Title of Invention

AN ELECTRONIC CIRCUIT TO GENERATE SHARP CUT-OFF FREQUENCY RESPONSE

Abstract

This invention relates to an electronic circuit to generate a sharp cut-off frequency response. In the present invention a circuit (A) using active and passive components gives a sharp cut-off frequency response (fc). A prototype HPF and a prototyupe LPF (i.e. any existing HPF and LPF filters) has been used and the output of both the filters are compared in a comparator and the output of that comparator is given to a switch which passes an input signal according to the comparator pulse.

Full Text

The invention relates to an electronic circuit to generate a sharp cut-off frequency response. An electronic filter is often a frequency selective circuit that passes a specified band of frequency and bolls or alternates signal or frequency outside this band. The filters are classified as analog and digital dependant upon the technique used and passive and active depending upon the component used. There are disadvantages with the present system of filters. One of the main disadvanteges of the fM"esent system of fitters using passive active components and also using digital technique wilt not give a sharp cut-off frequency response. Another disadvantages associated with the passive filters is that these will not produce a sharp cut-off frequency response because the linear components will not produce any discontinuities in their response. Yet another disadvantage associated with the passive filters in that these will only work t high frequencies i.e. at radio frequencies. At audio frequencies inductor becomes large, heavy and expensive. For tow frequency application more number of turns are required which in turn adds to the series resistance degrading inductor performance. Still another disadvantages associated with the active fitter is that the high frequency response is limited by the Gain Bandwidth (GBW) product and slow rate of the op-amp. Further disadvantages associated with the active filters is that high frequency active filters are more expensive than passive filters. These filters gives a flat response but not the sharp cut-off frequency response. Yet a further disadvantages associated with the digital filters is that the digital filter realization involves ^ding the co-effacements by using standard algorithms and time required to process these algorithms causes a delay which Inurns restricts to the sharp cut-off. Therefore the main object of the present invention is to provide a simple, effective ship cut-off fitter circuit which is less expensive and gives sharp- cut off frequency. Another object of the present invention of a sharp cut-off circuit which uses very few components. Yet another object of the present invention of a sharp cut-off fitter circuit which gives a linear phase response. According to the present invention there is provided an electronic circuit consisting of a prototype low pass filter (LPF) (2), a High Pass Filter (HPF) (3) and a comparator (4) to generate sharp cut-off frequency response (fi:) for control of opening or closing a switch (5) to allow ingress of the signal to an electrical device in an automotive mode, wherein in the circuit a LPF (2) is connected to the inverting terminal (9) of the comparator (4) and a HPF (3) is connected to the non inverting terminal (10) of the comparator or the said LPF and HPF are connected in reverse order terminal of the comparator, the input signal (1) to the circuit being applied to both the LPF, HPF and also to the switch (5), the output of the comparator being connected to the switch which allow the input signal to ingress or to be blocked according to the comparator output, the comparator generates cut-off frequency by differentia the output of LPF and HPF for a frequency of the input s\gnat\ and activate the switch to pass input signal to Ihe switch when the difference between output of LPF and HPF are positive or zero but block the input signal to the switch when such difference is negative. The nature of the Invention, Its objective and further advantages residing In the same will be apparent from the following description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawings :- Fig. 1 shows a block diagram of a high pass filter circuit (A); Fig. 2 shows graphically the frequency against comparator output; Fig. 3 shows note embodiment of a low pass filter (B); Fig. 4 shows another embodiment of a Band pass filter circuit (C) with two rap cut-off L.P.F,; Fig. 5 shows another embodiment of a Band elimination filter circuit (D) with two sharp cut-off L.P.F. Fig. 6 shows frequency response of L.P.F, filters using passive components as in prior art ; Fig. 7 shows frequency response of HPF filters using passive components as in prior arts Fig. 8 shows frequency response of LPF filters using active technique as in prior art; Fig, 9 shows frequency response of HPF filters using active technique as in prior art; Fig. 10 shows frequency response of Finite impulse response { FIR) filters using Blackman window. Fig, 11 shows frequency response of FIR filters using chebyshev type I LPF Presently the state of art of using different filters are as follows: 1. Filters usin2_Passive_components These filters are made up of LC/ RC or RL components which gives the frequency response as shown in Figs, 6 and 7 With LPF filter the gain is maximum at lowest frequency and with HPF filter/ it is just reverse. The cut-off frequency f is equal in both the case, 2. Filters_usin2_Active_com£onents These are made up of either transistor or op-amp and their frequency is as in Figs 8 and 9, The frequency response with LPF is reverse of HPF and the cut-off frequency f is same. The technique used FIR ( Finite Impulse Response) Filters and IIR (infinite Impulse Response] filters. The design process involves the determination of co - efficient of a casual FIR or IIR that filters that closely approximates the desired frequency response specification. In practice FIR filters are employed where there is a requirement for a linear phase characteristics within the pass - band of the filter and there is no linear phase characteristic is required when IIR fitters are used. The frequency response of FIR filter using Blackman window and Chebyshev type I LPF filter responses are shown in Figs. 10 & 11. In both situatton the cut - off frequency fc is similar. In the present invention a circuit (A) (see Fig.l) using active and passive components whidi gives a sharp cut-off frequency response (fc). A prototype HPF (3) and prototype LPF (2) (i.e. any existing HPF and LPF filters) has been used and the output of both the filters are compared in a comparator (4) and the output of that comparator (4) is given to a switch (5) which passes an output signal (6) according to the comparator (4) pulse. Its main features are ; It gives a SHARP CUT-OFF FREQUENCY RESPONSE. It gives a linear phase response. It uses very few components so it is very cheap and also its construction is very simple. We give now detailed description of the construction and operation of the filters. The preferred embodiment of the invented circuit with high pass filter (HPF) shown in Fig. 1 and Fig. 2 shows graphs of frequency with comparator output (6). 