CMX983 Datasheet, PDF (41/93 Pages) CML Microcircuits – Programmable Channel Filter

Analogue Front End (AFE) for Digital Radio
CMX983
Set this bit to 1 to enable the Tx channel A reconstruction filter and output gain stage, similar in
operation to bit 9.
TX_CON2 b0: FIR A coefficient select
Selects which coefficients the channel A interpolation filter uses:
0 = TX_COEFF0
1 = TX_COEFF1
TX_GAIN - $35: 16-bit Write
Reset value = $0000
Bit:
15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
0
Tx B
clamp
Tx B gain
0
Tx A
clamp
Tx A gain
TX_GAIN b15: Reserved, set to 0
TX_GAIN b14: Tx B clamp
When the Tx analog is disabled (TX_CON2 bit 9 = 0), this bit controls what happens to the DAC
output pins QTXP and QTXN: when the Tx B clamp bit is set to 1 then QTXP and QTXN get clamped
to a mid-rail reference voltage AV_DD/2; otherwise, QTXP and QTXN will become high impedance
(greater than 100kΩ).
TX_GAIN b13-8: Tx B gain
Set channel B output gain to between -11dB and +11dB in 0.5dB steps, or mute the output. The gain
setting is in 2’s complement format with an implicit binary point between bit 9 and 8:
100000 = mute
101010 = -11.0dB
101011 = -10.5dB
101100 = -10.0dB
...
111110 = -1.0dB
111111 = -0.5dB
000000 = 0.0dB
000001 = 0.5dB
000010 = 1.0dB
...
010100 = 10.0dB
010101 = 10.5dB
010110 = 11.0dB
TX_GAIN b7: Reserved, set to 0
TX_GAIN b6: Tx A clamp
Controls ITXP and ITXN clamp level, similar in operation to bit 14.
TX_GAIN b5-0: Tx A gain
Set channel A output gain, similar in operation to bits 13-8.
 2015 CML Microsystems Plc
41
D/983/6