CMX869E2 Просмотр технического описания (PDF) - CML Microsystems Plc
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CMX869E2 Datasheet PDF : 46 Pages
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Low Power V.32 bis Modem
4. External Components
CMX869
R1
X1
C1, C3, C8
100kΩ
6.144MHz
10uF
C2, C4, C7, C9 100nF
C5, C6
22pF
Resistors ±5%, capacitors ±20% unless otherwise stated.
Figure 2a Recommended External Components for a Typical Application
This device is capable of detecting and decoding small amplitude signals. To achieve this DVDD, AVDD
and VBIAS should be decoupled and the receive path protected from extraneous in-band signals. It is
recommended that the printed circuit board is laid out with both AVSS and DVSS ground planes in the
CMX869 area, as shown in Figure 2b, with provision to make a link between them close to the CMX869.
To provide a low impedance connection to ground, the decoupling capacitors (C1 – C4, C7, C8) must be
mounted as close to the CMX869 as possible and connected directly to their respective ground plane.
This will be achieved more easily by using surface mounted capacitors.
VBIAS is used as an internal reference for detecting and generating the various analogue signals. It must
be carefully decoupled, to ensure its integrity. If VBIAS needs to be used (other than as shown in figures
4a or 4b) to set external analogue levels, it must be buffered with a high input impedance buffer.
The DVSS connections to the Xtal oscillator capacitors C5 and C6 should also be of low impedance and
preferably be part of the DVSS ground plane to ensure reliable start up of the oscillator.
© 2003 CML Microsystems Plc
6
D/869/1
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