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FX802J View Datasheet(PDF) - CML Microsystems Plc

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Description
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FX802J
CML
CML Microsystems Plc CML
FX802J Datasheet PDF : 14 Pages
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Encoder and Decoder Control
Analogue Input and Output Switching
The Control Register, Byte 0 – bits 0 to 5, are used, in conjunction with the codec Powersave Bit (Byte 1 – bit 3) to control codec
input/output conditions and sample rates. Figure 3 shows the codec functional situation.
AUDIO IN
MOD
DEMOD
CVSD Codec
INPUT
BIAS
200k
(nom)
VBIAS
Fig.3 Analogue Control – with reference to Fig.1
AUDIO
BYPASS
AUDIO OUT
VBIAS
500k
(nom)
OUTPUT
BIAS
Control Register
Circuit Switches
Codec
Powersave
Bit
Decoder
Control
“5” “4” “3”
Audio Audio Output
By-Pass Out
Bias
0
0
0
0
OFF
ON
OFF
0
0
0
1
ON
OFF
OFF
0
0
1
0
OFF
OFF
OFF
0
0
1
1
OFF
ON
OFF
0
1
1
1
OFF
ON
OFF
1
0
0
0
OFF
OFF
ON
1
0
0
1
ON
OFF
OFF
1
0
1
0
OFF
OFF
ON
1
0
1
1
OFF
OFF
ON
1
1
1
1
OFF
OFF
ON
Encoder
Control
“2” “1” “0”
Input
Bias
0
0
0
0
ON
0
0
0
1
OFF
0
0
1
0
OFF
0
0
1
1
OFF
0
1
1
1
OFF
1
0
0
0
ON
1
1
1
1
ON
Table 5 Analogue Control – with reference to Fig.3
OFF
ON
= Switch Open
= Switch Closed
Decoder ‘idling’ fed with “1010101
....” pattern at 32kb/s.
Decoder running at the selected
sampling rate.
Note
1
1
Decoder circuits Powersaved
2
Encoder running at 32kb/s but
Encoder Data Output forced to ‘idle’
pattern “01010 ...”
Encoder running at selected
Sampling Rate
Encoder circuits Powersaved
Notes
1. If the Delta Codec is in the Direct Access mode, these
sampling rates will be as provided by the externally
applied clock.
2. The Input Bias switch is operated by the Control Register
Codec Powersave’ and ‘Encoder Control’ bits to provide a
relatively low impedance path for V to charge the input
BIAS
coupling capacitor whenever the codec is powersaved, or the
Encoder control bits are set to “0,” so that input bias can be
established quickly prior to operation.
Time Compression of Speech
The 25kb/s and 50kb/s sampling rate options are provided
for time compression (and subsequent expansion) of speech
signals.
For example, 1.0 second of speech stored at 50kb/s may
be transmitted in 0.8 seconds if played out at 64kb/s, and
finally restored to its original speed at the receiver by storing
at 64kb/s and playing out at 50kb/s. A similar result (with a
degraded SINAD) may be achieved by using 25kb/s and
32kb/s sampling rates.
However, the speech frequencies are raised by time
compression, and since the signal transmitted to air must be
band limited to 3400Hz, the effective end-to-end bandwidth
is 0.8 x 3400Hz, which is approximately 2700Hz.
9
 

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