TCM320AC56 Datasheet, PDF (2/23 Pages) Texas Instruments – VOICE-BAND AUDIO PROCESSORS (VBAP)

TCM320AC56, TCM320AC57
VOICE-BAND AUDIO PROCESSORS (VBAP)
SLWS016A – JUNE 1996 – REVISED APRIL 1997
description
The TCM320AC56 and TCM320AC57 voice-band audio processor (VBAP) integrated circuits perform the
transmit encoding (A/D conversion) and receive decoding (D/A conversion) together with transmit and receive
filtering for voice-band communications systems. Cellular telephone systems are targeted in particular;
however, these integrated circuits can function in other systems including digital audio, telecommunications,
and data acquisition.
These devices are pin-selectable for either of two modes — companded and linear — providing data in two
formats. In the companded mode, data is transmitted and received in 8-bit words. In the linear mode, 13 bits
of data, and either three bits of gain-setting control data, or three 0 bits of padding (to create a 16-bit word), are
sent and received.
The transmit section is designed to interface directly with an electret microphone element. The microphone input
signal (MICIN) is buffered and amplified with provision for setting the amplifier gain to accommodate a range
of signal input levels. The amplified signal is passed through antialiasing and bandpass filters. The filtered signal
is then applied to the input of a compressing analog-to-digital converter (COADC) when companded mode is
selected. Otherwise, the analog-to-digital converter performs a linear conversion. The resulting data is then
clocked out of DOUT as a serial data stream.
The receive section converts a frame of serial data on DIN to analog through an expanding digital-to-analog
converter (EXDAC) when the companded mode is selected; otherwise, a linear conversion is performed. The
analog signal then passes through switched capacitor filters, which provide out-of-band rejection, (sin x)/x
correction functions, and smoothing. The filtered signal is sent to the earphone amplifier. The earphone amplifier
has a differential output with adjustable gain and is designed to minimize static power dissipation.
A single on-chip high-precision band-gap circuit generates all voltage references, eliminating the need for
external reference voltages. An internal reference voltage, VMID, equal to V_CC /2 is used to develop the midlevel
virtual ground for all the amplifier circuits and the microphone bias circuit. Another reference voltage, MICBIAS,
can supply bias current for the microphone.
The TCM320AC5xC devices are characterized for operation from 0°C to 70°C. The TCM320AC5xI devices are
characterized for operation from – 40°C to 85°C.
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