The AS3372E is a general purpose signal processing device for audio tone sources. Included on-chip are:
- two channel voltage controlled input mixer with possibility of addition external signal
- dedicated 4-pole low pass voltage controlled filter with voltage controllable resonance
- quality final voltage controlled amplifier
- universal mixing/panning VCA-block .
With the exception of the filter cut-off frequency, 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 & Hold buffers.
The two input VCAs of the mixer feature audio taper control scales and high attenuation at zero control voltage. The signal inputs are low level (80mV.P.P. for 5% THD), allowing multiple tone sources to be conveniently mixed into each channel. “Mixer output” pin allows additional external signals to be mixed.
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 transconductans, low noise, low control feed-through, and a smooth behavior 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.