US2640879A - Band pass filter - Google Patents

Band pass filter Download PDF

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Publication number
US2640879A
US2640879A US763068A US76306847A US2640879A US 2640879 A US2640879 A US 2640879A US 763068 A US763068 A US 763068A US 76306847 A US76306847 A US 76306847A US 2640879 A US2640879 A US 2640879A
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Prior art keywords
circuit
crystal
frequency
electric
piezo
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Expired - Lifetime
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US763068A
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English (en)
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Tournier Marcel Charles
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International Standard Electric Corp
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International Standard Electric Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/545—Filters comprising resonators of piezoelectric or electrostrictive material including active elements

Definitions

  • the present invention relates to electric wave filters, and more particularly to electric wave filters comprising electro-mechanical vibrating elements such as piezo-electric crystals.
  • the invention relates more-specifically to piezoelectric crystals arranged to be used in radio broadcasting receivers.
  • the invention has in particular the object of the embodiment ofa mean frequency filter corresponding to the aboveconditions, that is tosay, having-sufficient pass band width'w'ith clear limits and a reduced attenuation which is substantially constant in the transmission band.
  • This filter also-has input impedance and very high output impedances so as to permit the stage to have an output of a high value.
  • a filter in accordance with the invention will consequently, consistofa mean frequency transformer consisting of two similar circuits coupled by mutual induction and placed respectively in anti-resonators in the output or anode circuit or anode of a valve, and in the input or grid circuit of the following valve, associated with two piezoelectric elements in the form of piezo-electric resonance transformers as will be explained in detail later on, one of these piezo-electric elements having a resonance which is slightly less at the first resonance frequency, or lowest resonance frequency of the mean frequency transformer, and the other a resonance frequency which is slightly higher than the second resonance frequency or the highest resonance frequency of v the mean frequency transformer.
  • a circuit oscillating in anti-resonance is placed in series with a resistance of a high value in the output or anode circuit of a valve and another anti-resonant oscillating circuit in series with a resistance of'an identical high value are placed in the grid or input circuit of the valve following.
  • the two oscillating circuits are inductively coupledone to the other and two piezoelectric elements arranged in resonance transformers are connected respectively in parallel at the input side at the terminals of the first resistance of high value, and in parallel with their respective inverse connections at the terminals ofdthe other high value resistance on the output s1 e.
  • the arrangement of the oscillating circuits which are'inductively coupled is the same, but the pieZo-electric transformers are associated to the said oscillating circuits by connecting respectively their inputs and their outputs in shunt to the said oscillating circuits, the same inversion of the piezo-electric transformer connections being provided for on the output side of the whole of the transformer.
  • Figure l represents'an embodiment of the piezoelectric transformer employed in the circuits of the invention.
  • Figure 2 represents amethod of electric representation equivalent to the piezo-electric transformer of Figure l
  • F gure3 represents-an example of the coupling device according-to the invention
  • Figures, 4'and'5 represents respectively thepotentials at the terminals of the secondary for the electro-magnetic transformer assumed alone, and the piezo-electric transformers and for the whole of the coupling in Figure 3 in absolute values;
  • Figure 6 represents another embodiment of the coupling device according to the invention.
  • Figure 7 represents an attenuation curve as a function of the frequency obtained experimentally with the mounting in Figure 6.
  • Figure 8 represents an electric circuit diagram which may be taken as an equivalent to the circuit in Figure 6.
  • Figures 9 and 10 represent curves relative to the diagram of Figure 8.
  • FIG. 1 An example of the piezo-electric transformer as used in the present invention is diagrammatically shown in Figure 1.
  • I represents a layer of Piezo-electric crystal covered at either end with metallic layers 2 and 3 of even surface and in the nodal points of which are fixed the lead-in electrodes 4, and the leadout electrodes 6, l by any suitable means, for example, by means of clamping pins or conducting lozenges to this on the surface of the crystal and soldered to electric connecting wires.
  • the sheet may be thin, for example 0.5 mm. in thickness approximately, cut in a plate of crystal of a section termed X, that is to say, with the electric axis X perpendicular to the sheet.
  • the direction of the greater length of the crystal forms an angle of 18 with the electrical axis in a straight crystal.
  • the length of the crystals may be in the neighbourhood of 16.5 mm., and their width 5 mm.
  • the actual frequency of the crystal is in the neighbourhood of 158 kilocycles and the vibration frequency on the harmonic three is 472 kilocycles approximately, which corresponds to the usual mean frequency of broadcast receiver sets of the superheterodyne type. It is, therefore, possible to determine with precision the nodal lines corresponding to the partial 3 and the electrodes 4, 5 and 6, 1 are fixed at these points. The whole is then metallised. Then the metal is stripped off at the edges of the crystal and from the middle section 8 of the length of the crystal.
  • the piezo-electric transformer in Figure 1 may, moreover, be electrically represented as indicated in the diagram in Figure 2.
  • the electrical properties of each half crystal may be represented by those of two identical circuits incapable of reacting on one another. Nevertheless, in assuming now that a mechanical contact is created between two points where they are cut. a part of the kinetic energy of each crystal can pass into the other end and there would, therefore, be an exchange of mechanical energy similar to the exchange of electro-magnetic energy between two circuits by mutual induction. The existence of this mechanical coupling modifies the period of each circuit. When the two half crystals are joined up completely again in such a Way as to reconstitute the original crystal everything happens as though the coeflicient of mutual coupling of the two equivalent circuits became equal to a whole.
