AUDIO DATA CONVERTERS
AUDIO CLOCK GENERATION
SLAS553A – NOVEMBER 2008 – REVISED SEPTEMBER 2009...................................................................................................................................... www.ti.com
The TLV320ADC3101 supports the following standard audio sampling rates: 8 kHz, 11.025 kHz, 12 kHz, 16 kHz,
22.05 kHz, 24 kHz, 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, and 96 kHz. The converters can also operate at
different sampling rates in various combinations, which are described further as follows.
The TLV320ADC3101 supports a wide range of options for generating clocks for the ADC section as well as the
digital interface section and the other control blocks, as shown in
Figure 31. The clocks for the ADC require a
source reference clock. The clock can be provided on device pins MCLK and BCLK. The source reference clock
for the ADC section can be chosen by programming the ADC_CLKIN value on page 0 / register 4, bits D1–D0.
The ADC_CLKIN can then be routed through highly flexible clock dividers, shown in
Figure 31, to generate
various clocks required for the ADC and programmable digital filter sections. In the event that the desired audio
or programmable digital filter clocks cannot be generated from the external reference clocks on MCLK and
BCLK, the TLV320ADC3101 also provides the option of using an on-chip PLL that supports a wide range of
fractional multiplication values to generate the required system clocks. Starting from ADC_CLKIN, the
TLV320ADC3101 provides for several programmable clock dividers to support a variety of sampling rates for the
ADC and the clocks for the programmable digital filter section.
The audio converters in fully programmable filter mode in the TLV320ADC3101 require an internal audio master
clock at a frequency of
≥ N × fS, where N = IADC (page 0 / register 21) when filter mode (page 0 / register 61)
equals zero; otherwise, N equals the instruction count from the ADC processing blocks (see
Table 6). The
master clock is obtained from an external clock signal applied to the device.
The device can accept an MCLK input from 512 kHz to 50 MHz, which can then be passed through either a
programmable divider or a PLL to get the proper internal audio master clock required by the device. The BCLK
input can also be used to generate the internal audio master clock.
A primary concern is proper operation of the TLV320ADC3101 at various sample rates with the limited MCLK
frequencies available in the system. This device includes a programmable PLL to accommodate such situations.
The integrated PLL can generate audio clocks from a wide variety of possible MCLK inputs, with particular focus
paid to the standard MCLK rates already widely used.
When the PLL is enabled,
fS = (PLLCLK_IN × K × R) / (NADC×MADC×AOSR × P), where
P = 1, 2, 3,…, 8
R = 1, 2, …, 16
K = J.D
J = 1, 2, 3, …, 63
D = 0000, 0001, 0002, 0003, …, 9998, 9999
PLLCLK_IN can be MCLK or BCLK, selected by page 0 / register 4, bits D3–D2.
P, R, J, and D are register programmable. J is the integer portion of K (the numbers to the left of the decimal
point), whereas D is the fractional portion of K (the numbers to the right of the decimal point, assuming four digits
of precision).
Examples:
If K = 8.5, then J = 8, D = 5000
If K = 7.12, then J = 7, D = 1200
If K = 14.03, then J = 14, D = 0300
If K = 6.0004, then J = 6, D = 0004
When the PLL is enabled and D = 0000, the following conditions must be satisfied to meet specified
performance:
512 kHz
≤ (PLLCLK_IN / P) ≤ 20 MHz
80 MHz
≤ (PLLCLK _IN × K × R / P) ≤ 110 MHz
4
≤ J ≤ 55
When the PLL is enabled and D
≠ 0000, the following conditions must be satisfied to meet specified
performance:
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