CMOS compression amp holds
promise for communications

Micronix Integrated Systems (Aliso Viejo, CA) has developed a compression amplifier implemented completely in CMOS. This type of amplifier has traditionally been designed in a bipolar process, but it lends itself more readily to low-power system-on-a-chip integration when done in CMOS.

Initially incorporated into a hearing-aid ASIC, this compression technology could find a variety of uses in the communications field. For the hearing aid, the CMOS design meant that the hearing aid itself would be small enough to be worn in the user's ear, yet still provide automatic control of volume.

The compression amplifier regulates sound levels by compensating for the limited dynamic range of the user's hearing as it varies across the audio frequency spectrum. In the past, this operation required a two-chip solution: a bipolar IC implementing a dynamic range compressor with variable compression ratios for each frequency band, and a CMOS device providing band-splitting filters and other functions in digital logic.

Bipolar technology is typically used for the log-antilog circuits that generate the exponents needed for compression. The Micronix chip produces exponents by cascading variable-gain amplifiers created with MOS transistors. For more information, call Mike Adams of Micronix Integrated Systems at 714-831-4622, ext. 225, visit http://www.mx asic.com .