  • I0 represents a pentode valve and II a triode valve of the mean frequency stage following the superheterodyne.
  • the pentode valve I0 is shown in the usual way with its cathode directly connected to the suppression grid, and an alternating supply source l2 between its cathode and its control grid.
  • a battery l3 supplies the necessary continuous potentials for its screen grid and its plate.
  • the valve II is represented with its plate battery I4 feeding its plate across a suitable operating circuit 15.
  • a resistance It of high value and an oscillating circuit consisting of an inductance I! and capacity I8 are inserted in series in the plate circuit of the pentode In.
  • a resistance I9 of the same value as the resistance l6 and the oscillating circuit 202l identical with the oscillating circuit l1-l8 are also introduced into the control circuit of the valve l l.
  • the two oscillating anti-resonant circuits ll-la and 20-2! are coupled by a mutual induction unit as shown in' 22.
  • Two piezoelectric ransformers of the type described above 23 and 33 are connectedpto the terminals of the resistances it and IS in the manner shown. These two piezo-electric transformers have their input terminals or primaries Ede-25 and Sill-e35 connected respectively and in the same direction to the terminals of the resistance it, whilst their input or secondary terminals 2'Ei2'l, 36?? are crossed and connected at the terminals of the resistance l9.
  • each of these transformers will have its own resonance frequency, one of these crystals will be adjusted in such a manner as to have a resonance frequency if! lower than fl and the other a resonance frequency f3 higher than 12.
  • the curve of these transformers is indicated by a continuous line 4
  • the direction of the mutual induction is selected in such a way that for frequencies comprised between ll and ill the potential given by the circuit and that given by the crystals is in opposite direcion.
  • the outgoing potential is called V.
  • the impedances Z2 are assumed to be coupled with a coupling coefficient a, and the impedances Z3 equally coupled with a coefiicient of coupling b, the two circuits being assumed to be identical.
  • the laws of Kirchhoff make it possible to write the relations between the currents and the potentials. These equations are the following, the currents and. nodes being shown at Figure 8.
  • M-andL will be chosenin such a way that the infinite attenuation occurs for a value fixed by the distance in frequency as from the resonance but I 1V g ab(a+b)aZ bZ
  • the resonance of the crystal may operate it is necessary that the quantity should have a modulus which is not negligible with relation to the unit, as a2 is of the order of magnitude of 1/100, and therefore the modulus of the quantity is of the order of magnitude of 100 and, consequently, in the second parenthesis of the denominator it is possible to neglect the unit in front of this quantity.
  • the invention provides for their calculation by a successive approximation which is always possible.
  • values of L and m are arbitrarily fixed which correspond to an ordinary mean .frequency coil and the curves of the ratio between the potentials V/U and the filter attenuation may be plotted, Under these conditions, as a rule they show maxima and minima which are very marked and, consequently, the values will not be correct. Accordingly, the value of m will be changed in order to see in what direction this difference between the maxima and 11 minima develops and then it is possible to always be able to determine an adequate value of 1 1 fairly quickly.
  • the invention supplies methods for the embodiment of a mean frequency filter, which presents clear cuts for a band width which is relatively large, and a reduced attenuation which is substantially constant throughout the width of the transmission band of the filter.
  • a band-pass filter having input and output terminals and comprising a pair of inductively coupled anti-resonant circuits and a pair of piezo-electric transformers each having input and output terminals, said transformer input terminals being connected in parallel with each other and in series with one of said circuits to the input terminals of said filter and said transformer output terminals being connected in parallel with each other and in series with the other of said circuits to the output terminals of said filter.
  • a band-pass filter having input and output terminals and comprising a pair of similar inductively coupled anti-resonant circuits and a pair of piezo-electric transformers each having input aand output terminals, said transformer input terminals being connected in parallel with each other and in series with one of said circuits to the input terminals of said filter and said transformer output terminals being connected in parallel with each other and in series with the other of said circuits to the output terminals of said filter and one of said transformers having a resonance frequency lower than the lower resonance frequency of said circuits and the other of said transformers having a resonance frequency higher than the higher resonance frequency of said circuits.
  • a band-pass filter having input and output terminals and comprising a pair of similar inductively coupled anti-resonant circuits, a pair of piezo-electric transformers each having input and output terminals, said transformer input terminals being connected in parallel with each other in the same phase sense and in series with one of said circuits to the input terminals of said filter and said transformer output terminals being connected in parallel with each other in an opposite phase sense with respect to each other and in series with the other of said circuits to the output terminals of said filter and one of said transformers having a resonance frequency lower than the lower resonance frequency of said circuits and the other of said transformers having a resonance frequency higher than the higher resonance frequency of said circuits, and a pair of impedances adapted to conduct direct current, one of said impedances being connected in parallel with the transformer input terminals and the other of said impedances being connected in parallel with the transformer output terminals.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Filters And Equalizers (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
US763068A 1939-08-08 1947-07-23 Band pass filter Expired - Lifetime US2640879A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR861831T 1939-08-08

