AN645 Datasheet, PDF (18/202 Pages) Silicon Laboratories – Si477X PROGRAMMING GUIDE

AN645
7. Digital ZIF I/Q Interface
The digital ZIF I/Q output can provide the down converted channelized AM/FM signal at baseband to a third-party
processor for AM/FM HD radio processor for IBOC signal processing (Si4777 only). The Si4777 provide a 500 kHz
BW signal for FM IBOC signal processing and a 30 kHz BW signal for AM IBOC signal processing. The ZIF I/Q 4-
pin interface consists of two data serial lines containing I and Q data, a bit clock, and a word frame for each data
sample. The interface operates in master mode and supports five different data formats:
I²S ZIF
Left-Justified ZIF
Right-Justified ZIF
DSP ZIF
DSP Left-Justified ZIF
Table 4. ZIF I/Q Interface Description
Pin
IOUT
QOUT
IQFS
IQCLK
Description
16-bit baseband I word
16-bit baseband Q word
Word frame sync for I and Q words
Bit clock for I and Q data
7.1. ZIF I/Q Data Formats
In I²S format, by default, the MSB is captured on the second rising edge of IQCLK following each IQFS transition.
The remaining bits of the word are sent in order, down to the LSB.
In Left-Justified format, by default, the MSB is captured on the first rising edge of IQCLK following each IQFS
transition. The remaining bits of the word are sent in order, down to the LSB.
In Right-Justified format, by default, the LSB is captured on the last rising edge of IQCLK in each valid IQFS
interval.
In DSP format, the IQFS becomes a pulse with a width of 1 IQCLK period. There are two options in transferring the
digital baseband I/Q data in DSP format: the MSB of I and Q data can be transferred on the first rising edge of
IQCLK following the IQFS pulse (left-justified DSP format) or on the second rising edge.
In all data formats, depending on the word size, IQCLK frequency, and sample rates, there may be unused IQCLK
cycles after the LSB of each word before the next IQFS transition and MSB of the next word. In addition, if
preferred, the user can configure the MSB to be captured on the falling edge of IQCLK via properties. The number
of baseband I/Q bits is configured for 16 bits.
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Rev. 0.3