AX.25 Modem
CMX7031/CMX7041
Figure 5 CMX7041 Power Supply Connections and De-coupling
Component Values as per Figure 3.
Notes:
It is important to protect the analogue pins from extraneous inband noise and to minimise the impedance
between the device and the supply and bias de-coupling capacitors. The de-coupling capacitors C3, C7,
C18, C19, C21, C22, C24 and C25 should be as close as possible to the device. It is therefore
recommended that the printed circuit board is laid out with separate ground planes for the AV , RFV
SS
SS
and DV supplies in the area of the CMX7031, with provision to make links between them, close to the
SS
device. Use of a multi-layer printed circuit board will facilitate the provision of ground planes on separate
layers.
V
BIAS
is used as an internal reference for detecting and generating the various analogue signals. It must
be carefully decoupled, to ensure its integrity, so apart from the decoupling capacitor shown, no other
loads should be connected. If V needs to be used to set the discriminator mid-point reference, it must
BIAS
be buffered with a high input impedance buffer.
The crystal X1 may be replaced with an external clock source.
The 2.5V VDEC output can be used to supply the 2.5V RFVDD, to remove the need for an external 2.5V
regulated supply. VDEC can be directly connected to RFVDD, in which case C23 should be omitted.
2013 CML Microsystems Plc
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CMLMICRO [ CML MICROCIRCUITS ]
