Sequential PROPHET-600 - Page 89

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CEM3372 uP CONTROLLABLE SIGNAL PROCESSOR
Preliminary 3/27
General Description
THe CEK3372 is a general purpose signal processing device for audi
tone sources. Included on-chip are a two channel voltage controlled lnp
mixer, a dedicated 4-pole lew pass voltage controlled filter with volta
controllable resonance, and a quality final voltage controlled amplifie
With the exception of the filter cut-off frequency, all control inputs
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 CMO
analog switch and hold capacitor, thus eliminating the usual Sample 5 H
buffers.
The two input VCAs of the mixer feature audio taper control scales
high attenuation at zero contol voltage. The signal inputs are low leve
(SOmV.P.P. for 5S THD), allowing multiple tone sources to be convenient
mixed into each channel.
The filter is the standard four pole low pass with Butterworth typ
response. Another VCA is provided to allow overall feedback, and hence
amount of resonance, to be voltage controlled. A unique feature of this
filter is that, unlike others of this type, the passband gain remains
constant as the amount of resonance is varied, thus eliminating the ann<
drop in volume at higher resonance settings. Other features include wid*
frequency control range, temperature compensated transconductors, low
noise, low control feedthrough, 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 o:
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 (*100nV
♦ 50nV). Owing to its exceptionally low noise and exceptionally low contr
feedthrough without trimming , this VCA is well suited to being controls
by fast transient waveforms7
F eatures
- 2 channel V.C. input mixer, 4-pole low pass VCF, 4 quality final VCA i
on one chip
- low external parts count
- low cost
- 0 to *5V, hi 2 control inputs for Level A S 5, Resonance, 4 Final Gair
interfaceable directly to CMOS multiplexer from DAC
- VCF uses open loop design for enhanced 3ound richness
- VCF has constant loudness as resonance changed
- temperature compensated VCF transconductors
- low level, non-inverting VCF frequency control input for easy mixing c
control sources
- final VCA has low feedthrough without trimming
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