Comments on U.S. Patent No. 6,813,485 – March 24, 2005

Summary
Based on the observations of a skilled radio frequency engineer, the ParkerVision patent No. 6,813,485 does not appear to contain new ideas or novel configurations. The reviewer of this patent built his first FM receiver in 1979, has read papers on switched capacitors and charge coupling since the early 1980s, and has reviewed papers for engineering journals since 1987. This commentary, however, makes no assertions regarding the validity of the ‘485 patent or any other patents assigned to or owned by ParkerVision Inc. Validity, enforceability, and potential infringement of an issued patent are very complex legal issues that are beyond the scope of the present analysis.

Introduction
U.S. Patent No. 6,813,485 (“the ‘485 patent), entitled “Method and System for Down-Converting and Up-Converting an Electromagnetic Signal, and Transforms for Same” was granted to Sorrells, et al. on November 2, 2004. The ‘485 patent, which is assigned to ParkerVision, Inc., issued from U.S. Patent Application Serial No. 09/838,387 (“the ‘387 application”), which was filed on April 20, 2001. The ‘387 application claims the priority of a Provisional Application for U.S. Patent filed on April 24, 2000, and at least partially claims the benefit of the filing dates of five previously filed U.S. Patent Applications, the earliest of which, U.S. Application Ser. No. 09/176,022 (“the ‘022 application”), was filed on October 21, 1998.(i) For the purposes of this analysis, all of the claims in the ‘485 patent are assumed to be entitled to the effective filing date of the ‘022 patent.(ii) None of the references discussed in this document was published later than October 21, 1997. Therefore, according to 35 U.S.C. §102 of the U.S. patent code, to the extent inventions claimed in the ‘485 patent are disclosed in the cited references, these references are fully effective as prior art that may affect the patentability of the ‘485 patent claims if the patent were ever litigated before a U.S. District Court.(iii)

The ‘485 patent includes numerous figures. Fig. 10, which is reproduced from the ‘485 patent below, shows an embodiment of the claimed “universal frequency upconverter” (UFU). Figures such as Fig. 11 appear to show more specific realizations of the invention.

Fig. 10 and Fig. 11 appear quite similar to the system shown in Fig. 1 of a 1995 paper by Madihian, et al.,(iv) a simplified reproduction of which is shown below:

Simplified Fig 1 of Upconverter in Madihian

Fig. 1 of Madihian et al. shows a circuit described as an “Upconverter equivalent circuit” that includes a switch module, or FET, driven by an oscillation, the “LO”, or local oscillator which switches the FET, and an IF, or control signal. The circuit is followed by a filter which leads to the RF, or radio frequency, output. Many similar figures, also published prior to 1997, may be found in the literature written by engineers working in radio frequency design.

A similar comparison may be made between Fig. 3A and Fig. 45 of the ‘485 patent and Fig. 2 of a 1997 paper by Parssinen all of which are reproduced below.(v) Fig. 3A and Fig. 45 of the ‘485 patent appear to show the various elements claimed in other claims of the patent. In Fig. 2 of Parssinen, Rsw is the realistic parasitic resistance of the switch.

Replica of Fig 2. in Parssinen (1997 IEEE MIT)

Although single diode sampling gates and mixers are and have been well known, most devices described in the literature use diode pairs and quads to create sampling gates because of the superior performance of multiple diodes. Fig 4 from a Hewlett-Packard application note on diode applications, is redrawn below.(vi) This figure may be compared with Fig. 2 from the ‘485 patent, which is also reproduced below.

Replica of Fig. 4 in Hewlett-Packard Application Note on Diode Applications

A review of the figures and disclosure of the ‘485 patent does not provide a full understanding of the potential strength of the patent. U.S. patents provide to their assignees a limited monopoly for up to 20 years from the first claimed filing date of the patent. This monopoly allows the assignee to prevent others from making, using, selling or offering to sell the invention as claimed in the patent during the enforceable lifetime of the patent.(vii) The ‘485 patent issued with 25 claims, of which claims 1, 7, 13, and 20 are independent. We note that analysis of the validity or any potential infringement of the claims of a patent is a legal question which requires a thorough consideration of, at a bare minimum, each claim, the full specification and figures of the patent, and the written record of the prosecution of the patent application before the U.S. Patent and Trademark Office. Such an analysis has not been attempted here. However, for illustration, Claim 1, the first independent claim in the patent, is briefly considered below in relation to prior art published prior to October 21, 1997.(viii) A brief interpretation of the terms and statements in the claim, from a skilled radio frequency engineer, is also presented in reference to each of the five elements of Claim 1.

