12
RC8650 VOICE SYNTHESIZER
RC SYSTEMS
Analog Audio Output
The analog output pins AO
0
and AO
1
are high impedance (10 k
typical) outputs from the RC8650’s internal D/A converters. When us-
ing these outputs, the addition of an external low-pass filter is highly
recommended. When laying out the printed circuit board, avoid run-
ning digital lines near the AO lines in order to minimize induced noise
in the audio path. If space permits, run a guard ground next to the
AO traces.
The circuit shown in Figure 1.8 is a low-pass filter/power amplifier ca-
pable of delivering 1.1 W to an 8
load, when operating from a +5 V
power supply (power output will be less when operating from +3.3 V).
Figure 1.8. 3 kHz Low-Pass Filter/Power Amplifier
The amplifier’s shutdown pin can be controlled by the TS
0
pin to mini-
mize current drain when the RC8650 is inactive.
Digital Audio Output
The digital audio pin DAOUT outputs the RC8650’s audio signal as
a digital audio stream consisting of 8 data bits per sample. The nor-
malized sampling rate for all text to speech modes and the DTMF
generator is 84 kbs (10,500 bytes/sec). The sinusoidal generator, pre-
recorded and real time audio playback mode rates are user program-
mable, so their normalized rates will vary. See the Pin Descriptions and
Audio Control Register command description for further details.
Figure 1.7. Method of Capturing Status Information for Driving External Circuitry