U.S. Philips Corporation

Microtel, B.v.

Adrianus Josephus Smulders

Jan Hendrik De Jonge

A motor assembly for an electret transducer, wherein spacing means supporting the diaphragm plate on the backplate are manufactured from a separate material which is applied on the backplate surface to achieve an accurately defined and reproduceable spacing therebetween. Such spacing means can be formed as a meshlike screen lying on the backplate surface. In an alternative embodiment wherein the backplate is constituted by substantially spherical, conductive particles sintered together, the spacing means are formed by an acoustical porous coating applied on the backplate surface, which coating also acts as an electret.

Electret transducers: acoustically transparent backplate of sintered

The invention provides a compact test sequence for testing integrated memories. First, all storage positions are filled with the bit '0'. Subsequently, in a given order of the addresses, the '0' bit written for each address is read; immmediately thereafter a '1' bit is written in those bit positions. The positions are again tested by reading the '1' bits. When the last address of the predetermined order is reached, the '1' is read in the same order for each address. Subsequently a '0' is written, which is finally tested by reading again. When the last address is reached, all addresses are read in the reverse order, and a '1' is written, which is tested again. When the first address is reached, all addresses are read, filled with a '0' and tested. This process may be repeated as many times as there are bits in the address. The significance of the address bits are modified to form the predetermined order, for example, by cyclic rotation. For example, in the first cycle the order may be the normal order of successive addresses, while in the second cycle first all 'even' and then all 'odd' addresses are treated.

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Hoogland, Netherlands

Adrianus Josephus Smulders