WO2009066183A2

WO2009066183A2 - Tightly-coupled pcb gnss circuit and manufacturing method

Info

Publication number: WO2009066183A2
Application number: PCT/IB2008/003796
Authority: WO
Inventors: Andrew J. Jakab; Nicholas J. Boorman
Original assignee: Hemisphere Gps Llc
Priority date: 2007-09-27
Filing date: 2008-09-28
Publication date: 2009-05-28
Also published as: US20090085815A1; WO2009066183A3; US7948769B2

Abstract

A tightly-coupled printed circuit board (PCB) circuit includes components mounted on a PCB enabling smaller integrations using decoupled lines extending between reference layers, such as ground planes, which lines form isolation islands on the PCB. The decouplers are capacitors, inductors and/or resistors in tandem with ground layers of the PCB. The isolated components can comprise high-frequency RF antennas and receivers, for example in a GNSS antenna-receiver circuit. Multiple antennas can be connected to one or more receivers with multiple, independent RF front end components by RF traces, which are either embedded within the PCB.

Description

TIGHTLY-COUPLED PCB GNSS CIRCUIT AND MANUFACTURING METHOD

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Patent Application Serial No.

12/239.312. filed September 26, 2008. which claims the benefit of U.S. Provisional Application No. 60/975.727. filed September 27. 2007, which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The present invention relates generally to printed circuit boards (PCBs). and in particular to a tightly-coupled PCB for mounting one or mo e receivers with multiple. independent radio frequency ( RF) front ends in close pιo\ir iity to multiple, respective antennas. The circuit is noise-filtered by electrically decoupling and i; dating the conductive reference planes of the PCB.

2. Description of the Related Art

[0003] PCB manufacturing techniques are well-developed and enable the cost-effective production of circuits w ith virtual ly unlimited configuratior s and combinations of components. Ty pical PCB construction comprises one or more reference lay ers, which can prov ide power and ground (common) planar sources for the entire circuit. Component conductors are connected to the reference layers as required for their operation. Other I∑ yers conduct signals, and can be photo-etched with trace conductors linking other componeni conductors. Still further, microstrip traces can be mounted on the PCB surfaces or w ithin the PCB layers for electrically coupling components.

[0004] Signal noise control represents a significant aspe ct of PCB circuit design. Such considerations are particularly significant in designing circi its with RF receiver and antenna components, because circuit noise from switching components, power sources, "skin effect" conductivity and other noise-producing elements can significantly interfere with the reception and processing of transmitted signals. For example, global lav igation satellite s>stem (GNSS. including global positioning system (GPS)) receivers operate in the microw ave frequency range, whose high frequencies tend to increase noise-related recepi ion problems and signal interference. For example, such systems are susceptible to multipath signal phenomena, which tend to reduce s> stem accuracy and performance.

[0005| A prc\ ions solution has been to physically isolate the receiver and antenna components, w hich can be connected by a shielded RF cabl :. However, it is often more cost- effective to mount as many system components as possible MI a single PCB. Moreover, locating the receiver and its anlenna(s) in close proximity tends to improve peiformance by eliminating relatively lengthy RF connecting cables, prov ided the potenlial for noise interference can be controlled. "Smart" antennas combining antennas and recen ers at single locations have previously been utilized, but do not electrically decouple the circuit components or utilize the ground reference planes for additional antenna area. [0006| Therefore, the design criteria lor GNSS receiver antenna PCBs would preferably included minimizing overall size, placing the receiver and antenna components in close proximity, accommodating multiple antennas and controllir g signal noise. Prev ious receiver- antenna PCBs and manufacturing methods have not provide il the advantages and features of the present invention.

-J-

SUMMARY OF THE INVENTION

[0007] In the practice of an aspect of the present invention, a PCB is designed in a manner to isolate and control the inter-frequenc_\ noise sources, and piovides for the use of components for decoupling reference lavers thereof, which can further separate and decouple lhe ground planes. A receiver w ith multiple, independent RF front end components can be mounted on the PCB in close proλimitv to multiple antennas. The receiver and ante nnas are connected b> optimized transmission lines embedded within the PCB between the ground planes, or bv surface microstrip antenna traces. The impedance of the transmission lines is controlled during the process of manufacturing the PCB.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. 1 is a schematic diagram of a tightly -coupled PCB circuit embodying an aspect of the present invention w ith a receiver and a pair of antennas located in proximity and trace- connected to each other on the PCB. [0009] Fig. 2 is a schematic diagram of another tightK-eoupled PCB circuit embod> ing another aspect of the present invention with three antennas I race-connected to a receiver on a single PCB.

[00010] Fig. 3 is a top schematic diagram of another tigh tly -coupled PCB embodying another aspect of the present invention w ith a modified line of decoupling capacitors. [00011] Fig. 4 is a bottom schematic diagram thereof.

