Sgs-thomson Microelectronics Limited

Sgs-thomson Microelectronics S.a.

Stmicroelectronics Asia Pacific Pte Limited

S Gs - Microelectronics Limited

Gee H Loh

Solomon K Ng

Kien Beng Tan

Hong Chean Choo

Mario Santi

Disclosed is keypad circuitry operable to detect a pressed key while reducing electromagnetic interference (EMI). The keypad circuitry is operable to reduce EMI in two ways: a) reducing the voltage swing occurring at the row circuitry and column circuitry of the keypad, and b) reducing the number of signal transitions by restricting the signal transitions to occurring at the column and row corresponding to a pressed key. By limiting signal transitions to occurring only at the row and column corresponding to a pressed key, fewer signal transitions occur, and thus, less EMI is produced. Additionally, reduced voltage swings at the row circuitry and column circuitry results in reduced EMI.

Low EMI keypad circuitry

A multiple output current mirror comprising at least three mirror-connected PNP transistors whose bases are connected to a first node, at least three cascode-connected transistors, each cascode transistor being associated to one mirror transistor, a current input corresponding to the collector of the first cascode transistor, and mirror outputs corresponding to the collectors of the two other cascode transistors. The current mirror further comprising means for detecting the base current of each mirror transistor and for reproducing this base current on the collector of the cascode transistor to which each mirror transistor is associated.

Multiple output current mirror

A source/sink current generating circuit is arranged to generate source and sink currents which are matched and insensitive to fan out. This is achieved by using a biasing transistor (Q13) between first and second current mirrors which generate respectively the source and sink currents.

Source/sink current generating circuit system

A circuit for providing a reference current comprises first and second matched transistors, each of which has a control node and a controllable path and each of which is connected so that a current setting resistor is in the controllable path of the second matched transistor, the current setting resistor having a value, current set in the controllable path of the second matched transistor is related to a difference in voltage characteristics between the first and second matched transistors and to the value of the current setting resistor, and third and fourth matched transistors, each of the third and fourth matched transistors having a controllable path connected respectively to the controllable paths of the first and second matched transistors, and control electrodes of the third and fourth matched transistors connected together; a set of output transistors connected to the circuit to supply the reference current in dependence on a set current; and a fifth transistor having a controllable path between a bias node related to a first supply voltage level and a node set at one voltage characteristic relative to a second supply voltage level so as to maintain a voltage across one of the third and fourth matched transistors at a value which is independent of the first supply voltage level to reduce a magnitude of changes in the reference current as a function of the first supply voltage, the fifth transistor having a control electrode connected to the conductive path of the first matched transistor.

Reference current source for low supply voltage operation

An audio amplifier comprises a first current mirror having an input coupled to an output of a cascade differential pair and an output coupled to an output of a first constant current source. A second constant current source (Q16, Q18, CC10) supplies the voltage reference (Q15) of the first constant current source. Hitherto a resistor has been used instead of the second constant current source to reduce noise. However, using a resistor results in the amplifier having a relatively low power supply rejection ratio, thereby degrading the performance of the amplifier. Accordingly the present invention uses a second constant current source to improve the power supply rejection ratio without degrading the noise performance.

Growing community of inventors

Singapore, Singapore

Gee H Loh