AMBE-2000 Digital Voice Systems, Inc., AMBE-2000 Datasheet - Page 57

• Manufacturer Part Number: AMBE-2000
• Description: 2.0 - 9.6 KBPS Single ic For Toll-quality, Low Data Rate, Real Time Speech Compression
• Manufacturer: Digital Voice Systems, Inc.

8.4
The Texas Instruments PCM3500 codec chip presents a simple low cost solution for use with DVSI’s AMBE-
2000™ or AMBE-2020™ vocoder chips. This application note provides information on alternative methods of
interfacing these components.
PCM3500
The block diagram in Figure 1 shows a sample interface between the PCM3500 codec and DVSI’s AMBE-2000™
vocoder chip. The AMBE-2000™ or AMBE-2020™ CODEC_SEL bits (see AMBE-2000™ or AMBE-2020™
users manual) must be set for use with a generic 16 bit linear codec (CODEC_SEL1,0 – 00).
There are two advantages to using the PCM3500 codec. The first is the single supply design. The PCM3500 supports a
single power supply design from +2.7 v to +3.6 v. The second advantage lies in its simplicity. There are no complicated
configuration schemes associated with the codec. For configuration information, please see the PCM3500 data sheet
and the reference circuit in Figure 2.
Notes On Analog Circuit Design
The example circuit assumes that a telephone handset is going to be used in the circuit. Typically,
handset microphones have a very small gain and the output is at moderately low levels (on the order of 50
millivolts peak to peak). The PCM3500 Voice Codec is designed for an analog input voltage of 2 volts
peak to peak. The analog input in the reference design is amplified (Gain = 22) in order to bring the
handset voltage to the level expected by the ADC.
The output section is designed using a low pass filter design with a gain of 1. The filter is designed to
allow the maximum amount of the voice signal to pass unimpeded. The output of the PCM3500 should
be filtered for maximum voice quality.
Capacitors C13 and C14 are for creating a very low noise DC bias signal. If a low noise DC bias is
available elsewhere in the circuit, they are not needed.
For optimum performance, the analog circuit should be adjusted for whatever input (and output) device is
used. Please reference the PCM3500 data sheet for the analog requirements.
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U1
CODEC_RX_CLCK
CODEC_RX_STRB
CODEC_RX_DATA
CODEC_TX_CLCK
CODEC_TX_STRB
CODEC_TX_DATA
AMBE-2000
Interfacing to the Texas Instruments PCM3500 Codec
www.dvsinc.com
27
33
37
29
31
41
Figure 1: The AMBE-2000™ Vocoder with the PCM3500 CODEC
8
9
11
10
DOUT
/BCK
FS
DIN
U2
PCM3500
M/S
Vdd
Vcc
6
13
24
Master/Slave
3.3V
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