Design Considerations for ISD1700 Family
quality is produced.
AN-CC1002
However, if the 10µF capacitors are changed to lower value or removed, the voice
quality obviously degrades with distortions or noise, which may only be suitable for
limited types of applications. Therefore, the existence of the Aluminum Electrolytic
capacitor plays an important role to the quality required. In this case, the dimension of
the PCB is about 1 �½ inches x 2 1/8 inches, which is substantially smaller than that of
Expt. 1. Fig. 4 shows the 1:1 ratio of the size of the PCB.
V
SSD
V
SSD
V
CCD
V
CCA
IS D 1 7 0 0
V
CCD
V+
Gnd
IS D 17 00
V
CCA
V
Gn
V
SSA
V
SSA
Fig. 3: PCB Dimension of Expt. 1
(1:1 ratio – PCB size)
Fig. 4: PCB Dimension of Expt. 2
(1:1 ratio – PCB size)
5. Recommendations
In general, the quality of speaker engaged and the design of speaker housing are
essential to the voice quality. The experimental results confirm that the voice quality can
also be influenced by any or all of the following factors:
•
The presence of the Aluminum Electrolytic decoupling capacitors on the power lines,
•
Appropriate layout techniques,
•
The dimension of the PCB.
Ideally implementing all above is strongly recommended. However, depending upon the
specifications of the system and what level of voice quality are required for the
applications, one can select an appropriate solution accordingly. Experiments are
suggested in order to optimize for the best voice quality on the end-product.
Nevertheless, there are trade-offs on which approach should be employed, pending upon
the final products. Therefore, compromise may be necessary between the cost
effectiveness and the voice quality.
January, 2006
Page 3 / 3
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