK2 is applied to φ1 and φ2, respectively, is v6', and the selectivity Q in this case is Σ times that of v4. The above relationships t are summarized in Table 5.

Table 5 Next, an example in which only the gain coefficient H is changed will be described.

Focusing on the α0 formula, the gain coefficient H is the clock frequency fa
+ and f, a function of 4. In order to arbitrarily change the gain coefficient H, f, 1 and f64 may be changed arbitrarily. Furthermore, when changing only the gain coefficient H independently, (
6), (7) and (10), the clock frequency Lx
Needless to say, it is possible to do this by changing only the following. FIG. 5(C) shows an example in which only the gain coefficient H is changed.

That is, with respect to the characteristics shown in 4 in FIG. 5(C), the characteristics when clock CK5 is applied to clock input terminal φ1 and clock CKa is applied to φ1 are as shown in V5'' in FIG. 5(C).
The gain coefficient H is multiplied by i.

Furthermore, a clock CK1, φ1 is input to the clock input terminal φ1.
When the clock cKz is applied to , the characteristic is v6''), the gain coefficient H is doubled. The above relationship is shown in Table 6.

Table 6 Note that the clock frequency can be controlled in the same manner not only for the piquat type filter which is an embodiment of the present invention but also for the leapfrog type filter.
Any filter characteristic of Hl) can be obtained.

By controlling the clock frequency, arbitrary filter characteristics can be obtained not only for Saraniha filters, low-pass filters, and band-pass filters, but also for bypass filters as well.

Thus, according to this embodiment, the center frequency, cutoff frequency for selectivity Q, and gain coefficient H, which are characteristic constants of the filter, can be arbitrarily varied by the external clock. When this filter is made into LS/1, whereas in the past, only the center frequency could be varied in the characteristics of a manufactured filter, the characteristic constants can be changed arbitrarily, and it is possible to sufficiently respond to changes in characteristics. Furthermore, since the capacitance value of the capacitor, which is a circuit constant, does not change, there is no need to add a capacitor for changing the characteristic constant. Therefore, the chip area is small, high integration is possible, and since no control terminal for switching capacitors is required, the number of unnecessary bins can be reduced.

-Second example- A second embodiment of the present invention is shown in FIGS. 6 to 9.

In this second embodiment, the same or overlapping parts as those shown in FIGS. 1 to 5 are given the same reference numerals and will be described below.

This second embodiment uses a group of switches so that the characteristic constants of the switched capacitor filter, such as the center frequency (fl)1 selectivity Q and gain coefficient H, can be arbitrarily and independently changed in one place using only the clock frequency. The switching capacitor filter is roughly divided into three parts, and changes in clock frequency are controlled with priority.The switched capacitor filter itself is the same as in the first embodiment, so a description thereof will be omitted.

In FIG. 6, numeral 300 indicates a clock signal generation circuit which generates a basic clock frequency f. This basic clock signal is sequentially frequency-divided by the continuously connected first counter 401, second counter 402, and third counter 403, and the frequency of each manual changeover selection switch 81 s 82 e s
s and each switched capacitor equivalent resistance circuit 5C1s 8Cx , 8Cs , S via the inverter 500
C4 clock input terminal φ1. φ1. φ2. φ2. φ3
．． It is φ3.

First, the case of changing the center frequency f will be explained. Focusing on the above equation (6), the center frequency f0 is a function of the capacitors Cr3, 0v4, CI and C2),
Further, it is expressed as a function of the clock frequency Ls. That is, in order to arbitrarily change the center frequency fo, (6)
Capacitor Cra g Cr4, which is a parameter of Eq.
In addition to changing the values of Ct and C2, the clock frequency f
It can be understood that υ can be changed by arbitrarily changing as. The clock frequency fax mentioned above is ('I)
Since the formula is also a parameter for the selectivity Q, the selectivity Q will also be changed at the same time. Therefore, in order to change only the center frequency f without changing the selectivity Q, 1.2
must also be changed to match the fax. Furthermore, if 1.2 is changed, the gain coefficient H will also be changed according to equation (8), so fms must also be changed in accordance with Ls.

