Quadrature Modulator
CMX993/CMX993W
4
External Components
4.1
Power Supply Decoupling
The CMX993/CMX993W has separate supply pins for the analogue and digital circuitry; a 3.3V nominal
supply is recommended for all circuits but a different voltage for VDDIO may be used (see section 5.4).
R9
VDDIO
VDD
+3.3V (Digital)
R8
R7
R6
R5
R4
VCC1
VCC2
VCC3
VCC4
VCC5
VCC6
VCC7
+3.3V
(Analogue)
R3
R1
C9
C8
C7
C6
C5
C4
C3
C1
Analogue
Ground Pad
GND
Digital Ground for
VDDIO and VDD
Figure 2 Power Supply Connections and Decoupling
C1 10nF
C3 10nF
C4 10nF
C5 10nF
C6 10nF
C7 10nF
C8 10nF
C9 10nF
R1 3.3
R3 10
R4 3.3
R5 3.3
R6 3.3
R7 3.3
R8 10
R9 100
Resistors 5%, capacitors and inductors 20% unless otherwise stated
Note:
It is expected that low frequency interference on the 3.3V supply will be removed by active regulation; a
large capacitor is an alternative but may require more board space and so may not be preferred. It is
particularly important to ensure that there is no interference from VDDIO (which supplies the digital I/O) that
might affect the sensitive analogue supplies, like VCC1, VCC2 etc. The supply decoupling shown is
intended for RF noise suppression. It is necessary to have a small series impedance prior to the
decoupling capacitor for the decoupling to work well; this may be cost effectively done with the resistor and
capacitor values shown. The use of resistors results in small dc voltage drops (up to approx 0.1V).
Choosing resistor values approximately inversely proportional to the dc current requirements of each
supply ensures the dc voltage drop on each supply is reasonably matched. In any case, the dc voltage
change that results is well within the design tolerance of the device. If higher impedance resistors are used
then greater care will be needed to ensure the supply voltages are maintained within tolerance, including
when parts of the device are enabled or disabled.
2013 CML Microsystems Plc
7
D/993/10
CMLMICRO [ CML MICROCIRCUITS ]
