TRANSFORMER-BASED BALUN WITH CORRECTION FOR DIFFERENTIAL IMBALANCE
20230107225 · 2023-04-06
Inventors
Cpc classification
H01F27/306
ELECTRICITY
H01F19/04
ELECTRICITY
H01F27/29
ELECTRICITY
H03H7/42
ELECTRICITY
International classification
H01F27/30
ELECTRICITY
H01F27/29
ELECTRICITY
Abstract
A circuitry including a first winding coupled to a second winding; a first terminal coupled to a first end of the first winding; a second terminal coupled to a second end of the first winding, wherein there is an imbalance between the first terminal and the second terminal when a current flows through the first winding; and a third terminal coupled to the second winding, wherein a terminal position of the third terminal along the second winding mitigates the imbalance on the first winding.
Claims
1. A circuitry comprising: a first winding coupled to a second winding; a first terminal coupled to a first end of the first winding; a second terminal coupled to a second end of the first winding, wherein there is an imbalance between the first terminal and the second terminal when a current flows through the first winding; and a third terminal coupled to the second winding, wherein a terminal position of the third terminal along the second winding mitigates the imbalance on the first winding.
2. The circuitry of claim 1, further comprising a differential port, wherein the differential port includes the first terminal and the second terminal.
3. The circuitry of claim 2, further comprising a single-ended port, wherein the single-ended port includes the third terminal and a ground terminal coupled to the second winding, wherein the ground terminal is connected to a reference signal.
4. The circuitry of claim 3, wherein the terminal position of the third terminal is off a center of the circuitry.
5. The circuitry of claim 1, further comprising an outer ring encircling the first winding and the second winding.
6. The circuitry of claim 5, wherein the outer ring is coupled to a ground reference signal.
7. The circuitry of claim 1, wherein the first winding includes one or more turns.
8. The circuitry of claim 1, where in the second winding includes a first turn and a second turn, wherein the first turn encircles the second turn.
9. A method of designing a circuitry comprising: determining an imbalance between a first terminal and a second terminal of a differential port coupled to a first winding; and determining a position of a single-ended port coupled to a second winding, wherein the position of the single-ended port mitigates the imbalance between the first terminal and the second terminal.
10. The method of claim 9, wherein determining the position of the single-ended port is based on a composition of the first winding.
11. The method of claim 9, wherein determining the position of the single-ended port is based on a composition of the second winding.
12. The method of claim 9, wherein determining the position of the single-ended port is based on a radius of the first winding.
13. The method of claim 9, wherein determining the position of the single-ended port is based on a radius of the second winding.
14. The method of claim 9, wherein determining the position of the single-ended port is based on a width of the first winding.
15. The method of claim 9, wherein determining the position of the single-ended port is based on a width of the second winding.
16. The method of claim 9, wherein determining the position of the single-ended port is based on a number of turns on the first winding or the second winding.
17. The method of claim 9, wherein determining the position of the single-ended port includes determining an angle of the single-ended port relative to the first terminal or the second terminal.
18. A circuitry comprising: a first winding coupled to a second winding; a single-ended port coupled to the second winding, wherein the single-ended port includes a single-ended terminal and a ground terminal; a first terminal coupled to a first end of the first winding; and a second terminal coupled to a second end of the first winding, wherein there is an imbalance between the first terminal and the second terminal when a current flows through the first winding, and wherein a first position of the first terminal and a second position of the second terminal along the first winding mitigates the imbalance on the first winding.
19. The circuitry of claim 18, further comprising a differential port, wherein the differential port includes the first terminal and the second terminal.
20. The circuitry of claim 19, wherein a position of the differential port is off a center line of the circuitry.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the exemplary principles of the disclosure. In the following description, various aspects of the disclosure are described with reference to the following drawings, in which:
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DETAILED DESCRIPTION
[0017] A balun may be equipped with lumped capacitors at certain points of the transformer winding, or coil, to tune a differential imbalance to zero at a given frequency point. For example, a differential port of a balun may be loaded with a capacitor on one side to cancel the differential imbalance. The location and value of capacitor may vary depending on the frequency.
[0018] Loading a lumped capacitor on the differential port may only correct the differential imbalance across a narrow frequency. Correcting the imbalance with a capacitor is fixed in correlation with the value of the capacitor on a single spot of the winding which is narrowband in nature.
[0019] Loading additional capacitors on a balun decreases the self-resonance frequency (SRF) of the transformer, which further limits the usable frequency range of the balun.
[0020] Additionally, a balun may include a dummy metal winding under the two main windings of a transformer balun to counteract a differential imbalance. The dummy winding may have two terminals or ports. For example, the dummy winding below the transformer winding may have one of its terminals tied to ground. Alternatively, the dummy metal winding may introduce different capacitive loading to the positive and negative terminals of the transformer winding. Introducing additional capacitance may lower the SRF of the balun.