Therefore, a counter 401140 that divides the clock signal is used.
2.403 are connected in cascade, and the output of the first counter 401 is applied to the clock input terminals φ3 and φ3. That is, when the frequencies of the clock input terminals φ3 and φ3 are changed, the counters 402 and 403 in the next stage and subsequent stages follow the above change, so that their output frequencies are automatically changed. Therefore, only the center frequency fo can be changed independently at one location. This will be explained in detail below using the clock waveform shown in FIG.

In the circuit of FIG. 6, selection switches 81°S2 and S
3, the output OB of counters 401, 402 and 403,
By selecting B' and B //, the clock input terminals φ1. Clocks CKtt, CK12 and CKta shown in FIG. 7(a) K are given to φ2 and φ3, and clocks ('Ktt, CK1
2 and CKss are inverted and provided by the inverter 500. Here, the frequency of the clock CKn is assumed to be f. The frequency-gain characteristic at this time is
Figure (a) shows VxK. vl in FIG. 8(a) shows an example in which the center frequency fo is 100 HzO. On the contrary,
When the selection switch S1 selects the first stage's neutral power (#)C, the clocks CKo' and CK shown in FIG.
12' and CKss' frequencies are each multiplied by 7 according to CKII'. The frequency-gain characteristic at this time is shown in v2 in Fig. 8(a), where only the center frequency fo is at the 8th
It is clear that the frequency becomes 50 Hz, which is one times the Vs in FIG. This can be easily understood by substituting equation (6) since the clock frequency J'ss is one time the basic clock frequency f.

Next, an example of changing only the selectivity Q will be described. Focusing on the above equation (7), the selectivity Q can be expressed as a function of the clock frequencies fas and fms. That is, in order to arbitrarily change the selectivity Q, f, 2 and f
This can be achieved by arbitrarily changing ax. However, if we change,f,3, the center frequency fo
Therefore, in order to change only the selectivity Q, it is better to change f,2. However, as mentioned above, f,2 is also related to the gain coefficient H, so j
'sl must also be changed to match J' m z.

Therefore, in the circuit shown in FIG. 6, the output of the second counter 402 is applied to the clock input terminals φ and φ2. That is, when the frequency applied to the clock input terminals φ2 and φ2 is changed, the frequency of the third counter 403 is automatically changed to follow the above change, and only the selectivity Q can be changed independently at one place. This will be explained in detail below using the clock waveform shown in FIG.

In the circuit of FIG. 1, selection switches Sl, 82 and S3
From the outputs of counters 401, 402 and 403, B,
By selecting B' and B", the clock CK shown in FIG. 7(C) is input to the clock input terminals φ1, φ2, and φ3.
zt, CKzz and CKxs are given. Here, the frequency of the clock CKu is f.

shall be. The frequency-gain characteristics at this time are shown in Figure 8(b).
It is shown in vl. On the other hand, when C' is selected from the output of the second counter 402 by the selection switch S2, φ1
．． Figure 7 (clock CKxi shown in
, CKzx' and CKzs' are given. This makes it possible to obtain a characteristic in which only the selectivity Q is doubled, as shown by V2' in FIG. 8(b).

This can be easily understood by substituting into equation (7) since the clock frequency fax is 1.01 times the basic tally clock frequency.

Next, an example in which only the gain coefficient H is changed will be described. Focusing on the above equation (8), the gain coefficient H can be independently changed at one location by arbitrarily changing only the clock frequency f81.

Therefore, in the circuit shown in FIG. 6, the output of the third kakunta 403 is applied to the clock input terminals φ1 and φ1. That is, since the output of the third counter 403 is applied only to the clock input terminals φ1 and φ1, h indicates that only the frequencies applied to the clock input terminals φ1 and φ1 can be changed independently. Therefore, formula (8),
Only the gain factor H can be changed independently. This will be explained in detail below using the clock waveform shown in FIG.