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US2640879A true US2640879A (en) 1953-06-02

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US (1) US2640879A (fr)
FR (1) FR861831A (fr)
GB (1) GB537803A (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3179906A (en) * 1965-04-20 By-pass netwoems when
US3437848A (en) * 1964-09-24 1969-04-08 Telefunken Patent Piezoelectric plate filter

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR861831A (fr) * 1939-08-08 1941-02-18 Materiel Telephonique Filtres d'ondes électriques

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1438828A (en) * 1920-03-29 1922-12-12 Harry W Houck Method and apparatus for selectively transferring electrical oscillatory energy
US1732710A (en) * 1923-09-20 1929-10-22 Westinghouse Electric & Mfg Co Wireless receiving system
FR796611A (fr) * 1935-01-07 1936-04-11 Materiel Telephonique Perfectionnements aux filtres d'ondes électriques
US2199921A (en) * 1938-07-28 1940-05-07 Bell Telephone Labor Inc Wave filter
US2244022A (en) * 1936-04-29 1941-06-03 Rca Corp Electrical filter
GB537803A (en) * 1939-08-08 1941-07-07 Standard Telephones Cables Ltd Electric wave filters

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1438828A (en) * 1920-03-29 1922-12-12 Harry W Houck Method and apparatus for selectively transferring electrical oscillatory energy
US1732710A (en) * 1923-09-20 1929-10-22 Westinghouse Electric & Mfg Co Wireless receiving system
FR796611A (fr) * 1935-01-07 1936-04-11 Materiel Telephonique Perfectionnements aux filtres d'ondes électriques
US2244022A (en) * 1936-04-29 1941-06-03 Rca Corp Electrical filter
US2199921A (en) * 1938-07-28 1940-05-07 Bell Telephone Labor Inc Wave filter
GB537803A (en) * 1939-08-08 1941-07-07 Standard Telephones Cables Ltd Electric wave filters

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3179906A (en) * 1965-04-20 By-pass netwoems when
US3437848A (en) * 1964-09-24 1969-04-08 Telefunken Patent Piezoelectric plate filter

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Publication number Publication date
GB537803A (en) 1941-07-07
FR861831A (fr) 1941-02-18

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