TWL1101

VOICE-BAND AUDIO PROCESSOR (VBAP

™)

SLWS074A – MAY 1998 REVISED MARCH 1999

4

POST OFFICE BOX 655303

functional description

power-on/reset

The power for the various digital and analog circuits is separated to improve the noise performance of the

the power-down state. An external reset must be applied to the active low RESET pin to guarantee reset upon

power on. After the initial power-on sequence the TWL1101 can be functionally powered up and down by writing

reference

A precision band gap reference voltage is generated internally and supplies all required references to operate

the transmit and receive channels. The reference system also supplies bias current for use with an electret

microphone at pin MBIAS. An external precision resistor is required for reference current setting at pin REXT.

low noise filter

The VBAP requires external decoupling capacitors at pins DECBG and DECOD.

five control registers: 1) power control, 2) mode control, 3) transmit PGA and sidetone control, 4) receive volume

control, 5) receive PGA gain control.

phase-locked loop

The internal digital filters and modulators require a 10.24-MHz clock that is generated by phase locking to the

2.048-MHz master clock input.

PCM interface

The PCM interface transmits and receives data at the PCMO and PCMI pins respectively. The data is

transmitted or received at the PCMCLK speed once every PCMSYN cycle. The PCMCLK may be tied directly

to the 2.048-MHz master clock (MCLK).

microphone amplifiers

The microphone input is a switchable interface for two differential microphone inputs. The first stage is a low

noise differential amplifier that provides a selectable gain of –2.62 dB or 5.38 dB, which is routed to output pins

MICOUTP and MICOUTN. The second stage amplifier gain is set externally. The first and second stages may

be tied directly together with a specified gain or an external filter may be added to enhance the transmit channel

performance.

analog modulator

The transmit channel modulator is a third-order sigma-delta design.

transmit filter and PGA

The transmit filter is a digital filter designed to meet CCITT G.714 requirements. The device operates in either

the 13-bit linear or 8-bit companded

defaults to 0 dB.

sidetone

A portion of the transmitted audio is attenuated and fed back to the receive channel through the sidetone path.

The sidetone path defaults to –12 dB. The sidetone path can be muted by writing to the Power Control register.