1. High Pass FiIter (HPF) (A) The block diagram of the HPF is shown in Fig. (1). Here a prototype of LPf (2) is connected to the inverting terminal (9) of the comparator (4) and a prototype of HPF (3) is connected to the non-inverting terminal (10). The output of the comparator (4) is connected to a switch (5) which allow the input signal according to comparator (4) output. The input signal (1) is applied to both prototype LPF (2), HPF (3) and also to the switch (5). Graphical explanation is shown in Fig. 2. Three frequencies have been considered for explanation. At fi the output of LPF (2) is more compared to HPF (3) and output of the comparator (4) is negative going and for this signal the switch (5) is not activated and it will not pass any signal (6). At k the outputs of both LPF (2) and HPF (3) are same and the output of the comparator (4) is zero and for this signal the switch (5) is activated and it will pass the input signal from this frequency which is the cut-off frequency (fc) of the filter. At f2 the output of the HPF (3) is more compared to LPF (2) and the output of the comparator (4) Is positive going and for this signal the switch (5) will be open and will pass the input signal. So we will get a sharp cut-off at k. The most important feature of the cut-off filter is that same input is applied to both prototype LPF (2) and HPF (3) and also the cut-off frequencies (fi, h, k) of both filters should be same. Low Pass Filter (LPF) (B) The btockdiagram for this is same as HPF but only the inverting and non-inverting terminals are interchanged. And the explanation is just opposite to that of HPF. The block diagram of LPF is shown in Fig. (3). Keeping these Ideas in mind we can design Band Pass Filters (6PF) (C) and Band elimination filters (BEF) circuits (D) very easily whose block diagrams are given in Fig. (4) and (5). Through the BPF and BEF currents having frequencies within specified nominal limits are freely allowed to pass and highly attenuated currents with frequencies outside these limits or signals having frequencies within a certain range or band are attenuated while freely passing those outside this range respectively. In Figures 4 & 5 two cut-off LPF (7&8) as generated by the circuit in Fig. 1. and Figure 3 are employed wherein the inverting and non inverting terminals are interchanged to allow frequencies to be passed through the band of frequencies or the frequencies are attenuated in the said ranges of frequencies. The explanation of the circuits is just like High Pass Fitter and Low Pass Filter operating circuits in Figs. (1) and (3). Applications These fitters give us a very sharp cut-off they are used in many fields which are listed below. 1. Radar and Sonar Application. 2. Television 3. Signal Processing and Reception etc. These filters give a very sharp cut-off response. The invention described hereinabove is in relation to a non-limiting embodiment and as defined by the accompanying claims. WE CLAIM 1. An electronic circuit consisting of a prototype tow pass filter (LPF) (2), a High Pass Filter (HPF) (3) and a comparator (4) to generate sharp cut-off frequency response (fc) for control of opening or closing a switch {5) to allow ingress of the signal to an electrical device in an automotive mode, wherein in the circuit a LPF (2) is connected to the inverting terminal (9) of the comparator (4) and a HPF (3) is connected to the non Inverting terminal (10) of the comparator or the said LPF and HPF are connected in reverse order terminal of the comparator, the input signal (1) to the circuit being applied to both the LPF, HPF and also to the switch (5), the output of the comparator being connected to the switch which allow the input signal to ingress or to be blocked according to the comparator output, the comparator generates cut-off frequency by differentiating the output of LPF and HPF for a frequency of the input signal and activate the switch to pass input signal to the switch when the difference between output of LPF and HPF are positive or zero but block the input signal to the swith when such difference is negative. 2. An electronic circuit as claimed in claim I wherein the input signal (1) to both the prototype low pass filter (2) and high pass filter (3) and the cut-off frequencies (fc) is same. 3. An electronic circuit acting as band elimination frequencies as claimed in claim 1 consisting of sharp cut-off L.P.F. (7, 8) having corresponding frequencies of f1 and f2, the cut-off LPF (7) being connected to the inverting terminal (9) of the comparator (4) and the cut-off LPF (8) is connected to the non-inverting terminal (10) of the comparator (4) and the frequency fi of the cut-off LPF (7) is less than frequency U of the sharp cut-off LPF (8). 4. An electronic circuit (C) as claimed in claim 1 acting as Band pass frequencies consisting of cut-off LPF (7,8) connected to the comparator (4) in reverse of the band elimination frequencies circuit (D). 5. An electronic circuit to generate sharp cut-off frequency response as herein described and illustrated in the accompanying drawings.

Documents:

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2773-mas-97 abstract-duplicate.pdf

2773-mas-97 abstract.pdf

2773-mas-97 claims-duplicate.pdf

2773-mas-97 claims.pdf

2773-mas-97 correspondence-others.pdf

2773-mas-97 correspondence-po.pdf

2773-mas-97 description (complete)-duplicate.pdf

2773-mas-97 description (complete).pdf

2773-mas-97 drawings.pdf

2773-mas-97 form-1.pdf

2773-mas-97 form-19.pdf

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2773-mas-97 petition.pdf