Codex Corporation v. Milgo Electronic Corporation, Codex Corporation v. Milgo Electronic Corporation

717 F.2d 622, 219 U.S.P.Q. (BNA) 499, 1983 U.S. App. LEXIS 25240
CourtCourt of Appeals for the First Circuit
DecidedAugust 2, 1983
Docket82-1644, 83-1076 and 82-1707
StatusPublished
Cited by34 cases

This text of 717 F.2d 622 (Codex Corporation v. Milgo Electronic Corporation, Codex Corporation v. Milgo Electronic Corporation) is published on Counsel Stack Legal Research, covering Court of Appeals for the First Circuit primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
Codex Corporation v. Milgo Electronic Corporation, Codex Corporation v. Milgo Electronic Corporation, 717 F.2d 622, 219 U.S.P.Q. (BNA) 499, 1983 U.S. App. LEXIS 25240 (1st Cir. 1983).

Opinion

BOWNES, Circuit Judge.

Milgo Electronic Corporation and International Communication (Milgo) appeal from an adverse declaratory judgment in a patent validity action brought by Codex Corporation and Yellow Freight Systems, Inc. (Codex). Codex cross-appeals because of the failure of the district court to grant all of the relief it sought and on the ground that the amount of attorney fees awarded it was too low. The district court opinion is reported, Codex Corp. v. Milgo Electronic Corp., 534 F.Supp. 418, 432 (D.Mass.1982).

The dispute revolves around three patents, all owned by Milgo as assignee:

(1) No. 3,524,023, Sang Y. Whang, inventor, Band Limited Telephone Line Data Communication System Whang 023);

(2) No. 3,619,503, Robert G. Ragsdale, inventor, Phase and Amplitude Modulated Modem (Ragsdale ’503); and

(3) No. 3,783,194, Viesturs V. Vilips, inventor, Data Modem Having a Fast Turnaround Time Over Direct Distance Dialed Networks (Vilips ’194),

I. Background

All computer machine languages operate on a binary number system. This system or language involves only two elements: positive or negative or, most commonly, 1 or 0.

Computers do not always operate alone; some are built to communicate with other computers. In order for one computer to talk with another some sort of communication link has to be established. At the time the patents in this case were issued the primary communication link was direct distance dialed telephone lines (DDD). Unfortunately for talking computers, binary or digital data cannot be transmitted over DDD lines rapidly and reliably. To transmit information through DDD lines the transmission must be made in an analog form. This analog transmission is best thought of in terms of a sinusoidal waveform (sine wave) as illustrated below:

[[Image here]]

The above illustration shows a sine wave with an amplitude of one and a cycle duration of T seconds. Both of these terms will be explored in some detail later.

For computers to talk one with the other it is necessary to transform digital signals to analog at the transmitting computer and back again at the receiving computer. This transformation is accomplished in both instances by a modem.

The word “modem” is short for modulator-demodulator. Modulation is the alteration of the sine wave in some manner so as to impart some information to it. For the *625 purposes of this litigation modulation can take one of three forms: phase modulation, amplitude modulation, or a combination of both phase and amplitude modulation.

Phase modulation, or more specifically in this case differential phase modulation, is accomplished by sending out a signal pulse during a modulation period followed by another modulation period with a signal pulse of a different phase. The receiving modem detects this phase shift which contains the information in each signal pulse.

Amplitude modulation is accomplished in the transmitting modem by changing the amplitude of the sinusoidal sine wave from one modulation period to the next. The receiving modem detects this change in amplitude thus reading the information contained in the signal pulse. The combination of phase and amplitude modulation is accomplished by changing both the phase and amplitude of the sine wave from one modulation period to the next.

The speed at which information can be transmitted depends primarily on two factors. First, it depends on the number of signal pulses (bauds) that can be transmitted per second, and secondly, it depends on the number of discrete “bits” of binary data (1 or 0) that can be encoded in each baud (bits per baud).

A problem with analog signal transmission is that some distortion of the signal is bound to occur; the received signal is not going to be identical to the one transmitted. This distortion is a function of two characteristics, one of the signal, the other of the DDD line itself.

The problem with the DDD line is that at the upper and lower ends of the frequency range available the analog signal is susceptible to amplitude and delay distortion. These distortions are fatal to fast and accurate transmission of information. It was well-known in the early 1960’s that at the center of this available frequency range there existed a “sweet spot.” The sweet spot is a band of about 1000 Hz 1 in a range between the frequencies of 1200 Hz and 2200 Hz which has the characteristic of being relatively free from distortions.

The problem with the signal occurs when it is modulated. Modulation causes a dispersal of energy up and down the frequency spectrum. This energy, outside of the sweet spot, is susceptible to delay and amplitude distortion. The delayed reception of this energy by the receiving modem will distort the apparent phase and amplitude of the received signal causing inaccurate decoding of the information.

To solve this problem of energy dispersal over the frequency spectrum a composite filter to filter out energy at all but the desired frequencies is used. This solution, however, causes its own problem, it spreads the signal out over time. The energy representing the signal in one baud is smeared in time so that some of it is still “ringing” or echoing in the bauds that succeed it. This ringing causes intersymbol interference or confusion from one baud to the next. The next step was to solve this problem.

In 1928 Harry Nyquist published his discovery that an information carrying pulse, or baud, of duration in time of T seconds required a bandwidth of 1/T Hz for accurate transmission. This basic constraint on the bandwidth is crucial to mitigating the intersymbol interference.

Nyquist went on to describe a filter which would accomplish this. The ideal Ny-quist filter, called “brickwall,” passes only this 1/T bandwidth. It was recognized that the actual construction of such a brickwall filter was not possible. Practical filter design requires the use of filters with a roll-off of greater than zero. The diagram and text which follows illustrates both the brickwall filter and the concept of roll-off.

*626 [[Image here]]

The carrier frequency (fc) is the frequency of the sine wave which is modulated by the modem to produce the information-carrying signal pulse. The portions of the bell-shaped curve that extend beyond the brick wall are known as the skirts. One way of defining the roll-off of the filter is by taking the ratio of the width of the skirt along the abscissa to the width of the Ny-quist ideal of 1/T Hz. A composite filter exhibits 50% roll-off when the sum of the skirts is 1/2T Hz. It should also be noted that to meet Nyquist’s criteria a roll-off of 100% is the maximum allowable.

One further necessary element of modem design is a mechanism for determining when a baud begins and ends. Concomitant with that determination is the need to know when or where to read the information contained in a baud. The mechanism for determining when to sample or read the information contained in a baud is called “clock” in the present art.

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Bluebook (online)
717 F.2d 622, 219 U.S.P.Q. (BNA) 499, 1983 U.S. App. LEXIS 25240, Counsel Stack Legal Research, https://law.counselstack.com/opinion/codex-corporation-v-milgo-electronic-corporation-codex-corporation-v-ca1-1983.