GB2084809A - Printed circuit transformers - Google Patents

Printed circuit transformers Download PDF

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Publication number
GB2084809A
GB2084809A GB8127804A GB8127804A GB2084809A GB 2084809 A GB2084809 A GB 2084809A GB 8127804 A GB8127804 A GB 8127804A GB 8127804 A GB8127804 A GB 8127804A GB 2084809 A GB2084809 A GB 2084809A
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GB
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Application
Patent type
Prior art keywords
tracks
secondary
printed
track
transformer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB8127804A
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GB2084809B (en )
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Communications Patents Ltd
Original Assignee
Communications Patents Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01FMAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00Details of transformers or inductances, in general
    • H01F27/28Coils; Windings; Conductive connections
    • H01F27/2804Printed windings
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00Printed circuits
    • H05K1/16Printed circuits incorporating printed electric components, e.g. printed resistor, capacitor, inductor
    • H05K1/165Printed circuits incorporating printed electric components, e.g. printed resistor, capacitor, inductor incorporating printed inductors
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00Printed circuits
    • H05K1/02Details
    • H05K1/0286Programmable, customizable or modifiable circuits
    • H05K1/0293Individual printed conductors which are adapted for modification, e.g. fusable or breakable conductors, printed switches
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/03Conductive materials
    • H05K2201/0302Properties and characteristics in general
    • H05K2201/0305Solder used for other purposes than connections between PCB or components, e.g. for filling vias or for programmable patterns
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09Shape and layout
    • H05K2201/09209Shape and layout details of conductors
    • H05K2201/09218Conductive traces
    • H05K2201/09236Parallel layout
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09Shape and layout
    • H05K2201/09209Shape and layout details of conductors
    • H05K2201/0929Conductive planes
    • H05K2201/093Layout of power planes, ground planes or power supply conductors, e.g. having special clearance holes therein
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09Shape and layout
    • H05K2201/09209Shape and layout details of conductors
    • H05K2201/09654Shape and layout details of conductors covering at least two types of conductors provided for in H05K2201/09218 - H05K2201/095
    • H05K2201/09663Divided layout, i.e. conductors divided in two or more parts
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/17Post-manufacturing processes
    • H05K2203/171Tuning, e.g. by trimming of printed components or high frequency circuits

Abstract

A printed circuit transformer comprises one primary track 1 and two secondary tracks 2, 3, the three tracks being located adjacent and substantially parallel to each other with one end of one of the secondary tracks and the other end of the other secondary track being connected to a common source of potential 7 (earth). The primary track is located between the secondary tracks and all the tracks are printed wholly on one side of the circuit board. Spaces 8, 9 between the ends of the secondary tracks and earth may be bridged by solder to vary the lengths of the tracks. <IMAGE>

Description

SPECIFICATION Printed circuit transformers The present invention relates to printed circuit transformers.

It is known to provide broad band mixer transformers for use in VHF applications by forming one primary and two series connected secondary tracks on a circuit board, the secondary tracks being immediately adjacent each other with the primary track to one side of them. Such printed circuit transformers may be made particularly compact. However, the configuration of the primary and secondary tracks used in these known printed circuit transformers requires the use of double sided circuit boards in order to provide for the fabrication of a cross-over connection in one of the secondary tracks. This in turn requires the provision of plated through holes to provide connections between the two sides of the board.The use of double sided circuit boards is expensive because of the difficulty in registering accurately the printed tracks on each side of the board, and the provision of plated through holes adds a further large element to their cost. A further disadvantage experienced with this known configuration arises from the fact that the secondary track which includes the cross-over connection differs in inductance and stray capacitance from the secondary track which is printed wholly on one side of the board. Since the two secondary tracks are not identical this can make it difficult to balance the output of the transformer.

It is an object of the present invention to provide a printed circuit transformer wherein the above mentioned problems may be obviated or mitigated.

According to the present invention there is provided a printed circuit transformer comprising one primary track and two secondary tracks, the three tracks being located adjacent and substantially parallel to each other with one end of one of the secondary tracks and the other end of the other secondary track being connected to a common source of potential, characterised in that the primary track is located between the secondary tracks and all the tracks are printed wholly on one side of the circuit board.

