PCM1715 Burr-Brown Corporation, PCM1715 Datasheet - Page 6

• Manufacturer Part Number: PCM1715
• Description: Dual Voltage Output CMOS Delta-Sigma DIGITAL-TO-ANALOG CONVERTER With On-Chip Digital Filter
• Manufacturer: Burr-Brown Corporation

THEORY OF
DELTA-SIGMA OPERATION
The delta-sigma section of the PCM1715 is based on a 5-
level amplitude quantizer and a 4th-order filter. This con-
verts the oversampled 16-bit input data to 5-level delta-
sigma form. A block diagram of the 5-level modulator is
shown in Figure 1.
This 5-level delta-sigma modulator has the advantage of
stability of delta-sigma loop and jitter sensitivity over the
typical 1-bit (2-level) delta-sigma modulator.
The combined oversampling rate of the delta-sigma modu-
lator and the internal 8x oversampling digital filter is 48fs at
a system clock speed of 384fs, 32fs at a system clock speed
of 256fs.
FIGURE 3. Quantization Noise Spectrum (256fs).
FIGURE 1. Block Diagram of 5-Level Delta-Sigma Quan-
FIGURE 2. Block Diagram of the Hf(z).
16 bits
8fs/
In
–100
–120
–140
–160
In
0
+
0
Hf(Z)
tizer.
®
b4
PCM1715U
–
+
5
+
5-level Quantizer
Z
–1
Frequency (kHz)
10
+
b3
Out
+
15
4
3
2
1
0
32fs/48fs
5-level
Z
–1
20
6
+
–a2
b2
A block diagram of the 4th-order filter section Hf(z) in the
delta-sigma modulator is shown in Figure 2.
In general, high order 1-bit delta-sigma modulators have
disadvantages due to loop instability. The 5 level delta-
sigma modulator of the PCM1715 uses phase compensation
techniques to obtain stable operation. In Figure 2, the coef-
ficients, b1 to b4, give the basic form of the filter and –a1
and –a2 are used for phase compensation of the feedback
loop.
The theoretical quantization noise performance of the 5-
level delta-sigma modulator is shown in Figures 3 and 4. In
the audio band, the quantization noise floor level of the
PCM1715 is less than –130dB (384fs).
MODE OF OPERATION
Serial inputs to MD, MC, and ML (Pins 26, 27 and 28)
control the following functions:
(1) Digital Attenuator [AL0 ~ AL7, AR0 ~ AR7]
FIGURE 4. Quantization Noise Spectrum (384fs).
+
+
Attenuation data is constructed by 8-bit/Lch, 8-bit/Rch
(total 16-bit), can be controlled as 255 step attenuation
by individual channel. AL0 and AR0 are LSB, and AL7
and AR7 are MSB. Attenuation Level ATT is given by:
–100
–120
–140
–160
0
ATT = 20LOG
0
Z
–1
5
+
–a1
10
b1
Frequency (kHz)
(ATT DATA/255) [dB]
+
+
10
Z
–1
15
Out
20