[0021] Traditionally, a balun has an equal distance between the single-ended port and both terminals of the differential port, resulting in a symmetrical structure of the balun. The single-ended port may include two terminals, one for carrying an unbalanced signal and the other connected to ground. The differential port may include a voltage, current, or impedance imbalance between the two differential terminals. To counteract an imbalance between the two differential terminals, we may introduce a new, controlled, imbalance to the balun design layout structure. Balancing the distance between the single-ended port on one winding of the balun and the two terminals of a differential port on another winding may introduce the new imbalance. This may result in an asymmetrical design of the balun. By moving the location of the single-ended port alone, the imbalance on the differential port may be mitigated. For example, the position of the single-ended may manipulate the imabalance so that the impedance transformation (e.g., signal transfer) from one winding to the other is better balanced on the differential port. The asymmetrical design, may create an adjustment of the electric field distributed across the entire transformer winding, which achieves a wideband correction compared to a cancellation based on a lumped capacitor.
[0022]
[0023] The distance between terminal 104a and port 114 is equidistant to the distance between terminal 104b and port 114. The equidistance design between differential port 104 and single-ended port 114 may introduce a differential imbalance as further described below. However, an asymmetrical design having varying distances between differential terminals 104a and 104b and single-ended port 114 may mitigate a differential imbalance.
[0024]
[0025] The design of balun 100 may generate a differential imbalance of approximately 0.3 dB. The asymmetrical design of balun 200 may differ from the symmetrical design of balun 100 in that the single-ended port may be 12 .Math.m left of center line 224 along second winding 210. The design of balun 200 may also include first winding 202 having a radius of 34.5 .Math.m from center 220 to inner metal edge of the turn coil of 34.5 .Math.m. First winding 202 may have a metal width (e.g., thickness) of 9.9 .Math.m. Second winding 210 may have a radius of 22.5 .Math.m from center 220 to the inner metal edge of the inner turn coil of the second winding. Additionally, second winding 210 may include a space of 7.9 .Math.m between the outer metal edge of the inner turn coil to the inner metal edge of the outer turn coil. Second winding 210 may also include a metal width of 5um.
[0026]
[0027] An asymmetric balun design will position at least one terminal configured to carry an unbalanced signal or single-ended port off of a center line of the balun. The position of the single-ended port may depend on several factors, including the composition material of the balun. For example, the balun windings may include radio frequency (RF)/thick metals which may affect the imbalance of the balun. RF technologies may include an optional thick metal layer on top, such as copper and aluminum, on top of other metal layers. This composition used in the design of a balun may be a parameter to determine the best placement of the single-ended port in an asymmetric balun design. Other parameters may include dimensions such as radius, spacing, width, shape such as octagon, rectangle, square of the windings, as discussed elsewhere in this disclosure.
[0028] Antennae, or sensors, may be single-ended. However, many circuit blocks in integrated chips are differential. State-of-the-art transceivers often have on chip baluns to reduce Bill-of -Materials (BOM) and module size. Because baluns are often located at the very front-end of a transceiver, reducing a differential imbalance in the balun is critical in achieving high linearity, high efficiency, and low noise of the entire wireless communication system. It is also highly desirable to have balanced differential signal swing from a circuit reliability perspective. This provides a performance improvement and longer life expectancy for a better user experience.
[0029] Baluns may convert a differential signal to single-ended signal or a single-ended signal to a differential signal. Among many types of baluns, transformer-based baluns are commonly used in radio frequency and mm-wave transceivers. Often, baluns are integrated on silicon and may be located at the very front-end of the chip. For example, at an RF pin of the chip.
[0030] A balun transformer may have two metal windings. When alternating current (AC) signal current flows on a first winding, the magnetic field generated by the current flow couples to the second winding. To implement the magnetic, inductive, coupling on the integrated chip, two windings are typically placed on top of each other. This also brings an electric, capacitive, coupling between windings. When a balun transformer is driven differentially on both ports, the electric coupling is well balanced and does not create imbalance between positive and negative terminals of a differential port. However, when a balun transformer is driven from a differential port to a single ended port, the positive and negative terminals of the differential port may experience different capacitive coupling, and there is an imbalance in the differential signal.
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[0032] In contrast,
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[0035] As previously described, transformers may be adopted for a differential to differential port coupling. In this case, a perfect symmetry on the center line (or line at the middle of terminals of each port) is desirable. However, when the transformer is used as a balun, a symmetric layout on the single-ended port is not required because the winding already carries single-ended (e.g., unbalanced) voltage signal. More importantly, it is not desirable because the symmetric transformer-based baluns will create unbalanced electric coupling to a differential port. To mitigate an unbalanced electric coupling, a single-ended port may introduce an imbalance an imbalance to counteract the imbalance on the differential port from electric coupling.
