CMX983 Datasheet, PDF (70/93 Pages) CML Microcircuits – Programmable Channel Filter

Analogue Front End (AFE) for Digital Radio
CMX983
13.2 Auxiliary Comparators
Each of the five analogue comparator channels can be individually enabled. The positive inputs of the
comparators are connected to the AUXADC4..0 input pins, and the negative inputs of the comparators are
connected to a set of five programmable threshold voltages. The threshold voltages can be individually set in
nominal 100mV increments, and can use either the analogue supply or an on-chip bandgap voltage as a
reference. Each comparator output can be optionally inverted so that a status flag is generated either when
the input pin is above or below the associated threshold voltage.
The following C-BUS registers are used to configure the auxiliary ADCs:
AUXCMP_CON0 - $76: 8-bit Write
AUXCMP_CON1 - $77: 8-bit Write
AUXCMP_CON2 - $78; 8-bit Write
AUXCMP_CON3 - $79: 8-bit Write
AUXCMP_CON4 - $7A: 8-bit Write
Reset value = $00
Bit:
7
6
5
4
3
2
1
0
CON0:
Enab Invert
cmp 0 cmp 0
Vref
sel 0
Comparator 0 threshold voltage
CON1:
Enab Invert
cmp 1 cmp 1
Vref
sel 1
Comparator 1 threshold voltage
CON2:
Enab Invert
cmp 2 cmp 2
Vref
sel 2
Comparator 2 threshold voltage
CON3:
Enab Invert
cmp 3 cmp 3
Vref
sel 3
Comparator 3 threshold voltage
CON4:
Enab Invert
cmp 4 cmp 4
Vref
sel 4
Comparator 4 threshold voltage
Each of these five registers controls one of the analogue comparators:
AUXCMP_CON0-4 Register b7: Enable comparator
Set to 1 to enable the associated channel (comparator + threshold voltage generator), or set to 0 to
disable and powersave the channel. The comparators are prevented from setting their associated flag
bit in the AUXCMP_STAT register when they are disabled, or for 256 CLK cycles after the enable bit
changes from 0 to 1 (to allow time for the internal threshold voltage to settle).
AUXCMP_CON0-4 Register b6: Invert comparator
Set to 1 to invert the comparator output, causing the comparator flag to be set when the input voltage
goes below the comparator threshold voltage. Set to 0 to cause the comparator flag to be set when
the input voltage goes above the comparator threshold voltage.
AUXCMP_CON0-4 Register b5: Voltage reference select
Set to 1 to use the internally generated voltage (2.5V) as the reference for the comparator threshold.
Set to 0 to use the analogue supply voltage (AV_DD) as the reference for the comparator threshold.
AUXCMP_CON0-4 Register b4-0: Comparator threshold voltage
Set the comparator threshold voltage from 0.0V (00000₂) to 3.1V (11111₂) in 100mV (nominal) steps.
Note: if using the internally generated voltage as a reference, then the maximum voltage that can be
set is 2.5V (11001₂).
 2015 CML Microsystems Plc
70
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