[00012] Fig. 5 is a top schematic diagram of another tightly-coupled PCB embodying another aspect of the present invention with a modified configuration and lav out. [00013] Fig. 6 is a bottom schematic diagram thereof. DETAILED DESCRIPTION OF THE PREFEKRED EMBODIMENTS

I . Introduction and Environment

|00014] As required, detailed embodiments of the preseni invention are disclosed herein: 5 however, it is to be understood that the disclosed embodime nts are merely exemplar) of the invention, which may be embodied in various forms. There fore, specific structural and functional details disclosed herein are not to be interpreted ;ιs limiting, but merely as a basis for the claims and as a representative basis for teaching one skil led in the art to variously employ the present invention in virtually any appropriately detailed structure.

I O [00015] Certain terminology will be used in the follow ing description for convenience in reference only and w ill not be limiting. For example, up. down, front, back, right and left refer to the invention as oriented in the view being referred to. The words "inwardly" and "outwardly " refer to directions toward and away from, respectively, the .'.eometric center of the embodiment being described and designated parts thereof. Said terminology w ill include the words

15 specifically mentioned, derivatives thereof and words of similar meaning.

II. Tightly-Coupled PCB Circuit 2

[00016] Referring to Fig. 1 of the draw ings in more detail, the reference numeral 2 generally designates a tightly-coupled printed circuit board (PCB) circuit embodying an aspect of the present invention. Without limitation on the generality of tightly-coupled PCB circuits for

20 which the present invention can be advantageously applied, the circuit 2 includes a pair of antennas 4 coupled to a sensing receiver 6. By way of example and without limitation, the receiver 6 can comprise a GNSS (e.g.. GPS) receiver operating in the microwave frequency range. |00017] The antennas 4 and the receiver 6 are mounted on a multi-layer PCB 8, w hich can

25 include multiple conductive layers separated by insulating layers foπned of epoxy or other suitable material. The conductive layers can include reference layers adapted for powering the circuit 2 via a positive, power layer and one or more groiinc or common lavers providing a ground plane(s) for the circuit. The PCB 8 can also include one or more signal layers, w hich can be photo-etched in a suitable circuit diagram partem(s) for t lectricalK coupling the circuit 5 components. For example, the antennas 4 and the receiver ό can be connected by RF transmission striplines or traces 10. w hich can be either embedded within the PCB 8 and shielded between the reference layers thereof in a sandwiching construction, or located on the PCB 8 surface and comprise surface microstrip antenna trac es. I f surface-mounted, the RF transmission striplines I O would be bottom-shielded by the lop la\er of the PCB 8. The function

I O of the RF transmission striplines I O is preferably optimized by controlling impedance (Z), e.g. b> v ary ing the thickness of the traces 10.

[00018] Multiple decouplers 12 form decoupling lines. 1 -. which extend from the receiver 6 to respective ends 16 of the PCB 8. The lines 14 include bends 1 8 and form grounded isolation islands 20 which are relatively noise-free b> virtue of the electrical decoupling function of the

15 decouplers 12. The RF inputs via the antennas 4 are near thi: ends 16 of the PCB 8. The decoupling lines 14 can be formed with bends and other configurations as necessary in order to locate the RF input signals as close as possible to the physiuil RF connectors from within the RF transmission striplines 1 0 in order to provide optimal RF signal paths from the antennas 4 to the receiver 6. The decouplers 12 can comprise capacitors, resistors or inductors, w hich are chosen

20 for impedance control based on characteristics and operating parameters of the circuit 2. The configurations and locations of the isolation islands 20 w ithm the PCB also provide impedance control, in conjunction w ith the decoupling lines 14 and the operating parameters of the circuit 2. Such operating parameters can include such variables as poiver, voltage, current, frequency and amplitude of the signals encountered bv the components of lhe circuit 2. including the operating ranges of such parameters. Multiple different capacitive values of the decouplers 12 can be utilized to filter specific frequencies between the decoupled component ground planes. |00019] The decouplers 12 and the isolation islands 20 preferably extend between, yet still allow, electrical connections between the reference layers (e.g., ground planes and/or positive reference la>er) of the PCB 8. The respective independent ground planes of the circuit components, such as the antennas 4. the receiver 6 and the HF transmission lines 10 are electrically decoupled by the decouplers 12. A relatively large area of isolation is preferably formed in the PCB 8 by the isolation islands 20 in order to maximize the signal noise-isolating operation of the decoupling lines 14. [00020] In operation, the PCB circuit 2 can encounter nc ise and electrical interference from a variety of interna! and external sources. High-frequency receivers, such as those utilized in GNSS (e.g., GPS). are somewhat susceptible to degradation of performance due to such interference, with the potential for resulting inaccuracies in their positioning functions. The isolation islands 20 tend to be relatively free of such noise signals whereby the antennas 4 can be located relatively close to the receiver 6 without being subj ected to excessive noise.

