TLV320AC56, TLV320AC57

3-V VOICE-BAND AUDIO PROCESSORS (VBAP

™)

SLWS044B – JUNE 1996 – REVISED OCTOBER 1997

15

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

conversion laws

The TLV320AC56 provides

µ-law companding operation that approximates the CCITT G.711 recommendation.

The TLV320AC57 provides A-law companding operation that approximates the CCITT G.711 recommendation.

The linear mode of operation uses a 13-bit two’s-complement format and is the same for both the TLV320AC56

and the TLV320AC57.

transmit operation

microphone input

The microphone input amplifier is designed specifically to interface to electret-type microphone elements, as

the microphone amplifier and a bias voltage to the electret microphone. The microphone amplifier output

(MICGS) is used in conjunction with a feedback network and applied to the amplifier inverting input (MICIN) to

set the amplifier gain. VMID appears at a terminal to provide a place to filter the VMID voltage.

TLV320AC56/57 VBAP

2 k

Ω

17

VMID

18

MICIN

19

MICGS

20

MICBIAS

To Transmit Filters

Microphone Amplifier

VMID Buffer

10 k

Ω

+

–

VMID Reference

For Amplifiers

1

µF

VMID

Generator

Electret

Microphone

–

+

3.3

µF

MICMUTE

6

10 k

Ω

–

+

VDD

470 pF

+

NOTE A: Terminal numbers shown are for the DW and N packages.

Figure 5. Typical Microphone Interface

microphone mute function

The MICMUTE input causes the digital circuitry to transmit all zero code on DOUT.

transmit filter

A low-pass antialiasing section is included on the device and achieves a 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.