Audio Scrambler and Sub-Audio Signalling Processor
CMX138A
5.1 PCB Layout Guidelines and Power Supply Decoupling
1
2
28
27
VDEC
DVSS
DVSS
AVSS
C14
26
C15
3
4
25
24
23
22
DVss
5
AVSS
DVss Ground
Plane
6
7
CMX138A
AVSS Ground
Plane
8
21
20
DVDD
9
VBIAS
10
11
19
C2
AVSS
C13 C12 C11
18
17
16
15
DVss
DVSS
AVDD
C5
12
13
14
C3
C4
AVSS
Figure 3 CMX138A Power Supply Connections and De-coupling
Notes:
1. It is important to protect the analogue pins from extraneous in-band noise and to minimise the
impedance between the device and the supply and bias de-coupling capacitors. The de-coupling
capacitors 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 AVSS, and DVSS supplies in the area of the
CMX138A, with provision to make links between them, close to the device. Use of a multi-layer
printed circuit board will facilitate the provision of ground planes on separate layers.
2. VBIAS 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 VBIAS needs to be used to set the discriminator mid-point
reference, it must be buffered with a high input-impedance buffer.
© 2010 CML Microsystems Plc
Page 11
D/138A/2
CMLMICRO [ CML MICROCIRCUITS ]