[00021| The relatively close proximities of the antennas 4 to the receiver 6 tend to minimize signal delays and electromagnetic interference (EMI) probl ems, which can be associated with greater separation and correspondingly longer RF connecting leads. Noise from such signal sources as multipath signals. PCB skin effect, power source fluctuations, phase noise and EMI in general tend to be effectively dissipated by the impedance (capacitive, inductive and/or resistive) of the decouplers 12. Effective decoupling improves signal quality from the antennas 4 to the receiver 6. In the case of GNSS systems, greater positioning accuracy can be achieved. Another benefit of decoupling the PCB circuit 2 is that the need for sophisticated filtering and processing functions, which are commonly performed by processors u>ing Kalman and other filtering software techniques, can be eliminated or at least reduced. A further advantage of the decoupled PCB circuit 2 is that the PCB ground planes provide additional antenna areas for increasing the effectiveness of the antennas 4. Still further, the additional costs associated w ith separate circuit boards and standalone components can be avoided by utilizing the decoupled PCB 8. III. First Alternative Aspect Tightly-Coupled PCB Circuit :^;2

5 |00022] A tightl} -coupled PCB circuit 52 comprising a first alternative aspect or embodiment of the present invention is shown in Fig. 2 and includes an additional antenna 4. Such three- antenna GNSS receiver circuits can be utilized in vehicle guidance s\ stems and machine control applications and are capable of determining vehicle and eqi ipment attitude with respect to three axes.

I U [00023] As show n in Fig. 2. a PCB 58 can be alternative y configured for the third antenna 4 and can assume various other alternative configurations for additional components, including additional antennas, receivers, etc. Still further, additional circuits can be placed on PCBs which are tightlv -coupled and create isolation islands according to the present invention. The tightly- coupled decoupled PC B circuit 52 includes decoupling line-, 64 of decouplers 62, which foπn

15 isolation islands 70 in w hich the antennas 4 are mounted in relatively noise-free isolation. Considerable cost sav ings can be achieved using the tight coupling of the present invention because the PCBs can be made smaller and components can be combined on single PCBs to form circuits that might have otherw ise required physical isolation and separation among different components of a circuit.

20 IV. Second Alternative Aspect Tightlv -Coupled PCB Circuit 102

|00024] A tightly-coupled PCB circuit 102 comprising a second alternative aspect or embodiment of the present invention is shown in Figs. 3 an J 4 and includes a PCB 103. The PCB circuit 102 includes a receiver 104. first and second GNSS antennas 106, 108 and a power suppl) 1 10. Multiple decoupling capacitors 1 12 form first and second decoupling lines 1 14. 1 16.

25 which generallj extend in opposite directions from the receiver 104 towards respective ends of the PCB 103 and define respective isolation islands 1 18. 12 ) for the antennas 106. 108 respectively. As shown in Fig. 4. first and second RF striphnes or traces 121 , 122 are surface- mounted on the bottom surface of the PCB 103 and extend iom the receiver 104 to the antennas 106, 108 respectively. V. Third Alternative Aspect Tightly-Coupled PCB Circuit 1 52

[00025] A tightly-coupled PCB circuit 152 comprising a third alternative aspect or embodiment of the present invention is shown in Figs. 5 and 6 and includes a PCB 153. The PCB circuit 152 includes a receiver 154. first and second G MSS patch antennas 156, 158 and a power supply 160. Multiple decoupling capacitors 162 torn first and second decoupling lines 164. 166. w hich form generally circular isolation islands 168. 1 70 at respective ends of the PCB 153 for the antennas 156, 158 respectiv ely. Additional decoupling capacitors 162 are provided adjacent to edges of the PCB 153. A central isolation island 169 is formed for the receiver 154 and a power supply 160. As shown in Figs. 5 and 6, the isolation island 169 can have an irregular shape. Internal first and second RF striplines or traces 1 71 , 172 are provided w ithin the PCB 153 and extend from the central isolation island 169 to the antennas 156. 158 located in the isolation islands 168. 1 70 respectively. Alternatively, the R F traces 1 71. 172 can be surface- mounted.

|00026] It is to be understood that the invention can be embodied in various forms, and is not to be limited to the examples discussed above. For example, the PCBs and the isolation islands can be formed in a variety of configurations. Moreover, various components can be assembled in different configurations to form a wide variety of PCB circuits, which can effectively utilize the closely-coupled construction of the present invention w ith isolation islands. For example, multiple antennas and receivers can be provided. Although GNSS receivers and patch antennas are shown, other RF receivers and antennas can be utilized. The range of components and confϊgLirations w hich can be utilized in the practice of the present invention is \ irtualk unlimited.

