DETAILED ACTION
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
Response to Arguments
Applicant’s arguments filed on 06/18/2026 have been fully considered but are moot or not persuasive for the reasons set forth below.
Despite the Examiner's clear guidance during the interview regarding the ambiguity of the claim language and the necessity of citing a secondary reference to support the design choice modification, the applicant elected not to amend the independent claims to overcome the prior art. Therefore, the rejections should be maintained (requiring a New Ground of Rejection to formally introduce the secondary reference for Claim 1).
Regarding Claim 1 and the modification of Chung: Applicant argues that the rejection of claim 1 over Chung is improper because Fig. 8 of Chung illustrates a different main line to sub-line connectivity than what is claimed. Specifically, applicant asserts that modifying Chung’s connection as proposed by the Examiner would cause a phase reversal, which destroys the intended function of the circuit, and therefore cannot be considered an obvious design choice.
This argument is not persuasive. As discussed during the Examiner Interview on April 15, 2026, configuring the terminals of a transmission line transformer (such as a Ruthroff balun) to achieve a specific phase polarity is a routine engineering decision. Reversing the connections to intentionally invert the phase is a well-known technique in RF circuit design to meet the specific phase-matching requirements of downstream components (such as the push-pull amplifier discussed in the rejection). To formally support this position under MPEP § 2144.03, the Examiner has cited a secondary reference in the accompanying rejection [Buckles et al. (U.S. Patent No. 6,756,874) and Kam (U.S. Patent No. 3,504,306)] which demonstrates that swapping transformer terminal connections to adjust phase polarity is a known and predictable design choice to a person having ordinary skill in the art. Therefore, the modification does not destroy the function of the balun, but rather predictably alters its phase output, which is obvious.
Regarding Claim 9 and the impedance matching network: Applicant argues that the limitations of claim 9 are not met by Gunnarsson because claim 9 requires the impedance matching network to be "coupled between" the second end of the first main line and the second end of the second sub-line, which applicant interprets strictly as a "series" topology. Applicant argues that element 8' of Gunnarsson is a shunt connection and therefore does not meet the claim limitation.
This argument is not persuasive. During the April 15, 2026, interview, the Examiner explicitly advised the applicant that the phrase "coupled between" is structurally ambiguous and does not inherently restrict the topology to a series connection. Under the Broadest Reasonable Interpretation (BRI) during patent prosecution, an element that is "coupled between" two nodes simply mean it is electrically situated in the circuit path separating those two nodes. This broad functional language encompasses both series components and shunt components that tap off the line between the designated nodes. Because the applicant elected not to amend claim 9 to specify a "series" connection as advised, the Examiner must continue to apply the broadest reasonable interpretation. Under this interpretation, the shunt impedance matching network (element 8') of Gunnarsson is electrically coupled between the recited points in the circuit, and the rejection is maintained.
As the applicant challenged the “Official Notice" of claim 1, under MPEP § 2144.03, the examiner is required to provide documentary evidence (a prior art reference) to back up the assertion in the current Office Action which constitutes a New Ground of Rejection (under MPEP § 706.07(a)).
Procedurally, when a New Ground of Rejection is made in a subsequent Office Action, that action generally cannot be made Final to provide the applicant another full opportunity to respond and amend the claims without needing to file a Request for Continued Examination (RCE) or pay additional fees. Therefore this office action is made a second non-Final Rejection.
Claim Rejections - 35 USC § 103
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
The factual inquiries set forth in Graham v. John Deere Co., 383 U.S. 1, 148 USPQ 459 (1966), that are applied for establishing a background for determining obviousness under 35 U.S.C. 103 are summarized as follows:
1. Determining the scope and contents of the prior art.
2. Ascertaining the differences between the prior art and the claims at issue.
3. Resolving the level of ordinary skill in the pertinent art.
4. Considering objective evidence present in the application indicating obviousness or nonobviousness.
Claims 1-8 are rejected under 35 U.S.C. 103 as unpatentable over Chung et.al. (“Design of Step-Down Broadband and Low-Loss Ruthroff-Type Baluns Using IPD Technology”, IEEE TRANSACTIONS ON COMPONENTS, PACKAGING AND MANUFACTURING TECHNOLOGY, VOL. 4, NO. 6, JUNE 2014, cited by the applicant), in view of Buckles et al. (U.S. Patent No. 6,756,874) and Kam (U.S. Patent No. 3,504,306).
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Fig. 8 of Chung annotated by the examiner for ease of reference.
