CMX994 Datasheet, PDF (35/61 Pages) CML Microcircuits – Local Oscillator

Direct Conversion Receivers
CMX994/CMX994A/CMX994E
7.11
7.11.1
VCO Control Register
VCO Control: $25 - 8-bit write only
This register controls the operation of the VCO and LO input. Operation is only enabled when b3 = ‘1’ in the
General Control Register ($11), as detailed in section 7.2 All bits of this register are cleared to ‘0’ by a General
Reset command.
Note: it is not recommended that the LO input and the VCO are enabled simultaneously.
7
FILT_ CAL
6
TXDIV1
5
TXDIV0
4
LO Input
EN
3
VCO_NR2
2
VCO_ NR1
1
VCO_ NR
En
0
VCO_
Buf En
b7
This bit, if set to ‘1’, will disable the Filter Calibration System. The default value is ‘0’.
b6,5 These bits control the output division of the Tx LO signal available at pin TXLO. The LO signal is
divided by the factor as shown in the following table.
b6 b5 Function
0
0 Divide by 2
0
1 Divide by 4
1
0 Divide by 6
1
1 No division
b4,b1, These bits control power up/power down of the various blocks of the device
b0
In all cases, ‘1’ = power up, ‘0’ = power down
b4 Enable LO input
b1 Enable VCO NR Amplifier. When disabled
the amplifier is bypassed to support the
application of an external LO signal.
b0 Enable VCO Buffer
b3,b2
VCO amplifier Negative Resistance (NR) control bits optimise phase noise performance. These bits
control the Negative Resistance (magnitude of the negative transconductance) of the on-chip VCO
NR amplifier. The NR minimum mode would thus be used with the lowest Q external tank circuit and
NR maximum with the highest Q value.
B3 B2 Function
0
0 NR maximum
0
1 NR intermediate value
1
0 NR intermediate value
1
1 NR minimum
7.11.2 VCO Control: $D5 - 8-bit read only
This register reads the value in register $25; see section 7.11.1 for details of bit functions.
 2015 CML Microsystems Plc
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