TCM320AC46 Datasheet, PDF (6/19 Pages) Texas Instruments – GEBERAL-PURPOSE AUDIO INTERFACE FOR DSP

TCM320AC46
ą
GENERALĆPURPOSE AUDIO INTERFACE FOR DSP
ą
SLWS001 − D4091, JUNE 1993
conversion laws
The TCM320AC46 provides µ-law companding operation. The linear mode utilizes a 13-bit 2s complement
format.
transmit operation
microphone input
The microphone input amplifier is designed to simplify interface to electret-type microphone elements as shown
in Figure 1. The VMID buffer circuit provides a voltage (MICBIAS) equal to V_CC /2 as a reference for the
microphone amplifier and a bias voltage to the electret microphone. The microphone amplifier output (MICGS)
is used in conjunction with a feedback network to the amplifier inverting input (MICIN) to set the amplifier gain.
VMID is brought out to provide a place to filter the VMID voltage.
microphone mute function
The MICMUTE input disables the microphone amplifier and attenuates the signal on the MICGS output to a level
that is 80 dB or more down from the signal on the MICIN input. MICMUTE also causes the digital circuitry to
transmit all zero code on DOUT.
1 µF
VMID
17
MICBIAS
20
VMID Buffer
+
−
VMID Reference
for Amplifiers
VMID Generator
2 kΩ
MICGS
+
−
0.1 µF
>10 kΩ
19
MICIN
18
Microcontroller ^MICMUTE
Electret
6
Microphone
Microphone Amplifier
−
+
TCM320AC46
To Transmit Filter
Figure 1. Typical Microphone Interface
transmit filter
A low-pass antialiasing section is included on the device. This section provides 35-dB attenuation at the
sampling frequency. No external components are required to provide the necessary antialiasing function for the
switched-capacitor section of the transmit filter.
6
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