Regarding claim 1, A unbalanced-to-balanced transformation circuit (the circuit of Fig. 8) comprising:
a first transmission line transformer (4:1 un-to-un TLT) configured to perform impedance transformation, to receive an unbalanced signal (across Rg) as an input signal (V and I), and to output an unbalanced signal as an output signal (V/2 and 2I at node 3);
a second transmission line transformer (1:4 TLT balun) configured to perform unbalanced-to-balanced transformation (from single ended to differential);
an unbalanced-signal input / output node (3); and
a pair of balanced-signal input / output nodes (4-5), wherein the first transmission line transformer (4:1 un-to-un TLT) comprises a first main line (M1) and a first sub-line (S1);
wherein the first main line (M1) and the first sub-line (S1) are coupled such that a direction from a first end (E1) of the first main line (M1) to a second end (E2) of the first main line (M1) is identical to a direction from a first end (E3) of the first subline (S1) to a second end (E4) of the first sub-line (S1),
wherein the second end (E2) of the first sub-line is coupled to the first end of the first main line, wherein the first end of the first sub-line is grounded1,
wherein the first end (E1) of the first main line (M1) is coupled to the unbalanced-signal input/output node (1), wherein the second transmission line transformer (1:4 TLT balun) comprises a second main line (M2) and a second sub-line (S2), wherein the second main line (M2) and the second sub-line (S2) are coupled such that a direction from a first end (E5) of the second main line (M2) to a second end (E6) of the second main line (M2) is identical to a direction from a first end (E7) of the second subline (S2) to a second end (E8) of the second sub-line (S2),
wherein the first end (E5) of the second main line (M2) is coupled to the second end (E2) of the first main line (M1), wherein the second end (E6) of the second main line (M2) and the first end (E7) of the second sub-line (S2) are grounded, and
wherein the first end (E5) of the second main line (M2) and the second end (E8) of the second sub-line (S2) are respectively coupled to the pair of balanced-signal input/output nodes (4-5).
Wherein contrary to the second end (E4) of the first sub-line (S1)’s coupling to the first end (E1) of the first main line (M1) as claimed, the first end (E3) of the first sub-line (S1) is coupled to the second end (E2) of the first main line (M1) and instead of the first end (E3) of the first sub-line (S1) being grounded, the second end (E4) of the first sub-line is grounded.
Chung does not explicitly disclose swapping the main-line to sub-line connections to match the claimed arrangement. However, Buckles (U.S. Patent No. 6,756,874) explicitly teaches that reversing the terminal connections of a transmission line transformer accomplishes a signal inversion. Specifically, Buckles discloses in the "Brief Description of the Drawings" section, "FIG. 3 showing how a simple connection reversal accomplishes a signal inversion" (Col. 2, Lines 35-36).
Furthermore, Kam (U.S. Patent No. 3,504,306), in the same field of endeavor of broadband RF amplifiers, teaches a "reversing transformer" utilizing a transmission line section to achieve a 180-degree phase shift by swapping the conductor connections to reverse the polarity, explicitly stating "the input signal is connected to outer conductor 20 at one end of the coaxial line while the output signal is obtained from the center conductor 18 at the opposite end" (Col. 2, Lines 14-18).
It would have been obvious to a person of ordinary skill in the art to modify the Ruthroff transmission line transformer of Chung by reversing the terminal connections—specifically coupling the second end (E4) to the first end (E1) and grounding the first end (E3) instead of the second end (E4)—as explicitly taught by Buckles and Kam.
The motivation for this modification would be to achieve a predictable and desired signal polarity or phase inversion required to properly offset the input and output signals for downstream components. This modification constitutes a predictable use of known prior art elements (reversing terminals) according to their established functions (phase/signal inversion) to achieve a predictable result.
Wherein per claim 2 Chung teaches that the first main line (M1), the first sub-line (S1), the second main line (M2), and the second sub-line (S2) are spiral conductive patterns in a common substrate (See Fig. 10), wherein one of the first transmission line transformer (3-D view of Fig. 10(a)) and the second transmission line transformer is surrounded by another of the first transmission line transformer and the second transmission line transformer in a plan view of the unbalanced-to-balanced transformation circuit.
And further per claim 3, Chung also teaches that the lines are spiral conductive patterns in a plurality of wiring layers in the substrate, and first main line and the first sub-line are in different wiring layers among the plurality of wiring layers, and the second main line and the second sub-line are in different wiring layers among the plurality of wiring layers (see Fig. 10(a) and 10(b)).
and wherein per claim 5, wherein at least a portion of the first main line coincides with at least a portion of the first sub-line in the plan view (essential for coupling, see Fig. 10(b), the orange trace and olive traces coincide with each other in different locations based on the requirement of coupling, the original paper is available in color and can be downloaded from online), and
wherein at least a portion of the second main line coincides with at least a portion of the second sub-line in the plan view (same is true for the second main transformer, see Fig. 10(c)). And per claim 6, Chung also teaches that at least a portion of a width of the first main line coincides with at least a portion of a width of the first sub-line in the plan view, and wherein at least a portion of a width of the second main line coincides with at least a portion of a width of the second sub-line in the plan view (see Figs.10(a) through 10(c)).
