DD211678A1 - FILTER CIRCUIT CONSISTING OF BAND PASS BASICS WITH SWITCHED CAPACITORS - Google Patents

Abstract

The invention relates to an electrical filter circuit using switched capacitor band-pass bases. The object of the invention is to provide higher-level band-pass circuits based on this principle, which can be monolithically integrated with economically justifiable expense. The essence of the invention is that the arrangement of a bandpass base member has been extended by a feedback branch with a switched capacitor for the purpose of increasing the gain. In addition, the signal is input via at least two switched capacitors, which allow the implementation of small coupling values by subtraction or the realization of any signs of the couplings in multi-coupled circuits (MLF). Possible fields of application of the invention relate to bandpasses in the LF range with displaceable band center frequency for spectral analysis and for selective level increase.

Description

Title of the invention;

Mlterschaltung consisting of bandpass basics with switched capacitors

Field of application of the invention;

The invention relates to an electrical fi lterschaltung for the ID? Area that works as a bandpass. Ba the Bandmittenfrequenz can be externally set by selecting the clock frequency, the circuit for purposes of spectral analysis (real-time operation) as well as for selective level increase applicable applications are the acoustic Measuring technology, the oscillation measuring technique, the communications technology and the control technology "The circuit according to the invention can be fully integrated",

Characteristic of the known technical solutions

From the literature (U _e W _{e e} Bruggers Switched-Capacitor Pilter Design for Gonnaunication Systems, European Conference on Circuit Theory and Design, Warsaw 1980, Digest of Technical Papers, pp. 73-84), the circuit of a bandpass basic link is switched Capacitors, two-phase clock and an amplifier known. For a large ratio of clock to band center frequency, the circuit leads to a very large ratio of maximum to minimum capacitance value, which is why it can not be monolithically integrated. Sine implementation with discrete components, however, is impossible for economic reasons.

Object of the invention

The aim of the invention is ea _f an economical, monolithic integrated design of Bandpaßschaltungen higher degrees with in Zweiphasentakt.geschalteten capacitors with a high ratio of! Clock to mid-band frequency (ca * 100) to allow «

of

It is an object of the present invention to reduce the ratio of maximum to minimum capacitance value to practically realizable values given a large ratio of clock to band center frequency, which can be achieved by monolithic integration. Moreover, the resulting attenuation distortion should be practically negligible Furthermore, narrowband bandpass filters with switched capacitors can be realized. The features of the invention are therein _? .in that bandpass basic element a periodically _umpoled} capacitor connected between the output and the non-connected between the two capacitors lying node is connected, resulting in a Signalmitkopplung results _β

Another feature of the invention is that the signal coupling is done via at least two switched capacitors which cause a difference in the input voltage and allow the realization of small meter constants of the transfer function. Another feature of the invention is that at least two bandpass bases combined, and a feedback from the output of the second bandpass basic element to the already mentioned node of the first bandpass basic element is present. The respective switches of the first and the second bandpass basic element are in the same clock half-period in opposite switching state Feedback is via a switched capacitor «, the switches are used as periodically switched on and off

Transistors running «,

With this arrangement, higher-order bandpasses can be realized with minimal attenuation distortion.

The invention will be explained in more detail below using an exemplary embodiment. In the accompanying drawing, j

1 shows the representation of a bandpass base member and

Figure 2 shows the interconnection of two bandpass basics to a fourth-order bandpass filter

In Figure 1, the signal to be filtered is supplied to the input E of the bandpass basic element BP. From the input E, the series connection of two switches S1, S2 leads to the node K, which is connected via the capacitor C1 to the inverting input of an operational amplifier Switch S1, S2 leads a capacitor C4 to ground * In addition branches from the input E, a series circuit consisting of the two switches S3j S4, which also leads to ground · From the connection point of the switch 33 * S4 branches off the capacitor C5, whose other terminal is connected to both the ground leading switch S5 and the switch S6 whose second connection leads to node K " The non-inverting input of the operational amplifier is grounded" Its output forms the output A of the bandpass basic element _β from the output A leads Connection via the capacitor G2 to the node K and another connection via a series circuit, be Standing from the switch S11 and the capacitor C6, to the connection point of the switches S5, S6 "From the connection point of switch S11 and capacitor C6 performs a connection via the switch S12 to ground · Finally, there is another outgoing from the output A connection to a series circuit of switch S8, capacitor 03 and switch S10 leads and ends at the inverting input of the operational amplifier · The two terminals of

Capacitor C 3 lead separately via a switch S7, S9 to ground «

Characteristic of the puncture of the bandpass basic element BP is that all switches are controlled in groups from a not belonging to the invention clock "Here, the switches can be classified into two groups" In the first half cycle of! Clock, for example, the switches S1, S3 _S S5 _? ST, S9 and S11 are closed, while the switches S2, S4, S6, S8, S10 and S12 are open. In the second half-period of the clock, the closed switches are opened and the opened switches are closed.

