Abstract: The position (XY coordinate) of a pointed stylus on a conductive sheet is determined by injecting current from the stylus into the sheet and measuring the current responses at three or more spaced apart electrodes connected to the sheet.

Abstract: A two-terminal rectifier circuit, useful for converting an input a.c. voltage into an output d.c. voltage, is formed by a power MOSFET which is provided with an electrical feedback comparator network designed to turn on the MOSFET once during each a.c. cycle when the input a.c. voltage is nearly equal to its peak positive value.

Abstract: A toroidal, saturable core reactor (14) is connected in series with the conductors (11,19 and 13,21) of a transmission line. A termination network (16) is connected across the transmission line conductors (19,21). In response to an a.c. test signal transmitted from a generator (48) on one of the conductors (11), a series of voltage spikes are induced at the reactor (14) and superimposed on the a.c. test signal. The superimposed a.c. test signal is returned through the termination network (16) and the other line conductor (13) to a current detector (50) for detecting the spikes. A d.c. signal is then applied along with the a.c. signal. If there is a fault beyond the reactor (14), the spikes will be displaced from their expected positions. If there is a fault before reactor (14), the spikes will not be displaced. For ease in signal discrimination against noise, the d.c. signal is modulated.

Abstract: Light-activated power FETs (18, 20, 80, 82) are utilized as switching elements in DC-to-DC converters. The FETs are characterized by high speed and low losses. As a result, the converters are capable of providing very low DC voltages in an efficient low-cost way.

Abstract: A circuit with low impedance for maintaining a single polarity at an output is disclosed. Switching is provided by light controlled switching devices which in one embodiment are field effect transistors (14, 15, 16, 17) which are optically triggered by one or more photo-responsive devices (26', 27', 28', 29') coupled to their gate electrodes. The ON-OFF state of each switch is determined by the presence or absence of light from an adjacent line-powered LED (26, 27, 28, 29). A diode (32, 33, 34, 35) may be included in parallel with each switching device to provide surge protection.

Abstract: A gain and frequency compensated barrier circuit is disclosed for use with a telephone transmission line having variable loop lengths. A DC component of the input signal is provided to the input side of the barrier circuit. Loop length losses, as well as barrier gain variations, are adjusted on the output side of the circuit by comparing a barrier DC voltage level with a DC reference level and adjusting the AC gain in accordance therewith. Frequency response, which is also a function of loop length, is corrected by using the DC input voltage to generate an effective loop length dependent capacitor for further controlling the output signal level. An optocoupled circuit is disclosed for use in one embodiment of the disclosure.

Abstract: A remote gain controlled optocoupled device is disclosed utilizing a DC reference voltage in the output section to compensate for variations in the optocoupling characteristics of the circuit. The DC voltage level output of the photodetector, which is a function of the light transfer characteristics of the circuit, is compared to a remotely controlled reference DC level. The output AC signal level, which substantially tracks the DC voltage output, is gain adjusted under control of the compared DC voltage levels.

Abstract: An optically controlled bidirectional (bilateral) electrical switch is formed by a pair of photo-Darlington devices connected in series opposing (back-to-back) relationship between the two controlled terminals of the switch. Each of these photo-Darlington devices is shunted by a separate unidirectional diode element, such as a PN junction diode, arranged to conduct current only in the opposite direction from that of current flow through the corresponding shunted photo-Darlington device in its "on" condition. Four embodiments are shown.