Abstract: A modem transceiver circuit and method is disclosed, the transceiver circuit having a line drive transformer, a transmit circuit and a receive circuit. The receive circuit features a receive operational amplifier which is enabled when the voltage magnitude of a data signal received by the modem transceiver circuit is below a predetermined threshold. The receive operational amplifier is disabled when the voltage magnitude of the data signal is greater than or equal to the predetermined threshold. When enabled, the receive operational amplifier amplifies the data signal for further processing by other modem circuitry. When disabled, a series resistance comprising an input resistance and a feedback resistance attenuates the data signal for further processing by other modem circuitry.

Abstract: A modem transceiver circuit and method is disclosed, the transceiver circuit having a line drive transformer, a transmit circuit and a receive circuit. The receive circuit features a receive operational amplifier which is enabled when the voltage magnitude of a data signal received by the modem transceiver circuit is below a predetermined threshold. The receive operational amplifier is disabled when the voltage magnitude of the data signal is greater than or equal to the predetermined threshold. When enabled, the receive operational amplifier amplifies the data signal for further processing by other modem circuitry. When disabled, a series resistance comprising an input resistance and a feedback resistance attenuates the data signal for further processing by other modem circuitry.

Abstract: The present invention entails a circuit and method for determining the distortion created by a transformer used in data communications. The circuit according to the present invention comprises a transmitting circuit, a back matching circuit, and a subtracting circuit. The transmitting circuit generates a test signal to be transmitted into a transformer, the transmitting circuit having a transmitting output for coupling to a transformer. Once applied to the transformer, the test signal is distorted by the transformer, where the transformer creates harmonics of the test signal and other signal distortion. The back matching circuit generates a scaled test signal that is subtracted from the distorted test signal in the subtraction circuit. The result is a diminished peak at the test signal in comparison to the harmonics such that the distortion by the transformer can be determined using a measuring device with a relatively low dynamic range.

Abstract: A signal coupler includes a transformer having a primary and a secondary winding. Each transformer winding has a pair of associated winding terminals and is also split at an intermediate winding position to form a pair of supplemental winding terminals. Circuitry is provided between each pair of supplemental winding terminals so as to provide different impedances in different frequency bands. In particular, a first circuit, which provides a first impedance in a first frequency range, is connected across the supplemental winding terminals of one winding. A second circuit, is connected across the supplemental winding terminals of the other transformer winding. This second circuit, in combination with the first, provides a second impedance in a second frequency range. In the disclosed embodiment, the first circuit provides an impedance of 600 ohms in the voiceband frequency range. The second circuit in combination with the first provides an impedance of 100 ohms in a frequency range extending above 40 kHz.

Abstract: The disclosure is of a system and method of detecting or identifying a received TV program by forming a database of identifying digital bits for a plurality of programs, processing a TV program by modulating the luminance of pairs of lines of the program and reconstituting the program with said modulated line pairs and the other components of a TV program signal. The reconstituted program is transmitted to a location at which it is decoded to recover the digital identifying bits and comparing such bits with bits in the database to identify the transmitted program.