Claims

CLAIMSHaving thus described the invention, w hat is claimed as new and desired to be secured by Letters Patent is:

1 . A method of tightly coupling a printed circuit board ( PCB). which method 5 comprises the steps of: providing a PCB w ith multiple conductive layers; separating said conductive layers with insu lating layers: providing a positive reference layer; providing a ground plane comprising a grounded reference la\ er: I O providing a signal lay er; photoetching the signal layer to define a circuit: providing electrical components: connecting each electrical component to one or more layers: forming a decoupling line in said PCB; and 1 5 forming an electrical isolation island in said PCB with said decoupling line.

2. The method of claim I w herein one ot said components comprises a receiver, which method includes the additional steps of: providing said PCB w ith a perimeter: connecting said receiver to said PCB; and 0 extending said decoupl ing line from said receiver to F¹CB perimeter.

3. The method of claim 2 w herein said components include an antenna, w hich method includes the additional steps of: providing an RF transm ission line connecting said antenna to said receiver; and 25 locating said antenna in said isolation island.

4. The method of claim 3. w hich include -; the additional steps of: - I I - forming an optimal RF path from the antenna to the receiver, thereby creating a decoupling line: and forming said isolation island along said decoupling line path.

5. The method of claim 2, which includes the additional steps of: locating said receiver in an interior area of said PCB: providing a pair of said decoupling lines: and extending said decoupling lines from said receiver to said PCB perimeter.

6. The method of claim I . which include:; the additional step of:

forming said decoupling line with a plurality of discrete decouplers each extending through said PCB la>ers.

7. The method of claim 3. which includes the additional steps of:

providing said PCB v\ ith three sections each teπninat ng at an outer end:

locating said receiver centrally with said PCB section:; extending outwardly therefrom:

mounting an antenna in each of said sections in proxi nity to its outer end;

extending a pair of said decoupling lines from said receiver to each said PCB section outer end: and

formin 'ag an isolation island in each said PCB section with said antenna located therein.

8. A method of manufacturing a tightly-coupled PCB circuit w ith a power suppl) . a GNSS receiver and first and second GNSS antennas, w hich method comprises the steps of:

providing a PCB with multiple conductive layers: separating said conductive layers with insulating layers: providing a positive reference layer: prov iding a ground plane comprising a giounded reference layer: prov iding a signal layer; photoetching the signal la>er to define a circuit; prov iding said PCB with a perimeter; mounting said power supply and said GNSS receiver .MI said PCB- connecting said power supply and said GNSS receive to said positive and grounded reference layers; prov iding multiple decoupling capacitors; connecting each said capacitors to multiple said PCB layers and electrically closely- coupling said PCB layers with said capacitors; determining optimal first and second RF paths from the antennas to the receiver; aligning multiple said decoupling capacitors along said optimal RF paths and thereb> creating first and second decoupling lines each extending from said receiver to said PCB edge in proximity to a respective antenna; forming first and second isolation islands along said Irst and second decoupling line paths respectively; prov iding first and second RF transmission lines connecting said receiver to said first and second antennas respectively ; and locating said first and second antennas in said first and second isolation islands respectively .

9. A tightly -coupled printed circuit board (PCB) circuit, which includes: multiple conductive layers; insulating layers separating said conductive lay ers, a positive reference layer: a ground plane comprising a grounded reference lay ei : a signal layer: a circuit photoetched in the signal layer; multiple electrical components each connected to one or more lavers: a decoupling line in said PCB: and an electrical isolation island formed by said decoupling line in said PCB.

10. The circuit of claim 9, which includes one of said components comprising a receiver: said PCB including a perimeter: said receiver being connected to said PCB: and said decoupling line extending from said receiver to said PCB perimeter

1 1 . The circuit of claim 10, which includes: said components including an antenna located in said isolation island: and an RF transmission line connecting said antenna to said receiver.

12. The circuit of claim 1 1. which includes: an optimal RF path from the antenna to the receiver, said decoupling line generally follow ing said optimal RF path; and said isolation island being formed along said decoupl ng line path.

13. The circuit of claim 10. w hich includes: said receiver being located in an interior area of said I 'CB: a pair of said decoupling lines: and said decoupling lines extending from said receiver to said PCB perimeter.

14. The circuit of claim 9. which include-.:

said decoupling line being formed with a plurality of discrete decouplers each extending through said PCB la\ ers.

15. The circuit of claim 1 1 , which includes:

said PCB havin« three sections each terminatin^g at an outer end: said receiver being located centrally \\ iih said PCB sections extending outwardly therefrom;

three antennas each mounted in a respective section in proximity to its outer end;

a pair of said decoupling l ines each extending from si iό receiver to a respective PCB section outer end; and

three said isolation islands each located in a respective PCB section and each having a respective antenna located therein.