CMX971 Datasheet, PDF (6/25 Pages) CML Microcircuits – Small 16-lead VQFN Package

Quadrature Modulator
4 External Components
CMX971
4.1 Power Supply Decoupling
The CMX971 has separate supply pins for the RF, analogue and digital circuitry; a 3.3V nominal supply is
recommended for all circuits. It is recommended that the digital supply be decoupled from the RF and
analogue supply; an example of such decoupling is shown in Figure 2.
V_SUPPLY
R2
R1
VCC
VDD
V_GROUND
C1
C2
LOGND
RFGND
VSS
Figure 2 Power Supply Connections and Decoupling
C1 10nF
C2 10nF
R1 10
R2 3.3
Resistors 1%, capacitors 20%
Table 3 Power Supply Component Values
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. 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 achieved cost
effectively using the resistor as shown. The use of resistors results in small dc voltage drops. Choosing
resistor values approximately inversely proportional to the dc current requirements of each supply pin
ensures the dc voltage drop on each supply is reasonably matched. In any case, the dc voltage change
that results are well within the design tolerance of the device. If higher impedance resistors are used then
greater care will be needed to ensure that the supply voltages are maintained within tolerance, including
when parts of the device are enabled or disabled.
 2015 CML Microsystems Plc
6
D/971/4