STA309A
Registers
Doc ID 13855 Rev 4
23/67
Interpolation ratio select
The STA309A has variable interpolation (oversampling) settings such that internal
processing and DDX output rates remain consistent. The first processing block interpolates
by either 4 times, 2 times, or 1 time (pass-through).
The oversampling ratio of this interpolation is determined by the IR bits.
I
Setting the DSPB bit bypasses the biquad function of the Omega DDX core.
Table 11.
Interpolation ratio bits
Bit
RW
RST
Name
Description
3
RW
0
IR0
Interpolation ratio select: selects internal interpolation
ratio based on input I
2
S sample frequency
4
RW
0
IR1
Table 12.
IR sample rates
IR[1,0]
Input sample rate
fs (kHz)
1
st
stage interpolation ratio
00
32
4-times oversampling
00
44.1
4-times oversampling
00
48
4-times oversampling
01
88.2
2-times oversampling
01
96
2-times oversampling
10
176.4
Pass-through
10
192
Pass-through
11
DSD
DSD to 176.4 kHz conversion
Table 13.
DSPB bit
Bit
RW
RST
Name
Description
0
RW
0
DSPB
DSP bypass bit:
0: normal operation
1: bypass of biquad and bass/treble functions
Table 14.
COS bits
COS[1,0]
CKOUT frequency
00
PLL output
01
PLL output / 4
10
PLL output / 8
11
PLL output / 16