CMX983 Datasheet, PDF (33/93 Pages) CML Microcircuits – Programmable Channel Filter

Analogue Front End (AFE) for Digital Radio
CMX983
Selects which bank of coefficients the channel A FIR filter uses:
00 = RX_COEFF0
01 = RX_COEFF1
10 = RX_COEFF2
11 = RX_COEFF3
RX_VERNIER - $26: 16-bit Write
Reset value = $0000
Bit:
15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
0
0
Phase vernier B
0
0
Phase vernier A
RX_VERNIER b15-14: Reserved, set to 0
RX_VERNIER b13-8: Phase vernier B
Allows fine adjustment of the channel B signal phase by setting which sinc output sample the first
downsampler selects. Setting the phase vernier value to 0 gives an ‘on-time’ signal; setting the value
to N gives a ‘late’ signal, delayed by N cycles of the CR1 clock. The phase vernier value must be less
than the value set for the first downsample rate in the associated decimator control register
RX_CON1.
RX_VERNIER b7-6: Reserved, set to 0
RX_VERNIER b5-0: Phase vernier A
Allows fine adjustment of the channel A signal phase (similar in operation to bits 13-8).
RX_BITSEL1 - $27: 16-bit Write
Reset value = $0000
Bit:
15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
0
0
0
Rx B first bit select
0
0
0
Rx A first bit select
RX_BITSEL1 b15-13: Reserved, set to 0
RX_BITSEL1 b12-8: Rx B first bit select
In Rx channel B, selects which 20 bits of the 37-bit sinc filter accumulator are passed to the following
phase vernier and downsample stage. This value determines the number of most-significant bits
discarded (valid range = 0 to 17): a value of 0 selects the most significant 20 bits of the sinc
accumulator, a value of 1 discards the MSB of the accumulator and selects the next most significant
20 bits, and so on. Convergent rounding is applied to the selected bits and the selector output
saturates in the case of an overflow (positive saturation = $7FFFF, negative saturation = $80000). To
assist with setup, an overflow causes a status bit to be set in the RX_STATUS register.
RX_BITSEL1 b7-5: Reserved, set to 0
RX_BITSEL1 b4-0: Rx A first bit select
Rx channel A first bit select, similar in operation to bits 12-8.
 2015 CML Microsystems Plc
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