XE3005 데이터 시트보기 (PDF) - Semtech Corporation

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XE3005

Low-Power Audio CODEC

Semtech Corporation 

XE3005/XE3006

2.1.3 DAC Signal Channel

The DAC is based on a multi bit sigma-delta modulator, which operates at a frequency of 8 times the sampling rate. The

outputs of the modulator are 2’s complement words of 6 bit. A pulse-width modulator (PWM) converts the 6 bit words into

2 single bit streams at 256 times the sampling frequency. Finally the 2 bit streams are supplied to the power amplifier.

The Power Amplifier is a Class D amplifier, which offers higher efficiency than the traditional Class AB topologies. It uses

a three-state unbalanced PWM. This means that both channels of the PA (AOUTP and AOUTN) will not switch at the

same time, therefore the outputs are not purely differential (see figure 5 and 6)

XE3005/6

From Serial Audio

Interface

Interpolator

&

Modulator

P

Pulse Width

Modulator N

dac_in(15:0)

@ Fsync

pwm_in(5:0)

@ 8xFsync

bit streams

@ 256xFsync

VDDPA

P

N

Power

Amplifier

P

N

AOUTP

AOUTN

VSSPA

s

s=1 s=0

Figure 6: DAC block diagram

Figure 6 shows the relation of input and output samples of the PWM (The timing diagram is not to scale in the time-axis).

pwm_in(5:0) = 1

1

0

1

0

VDDPA

VSSPA

-VDDPA

pwm_in(5:0) = -1 pwm_in(5:0) = 0 pwm_in(5:0) = 2

1/(256 x Fsync)

P

N

OUTP-OUTN

1/(256 x Fsync)

1/(8 x Fsync)

2/(256 x Fsync)

Figure 7: Examples PWM in and out (not to scale)

The DAC receives 16-bit wide 2’s complement format through the Serial Audio Interface. The protocol can be selected

through register J. The complete DAC and PA amplifier chain can be powered-down through register I.

© Semtech 2005

www.semtech.com

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