TWL1103T-Q1

VOICE-BAND AUDIO PROCESSOR (VBAP

)

SGLS120A – APRIL 2002 – REVISED MAY 2002

4

POST OFFICE BOX 655303

functional description (continued)

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 15-bit linear or 8-bit companded

transmit PGA 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 enabled by writing to the power control register.

receive volume control

The receive volume control block acts as an attenuator with a range of –18 dB to 0 dB in 2 dB steps for control

of the receive channel volume. The receive volume control gain defaults to 0 dB.

receive filter and PGA

The receive filter is a digital filter that meets CCITT G.714 requirements with a high-pass filter that is selectable

µ-law or A-law companded

for a 32-

Ω load impedance and the corresponding digital full scale PCMI code. The gain may be set to –2 dB

for the respective 3-dBm0 level for a 16-

digital modulator and filter

The second-order digital modulator and filter convert the received digital PCM data to the analog output required

by the earphone interface.

earphone amplifiers

The analog signal can be routed to either of two earphone amplifiers, one with differential output (EAR1ON and

EAR1OP) and one with single-ended output (EAR2O). Clicks and pops are suppressed for EAR1 differential

output only.

tone generator

The tone generator provides generation of standard DTMF tones and single tone frequencies which are output

to the following devices: 1) The buzzer driver, as a pulse density modulation (PDM) signal 2) The receive path

digital/analog converter (DAC) for outputting through the earphone. There are 255 possible single tones. The

tone integer value is determined by the following formula:

Round (Tone Freq (Hz)/7.8135 Hz)

The value is loaded into one of two 8-bit registers, the high-tone register (04), or the low-tone register (05). The

tone output is 2 dB higher when applied to the high-tone register (04). When generating DTMF tones, the high

DTMF tone must be applied to the high-tone register and the low frequency tone to the low-tone register.