[0036] Positioning a port off of the center line along a single-ended winding may create a correction to the imbalance on the differential port on the transformer winding. For example, the balun designs as described in
[0037] Positioning a single-ended port off of a balun center-line, may correct the capacitance distributed across the entire winding. The correct capacitance achieves wideband cancellation as demonstrated in simulation results below. Additionally, the off center position does not add additional components to traditional balun design layout patterns. Therefore, no additional parasitic components are added. Finally, the circuit on the differential side of the transformer still sees perfectly balanced coil self-inductance, which is highly desirable for differential amplifiers.
[0038]
[0039] Terminal 802 is single-ended port simulation on a single-ended metal winding. Terminals 804 and 806 are placed in series combination, to simulate imbalance between terminals 804 and 806 on the differential port. An S21 parameter from port 804 to 802 and S31 parameter from port 806 to port 802 simulation are compared to evaluate imbalance on the differential side 810. Using such a simulator, one can determine the imbalance and adjust port placement to reduce or eliminate the differential imbalance. For example, the balun design simulator may allow for testing different designs before producing a balun. One can input parameters of a symmetrical design to measure a differential imbalance on the balun design. The parameters may be changed to reduce the measured imbalance. For example, the position of port 802 may be moved along the transformer winding to determine its effect on the differential imbalance. Alternatively, an angle of port 802 relative to ports 804 and/or 806 may be modified to determine the angle’s effect on the differential imbalance.
[0040] Using an algorithm to minimize the differential imbalance in conjunction with the simulator may optimize determining the optimal placement of port 802. Such an algorithm may evaluate incremental changes of port 802’s position along a segment of the transformer winding. Alternatively, the algorithm may evaluate changes in the angle between a differential port, terminals 804 and 806, and a single-ended port 802. More than one optimal port position may minimize the differential imbalance. The algorithm may be configured to return the first port position to minimize the differential imbalance or return after determining all port positions which minimize the differential imbalance. The algorithm may consider other factors to determine an optimal port position. For example, a port position on the same winding segment as a symmetrical balun design may be considered more desirable as a port position which is on a different winding segment as a symmetrical balun design. Additionally, the algorithm may be configured to with an incremental change to reduce execution time. For example, the algorithm may only evaluate 0.5 .Math.m incremental changes in position and/or integer angle measurements.
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[0042] Plot 900 plots the magnitude (mag_mm) imbalance in dB as a function of single-ended port position, where position 0 is the position along vertical center line 906 as shown in balun design 902. Plot 900 shows the incremental changes as determined by an algorithm. From the reference balun design 900, a negative port position indicates a movement to the left and a positive port position indicates a movement to the right. The imbalance is measured for the port position at different points along the x-axis. For example, positioning the single-ended port at -12 .Math.m results in a 0 or near 0 simulated differential imbalance measured in dB. Balun design 910 shows the port position 912 which may reduce a differential imbalance to 0 or near 0 dB. Please note that the desirable location will differ from design to design and there may be more than one position to achieve the goal of 0 or near 0 imbalance. An imbalance of a symmetrical port position design also differs from design to design, where the design parameters may include a winding radius, a winding composition, a winding spacing, and/or inclusion of a guard ring.
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[0046] Transformer baluns have had an increased use in fifth-generation (5G) applications. Transformer baluns may be integrated in radio transceivers. A transformer balun may be designed for millimeter-wave frequencies and implemented on a complementary metal oxide semiconductor (CMOS) with an integrated mixer. For example, an integrated balun may be configured for up to a measured amplitude of 5 dB and phase balance of 7 degrees over 50-70 GHz frequency band. This may achieve a relatively small footprint, simple layout, and wide operational frequency range.
[0047]
[0048] While the above descriptions and connected figures may depict electronic device components as separate elements, skilled persons will appreciate the various possibilities to combine or integrate discrete elements into a single element. Such may include combining two or more circuits for form a single circuit, mounting two or more circuits onto a common chip or chassis to form an integrated element, executing discrete software components on a common processor core, etc. Conversely, skilled persons will recognize the possibility to separate a single element into two or more discrete elements, such as splitting a single circuit into two or more separate circuits, separating a chip or chassis into discrete elements originally provided thereon, separating a software component into two or more sections and executing each on a separate processor core, etc.
[0049] It is appreciated that implementations of methods detailed herein are demonstrative in nature, and are thus understood as capable of being implemented in a corresponding device. Likewise, it is appreciated that implementations of devices detailed herein are understood as capable of being implemented as a corresponding method. It is thus understood that a device corresponding to a method detailed herein may include one or more components configured to perform each aspect of the related method.
[0050] All acronyms defined in the above description additionally hold in all claims included herein.