ALFA RPAR AS3372-SMT Signal Processor (SOIC-24)

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The AS 3372 is a general purpose signal processing device for audio tone sources. Included on-chip are a two channel voltage controlled input mixer, a dedicated 4-pole low pass voltage controlled filter with voltage controllable resonance, universal mixing/panning VCA-block and a quality final voltage controlled amplifier.

With the exception of the filter cut-off frequency, (the filter frequency control voltage ranges from - 150mV to +100mV) all control inputs are very low bias current, high impedance inputs which range from 0 to +5 volts. This feature allows the common DAC output voltage in a microprocessor system to be multiplexed to these inputs with only a CMOS analog multiplexer and hold capacitors, thus eliminating the usual sample-and-hold buffers.

A unique feature of the 24dB/octave filter is that, unlike others of this type, the passband gain remains constant as the amount of resonance is varied, thus eliminating the annoying drop in volume at higher resonance settings. Other features include wide frequency control range, temperature compensated transconductors, low noise, low control feed-through, and a smooth behaviour when swept.

The final output VCA is a current in, current out type, allowing multiple inputs to be easily mixed into its input, and easy interface of its output to the rest of the system. The control scale is very linear, and the point at which the VCA shuts off is very well defined (+100mV ± 50mV). Owing to its exceptionally low noise and exceptionally low control feedthrough without trimming, this VCA is well suited to being controlled by fast transient waveforms.

Universal mixing/panning VCA block provides flexible signal processing solutions

Features

• 2-channel VC input mixer with external input
• 4-pole low pass VCF & Quality Final VCA
• Universal mixing/panning VCA-block
• 0 to +5V high Z control Inputs for direct interface to system DAC from CMOS multiplexer
• VCF uses open loop design for enhanced sound richness
• VCF has constant loudness as resonance changes
• VCF is temperature compensated

References