Also, per claim 4, Chung teaches in an exemplary embodiment of Fig. 10(c) that
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the first main line and the second main line are spiral conductive patterns in the same wiring layer (p. 971, left col. See insert).
Per claim 7, Chung teaches that the first main line, the first sub-line, the second main line, and the second sub-line are spiral conductive patterns in a plurality of wiring layers (3-D view of Fig. 10(a)) provided in the substrate,
Wherein the first main line and the first sub-line are in the same wiring layer among the plurality of wiring layers (dark green color traces on one metal layer and olive green color traces on a different metal layer, see Fig. 10(a), the original paper is available in color and can be downloaded from online), and the second main line and the second sub-line are in the same wiring layer among the plurality of wiring layers.
Further per claim 8, Chung teaches that a first external connection terminal (balanced ports, Fig. 10(a)) for a first balanced signal and a second external connection terminal for a second balanced signal that are at the substrate;
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Fig. 10(a) of Chung annotated by the examiner for ease of reference.
a first wiring line coupling the first external connection terminal (the unbalanced ports) to the first end of the second main line (M1); and
a second wiring line coupling the second external connection terminal to the second end of the second subline, wherein the first transmission line transformer is surrounded by the second transmission line transformer in the plan view (Fig. 10(a)),
wherein the first external connection terminal and the second external connection terminal are arranged parallel to the second main line and the second sub-line, outside a region defined by the second transmission line transformer, in the plain view (see Fig. 10(a) above),
wherein the first wiring line extends in a direction perpendicular (see Fig. 10(b) and 10(c) for clearer view of the orthogonality of the trances to make connections to the external ports) to the second main line from the first end of the second main line to a location outside the region defined by the second transmission line transformer, and
wherein the second wiring line extends in a direction perpendicular (see Fig. 10(b) and 10(c) for clearer view of the orthogonality of the trances to make connections to the external ports) to the second sub-line from the second end of the second sub-line to a location outside the region defined by the second transmission line transformer.
Claims 9-10 are rejected under 35 U.S.C. 103 as unpatentable over Chung et.al. in view of Gunnarsson.
Regarding claims 9 and 10, Chung also teaches that the integrated passive devices (IPDs) unbalanced-to-balanced transformation circuit is employed to produce high-quality low-loss matching networks (p. 967, right col., lines 1-5). Wherein Chung shows in Fig. 8, teaches as 4: 1 transformer configuration cascaded by a 1:4 balun which provides impedance matching a source impedance of Rg to a load impedance of Rdiff over a wide frequency range (1-dB bandwidth of 6.56 GHz is from 2.02 to 8.58 GHz, plot of Fig. 9(b)).
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Fig. 2 of GUNNARSSON annotated by the examiner for ease of reference.
Chung exemplarily discloses in Fig. 3(b) a phase compensation line as an effort to impedance matching circuit coupled between the first end (E1) of the first main line (M1) and the unbalanced-signal input/output node (1),
In a similar field of endeavor, Gunnarsson teaches in a balanced-unbalanced transformer, connection of series L-C resonators at different section of the main-line and sub-line of the transformer (Gunnarsson: §0033-§0034).
Therefore, it would have been obvious to a person of ordinary skill in the art to use proper phase matching or impedance matching elements between the unbalanced port (1) of the transformer and the first end (E1) of the main line (M1) and between different other sections of the transformer (taught by Gunnarsson) such as the second end of the first main line and the second end of the second sub-line, and the pair of balanced-signal input/output nodes of the transformer for appropriate impedance and phase matches between the source and load impedances to which the transformer is connected (i.e. converting the unbalanced signal into a balanced signal or vice versa.
Claims 11 and 12 are rejected under 35 U.S.C. 103 as unpatentable over Lin et al., (US 2021/0194451 A1) in view of Chung.
Regarding claims 11, Lin teaches an amplifier circuit (310, Fig. 7A) comprising:
a differential amplifier (305, 306) comprising a pair of input nodes (3-2) and a pair of output nodes (3-2); and
a first unbalanced-to-balanced transformation circuit (input balun 301) according to Claim 1,
wherein the pair of balanced-signal input/output nodes (3-2) of the first unbalanced-to-balanced transformation circuit (301) is coupled to input pair of nodes (3-2) of the differential amplifier.