While the discussion below is not a legal analysis of the validity of Claim 1, it is helpful to briefly consider the basic requirements of patentability according to U.S. Patent Law as set out in 35 U.S.C. §102 and §103.(ix) 35 U.S.C. §102 addresses the novelty requirement for patentability of a claimed invention. In short, a person is not entitled to a patent for a claimed invention if all of the elements of the invention as claimed are present in a device or method as described in a single prior art reference. 35 U.S.C. §103 provides a further requirement for patentability over the novelty requirement of 35 U.S.C. §102: the invention as claimed must further not have been obvious to one of ordinary skill in the art at the time of the invention. Under 35 U.S.C. §103, an invention is not patentable if a) all of the elements of the invention as claimed are described or suggested in one or more prior art references and b) the prior art also would have motivated or suggested to one of ordinary skill in the art the desirability of the claimed invention and c) provided the person of ordinary skill in the art a reasonable expectation of the invention being successful.

Claim 1:
1. A method for down-converting an electromagnetic signal, comprising:
(1) periodically coupling a received electromagnetic signal to an energy storage device, the received electromagnetic signal including a carrier signal having a nominal frequency F, the periodic coupling occurring at a rate that is less than twice the nominal frequency F of the carrier signal;
(2) acquiring energy from an approximate half cycle of the carrier signal during each of the periodic couplings;
(3) increasing an amount of energy stored by the energy storage device during each of the periodic couplings, the increase in the amount of energy stored by the energy storage device being proportional to the energy acquired during each of the periodic couplings;
(4) decreasing the amount of energy stored by the energy storage device between each of the periodic couplings, the decease in the amount of energy stored by the energy storage device being proportional to an amount of energy supplied to a load between each of the periodic couplings; and
(5) generating an information signal proportional to the amount of energy stored by the energy storage device.

Element (1) of Claim 1 recites periodically coupling a received electromagnetic signal to an energy storage device. This appears to be a simple switched capacitor filter. Fig. 3A within the patent would appear to confirm this intent. Examples of switched capacitor filters used for down-converting an electromagnetic signal are shown in Figure 7 of Shen’s paper in the December 1996 issue of the IEEE Journal of Solid State Circuits, and in Fig. 2 of Parssinen’s paper in the Dec 1997 issue of the IEEE Transactions on Microwave Theory (also shown above). The switched capacitor downconversion technique became popular in the early 1990’s as CMOS circuitry approached GHz frequencies. Element (1) further recites sampling at less than twice the nominal frequency of the carrier. This is usually called sampling below the Nyquist frequency, or subsampling as discussed by Parssinen and others. Such sampling causes signal aliasing which is discussed in many signal processing textbooks, such as Oppenheim and Schaefer’s Digital Signal Processing and is the basis of both the papers already cited.

The use of approximately half a cycle as recited in element (2) of Claim 1 would appear to again relate both to the Nyquist rate (which says a complete sampling of signal requires at least two samples per cycle - see Carlson’s Communication Systems , as well as a well known phenomena of harmonic conversion working best when the sampling aperture corresponds to odd multiples of a half period. An excellent example of this is given in Fig. 6.1 of Faber’s book on Microwave and Millimeter-Wave Diode Frequency Multipliers published by Artech House in 1995. Shen’s paper, cited above, also includes this as the sampling rate is 78 MHz, well below the carrier frequency, and the 23 harmonic of 78 MHz corresponds nearly exactly to a half-cycle of the carrier frequency which satisfies the second step of the claim. While impulse sampling is mentioned in the ‘485 patent, workers skilled in radio frequency circuit design have known for many years prior to 1997 that impulse samplers were a convenient theoretical idea although not the most practical realization of a sampler. Texts such as Vlach’s Computer Methods for Circuit Analysis analyze switched capacitor networks with finite sampling intervals.

Element (3) of Claim 1 appears to do little more than describe a fact of basic physics. Specifically, when the switch closes the capacitor is charged, storing energy from the incoming signal (see Fig 3A of the patent). This is described in textbooks such as Skilling’s Electric Networks and Geiger’s VLSI Design Techniques for Analog and Digital Circuits, as well as many others. Inherent properties of a claimed invention generally can not be used by a patent applicant to establish novelty and/or non-obviousness of the claimed invention.(x)

Energy loss due to the load attached to an energy storage device such as a capacitor as recited in element (4) of Claim 1 is also a well known, inherent, physical phenomenon described in the texts mentioned above in regards to element (3). Any measurement of the energy stored on the capacitor will consume some of the energy stored. Measurement of the energy stored on the capacitor is necessary to collect the information signal.

Finally, with regards to element (5), the generation of an information signal proportional to the amount of stored energy would seem to be little more than an assertion that the process is linear, which is well described in texts such as Carlson (mentioned above). Paper’s such as Shen’s include all of these steps, although it may not be clear to those not skilled in this art. If the energy loss of element (4) is too small, the stored energy replicates only the peak signal level, causing it to be a peak detector, and losing the transmitted information. If the energy loss of element (4) is too large, the switched capacitor does not reject enough of the carrier signal from the desired information signal. This has been described in communication textbooks for over 40 years (Zimmermann’s Electronic Circuit Theory, and Clarke’s Communication Circuits).

