xe3006 Semtech Corporation, xe3006 Datasheet - Page 7

• Manufacturer Part Number: xe3006
• Description: Sandman? Codec | Semtech
• Manufacturer: Semtech Corporation

2.1.3
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)
Figure 6 shows the relation of input and output samples of the PWM (The timing diagram is not to scale in the time-axis).
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
-VDDPA
VDDPA
VSSPA
1
0
1
0
DAC Signal Channel
From Serial Audio
Interface
1/(256 x Fsync)
pwm_in(5:0) = 1
dac_in(15:0)
@ Fsync
Interpolator
Modulator
pwm_in(5:0) = -1
&
1/(256 x Fsync)
1/(8 x Fsync)
Figure 7: Examples PWM in and out (not to scale)
pwm_in(5:0)
@ 8xFsync
Figure 6: DAC block diagram
Pulse Width
Modulator
pwm_in(5:0) = 0
7
@ 256xFsync
bit streams
P
N
pwm_in(5:0) = 2
2/(256 x Fsync)
P
P
s
Amplifier
VDDPA
XE3005/6
VSSPA
Power
XE3005/XE3006
s = 1 s = 0
OUTP-OUTN
N
N
P
N
AOUTN
AOUTP
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