US-12621926-B2 - Printed circuit board including interdigital slots and/or splits on reference planes for reducing EMI

Abstract

The invention is particularly related to design slot and splits on the reference planes of printed circuit boards with an interdigital geometry having conductive fingers protruding from the opposite edges of the slits and/or splits, and placing these conductive fingers in a way that they are intertwined without contacting each other so as to reduce the electromagnetic radiation level originating from the slots and splits, and to preserve the signal integrity.

Inventors

• AHMET YASIN CITKAYA
• SEYIT AHMET SIS
• COSKUN COSAR
• EKREM DEMIREL
• FATIH USTUNER

Assignees

• TURKIYE BILIMSEL VE TEKNOLOJIK ARASTIRMA KURUMU

Dates

Publication Date

20260505

Application Date

20220211

Priority Date

20210212

Claims (2)

1. 1 . A printed circuit board that limits electromagnetic radiation and preserves signal integrity by reducing unwanted electromagnetic radiation comprising at least a signal layer of the printed circuit board, and at least a reference plane on another layer of the printed circuit board wherein the printed circuit board comprises: at least one slot ( 9 . 8 ) in an interdigital structure consisting of intertwining conductive fingers ( 9 . 8 . 1 ) protruding from their opposite edges wherein the fingers coming out from opposite sides in the interdigital structure increase the capacitance value between the two edges, allowing the interdigital slot to exhibit lower impedance within a certain frequency range compared to a normal slot, thereby allowing more of the return current to complete its loop through a shorter path as a displacement current instead of touring around the slot, and wherein the interdigital slot on the reference plane and the signal line are perpendicularly oriented to one another.
2. 2 . A printed circuit board that limits electromagnetic radiation and preserves signal integrity by reducing unwanted electromagnetic radiation comprising; at least two reference planes on two different layers of the printed circuit board, wherein at least one of the layers comprises: at least one slot ( 9 . 8 ) in the form of an interdigital structure consisting of intertwining conductive fingers ( 9 . 8 . 1 ) protruding from their opposite edges, wherein the length of the two opposite sides facing each other increases due to the interdigital structure, and this increase in the capacitance decreases the impedance and increases the displacement current, thereby reducing electromagnetic radiation within a certain frequency range; and wherein at least a signal layer between any two of the adjacent reference planes, and the interdigital slot on the reference plane and the signal line are perpendicularly oriented to one another.

Description

TECHNICAL FIELD OF THE INVENTION The invention is related to a method for improving the printed circuit boards (PCBs) in terms of electromagnetic interference (EMI) and signal integrity (SI). The invention is also related to a method for limiting the electromagnetic radiation sourced from the slots and/or splits patterned on the reference planes of the PCBs for use in separating the different voltage levels and/or also isolating the sensitive RF/analog circuits from the noisy digital circuits. The invention is particularly related to forming a capacitance to allow high-frequency signals selectively pass through the slot/split in the reference plane by designing these slots and splits in an interdigital (comb) geometry consisting of intertwined fingers in various configurations. PRIOR ART Printed circuit boards are composed of superimposed conductive and insulating plane layers on which electronic circuits are produced at low cost and in mass. Modern printed circuits are extremely complex and multifunctional structures and are therefore often made of multilayered structures. A cross-section of a multilayer printed circuit board is given in FIG. 1(a) and a top view is given in FIG. 1(b). As seen in FIG. 1, some layers are used as signal layers (1.1, 1.3, 1.4, 1.6), while some layers are power or ground planes called reference planes (1.2, 1.5). Such a complex printed circuit board contains multiple direct current (DC), digital, analog, and even radio frequency (RF) circuits. This complexity requires creating power or ground islands at different DC voltage levels on the reference plane. Digital circuits are more tolerant to noise than analog and RF circuits, and even such circuits are noise sources themselves. A typical approach to separate sensitive analog and RF circuits in printed circuit boards from noisy digital circuits is to create islands or peninsulas by placing slots or splits between the reference planes of each circuit. In FIG. 1(b), the split (1.7) and slot (1.8) structures are shown in the reference plane (1.2) on the second layer. Due to the complexity and compact nature of the card, a signal path in the upper or lower signal layer may have to cross these slots and splits perpendicularly. Therefore, unwanted electromagnetic radiation is generated due to the return currents flowing from the edges of the slots and splits. The representation of the slots created in various configurations for isolation on the reference plane in a printed circuit in the current technique and on which stitching capacitors are used in different numbers and at different positions is given in FIG. 2 for an example two-layer printed circuit board (2). In FIG. 2, a signal path (2.1) in the signal layer passes over the slot (2.2) on a reference plane in the lower or upper layer, intersecting the slot at right or different angles. The slot (2.2) here creates an inductive impedance on the path of the return current flowing on the reference plane, limiting the noise current to flow over the ground line. The reason why this inductive impedance occurs is that the return current does not flow directly under the microstrip signal line (2.1) but completes its loop by wrapping around the slot (2.2). However, the current flowing through this extended path increases the electromagnetic radiation. To provide a low impedance path for the signal return current and reduce the electromagnetic radiation from the slot (2.2), one or more stitching capacitors (2.3) are placed at various positions on the reference plane to connect the two edges of the slot (2.2). Different shaped slot geometries are also possible, such as zigzag slot (3.2) designs. Stitching capacitors (3.3) are used to reduce the electromagnetic radiation level in such slots with different geometries. Again, in the current technique, the representation of the splits, created for the same purpose and on which stitching capacitors are used, is given in FIG. 3 for an example two-layer printed circuit board (4). In FIG. 3, a signal path (4.1) in the signal layer passes over the split (4.2) on a reference plane in its lower or upper layer, at right or different angles. The split (4.2) here divides the reference plane completely into two pieces. Here, although the return current can not complete its path on the reference plane directly on the conductor due to the discontinuity formed by the split (4.2), it completes its path as a displacement current due to the capacitive effect on the split (4.2) at the high frequencies. Because of this discontinuity in the return current, current flows along the edge of the split, which increases the level of electromagnetic radiation. To provide a low impedance path for the signal current and reduce the electromagnetic radiation caused by the existence of the split (4.2), one or more stitching capacitors (4.3) are placed at various positions on the reference plane to connect the two edges of the split (4.2). Split geometries of different shapes,