This paper explores voltage-controlled amplifier (VCA) designs based on operational transconductance amplifiers (OTAs) on a floating-gate--based Field-Programmable Analog Array (FPAA). Although preconfigured OTAs are available on the target FPAA, their gain must be fixed during the programming stage. Hence, the OTA that forms the variable-gain element the VCA must be constructed from the individual transistors that are also available on the FPAA. The current output of this more-flexible OTA is converted to a voltage via one of the built-in fixed-gain OTAs. The authors show how the use of a special floating-gate OTA with voltage attenuation at its inputs arising from capacitor dividers (analogous to resistor dividers used in traditional printed circuit board--level VCA designs) helps prevent a diverging nonlinearity from ruining the current-to-voltage conversion process. This exercise highlights the counterintuitive challenges facing engineers moving from board-level audio design with off-the-shelf chips and discrete bipolar junction transistors to very large--scale integration--level design with complementary metal oxide semiconductor technology.
https://www.aes.org/e-lib/browse.cfm?elib=22026
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