Abstract: Telephone instruments generally comprise a mechanical hookswitch connected across the pair of speech wires. This specification discloses solid state hookswitch circuitry comprising a switching transistor controlled by a hookswitch and connected in series with the output of a rectifier, the rectifier being connected directly to the incoming speech wires. Because the hookswitch controls a switching transistor, rather than having to switch line voltages directly, any reliable low current make/break switch may be employed.

Abstract: It is desirable to be able to sense the temperature of a semiconductor element to detect, for example, overheating of that element. A temperature sensing apparatus is disclosed which comprises a polysilicon device, functioning as a temperature transducer and integrated with a semiconductor element. A silicon oxide layer separates the temperature transducer device from the element.

Abstract: A bridge rectifier circuit comprises a bridge of switching transistors 1 to 4 having their control terminals connected to switch the transistors to provide either full wave rectification of an a.c. input voltage or polarity correction of a d.c. input voltage of either polarity appearing at terminals A and B. The switching transistors are all of the same polarity type and at least two floating drivers 6 and 7 are connected to generate and supply control potentials to the control terminals respectively of a pair of the switching transistors.In a preferred embodiment the switching transistors comprise field effect transistors. The floating drivers can comprise at least one respective bridge rectifier 12 capacitively linked to a source of voltage pulses 10 when the input voltage has a predetermined polarity, to generate the control potentials. Alternatively the floating drivers can comprise a voltage doubler or quadrupler capacitively linked to the source of voltage pulses.