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

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.


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