Datasheet

LargestPositiveNumber:
=0.111 1111 1111 111
=0.999969482421875=1.0 – 1LSB
1
LargestNegativeNumber:
=1.0000 0000 0000 000
=0x8000= –1.0(bydefinition)
1 1 1
1 1 1
S.xxxx xxxx xxxx xxx.. x x x
SignBit
2 Bit
–1
2 Bit
–4
2 Bit
–15
Fraction
Point
TLV320DAC3100
SLAS671A –FEBRUARY 2010–REVISED MAY 2012 www.ti.com
5.5.1.3 DAC User-Programmable Filters
Depending on the selected processing block, different types and orders of digital filtering are available. Up
to six biquad sections are available for specific processing blocks.
The coefficients of the available filters are arranged as sequentially-indexed coefficients in two banks. If
adaptive filtering is chosen, the coefficient banks can be switched in real time.
When the DAC is running, the user-programmable filter coefficients are locked and cannot be accessed
for either read or write.
However, the TLV320DAC3100 offers an adaptive filter mode as well. Setting page 8 / register 1, bit D2 =
1 turns on double buffering of the coefficients. In this mode, filter coefficients can be updated through the
host and activated without stopping and restarting the DAC. This enables advanced adaptive filtering
applications.
In the double-buffering scheme, all coefficients are stored in two buffers (buffers A and B). When the DAC
is running and the adaptive filtering mode is turned on, setting page 8 / register 1, bit D0 = 1 switches the
coefficient buffers at the next start of a sampling period. This bit is set back to 0 after the switch occurs. At
the same time, page 8 / register 1, bit D1 toggles.
The flag in page 8 / register 1, bit D1 indicates which of the two buffers is actually in use.
Page 8 / register 1, bit D1 = 0: buffer A is in use by the DAC engine; bit D1 = 1: buffer B is in use.
While the device is running, coefficient updates are always made to the buffer not in use by the DAC,
regardless of the buffer to which the coefficients have been written.
Table 5-12. Adaptive-Mode Filter-Coefficient Buffer Switching
DAC Running? Page 8, Reg 1, Bit D1 Coefficient Buffer in Use Writing to Updates
No 0 None Buffer A Buffer A
No 0 None Buffer B Buffer B
Yes 0 Buffer A Buffer A Buffer B
Yes 0 Buffer A Buffer B Buffer B
Yes 1 Buffer B Buffer A Buffer A
Yes 1 Buffer B Buffer B Buffer A
The user-programmable coefficients for the DAC processing blocks are defined on page 8 and page 9 for
buffer A and page 12 and page 13 for buffer B.
The coefficients of these filters are each 16-bit, 2s-complement format, occupying two consecutive 8-bit
registers in the register space. Specifically, the filter coefficients are in 1.15 (one dot 15) format with a
range from –1.0 (0x8000) to 0.999969482421875 (0x7FFF) as shown in Figure 5-13.
Figure 5-13. 1.15 2s-Complement Coefficient Format
26 APPLICATION INFORMATION Copyright © 2010–2012, Texas Instruments Incorporated
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