Abstract: A bandgap reference circuit is described in which two transistors share a current with their bases coupled together and to an output terminal. A pair of resistors is coupled in series between the emitter of one of the transistors and ground, the emitter of the other transistor being coupled to a node between the resistors. A further transistor is coupled between the output terminal and the node with its base coupled to a second node between two further resistors connected in series between the output terminal and ground. The further transistor and resistors allow the circuit to be compensated for higher order temperature dependence.

Abstract: A telecommunication system of the kind having a telephone handset connected to an exchange via a line incorporates a beacon (22) in the line for receiving a question signal from test equipment associated with the exchange and for sending an answer signal to the test equipment. The beacon (22) senses voltages in the two wires making up the line but is otherwise isolated from the line via a diode bridge (20) and a protection circuit (21) and high value resistor R.sub.p. Previously known beacons were connected directly into the line to sense current and thus could not be protected by high value resistors.

Abstract: The invention relates to a signal processing arrangement which in a preferred form is part of a telephone speech circuit.The circuit arrangement includes an operational amplifier for processing signals coupled to an input terminal via a capacitor. In order to control output current provided by the arrangement a current is coupled to the input terminal of the amplifier which is fed with the signals to be amplified and an equal and opposite current is fed to the opposite side of the capacitor so that the effects of any unwanted A.C. components in the control current may be reduced.The use of the circuit allows a single capacitor to perform multiple functions thereby reducing the number of capacitors and the number of terminal pins of an integrated circuit package incorporating the circuit.The invention is particularly suitable for use in a telephone speech circuit.