And per claim 12, a second unbalanced-to-balanced transformation circuit (302), wherein the pair of balanced-signal input/output nodes (3-2) of the second unbalanced-to-balanced transformation circuit (302) is coupled to the pair of output nodes of the differential amplifier (305-306).
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Fig. 7A of Lin et al. annotated by the examiner for ease of reference.
Lin is not explicit about the transformer as recited in claim 1.
However, Chung teaches the broadband IPD transformer circuit as recited in claim 1, having superior bandwidth and low loss performance.
Therefore, a person of ordinary skill in the art would find it obvious to replace the input and output balanced unbalanced transformer of Lin with the Chung Ruthroff transformer (as discussed in regard to claim 1) for obvious benefits of broad band operation with spurious rejection and phase transformation in order to accomplish better match and combining transformation necessities of the Push pull amplifier of Lin.
Claims 13 and 142 are rejected under 35 U.S.C. 103 as unpatentable over Chung et al. (“Design of Step-Down Broadband and Low-Loss Ruthroff-Type Baluns Using IPD Technology”) in view of Fritz et al. (U.S. Patent No. 9,106,204).
Regarding claims 13 and 14, Chung teaches the core unbalanced-to-balanced transformation circuit (Ruthroff-type transmission line transformer/balun) comprising an unbalanced-signal input/output node, a pair of balanced-signal input/output nodes, and a ground connection, as set forth in base Claim 1.
Chung, however, does not explicitly disclose a first and second capacitor coupled between the balanced-signal input/output nodes and external connection terminals (Claim 13), nor a third capacitor coupled between the unbalanced node and an external terminal, and a fourth capacitor coupled to a ground node (Claim 14).
Fritz (U.S. Patent No. 9,106,204), in the same field of endeavor of RF baluns interfacing with transceivers, explicitly recognizes that certain balun designs 'do not have a DC blocking capability between balanced and unbalanced ports' (Fritz, Col. 2, lines 25-27). To resolve this, Fritz teaches the necessity of integrating capacitors into the balun circuit to provide this required DC blocking capability, noting that 'Generally, capacitors act as DC-block, and therefore no additional blocking capacitors are required' (Fritz, Col. 6, lines 34-36; see also Claim 7). Furthermore, Fritz teaches coupling capacitors between internal nodes and ground to act as an AC ground or bypass to suppress unwanted oscillations from DC paths (Fritz, Col. 16, lines 10-15). It is a notoriously well-known and standard engineering practice in RF design to utilize capacitors in series with RF ports to block DC while passing RF signals, and to utilize capacitors at ground nodes to provide an AC ground while maintaining DC isolation.
It would have been obvious to a person having ordinary skill in the art to modify the Ruthroff-type transmission line transformer of Chung by adding the first, second, and third capacitors in series with the balanced and unbalanced nodes and their respective external connection terminals, and a fourth capacitor between the ground node and a fourth external terminal, to incorporate the DC blocking capabilities identified by Fritz.
The motivation to include these capacitors, as explicitly recognized by Fritz and standard RF engineering principles, is to provide necessary direct-current (DC) blocking and isolation between the balun's transmission lines and external single-ended or differential transceiver circuits (such as the differential amplifier recited in Claim 11). Because transmission line transformer windings physically act as a DC short to ground, a person of ordinary skill would recognize that series capacitors at the input/output ports and/or bypass capacitors at the ground node are strictly required to prevent external DC bias voltages from shorting to ground or improperly biasing downstream active components, while allowing high-frequency AC/RF signals to pass unimpeded. This modification represents the predictable use of known prior art elements (capacitors) according to their established functions (DC blocking/AC coupling) to yield an expected and predictable result.
Conclusion
Any inquiry concerning this communication or earlier communications from the examiner should be directed to HAFIZUR RAHMAN whose telephone number is (571)270-0659. The examiner can normally be reached M-F: 10-6.
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If attempts to reach the examiner by telephone are unsuccessful, the examiner’s supervisor, Jessica Han can be reached on (571) 272-2078. The fax phone number for the organization where this application or proceeding is assigned is 571-273-8300.
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/HAFIZUR RAHMAN/Primary Examiner, Art Unit 2843.
1 The greyed out claim limitation is not met by the prior art.
2 The Examiner has determined that the newly added claims 13 and 14 do not contain allowable subject matter. The addition of coupling/blocking capacitors at the input, output, and ground ports of an RF transformer is a routine and universally applied engineering practice to isolate DC bias voltages.
Prosecution Insights