In the circuit of FIG. 6, selection switches S1, S2 and S
By selecting 2, 9, B, B', and B'', CKst, CKaz, and CKss are applied to the clock input terminals φ1, φ2, and φ3 as shown in FIG. 7(e)K. Here, the clock CKss Let the frequency of be f.

The frequency-gain characteristic at this time is shown at Vl in FIG. 8(C). On the other hand, when the selection switch S3 selects the output of the third capunter 403, the clock input terminal φ1. Clocks CKst, CKaz and CKss shown in FIG. 7(f) are applied to φ2 and φ8. From this, it is possible to obtain a characteristic in which only the gain coefficient H is 1 times, as shown in (2) of FIG. 8(C).

This can be understood by substituting into equation (8) since the clock frequency Lx is one time the basic clock frequency f.

As described above, by giving priority to changing the clock frequency, the characteristic constant of the filter can be changed independently at one location. That is, to summarize, when the clock frequency for changing %fo is changed, the clock frequency for changing Q and H is also changed. Furthermore, when the clock frequency for changing Q is changed, the clock frequency for changing H is similarly changed, but the clock frequency for changing fo is not changed. Even if you change the clock frequency for H change, fo
And the clock frequency for Q change is not changed.

FIG. 4 is an inclusive diagram showing the priority of changing the clock frequency according to the present invention.

The present invention can be sufficiently applied to low-pass filters, bypass filters, etc. other than the band-pass filters described in the embodiments of the present invention.

Furthermore, it goes without saying that the invention can be applied not only to piquat type filters but also to leapflock type filters.

〔Effect of the invention〕

As described above, according to the present invention, each characteristic constant of the switched capacitor filter can be changed independently by changing only the clock frequency.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of a switched capacitor filter, and Figure 2 is a block diagram showing the embodiment of Figure 1.
(a) is a block diagram when only the center frequency f is changed; (b) is a block diagram when only the selectivity Q is changed;
(C) is a block diagram when only the gain H is changed;
The figure is a time chart of the clock signal applied to each clock input terminal, FIG. 4(a) is a characteristic diagram showing changes in the center frequency fo of the bandpass filter, and FIG. (C) is a characteristic diagram showing the change in the gain H, FIG. , (C) is a characteristic diagram showing the change in the gain H, FIG. 6 is a block diagram showing the second embodiment, FIG. 7 is a time chart of the clock signal applied to each block input terminal, and FIG. 8 ( a) is the center frequency f of the bandpass filter
, Φ) is a characteristic diagram showing changes in selectivity Q, (C) is a characteristic diagram showing changes in gain H, FIG. 9 is an explanatory diagram showing priority eaves, FIG. 10 is the switch
FIG. 3 is an explanatory diagram of capacitor equivalent resistance. SC1~SC4...Switch capacitor equivalent resistance, S Wl-S Wzo...Analog switch, CF
1~C74... Capacitor, CL, C2... Integrating capacitor, Figure 2 (b, 1 (C) F?Ezuency
Hre+1ueThcy - Figure 6 CKI3'CK23' Kaya Figure 8 also Figure 10

Claims (1)

[Claims] 1. In a switched capacitor filter in which a plurality of switched capacitor circuits each consisting of an analog switch and a capacitor driven by a clock signal of a predetermined frequency are used as resistance elements of the filter circuit, the plurality of switched capacitor circuits are By dividing the filter into groups and changing the clock frequency element included in the characteristic expression of the filter characteristic constant to be changed for each group, one characteristic constant of the filter is individually changed, and at the same time, the characteristic constant of the filter is changed individually. A method for driving a switched capacitor filter, characterized in that a clock frequency element and other characteristic constants having the same element are changed in accordance with the same.