The common source of fixed potential effectively forms a centre tapping on the secondary defined by the two secondary tracks. Thus a balanced output can be derived from the secondary tracks.

Preferably the secondary tracks are connected to a common printed conductive area which is maintained at the said potential, the printed conductive area extending to adjacent the ends of all the tracks. The printed conductive area also extends parallel to at least a portion of each of the secondary tracks such that an elongate gap is defined between the printed conductive area and at least part of the length of each secondary track. The effective length of one or both of the secondary tracks may be reduced to trim the transformer by bridging a portion of the gap between that track and the printed conductive area with a conductive material.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a printed circuit transformer embodying the present invention; Figure 2 is a schematic circuit diagram of the transformer of Fig. 1; Figure 3 illustrates the use of transformers according to the invention in a VHF amplifier; and Figures 4 and 5 illustrate the use of a transformer according to the invention to provide signals with a phase difference of 180 in a measuring instrument.

Referring to Fig. 1 there is shown a printed circuit board band mixer transformer comprising a primary track 1 and two secondary tracks 2, 3. The primary track 1 is located equidistant from the tracks 2 and 3 which ensures that coupling between the primary track and each secondary track 2, 3 is equal.

Connection to the primary track 1 is provided through a contact (not shown) to which the left hand end 4 of the primary track extends, and to the secondary tracks 2 and 3 through contacts 5 and 6. The other ends of all the tracks are connected to a common printed area 7 which is maintained at earth potential.

The area 7 extends parallel to at least a proportion of each of the secondary tracks 2, 3 to define gaps 8, 9. The effective lengths of the secondary tracks can be reduced by bridging the gaps 8, 9 with solder.

This arrangement of tracks enables the whole of the transformer to be printed on one side of the circuit board. The transformer may be easily trimmed for best balance and return loss ratio (matching to the load) simply by connecting solder bridges across the gaps 8, 9. Since the frequency of operation of the transformer is not determined by the length of the tracks the transformer may be made as compact as required, regardless of the operating frequency.

The connection of solder bridges across the gaps 8, 9 to trim the transformer is only necessary when exceptionally close balance is required. Normally the necessary lengths of the secondary tracks which are decided upon during development for a particular application could be reproduced with sufficient accuracy by standard printed circuit production methods.

Fig. 2 shows a schematic circuit diagram of the printed circuit transformer of Fig. 1. The primary and secondary of the transformer and their connections have been given the same reference numbers as in Fig. 1.

The transformer according to the invention can be usefully applied to a broad band high power VHF amplifier as used in C.A.T.V.

systems. Such amplifiers may comprise a preamplifier the stages of which are all of singleended configuration and a high power amplifier the stages of which are all of push-pull configuration.

The high anplifier requires an input transformer and an output transformer, both of which may be transformers in accordance with the present invention.

Referring to Fig. 3, a high power push-pull amplifier is schematically illustrated. The output of a single-ended pre-amplifier is applied via diode 10 to the primary winding 1 of a transformer of the type described with reference to Fig. 1. The outputs of the transformer secondaries 2 and 3 are applied to respective sides of a push-pull transistor amplifier stage represented schematically by boxes 11 and 1 2. The configuration of the push-pull stage is conventional and therefore is not shown in detail. Furthermore, although only one pushpull stage is shown, in practice there will be for example four stages.

The outputs of the stage 11 and 1 2 are applied to the centre tapped winding 2, 3 of a further transformer of the type described with reference to Fig. 1, the amplifier output being taken from winding 1.

The use of an output transformer in accordance with the invention makes it possible to avoid providing feedback networks between the last push-pull stage of the amplifier and the output transformer. Such feedback networks are provided in prior art systems. It is highly advantageous to dispense with such feedback networks in VHF systems as it is very difficult to control the phase changes of signals passing through them.

Referring now to Figs. 4 and 5, a further example of an application of the transformer according to the invention will be described.

Fig. 4 shows part of the circuit diagram of an automatic test apparatus for measuring the goodness of balance of subscriber's inserts used in cable television. These inserts comprise transformers and impedance networks by which subscriber's recievers are isolated from the cable network so as to minimise mutual interference and minimise the transference of impedance imperfections from the receiver to the network. A measure of the balance of the insert is derived from the ratio of the output voltage it gives when it has applied to it (i) a push-pull signal, and (ii) a push-push signal.

