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A Transistor Ladder Voltage-Controlled Filter Implemented on a Field Programmable Analog Array

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Because some audio enthusiasts argue that analog systems have more warmth than digital implementations, analog circuits are still of interest in music synthesis. The recent development of Field-Programmable Analog Arrays (FPAAs) offers a way to connect analog components together in an arbitrary fashion on a mixed-signal CMOS chip. This allows for the creation of analog synthesizers with the ease of rapid reconfigurability, a property associated with their digital counterpart. The authors use an FPAA to implement a particular voltage-controlled filter, the transistor ladder. The FPAA consists of three primary blocks: (1) the Computational Analog Block (CAB), a physical grouping of analog circuits that serve as computation elements; (2) the Switch Matrix (SM) that allows local routing between elements inside a CAB, as well as routing between CABs; and (3) the Programmer, which selects a floating-gate device in the SM and allows each devices to be turned on, off, or in between. Multiple CABs and SMs are arrayed in a single FPAA, allowing for large, reprogrammable analog systems.

JAES Volume 62 Issue 9 pp. 611-618; September 2014
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