RALCWI Vocoder
CMX608/CMX618/CMX638
4.1.
PCB Layout Guidelines and Power Supply Decoupling
Figure 4 CMX618/CMX638 Power Supply 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 CMX618/CMX638 and the power supply and bias de-coupling capacitors. The de-coupling
capacitors C4, C6, C7, C8, C9, C10, C12, C13 and C14 should be as close as possible to the
CMX618/CMX638. It is therefore recommended that the printed circuit board is laid out with separate
ground planes for the AV and (digital) V supplies in the area of the CMX618/CMX638, with provision
SS
SS
to make links between them close to the CMX618/CMX638. The use of a multi-layer printed circuit board
will facilitate the provision of ground planes on separate layers. The layout of a CMX608 printed circuit
board should make use of a single ground plane covering the whole chip area shown above.
On CMX618/CMX638, V
is used as an internal reference for detecting and generating the various
BIAS
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 an external mid-
BIAS
point reference, it must be buffered with a high input impedance buffer.
2014 CML Microsystems Plc
11
D/608_18_38/11
CMLMICRO [ CML MICROCIRCUITS ]
