Abstract: A secure circuit is protected from reverse engineering by sensing radiation to which the circuit is normally not exposed, but which is present in its analysis. The circuit is modified in response to such radiation so that it is not compromised by subsequent analysis. The secure circuit can be implemented as a volatile memory having a power supply circuit that is interrupted in response to radiation exposure. Alternately, a circuit used to burn out the secure circuit, or to reprogram the circuit in the case of a programmable memory, could be actuated by the radiation exposure. Reprogramming mechanisms include an operational amplifier with its input state controlled by a photodiode, a random access memory cell with inherently photosensitive transistors, and a photosensitive transistor switch connecting a multi-vibrator to a memory address line.

Abstract: An adjustable balancing circuit (900) for an adaptive hybrid is suitable for use with a two-conductor transmission line in full duplex communications. In a preferred example, the adjustable balancing circuit (900) includes a first impedance structure (902), a second impedance structure (904), a plurality of N resistor-inductor-capacitor (RLC) networks (908), a first plurality of N switch circuits (912), and a second plurality of N switch circuits (914). The first plurality of N switch circuits (912) switchably cascadingly couples the first plurality of N RLC networks (908) to a first end of the first impedance structure (902). The second plurality of N switch circuits (914) switchably couples a first end of the second impedance structure (904) to a first end of each RLC network. When properly configured, the adjustable balancing circuit (900) cancels reflected transmit signals caused by the presence of short bridged taps on the two-conductor transmission line.

Abstract: A secure circuit structure includes a pair of opposed substrates having a volatile circuit fabricated on at least one, and preferably both substrates. A maintenance circuit for the volatile circuit extends between the substrates so that it is interrupted, thereby altering the volatile circuit and rendering reverse engineering attempts futile, if the substrates are moved with respect to each other by opening the circuit package. The maintenance circuit preferably includes a series of mating conductive indium bumps that extend from the opposed substrates and mechanically bond the substrates together. The secured volatile circuit may be a random access memory storing an access code, maintained by a battery power supply circuit.