In summary, as discussed above, this commentary makes no assertions regarding the validity of the ‘485 patent or any other patents assigned to or owned by ParkerVision Inc. Validity, enforceability, and potential infringement of an issued patent are very complex legal issues that are far beyond the scope of the present analysis. This commentary merely summarizes a number of observations of a skilled radio frequency engineer regarding the ‘485 patent. This reviewer built his first FM receiver in 1979, has read papers on switched capacitors and charge coupling since the early 1980s, and has reviewed papers for engineering journals since 1987. He has encountered many genuinely novel radio concepts that are published and patented every year; however, in his opinion the ‘485 patent does not appear to contain new ideas or novel configurations.

Notes
i. As noted on the front page of the ‘485 patent, the ‘387 application is a continuation-in-part of U.S. Application Ser. No. 09/550,644, filed Apr. 14, 2000, which is a continuation-in-part of U.S. Application Ser. No. 09/521,879, filed March 9, 2000 (now abandoned), which is a continuation-in-part of pending U.S. Application Ser. No. 09/293,342, filed April 16, 1999, which is a continuation-in-part application of the ‘022 application, filed October 21, 1998 (now U.S. Pat. No. 6,061,551).

ii. A patent application that is a continuation-in-part of an earlier application is entitled to the benefit of the earlier-filed application to the extent that the earlier filed application fully discloses and/or enables the invention(s) claimed in the continuation-in-part application. For the purposes of this analysis, the claims of the ‘485 patent are assumed to be fully supported and/or enabled by the disclosure of the ‘022 application and therefore entitled to an effective filing date of October 21, 1998. Please note that this assumption may, in fact, not be true. Thus, this analysis gives the ‘485 patent the greatest benefit of the doubt with regards to its priority date.

iii. 35 U.S.C. §102 reads, in relevant part: “A person shall be entitled to a patent unless … (b) the invention was patented or described in a printed publication in this or a foreign country or in public use or on sale in this country, more than one year prior to the date of the application for patent in the United States … “
Thus, it is possible to defeat a reference published less than one year prior to the filing date of a U.S. application if the applicant can prove conception of the invention and diligence from the date of conception until reduction to practice. This procedure is not available for references published more than one year prior to the application filing date.

iv. M. Madihian, L. Desclos, K. Maruhashi, K. Onda, and M. Kzuhara, A K-Band Monolithic CPW Upconverter Utilizing a Source Mixing Concept, IEEE Microwave and Millimeter Wave Circuits Symposium, pp. 163-166,1995.

v. A. Parssinen, R. Magoon, S.I. Long, and V. Porra, “A 2-GHz Subharmonic Sampler for Signal Dowconversion,” IEEE Trans Microwave Theory and Techniques, Vol. 45, No. 12, pp. 2344-2351, Dec. 1997.

vi. Staff, Diode Applications, Application Note, Hewlett Packard, 1968.

vii. 35 See 35 U.S.C. §271(a)

viii. As noted above, October 21, 1997 is one year before the earliest possible filing date to which the claims of the ‘485 patent could possibly be entitled. Disclosure of the claimed invention in such a prior art reference presents an absolute bar to patentability.

ix. 35 U.S.C. §§102 and 103 deal with novelty and obviousness of a claimed invention, respectivly. Other requirements of patentability are set out in 35 U.S.C. §101 (Utility of the invention) and 35 U.S.C. §112 (claims must be clear, concise, and non-ambiguous, and the specification must provide a complete written description, properly enable the invention, and disclose the best known mode of practicing the invention).

x. See §2112 of the Manual of Patent Examination Procedure (8th edition): “The express, implicit, and inherent disclosures of a prior art reference may be relied upon in the rejection of claims under 35 U.S.C. 102 or 103.”


Bibliography
A.B. Carlson, Communication Systems, McGraw-Hill, New York, NY, 1968.

K.K. Clarke and D.T. Hess, Communication Circuits, Addison-Wesley, Reading, MA, 1971.

M.T. Faber, J. Chramiec, and M.E. Adamski, Microwave and Millimeter-Wave Diode Frequency Multipliers, Artech House, Norwood, MA, 1995.

R. L. Geiger, and P. E. Allen, VLSI Design Techniques for Analog and Digital Circuits, McGraw-Hill, New York, NY, 1990.

A.V. Oppenheim and R.W. Schafer, Digital Signal Processing, Prentice-Hall, Englewood Cliffs, NJ, 1975.

H.H. Skilling, Electric Networks, John Wiley & Sons, New York, NY, 1974.

J. Vlach and K. Singhal, Computer Methods for Circuit Analysis and Design, Van Nostrand Reinhold, New York, NY, 1983.

H.J. Zimmermann, and S.J. Mason, Electronic Circuit Theory, John Wiley & Sons, New York, NY, 1959.