SBASAI6 September 2023 ADC32RF52
PRODUCTION DATA
The SYSREF input signal is used to reset internal digital blocks and align them to the internal multi-frame clock to achieve deterministic latency subclass 1. The SYSREF input signal can be AC or DC coupled (selected via SPI register option) as shown in Figure 7-12. The ADC32RF5x has internal 100-Ω termination for DC coupling and internal biasing when using AC coupling.
A register mask can be used to only give SYSREF to the NCO (see NCO section) in the decimation filter block and leave all other blocks such as JESD interface unaffected.
When giving a periodic SYSREF signal, the frequency must be a sub-harmonic of the internal local multi-frame clock (LMFC). The LMFC frequency is determined by the selected decimation: frames per multi-frame setting (K), samples per frame (S), and the device sampling frequency (FS).
Operating Mode | LMFS Mode | LMFC Clock Frequency | SYSREF Frequency |
---|---|---|---|
DDC Bypass Mode | 82820 | FS / (20 x K) | FS / (N x 20 x K) |
8224 | FS / (4 x K) | FS / (N x 4 x K) | |
Decimation | Various | FS / (D x S x K) | FS / (N x D x S x K) |
Where N is an integer value (1, 2, 3...).
After enabling SYSREF input, the internal SYSREF input ignores any incoming SYSREF pulse after the first 16 pulses.
The internal synchronization using the external SYSREF signal can be enabled with the following register writes (see Table 7-9)
ADDR | DATA | DESCRIPTION |
---|---|---|
0x05 | 0x02 | Select DIGITAL page |
0x236 | 0x02 | Enable internal SYSREF input and clear SYSREF pulse counter |
0x236 | 0x03 | Starts internal SYSREF counter |
AC coupling with internal biasing of the SYSREF input can be enabled with the following SPI register writes (see Table 7-10)
ADDR | DATA | DESCRIPTION |
---|---|---|
0x05 | 0x40 | Select ANALOG page |
0xB4 | 0x01 | Enable external AC coupling with internal biasing on SYSREF |