The testing apparatus is arranged to provide such signals by using a transformer in accordance with the present invention as described with reference to Fig. 1 in conjunction with a switching arrangement comprising relays controlling contacts 13, 14, 15 and 16. With contacts 1 3 and 1 6 closed, a push-pull output is obtained, whereas with contacts 14 and 15 closed a push-push output is obtained. The signal applied to input terminal 1 7 may be a carrier wave or an amplitude or frequency modulated wave depending upon the characteristics of the detector employed which is described below. The output terminals 18, 1 9 are connected to the insert under test.

The insert and detector to which the signals from the arrangement af Fig. 4 are applied is shown in Fig. 5. The test signals from terminals 18, 1 9 of Fig. 4 are applied to the insert 20 via terminals 21, 22. The insert comprises an autotransformer 23, the winding being interrupted at the centre to allow the insertion of a capacitor 24, the capacitance of which (about 2000pF) is chosen to present a high impedance at audio frequencies and a low impedance at the radio frequencies over which it is designed to operate. This capacitor 24 is necessary because T.V. signal cables also carry audio programmes at a level of for example 55 volts. If any appreciable part of these audio signals were allowed to flow through the winding 23 its ferrite core would be magnetically saturated and it would cease to act as a transformer.

The selected signal level to be provided to the subscriber is determined by the output tapping points 25 and 26 on the transformer 23. The tapped portion of the signal is passed through a bifilar choke 27, the purpose of which is to minimise push-push current at the output terminals 28, 29, i.e. to improve the balance of the device. Resistors 30 and 31 are equal in value and substantially define the output impedance of the insert.

In order to carry out the balance test, it is necessary to measure the voltage appearing at the terminals 28 and 29. A voltmeter 32 is shown which may be a sensitive valve voltmeter or a measuring receiver, i.e. a communications receiver with a calibrated detector voltage. In the case where an amplitude or frequency modulated wave is applied to the terminal 1 7 of Fig. 4, the audio output terminals of the communications receiver may be applied to an audio millivoltmeter to indicate the measured quantity.

The balance of the insert 20 is measured by applying a balanced signal from the circuit of Fig. 4 (push-pull) to the terminals 21 and 22 and noting the output registered by the voltmeter 32. Unbalanced signals are then applied from the circuit of Fig. 4 (push-push) to the terminals 21 and 22 and the lower output noted. The ratio of the two output voltages, expressed in decibels, is a measure of the balance of the insert.

Claims (3)

1. A printed circuit transformer comprising one primary track and two secondary tracks, the three tracks being located adjacent and substantially parallel to each other with one end of one of the secondary tracks and the other end of the other secondary track being connected to a common source of potential, characterised in that the primary track is located between the secondary tracks and all the tracks are printed wholly on one side of the circuit board.
2. A printed circuit transformer according to claim 1, characterised in that the secondary tracks are connected to a common printed conductive area extending to adjacent the ends of all of the tracks, the printed conductive area also extending parallel to at least a proportion of each of the secondary tracks such that an elongate gap is defined between the printed conductive area and at least part of the length of each secondary track, whereby the effective length of one or both of the secondary tracks may be reduced by bridging a portion of the gap between that track and the printed conductive area with a conductive material.
3. A printed circuit transformer substantially as hereinbefore described with reference to the accompany drawings.
GB8127804A 1980-10-01 1981-09-15 Printed circuit transformers Expired GB2084809B (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB8031656 1980-10-01
GB8127804A GB2084809B (en) 1980-10-01 1981-09-15 Printed circuit transformers

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8127804A GB2084809B (en) 1980-10-01 1981-09-15 Printed circuit transformers

Publications (2)

Publication Number Publication Date
GB2084809A true true GB2084809A (en) 1982-04-15
GB2084809B GB2084809B (en) 1984-01-18

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB8127804A Expired GB2084809B (en) 1980-10-01 1981-09-15 Printed circuit transformers

Country Status (1)

