TCM320AC36, TCM320AC37

VOICE-BAND AUDIO PROCESSORS (VBAP

™)

SLWS003C – MAY 1992 – REVISED APRIL – 1998

2

POST OFFICE BOX 655303

description

The TCM320AC36 and TCM320AC37 voice-band audio processor (VBAP) integrated circuits are designed to

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 zero 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 band-pass 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 takes a frame of serial data on DIN and converts it 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

virtual ground for all the amplifier circuits and the microphone bias circuit. Another reference voltage, MICBIAS,

can supply bias current for the microphone.

The TCM320AC3xC devices are characterized for operation from 0

°C to 70°C. The TCM320AC3xI devices are

characterized for operation from – 40

°C to 85°C.