RALCWI Vocoder
CMX608/CMX618/CMX638
Bit 2 and 3
PERIOD
These two bits control the period/frequency of the sync pulse output from SYNC
pin 25, when it is set to produce sync pulses.
Bit 3
Bit 2
Description
0
0
1
1
0
1
0
1
8kHz square wave
Pulse every 20ms
Pulse every 40ms
Pulse every 60ms
Bits 4 to 7
These bits are unused and should be cleared to '0'.
5.10.2.
8 Bit Write-Only Registers
AIG register address $05 (CMX618/CMX638 only. No function on CMX608.)
7
6
0
5
0
4
0
3
2
1
0
INPUT GAIN SWITCH
INPUT GAIN
This is the analogue input gain control register. Because the amplitude of speech fluctuates, it is
important to set the average speech level such that the level of distortion that results from the
occasional overdriving of the inputs is at an acceptable level. The ADC is designed not to saturate,
but will clip input signals which are too large. The ADC is a sigma-delta design with a sampling
frequency of 2.4MHz and subsequent decimation by a factor of 300.
Bits 0 to 3
These bits control the input gain stage according to the following table:
INPUT GAIN
Bit 3
Bit 2
Bit 1
Bit 0
Gain (dB)
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0 (default)
1.5
3.0
4.5
6.0
7.5
9.0
10.5
12.0
13.5
15.0
16.5
18.0
19.5
21.0
22.5
Bits 4 to 6
These bits are unused and should be cleared to '0'
Bit 7
INPUT
GAIN
A '0' in this bit sets the microphone amplifier gain to 0dB. A '1' in this bit sets the
microphone amplifier gain to +20dB. Using this switch will achieve a better noise
performance than using an equivalent gain setting in bits 0-3.
SWITCH
2012 CML Microsystems Plc
34
D/608_18_38/10
CMLMICRO [ CML MICROCIRCUITS ]