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GB (1) GB2084809B (en)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1988007412A1 (en) * 1987-04-01 1988-10-06 Fläkt Ab A voltage converter
EP0324240A2 (en) * 1988-01-15 1989-07-19 Northern Telecom Limited Balanced planar transformers
FR2644664A1 (en) * 1989-03-20 1990-09-21 Alcatel Radiotelephone Transformer printed on print circuit, and circuit power divider prints having such a transformer
FR2652210A1 (en) * 1989-09-20 1991-03-22 Alcatel Radiotelephone Modulation circuit in phase and in amplitude.
FR2652197A1 (en) * 1989-09-18 1991-03-22 Motorola Semiconducteurs Borde Balun transformers IMPROVED type.
EP0419756A2 (en) * 1989-09-26 1991-04-03 Astec International Limited Printed circuit transformer
FR2656159A1 (en) * 1989-12-19 1991-06-21 Portenseigne Radiotechnique Balun.
EP0570125A1 (en) * 1992-05-08 1993-11-18 Sony Corporation Unbalanced-balanced converter as a mixer input circuit
US5304959A (en) * 1992-10-16 1994-04-19 Spectrian, Inc. Planar microstrip balun
WO2001054149A1 (en) * 2000-01-24 2001-07-26 Ronald Kevin Fricker A planar transformer
DE10105696A1 (en) * 2001-02-08 2002-08-14 Rohde & Schwarz Balun

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1988007412A1 (en) * 1987-04-01 1988-10-06 Fläkt Ab A voltage converter
EP0324240A2 (en) * 1988-01-15 1989-07-19 Northern Telecom Limited Balanced planar transformers
EP0324240A3 (en) * 1988-01-15 1990-07-25 Northern Telecom Limited Balanced planar transformers
FR2644664A1 (en) * 1989-03-20 1990-09-21 Alcatel Radiotelephone Transformer printed on print circuit, and circuit power divider prints having such a transformer
EP0389344A1 (en) * 1989-03-20 1990-09-26 Alcatel Mobile Communication France Transformer printed on printed circuit and power-dividing printed circuit having such a transformer
EP0418538A1 (en) * 1989-09-18 1991-03-27 Motorola Semiconducteurs S.A. Improvements in or relating to balun transformers
FR2652197A1 (en) * 1989-09-18 1991-03-22 Motorola Semiconducteurs Borde Balun transformers IMPROVED type.
US5061910A (en) * 1989-09-18 1991-10-29 Motorola, Inc. Balun transformers
EP0418775A1 (en) * 1989-09-20 1991-03-27 Alcatel Mobile Communication France Phase and amplitude modulation circuit
FR2652210A1 (en) * 1989-09-20 1991-03-22 Alcatel Radiotelephone Modulation circuit in phase and in amplitude.
EP0419756A2 (en) * 1989-09-26 1991-04-03 Astec International Limited Printed circuit transformer
EP0419756A3 (en) * 1989-09-26 1991-09-11 Astec International Limited Printed circuit transformer
EP0434144A1 (en) * 1989-12-19 1991-06-26 Philips Electronique Grand Public Balun
FR2656159A1 (en) * 1989-12-19 1991-06-21 Portenseigne Radiotechnique Balun.
EP0570125A1 (en) * 1992-05-08 1993-11-18 Sony Corporation Unbalanced-balanced converter as a mixer input circuit
US6011966A (en) * 1992-05-08 2000-01-04 Sony Corporation Mixer input circuit with Imbalance-balance circuit having distributed constant line
US5304959A (en) * 1992-10-16 1994-04-19 Spectrian, Inc. Planar microstrip balun
WO2001054149A1 (en) * 2000-01-24 2001-07-26 Ronald Kevin Fricker A planar transformer
US6608545B2 (en) 2000-01-24 2003-08-19 Nucleus Ecopower Limited Planar transformer
DE10105696A1 (en) * 2001-02-08 2002-08-14 Rohde & Schwarz Balun
US6917254B2 (en) 2001-02-08 2005-07-12 Rohde & Schwarz Gmbh & Co. Kg Balanced-to-unbalanced transformer

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Publication number Publication date Type
GB2084809B (en) 1984-01-18 grant

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Legal Events

Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee