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 Argument
The Examiner acknowledges Applicant’s Amendment and Remarks dated January 23, 2026, and appreciates the clarifications provided therein.
Although the Office Action dated November 12, 2025, identified claims 5 and 14 as containing allowable subject matter, following a careful review of the amended claims and considering the newly presented claim limitations, the Examiner has conducted a further search and reconsidered the prior position.
Upon this review, the Examiner determines that the amended claims are unpatentable over Pidgeon et al. (U.S. Patent No. 5,481,389) in view of secondary references within the same field of endeavor. Specifically, while Pidgeon explicitly discloses a post-distortion (PD) linearization circuit employing GaAsFET technology, the application of high electron mobility transistors (HEMTs)—including those utilizing indium arsenide composite channel (IACC) technology—is an obvious modification to one of ordinary skill in the semiconductor amplifier art.
As evidenced by the secondary prior art of record, HEMT devices were well known at the time of the invention to provide improved gain, linearity, and noise performance across comparable RF frequency ranges. Therefore, it would have been obvious to substitute Pidgeon’s GaAsFET devices with IACC HEMTs to achieve predictable performance enhancements without changing the fundamental operation of the post-distortion linearization scheme.
Accordingly, the Examiner maintains that the amended claims do not overcome the §103 rejection, as the substitution of GaAsFET devices with InAs-based composite channel HEMTs represents a routine design choice based on known semiconductor performance characteristics.
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 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 1-4, 6-8, 10-13 and 15-17 are rejected under 35 U.S.C. 103 as being unpatentable over Pidgeon et. al. (US 5,481,389) in view of Guan et al. (CN 106788278 B).
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Fig. 2 of Pidgeon annotated by the examiner for ease of reference.
Regarding claims 1, 5 and 10, Pidgeon discloses an RF amplifier circuit operating within a range of frequencies, such as the CATV frequency range (col. 1, line 45), in which signal linearity is improved by reducing intermodulation products at the final output (Fig. 2). Specifically, Pidgeon teaches:
a low-noise amplifier (photodetector amplifier 34), which produces RF signals at its output (col. 5, lines 6–9);
a load coupled to the amplifier output to receive the RF signals (col. 11, lines 43–45);
a post-distortion (PD) circuit (elements 120–123, Fig. 2) comprising semiconductor devices such as GaAs FET transistors (col. 6, line 61) having a control gate biased to operate in a nonlinear region near pinch-off (col. 6, lines 61–67);
the PD circuit having ports (110, 116) coupled to the output of the low-noise amplifier;
the PD circuit generating at least one post-distortion intermodulation product (col. 5, lines 35–40) that is out of phase with the intermodulation product generated by the low-noise amplifier (col. 6, lines 1–5); and
the generated PD intermodulation product combining with that of the amplifier to reduce the overall intermodulation distortion present at the load (col. 11, lines 39–41).
Although Pidgeon does not expressly quantify the degree of intermodulation reduction, it is an inherent result of the described operation that one of ordinary skill in the art would have optimized the circuit parameters—specifically attenuation, gain, phase, and delay—to maximize cancellation of distortion components. The Hewlett-Packard Application Note 1288-4 (“How to Characterize CATV Amplifiers Effectively” p. 23, Fig. 16) teaches that substantial cancellation is desired to achieve low composite triple beat (CTB) distortion (−97 dBc), directly related to third-order intermodulation. Accordingly, achieving at least a 10 dB reduction in intermodulation products would have been an obvious design optimization within the skill of an ordinary practitioner seeking linearity improvement for CATV applications.
Pidgeon, however, employs GaAsFET devices as the active components of the PD circuit.
Guan teaches that Schottky-gate InAs/AlSb high electron mobility transistors (HEMTs) provide enhanced gain (S21 ≈ 20 dB), low noise, and low intermodulation distortion in the 12–18 GHz band, while maintaining excellent linearity and stability.
Similarly, Aparin teaches that AlGaAs/InGaAs HEMT transistors having differing gate widths and bias voltages (i.e., derivative superposition design) achieve improved third-order intercept point (IIP3) linearity and intermodulation suppression, albeit with a modest increase in noise figure.
It would have been obvious to a person of ordinary skill in the art at the time of the invention to substitute the GaAsFET devices of Pidgeon with HEMT transistors such as those taught by Guan or Aparin, because both references are in the field of RF amplifier and post-distortion linearization technologies and address similar linearity issues. The motivation for such substitution lies in the well-documented advantages of HEMT technology—namely, improved gain, reduced noise figure, and better intermodulation performance. Incorporating an InAs composite-channel (IACC) HEMT, as claimed, into Pidgeon’s PD circuit would thus represent a predictable variation providing the same or improved linearity benefits, in accordance with KSR Int’l Co. v. Teleflex Inc., 550 U.S. 398 (2007).
Therefore, the modification of Pidgeon’s PD circuit to employ HEMT devices utilizing InAs-based composite channel technology in place of GaAsFETs would have been well within the skill of a semiconductor circuit designer, yielding predictable improvement in performance without altering the fundamental operation of the post-distortion linearization scheme.
Accordingly, when viewed as a whole, it would have been obvious to one of ordinary skill in the art, before the effective filing date of the present application, to combine the teachings of Pidgeon with those of Guan and Aparin to arrive at the claimed invention, including the use of IACC HEMT devices in a post-distortion circuit to achieve at least a 10 dB reduction in intermodulation distortion at one or more frequencies within the operating range.
further per claims 2 and 11, the PD circuit being coupled to the low noise amplifier only by an AC coupling (coupler doesn’t allow any DC signal to be coupled to the PC path) so that no DC power used by the low noise circuit is utilized by the PD circuit (well known in the art that RF couplers only allow AC power coupling (no DC power is coupled).
wherein per claims 3 and 12, the at least one PD intermodulation product and the intermodulation product produced by the low noise amplifier are each second order (Composite Second Order Beat (CSO), col. 5, lines 35-40) intermodulation products.
further per claims 4 and 13, a DC bias circuit, coupled to the control gate (DC gate bias 230 and 230’, see Fig. 3B, col. 6, lines 17-25) of the active semiconductor device (field effect transistors 220 and 220', col. 6, line 8) of the PD circuit, provides a biasing voltage that establishes a DC quiescent point at or near pinch-off (Field effect transistors 220 and 220' are biased from gate bias sources 230 and 230' to near pinch-off, col. 6, lines 30-33) of the active semiconductor device.
further per claims 6 and 15, Pidgeon also teaches a resistor (115, Fig. 2) in series between the PD port (110) and the output of the low noise amplifier (RF input with distortion from the amplifier 34), where a value of the resistor (as plug-in-pad, Fig. 2) determines an amount of coupling between the PD circuit and the output of the low noise amplifier.
further per claims 7 and 16, Pidgeon exemplarily teaches (in Fig. 3B) at least one of an inductor (Push-Pull transformer) and a capacitor (214 and 214’) connected between the PD port (from pad 115) and the output of the low noise amplifier (RF input from the amplifier 34), where a value of the at least one inductor and capacitor contributes to determining a frequency with the range of frequencies where a maximum reduction of the intermodulation product at the load occurs (it is well known in the art that the inductor and capacitor needs to resonate at the center frequency of the desired frequency range where intermodulation cancelation needs to be maximized) as a result, therefore, per claims 8 and 17, this inductor and capacitor contributes to determining a frequency with the range of frequencies where a maximum reduction of the intermodulation product at the load occurs.
Allowable Subject Matter
Claim 9 is objected to as being dependent upon a rejected base claim 1 but would be allowable if rewritten in independent form including all of the limitations of the base claim 1 and any intervening claims.
Claims 18-20 are allowed.
Claims 9 and 18 are allowable because the closest prior art of record, Pidgeon is not explicit about the low noise amplifier comprising two dual gate devices with first and second transistors biased at a DC quiescent voltage of specific unequal ratio of the total voltage wherein the unequal DC quiescent voltages across the first and second transistors causing a reduction of a second intermodulation product produced by the first and second transistors as compared with a second intermodulation product that would be produced by the first and second transistors operating with equal DC quiescent voltages across the first and second transistors.
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.
Examiner interviews are available via telephone, in-person, and video conferencing using a USPTO supplied web-based collaboration tool. To schedule an interview, applicant is encouraged to use the USPTO Automated Interview Request (AIR) at http://www.uspto.gov/interviewpractice.
If attempts to reach the examiner by telephone are unsuccessful, the examiner’s supervisor, Andrea Lindgren Baltzell can be reached on (571) 272-1769. The fax phone number for the organization where this application or proceeding is assigned is 571-273-8300.
/HAFIZUR RAHMAN/Primary Examiner, Art Unit 2843.