CMX983 Datasheet, PDF (28/93 Pages) CML Microcircuits – Programmable Channel Filter

Analogue Front End (AFE) for Digital Radio
CMX983
RX_OVF - $1E: 16-bit Write
Reset value = $0000
Bit:
15 14 13 12 11 10 9
8
0
Filt
length
B
Enab
i/p B
over-
flow
Overflow threshold B
7
6
5
4
3
2
1
0
0
Filt
length
A
Enab
i/p A
over-
flow
Overflow threshold A
The input overflow circuit uses a separate running average filter for each of the modulator output
bitstreams (channels A and B) using a selectable window width of 32 or 64 bits. The modulator output
bits have a weighting of ± ½, so the maximum theoretical filter output value is ± 16 (with a window
width of 32) or ± 32 (with a window width of 64). The average filter output value, for a dc level of 1V
pk-pk at the input of the sigma-delta modulator, is approximately 4.82 (window width = 32) or 9.64
(window width = 64). If at any time the filter output for a channel exceeds the specified threshold
value (in either the positive or negative direction), and if the overflow flag is enabled, then the
associated status bit in the RX_STATUS register gets set to 1.
RX_OVF b15: Reserved, set to 0
RX_OVF b14: Filter length B
For channel B, set to 1 for a running average filter length of 64, set to 0 for a filter length of 32.
RX_OVF b13: Enable input overflow B
For channel B, set to 1 to enable the filters, set to 0 to disable the filters.
RX_OVF b12-8: Overflow threshold B
If the absolute value of the (enabled) channel B running average filter output is greater than the
overflow threshold B value, then an overflow is flagged in the RX_STATUS register.
RX_OVF b7: Reserved, set to 0
RX_OVF b6: Filter length A
For channel A, set to 1 for a running average filter length of 64, set to 0 for a filter length of 32.
RX_OVF b5: Enable input overflow A
For channel A, set to 1 to enable the filters, set to 0 to disable the filters.
RX_OVF b4-0: Overflow threshold A
If the absolute value of the (enabled) channel A running average filter output is greater than the
overflow threshold A value, then an overflow is flagged in the RX_STATUS register.
 2015 CML Microsystems Plc
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