Due to the puncturing principle of the switched capacitors in the underlying circuit, it is possible to replace the unsuitable for integration ohmic resistances by MOS transistors and capacitors «The influence of the unavoidable, parasitic capacitances of the switching transistors is minimized by the described switch assembly * The circuit shown represents an analog sampling circuit «Its transfer function H (ζ) is in the z range

HC3 (ä <i) / (CtCz) - & '£ / CW-i h

+ C3 (cn + Cs * Cz) I (O-Cz)

In this Besiehung the capacitors CI, _βββ , C6 and Y er shift operator ζ enter, "The Yer shift operator ζ results from the imaginary unit j, the signal frequency f, the clock frequency f and the circle constant Ji

= e

For a practical dimensioning when specifying the maximum capacitance C, the bandmix circle frequency A ^ ₀ J of the basic quality Q, the quality Q, the counter constant k and the ratio V, which represents the quotient of clock frequency f and band center frequency f, the following equations result?

Q.-a »Z / r _c Yc j

2.-IL. >

The above sizing is based on minimizing the deviation from the analog target transfer function H ^ Cj ^ "),

⁷ (t & J +

where the normalized angular frequency C & - is taken into account.

FIG. 2 shows the interconnection of two bandpass basic elements BP and BP ¹ to a fourth-order bandpass filter. In this case, the output A of the bandpass basic element BP is connected to the input S 'of the bandpass filter

Band-pass basic element BP 'connected. Apart from the devices belonging to the bandpass basic elements BP and BP', a connection is found from the output A ^{f of} the overall arrangement formed by the output of the operational amplifier of bandpass base element BP ' , which via a series circuit, consisting of switch S13> capacitor C7 and switch S15, to node K of the bandpass element BP leads «It consist of two terminals of the capacitor C7 via a respective switch 814 and S16 'connections to ground« It should be noted that the switches S1, S3j S5, S7 * S9 and S11 of the bandpass basic element BP and the switches S1 ' ₉ 33% S5', S '', 39 "and S11» of the bandpass basic element BP 'are driven in the opposite direction Issue concerns the switches S2 ₉ S4 _? S6, S8, SIO and S12 and the switches S2 ^f , S4 ' _s 36% SS', SIO 'and S12 ^f .

Also, the switches S13, »», S16 are driven by the same clock as all the switches of the two bandpass basic elements BP and BP '. In this case, the switches S13 and S15 each have the same switching state as the switches S2, «« *, S12 and the switches S14 and S16 have the same switching state as the switches SI ₅ V ··, S11 ·

The interconnection of the two bandpass basic elements BP and BP ^? enables the realization of sensitivity-optimized _s multi-coupled (MLP) circuits *

Claims (2)

He made an announcement 1 "PiIterschaltung consisting of band-pass basic elements with switched capacitors, each alternately a part of the electronic switch open and the other switches are closed and opening and closing the switch is periodically and against each other delayed, with an operational amplifier j whose non-inverting input is grounded and whose inverting input via a series circuit of two capacitors leads to its output, each with a switched capacitor at the input and between the output and inverting input of the operational amplifier, characterized in that in the bandpass basic element (BP) from the output (A) of the operational amplifier, a series circuit consisting of switch (SH) ₅ capacitor (C6) and switch (So) ₅ to the node (K), which is formed by the Yerbindungspunkt of the capacitors (C1, C2), which in known manner the output (A) of Operational amplifier with its inverting input connect that of both terminals of the capacitor (Cö) via a respective switch (35; S12) has a connection to ground, that from the output of the operational amplifier, a further series circuit consisting of switch (38), the known capacitor (C3) and switch (S10) leads to the inverting input that both terminals of the capacitor (G3) via a switch (57, S9) are connected to earth in each case in such a way that from the input (E) a series connection of two switches (S1, S2) leads to the node (K), that the connection point of the switches (S1, S2) over the known capacitor (C4) is connected to ground, that from the input (S) a further series circuit consisting of the switches (S3, S4) leads to ground, that the Yerbindungspunkt the switch (35, 36) via the capacitor (05) to the Yerbindungspunkt of the switches (S3; S4) leads that in the first half-period of the clock switches (S1; 'S3;S5;S7;S9; 311) are closed and the switches (S2; S4; S6; SS; S10; S12). are open and that in the second half-period of the clock a reversal of the state of preservation, it "exists," The circuit according to item "I _{5 is} characterized by the fact that the output (A) 'of a bandpass basic element (BP) is connected to the input (E') of a second bandpass basic element (BP ^r ) having the same construction Like the bandpass basic element (BP), j has the output (A ') of the second bandpass basic element (BP') connected in series with a switch (313), a capacitor (C7) and a switch (S15) with the node (31). K) of the first bandpass base member (BP) is connected, that the two terminals of the capacitor (C7) via the switches (S14, S16) lead to ground ^ that the corresponding switches of the bandpass base member (BP) and the bandpass filter Each of the switches (S14; S16) has the same switching state as the switches (S1; S3; S5; S7; S9; S11) and the switches (S13; S15) each have the same switching state how the switches (S2; S4; S6; S8; S10; S12) have « 2 sheets of drawings *